Penalizing mecanum wheeled robots durring alliance selection.

[Max Boord]

Over the years as mecanum drive robots increse in popularity its become incresingly common for teams that seed in the top 8 to penalize 1st round picks for having a mecanum drivetrain. So CD comunity, what does your team do when it comes to mecanum drive robots?

[BBray_T1296]

We built mecanum robots in both 2011 and 2012. We were (for give my narcissism) very good both years, and mecanums proved to be advantageous in both games.

The single only reason we didn't use them last or this year, is specifically because other teams don't like them immediately.

I have never seen a mecanum implementation (code etc) better than ours, but nonetheless, it is painful to be judged by stereotypes than performance

[AllenGregoryIV]

We have picked Mecanum wheeled robots in the past to be on our alliance. Most notably at Arkansas in 2013 when our 1st selection (Ubotics, FRC#3507) was a mecanum wheeled robot and our alliance made it to the finals.

However the biggest impact mecanum wheels have on our pick list is with 2nd round selections. Defense normally plays a bigger role in our choice for a 3rd member of our alliance and more often than not a kit bot drive base will beat a mecanum robot when it comes to standard defense techniques.

There are teams that have used mecanum wheels very effectively but similarly to crab/swerve if you are not one of the teams doing it at high level it rarely pays off. I often advise rookie and young teams from using them on their competition robots.

[Koko Ed]

Last year we had mechanum wheels and were the 15th highest OPR on our field but our robot was slow and could not go under the pyramid and could only load in station and we went unpicked.

[DampRobot]

Maybe meccanums are less popular in NorCal, but I didn't have to make a decision about picking a team with meccanums all that often.

(The following is about how I helped choose picks for 100, so don't read anything about 971 into my statements.)

For first round picks (if you are in that position, we were only there once when I was helping choose our picks), it's often fairly obvious who the next best team is, or if not, it's a choice between two teams. Usually, the teams who are picking from the top 8 have done their homework, and base their picks off objective statistics at least in part. Most teams that have a good shot at getting picked first have already chosen not to use meccanums, so it's usually not an issue. But, if I was in the position of picking first, and there was a team that was clearly better than anyone else available who ran meccanums, I would pick them.

Second picks are a lot harder, because there's a larger pool of teams that it might make sense to pick, and frankly most of the teams left over really aren't that good. Of course, it depends on the game, but in my experience, you're looking for a team that has a strong drivetrain and knows how to drive it, and if possible can hit auto and help with the endgame. If there's a team with a reasonably well built WCD and good drivers left by the time that we can pick them, we'll go for them 4/5 times. Offensive ability (which meccanum bots may or may not possess) is secondary, as the captain and 1st pick will likely be doing essentially all of the scoring. You want a good defensive team for your second pick, and for whatever reason, in my experience a well built WCD works best for that.

I don't think there's some vast conspiracy to never ever pick meccanum bots, but I do think (from being there in the past) that given a few roughly equivalent robots, teams will usually pick tank drives over meccanum drives. Going meccanum is usually a decision based on coolness, and teams with meccanums are often kind of wild cards. It often just feels safer to pick a team without diagonal rollers on their wheels.

[Caleb Sykes]

Great poll and thread. I am very interested to see how the results turn out. As for me, I chose "does not affect position".

Interestingly enough, for some of the regionals I have attended, I might actually be more prone to select a mecanum bot than a tank bot for a defensive pick. The reason why is because a mecanum robot always* has 4 drive motors, while too many teams still use only 2 drive motors for tank drive. I would still pick the robot that is the best driven for a defensive pick, but all else equal, I would feel better about having a mecanum bot on my alliance than a 2-motor tank drive robot.

*Although I have heard of teams that try to drive a mecanum configuration with only 2 motors. *shudder*

[Max Boord]

for some of the regionals I have attended, I might actually be more prone to select a mecanum bot than a tank bot for a defensive pick.

Our alliance did this at Panther Prowl last year. We could not have been more pleased with the outcome.

[evanperryg]

Generally, mecanum is a major detractor when my team is assembling the pick list. However, we will pick a mecanum robot if it offers us what we need. We picked 2 at the crossroads regional. Personally, I think mecanum is a poor drivetrain solution, but some teams do it very well.

[g_sawchuk]

For our team, if a team has mechanum wheels on their robot or not is a feature that we check, but wheels in general are a feature to consider while picking. We don't judge just by one feature, we look at all aspects of the robot, then choose. Although our team commonly makes jokes about mechanum wheels as they don't have the best reputation, we have yet to penalize a bot on our pick list because of mechanum wheels.

[Nick Lawrence]

It honestly depends on if the team knows the limitations (reduced pushing capability, vulnerability in open spaces,) of their drivetrain, and if they use it effectively. I'd have no problem picking a team with a mecanum drive so long as they effectively take advantage of their drivetrain and play smart with it.

Unless we're playing a full contact game like Aerial Assist. I would not pick a team that has a pure mecanum drive for a game like this. IMHO, drives with traction wheels were king, even octocanum/butterfly.

-Nick

[ShinyShips]

For this year's game our team used mecanums and knew that we were slow and easily pushed. Seeing that, we preferred to have our alliance partners have a decent tank drive to not only keep our play at a decent speed, but also to have a good defense while they weren't handling the ball. It may be a little hypocritical, but defense was a major part of this year's game.

[Jon Stratis]

For us it's all about performance. It doesn't matter what drive train a team has, so long as they effectively use it and are the best available team at that point in the selection process. If we need someone who can score, we look at the team that has best shown the ability to score the most points per match. If we need someone to play defense, we look at the team that has been able to decrease an opponents score the most. In the end, it's all about the bottom line - can you score more points than someone else. Ignoring a team who has proven they can affect the bottom line the most of everyone available just because you don't like a feature of the robot? We try to avoid that.

[SeanFitz]

I think it really comes down to how big your wheels are. In 2013 we bought big 8" diameter, 2" width wheels and were actually one of the better pushing robots out there (didn't get picked, but that was mainly because our shooter was awful). In contrast, we used 6" diameter, 1" width wheels in 2010 and got pushed all over the place.

[Andrew Schreiber]

If they are the team that best meets my criteria I pick them. If they aren't, I don't. This is the same logic I apply to any other team.

So, no I don't penalize them. I just tend to rank features they traditionally lack as higher priority than the features they excel at.

[Rypsnort]

I have not personally been a part of selecting teams, but I have noticed that you have to have a strategy in your alliance that accommodates a mecanum drive bot. Mecanum is good for being evasive (if built and driven well) but is bad for being physical and getting in pushing matches. If you don't have a need for it don't pick it(mecanum drive).

[Pat Fairbank]

Automatic DNP, unless there are too many mecanum bots for that to be possible.

It's not that mecanum wheels are inherently bad, just that 99% of the implementations we see are.

[TAlholm]

If the team drives the mecanum drivetrain well, I see no reason to leave them off the list.
Then again, I don't do any scouting.

[ChuckDickerson]

In my fantasy world I would dearly love to see Teh Chezy Pofs do mecanum just one year so they can show us all how we have been doing it wrong all this time and then maybe everyone else would stop the mecanum bashing and shut up about how mecanums are never on Einstein.

[DampRobot]

In my fantasy world I would dearly love to see Teh Chezy Pofs do mecanum just one year so they can show us all how we have been doing it wrong all this time and then maybe everyone else would stop the mecanum bashing and shut up about how mecanums are never on Einstein.

I think you'll see it when they decide that powdercoat looks kind of stupid, wires don't care if they're ziptied down or not, and that they should stop driver practice because it distracts from watching South Park.

[Chris is me]

Over the years as mecanum drive robots increse in popularity its become incresingly common for teams that seed in the top 8 to penalize 1st round picks for having a mecanum drivetrain. So CD comunity, what does your team do when it comes to mecanum drive robots?

We're not penalizing anybody. We're picking robots that best complement our robot and the strategy we want to play in the elims.

In 2014, there was no place for a (pure) mecanum drive robot on our alliances. The ability to resist pushing was viewed by us as essential to forming a 3 assist cycle. Resisting pushing with traction allows for "wall" defense and also helps avoid being spun while shooting or ejecting. People argue about whether mecanum can push or not, but they're really missing the point - pushing resistance is where mecanum robots really struggle.

There were some robots at our events that were mecanum drive that played fairly well but without traction they just could not get into and hold position where they needed to be. Setting up truss shots or passes with them was just too difficult when they could be spun by defense. In spite of this, there was just one other robot on our list between our alliance's second pick and a mecanum drive robot at Finger Lakes.

In other years, the "cost" of a mecanum robot versus a traction robot varies. I feel it's worth noting that more often than not the best several teams at a regional are all tank drive. In this case the teams aren't being selected because they aren't mecanum, but because their robots are overall better than the mecanum robots are. In addition, in the somewhat rare event that the best teams at a regional include mecanum robots, these robots tend to have well driven and implemented mecanum drive systems.

To be quite frank, I think a lot of teams that aren't very good pick mecanum drive because they feel like the ability to strafe allows them to drive better with less practice. It seems more trivial to just gun the robot forward into a scoring zone, then strafe to where you actually wanted to be, than it is to drive in a smooth arc up to where you wanted to score. However, without plenty of drive practice, it doesn't matter what your wheels are, you're a lot less likely to be a first round pick at all.

In short, there's almost no situation where all other things equal, a mecanum drive is a net gain over a tank drive for our alliance, and I've observed a correlation between teams choosing mecanum wheels and teams dropping down our pick list due to poor manipulator design.

Also, if you're the kind of team that gives teams grief for making choices differently than you and assume teams were too stupid and biased to pick your obviously superior robot based on its wheels, maybe you're not the kind of alliance partner we would want to work with?

[MARS_James]

there's a correlation between teams choosing mecanum wheels and teams with poor manipulator design.


Despite formerly being on 1523 (who has used mecanums since 2011) with the OP for years I agree with all your statements except for the above, where is the data to support that statement since mecanums have nothing to do with a manipulator?

[Andrew Schreiber]

Despite being on 1523 (who has used mecanums since 2011) with the OP for years I agree with all your statements except for the above, where is the data to support that statement since mecanums have nothing to do with a manipulator?

Purely anecdotal. My experience supports this claim but I cannot say that there is correlation with any sort of certainty.

[Chris is me]

Despite being on 1523 (who has used mecanums since 2011) with the OP for years I agree with all your statements except for the above, where is the data to support that statement since mecanums have nothing to do with a manipulator?

Correlation doesn't necessarily imply causation here, and mecanum robots aren't considered by us to have poor manipulators *because* of their wheel choice. I'm trying to say that many teams that have mecanum wheels didn't get picked for other reasons as well, not just their wheel choice.

As for data, the robots that are near the bottom of our pick lists or on our DNP lists are more likely to have mecanum wheels than the robots near the middle or top of our pick lists. I could publish our Finger Lakes pick list from this year if you really want hard numbers, but it's just a trend I've noticed. There are exceptions, and I'm reasonably sure that 1523 would be one.

[pastelpony]

We saw a lot of mecanum-powered robots at the Pine Tree district event earlier this year. Generally, mecanum robots weren't really good at offense, but were crushing in defensive scenarios (important in an event where both teams in the finals relied on parking at the 1-goal and firing.) However, like most teams, we wanted offense over defense. Unless the mecanum bot isn't one dimensional, we don't really have them high up on our list.

[MARS_James]

Correlation doesn't necessarily imply causation here, and mecanum robots aren't considered by us to have poor manipulators *because* of their wheel choice. I'm trying to say that many teams that have mecanum wheels didn't get picked for other reasons as well, not just their wheel choice.

As for data, the robots that are near the bottom of our pick lists or on our DNP lists are more likely to have mecanum wheels than the robots near the middle or top of our pick lists. I could publish our Finger Lakes pick list from this year if you really want hard numbers, but it's just a trend I've noticed. There are exceptions, and I'm reasonably sure that 1523 would be one.

Maybe it is a region thing, for the most part in Florida the mecanum bots do not have poor manipulators, though a lot do follow your statement about drivers not being as well versed with driving as their traditional drive counterparts. Like you said their are exceptions to every rule though your offer of data does bring up something, if possible I think it would be interesting for someone to compile data from events and see if there is a correlation between drivetrains and their ranking, and elimination selection/performance.

[thatprogrammer]

Maybe it is a region thing, for the most part in Florida the mecanum bots do not have poor manipulators, though a lot do follow your statement about drivers not being as well versed with driving as their traditional drive counterparts. Like you said their are exceptions to every rule though your offer of data does bring up something, if possible I think it would be interesting for someone to compile data from events and see if there is a correlation between drivetrains and their ranking, and elimination selection/performance.

1065 has a SOLID robot this year, despite having mecanum wheels. We picked them during elimination matches and made it to semi-finals. :D

[MARS_James]

1065 has a SOLID robot this year, despite having mecanum wheels. We picked them during elimination matches and made it to semi-finals. :D

I think Moose had a drop down traction wheel on each side this year

[Max Boord]

1065 has a SOLID robot this year, despite having mecanum wheels. We picked them during elimination matches and made it to semi-finals. :D

1065 was not pure mecanum. They had jump drive which was powerful enough to push 233's 8WD sideways (http://youtu.be/FOQT4hmI2P8?t=1m16s). Im shocked we where able to pick them in Orlando as the #4 seed.

[thatprogrammer]

I think Moose had a drop down traction wheel on each side this year

Yeah, they had 2 1" diameter traction wheels bolted together on each side. As fart as I know, they only used them during pushing matches though. *So when you tried to stop shots into the goal :p*

[Max Boord]

In my fantasy world I would dearly love to see Teh Chezy Pofs do mecanum

Who knows, Skystalker V2 may come equipped with 8 wheel drop center mecanum.

mecanums are never on Einstein.
They where this year. (http://www.chiefdelphi.com/media/img/8f3/8f37f7be15b7fa2e6d424282605c365a_l.jpg)

[Justin Montois]

All other things being equal, we would most likely pick a non mecanum drive over a mecanum drive.

However, I think it's important to point out that rarely are all other things equal. Like anything else, design to play the game well and be consistently contribute to the alliance in a positive manner.

[magnets]

They where this year. (http://www.chiefdelphi.com/media/img/8f3/8f37f7be15b7fa2e6d424282605c365a_l.jpg)

Yeah, but they never touched the carpet ;)

[pabeekm]

This year, the robot's drivetrain didn't matter to us nearly so much as how the robot was being driven. This was probably our biggest selection factor; I asked scouters specifically to note great or poor maneuvering (especially around defense). We even used our first pick as 2nd seed at North Carolina on a 44th seeded box bot, just because they drove very well. Likewise, plenty of drivers at champs proved that mecanum was no hinderance if utilized well.

Discriminating against robots for particular attributes should not be done if they can hold their own on the field, period. Unfortunately, teams with such attributes do have to prove themselves to overcome doubters, and even then, the tiniest of concerns might be enough for alliance captains to discredit them.... it's really unfortunate, but it happens, whether you're a mecanum bot, rookie team, or had no intake this year :( (cries in corner).

[Peyton Yeung]

When teams were scouting our robot it seemed like they were penalizing us for having mecanums even when we told them we were using 4 cims and 4 mini cims.

[indubitably]

8 motor mecanum isn't bad

[MARS_James]

When teams were scouting our robot it seemed like they were penalizing us for having mecanums even when we told them we were using 4 cims and 4 mini cims.

You have peaked my interest, was there any noticeable difference in performance in comparison to the traditional 4 motor? Specifically in terms of pushing power or resistance?

[Sam_Mills]

I have not personally been a part of selecting teams, but I have noticed that you have to have a strategy in your alliance that accommodates a mecanum drive bot. Mecanum is good for being evasive (if built and driven well) but is bad for being physical and getting in pushing matches. If you don't have a need for it don't pick it(mecanum drive).

Not to call you out specifically, but you mentioned something that is frequently spread around, and not quite true. Mecanum is often touted as being good for being evasive, but due to the fact it must be geared slower (for more torque) to strafe well, they typically can't outmaneuver a tank drive (this is especially true in the 6 CIM era). If you want an example of this, look to Ultimate Ascent;

There was a very small handful of robots able to complete 7 cycles, which was a task that required nearly no pushing, and all maneuverability. If mecanum wheels were more maneuverable, you would expect the best cyclers to be mecanum robots, but this was not the case. 118, 469, 610, 245, 868, 11, etc., were all tank drive robots.

I think it really comes down to how big your wheels are. In 2013 we bought big 8" diameter, 2" width wheels and were actually one of the better pushing robots out there (didn't get picked, but that was mainly because our shooter was awful). In contrast, we used 6" diameter, 1" width wheels in 2010 and got pushed all over the place.

"Pushing Power," is a function of coefficient of friction with the floor, robot weight, and torque. Wheels sizes (widths) can influence coefficient of friction, but tread material is typically a more important factor. Wheel diameter can also affect coefficient of friction by changing the size of the flat patch you have on the carpet, but this has a pretty minor effect. Torque is a function of your gear ratios and wheel diameter together, as well as the efficiency of your transmission, but you can gear for as much toque as you want, regardless of wheel size.

TL;DR: You can push with small wheels if you want to, just be aware of the variables at play.

[1493kd]

As a team that went with mecanum this year (as much as I did not want to) I can say that it was a factor in teams selecting us. At TVR we had teams tell us they would pick us if we switched to traction wheels. I believe we had a great bot design for the game but the mecanum just made us a bot that could get pushed all over ( esp by 2791). Needless to say we have switched them out for offseason events, Im looking forward to seeing the results.

[marshall]

it's really unfortunate, but it happens, whether you're a mecanum bot, rookie team, or had no intake this year :( (cries in corner).

Wait, being fed by human player doesn't count as an intake? ;)

[BrendanB]

Yes, if you have mecanum wheels it will lower you on my picklist. Especially for our third pick robot we try to avoid teams with mecanums because its very hard to play effective defense with mecanums. It is possible I have seen it done but most of the times these teams have a solid offensive strategy too meaning we wouldn't want them to play defense to begin with as we need them to score.

We have picked/accepted invitations from teams with mecanums more notably this year we allied twice with 58 and once with 126 both were very effective robots on the field with mecanums. If there were identical robots to them just with tank drives I would have rather gone with the tank drive.

You might call it "penalizing" but I see it as a weakness if the other alliance can push you around as much as they please.

[Chadfrom308]

Our mecanums this year were the best i've ever seen. We had 4 CIMs and 4 mini-CIMs.

We ended up pushing practically everyone. Yes, there are a few battles that we lost, but we just spun around them and continued. I was surprised by the amount of power that we could put down.

We pushed a whole bunch of 6 CIM 6/8 wheel drivetrains.

[Peyton Yeung]

You have peaked my interest, was there any noticeable difference in performance in comparison to the traditional 4 motor? Specifically in terms of pushing power or resistance?

Well it definitely made for a heavy robot(~22 pounds in motors and motor controllers). It had quite a bit of torque but it was still hard keeping 6 wheel drives off us.

[Jared Russell]

Our mecanums this year were the best i've ever seen. We had 4 CIMs and 4 mini-CIMs.

We ended up pushing practically everyone. Yes, there are a few battles that we lost, but we just spun around them and continued. I was surprised by the amount of power that we could put down.

We pushed a whole bunch of 6 CIM 6/8 wheel drivetrains.

Any videos of this?

[DampRobot]

Any videos of this?

Not quite the same thing, but reminds me of this (http://www.chiefdelphi.com/forums/showthread.php?t=89737) thread.

[cadandcookies]

2220 has been picked by a certain MN team that has used mecanum for the last few years-- 2052 (who has also won three regionals in a row now).

However, frankly, they're the only team I've ever seen that was successful with mecanum-- and that's because a whole lot of driver practice (they're also the only mecanum bot I've seen that actually "runs circles" around others in terms of evasiveness), and just generally the great quality that they build into their robots.

It's all performance/quality based. I will admit that I tend to scrutinize mecanum more than tank, just because I've seen more subpar, problematic, or nonfunctional mecanum bots than "conventional" NWD bots.

[T^2]

Any videos of this?

I checked out a few of their videos, and in qual 89 of MSC (https://www.youtube.com/watch?v=rJEU99kOSzQ) there are a few moments when they cause noticeable forced lateral motion of an opposing robot.

[Caleb Sykes]

There was a very small handful of robots able to complete 7 cycles, which was a task that required nearly no pushing, and all maneuverability. If mecanum wheels were more maneuverable, you would expect the best cyclers to be mecanum robots, but this was not the case. 118, 469, 610, 245, 868, 11, etc., were all tank drive robots.


2052 completed 7 cycles (https://www.youtube.com/watch?v=xiO4c9K7TfI&list=UUFLvoBMraa3-X0EtsrpiITg) with a mecanum drive train, so the 7-disk cycle club was not exclusively made up of tank drive robots.

[jwfoss]

This is my opinion and should not reflect on my current or any former teams.

Before I state anything, I understand that there have been successful teams running mecanum wheels or some form of mecanum-traction combos, locally 126 and 230 have had successful seasons on these wheels.

Far too many teams pick mecanum wheels for the "cool factor" without a solid understanding of the pro's and con's of the system. I would in fact rather pick a partner running an off the self kitbot then a mecanum drive robot.

Generally speaking, drivetrain quality (like bumper quality) can be an indicator of overall robot performance or in the case of our current pre-match scouting and point of interest to determine an alliances strengths and weakness.

[Andrew Schreiber]

2052 completed 7 cycles (https://www.youtube.com/watch?v=xiO4c9K7TfI&list=UUFLvoBMraa3-X0EtsrpiITg) with a mecanum drive train, so the 7-disk cycle club was not exclusively made up of tank drive robots.

At a real event.

[Bryan Herbst]

At a real event.

Are you implying that the Minnesota State Championship is not a real event because it doesn't occur during the regular season?

Realize that all robots attending the state championship must be bagged between their final event and the championship, minus a short unbag perior similar to a district championship. The event uses a real field with the FMS, an FTA, and all the workings of a standard FIRST event. It also includes only the best teams in the state, which makes it more competitive than the "real events" that happen in the state.

I'm curious as to how it isn't a "real event."

mecanums are never on Einstein.
I would argue that this is an effect of the inherent bias against mecanums by all of the teams that regularly make it to Einstein more than evidence that robots with mecanum wheels are inherently worse than traditional tank drive robots.

[Andrew Schreiber]

Are you implying that the Minnesota State Championship is not a real event because it doesn't occur during the regular season?

Realize that all robots attending the state championship must be bagged between their final event and the championship, minus a short unbag perior similar to a district championship. The event uses a real field with the FMS, an FTA, and all the workings of a standard FIRST event. It also includes only the best teams in the state, which makes it more competitive than the "real events" that happen in the state.

I'm curious as to how it isn't a "real event."


I would argue that this is an effect of the inherent bias against mecanums by all of the teams that regularly make it to Einstein more than evidence that robots with mecanum wheels are inherently worse than traditional tank drive robots.


It's an off season event. I treat it like all other off season events. Just like post/pre season performance doesn't factor into stats in sports.

Or, put a really simple way, if it's not an official event it's not real, it's just for play.

[Karthik]

I would argue that this is an effect of the inherent bias against mecanums by all of the teams that regularly make it to Einstein more than evidence that robots with mecanum wheels are inherently worse than traditional tank drive robots.

Yup, there's an international conspiracy of discrimination against mecanum robots by the perennial Einstein teams. These teams have foregone maximizing their utility and competitiveness by collectively (or coincidentally) making the same inefficient alliance selection decisions. Right.

[Andrew Schreiber]

Yup, there's an international conspiracy of discrimination against mecanum robots by the perennial Einstein teams. These teams have foregone maximizing their utility and competitiveness by collectively (or coincidentally) making the same inefficient alliance selection decisions. Right.

You forgot the collaboration with the Shadow Government. Clearly this is their insidious work.

[magnets]

I don't think mecanum wheels are a great drivetrain. That said, I think a lot of teams who choose mecanum wheels also make other poor choices for their robot, and that is the real reason they aren't on Einstein.

The Einstein level teams pick teams who have high quality and reliable robots, which are generally made by teams who don't use mecanum wheels.

That is not meant to be a blanket statement, but my general view and opinion.

[pntbll1313]

2220 has been picked by a certain MN team that has used mecanum for the last few years-- 2052 (who has also won three regionals in a row now).

However, frankly, they're the only team I've ever seen that was successful with mecanum-- and that's because a whole lot of driver practice (they're also the only mecanum bot I've seen that actually "runs circles" around others in terms of evasiveness), and just generally the great quality that they build into their robots.

Thanks for the complements! (We've actually won 4 regionals in a row, and 2 state championships, but who's counting :) )

[Bryan Herbst]

It's an off season event. I treat it like all other off season events. Just like post/pre season performance doesn't factor into stats in sports.

Or, put a really simple way, if it's not an official event it's not real, it's just for play.

I can see that when talking about rankings and official stats (IRI winners will never be truly be considered FRC world champions), but I think when we are discussing the subjective capabilities of a drive train, we can take into account all of the data available to us.

Yup, there's an international conspiracy of discrimination against mecanum robots by the perennial Einstein teams. These teams have foregone maximizing their utility and competitiveness by collectively (or coincidentally) making the same inefficient alliance selection decisions. Right.
If I came across as conspiratorial, I apologize. I'm not trying to claim that there's a conspiracy against mecanum wheels- I'm just saying that it is unlikely that a team with mecanum wheels will make it to Einstein as a second or third (or fourth) pick by one of the perennial Einstein teams because mecanum is an automatic DNP for many of those teams.

For a mecanum team to make it to Einstein, I think they will have to be an alliance captain. That is the point I was trying to make.

[Max Boord]

I think a lot of teams who choose mecanum wheels also make other poor choices for their robot, and that is the real reason they aren't on Einstein.

So your saying alot teams that choose X drivetrain will also choose Y gamepiece minipulation design? Are you also implying that that mechanism is inferrior? If so my eyes and statistics disagree.

That is not meant to be a blanket statement, but my general view and opinion.

Sure looks like one.

[Andrew Schreiber]

I can see that when talking about rankings and official stats (IRI winners will never be truly be considered FRC world champions), but I think when we are discussing the subjective capabilities of a drive train, we can take into account all of the data available to us.


"Quarterback X is the worst quarterback ever"

"Why?"

"Their completion percentage is crap if you include all the practice games they played in"

See the problem with including all data?

Of the teams that completed 7 cycles DURING THE COMPETITION SEASON not a single one of them was mecanum wheeled.

Why is this? If they are touted as more mobile why were these "inferior" drivetrains able to accomplish something that they were not?

What did 2052 do after the season to be able to accomplish 7 cycles? Why did they not accomplish it during the season?

[Jared Russell]

For a mecanum team to make it to Einstein, I think they will have to be an alliance captain. That is the point I was trying to make.

It totally depends on the game. FIRST has given us games where defense was nonexistent (2001), and they could do so again. But every game in the three-team alliance era has involved physical contact between opposing robots in any role (scoring, defense, or counter-defense) once the level of play gets sufficiently high. In such situations, pure mecanum drives are clearly at a disadvantage. Depending on the game and the machine, perhaps good driving or superior scoring functions more than make up the difference. But in my experience this is the exception rather than the rule, especially once you get to Champs and there is a large pool of effective robots.

So I agree with you, unless FIRST really departs from recent game design trends.

[magnets]

So your saying alot teams that choose X drivetrain will also choose Y gamepiece minipulation design? Are you also implying that that mechanism is inferrior? If so my eyes and statistics disagree.
The fact that no mecanum wheeled robots on Einstein has occurred means any number of these 4 things.

1. Mecanum wheels somehow prevent teams from going to Einstein
2. Teams who chose mecanum wheels also do things that prevent them from going to Einstein
3. Teams who build robots who are capable of going to Einstein do not chose mecanum wheels
4. Einstein has gotten unlucky. This is unlikely, as we've seen an incredible number of robots on Einstein since mecanum wheels first entered FIRST, and none of them have mecanum wheels.

I will rewrite my statement with more disclaimers.

From events in a specific region that I have attended since 2011 and robot that I have seen on the field, I have seen that the majority of mecanum wheeled robots make other decisions that I do not agree with. On a world wide scale, I have yet to see more than one or two mecanum wheeled teams be very successful and claim it had to do with their mecanum wheels.

Also, in the year that mecanum was most useful (IMO, 2011), 254 won with a simple 6WD, proving that you don't need mecanum. In fact, every single Einstein match ever proves that you don't need mecanum to be a very successful team. Personally, I prefer to work with a team that realizes that something like mecanum drive is not something needed to be the very best and spent more time on other parts of their robot.

This is an opinion, and only applies to robots that have only mecanum wheels on drive.

[Lil' Lavery]

Guys, mecanum wheels were on Einstein this year.
http://www.chiefdelphi.com/media/img/57b/57ba6ab5b762ccdb4ecbaa6c45c1289c_l.jpg
:cool:

[notmattlythgoe]

The fact that no mecanum wheeled robots on Einstein has occurred means any number of these 4 things.

1. Mecanum wheels somehow prevent teams from going to Einstein
2. Teams who chose mecanum wheels also do things that prevent them from going to Einstein
3. Teams who build robots who are capable of going to Einstein do not chose mecanum wheels
4. Einstein has gotten unlucky. This is unlikely, as we've seen an incredible number of robots on Einstein since mecanum wheels first entered FIRST, and none of them have mecanum wheels.

I will rewrite my statement with more disclaimers.

From events in a specific region that I have attended since 2011 and robot that I have seen on the field, I have seen that the majority of mecanum wheeled robots make other decisions that I do not agree with. On a world wide scale, I have yet to see more than one or two mecanum wheeled teams be very successful and claim it had to do with their mecanum wheels.

Also, in the year that mecanum was most useful (IMO, 2011), 254 won with a simple 6WD, proving that you don't need mecanum. In fact, every single Einstein match ever proves that you don't need mecanum to be a very successful team. Personally, I prefer to work with a team that realizes that something like mecanum drive is not something needed to be the very best and spent more time on other parts of their robot.

This is an opinion, and only applies to robots that have only mecanum wheels on drive.

My one defense for mecanum is, when done right, they can be extremely intuitive to drive. Our 2011 robot that made it into the Curie elimination rounds was an extremely easy robot to drive, and I believe that help us succeed that year.

With that said, we have not used mecanum since, including *winning* Galileo this season.

[Gregor]

Guys, mecanum wheels were on Einstein this year.


I had no idea. (http://www.chiefdelphi.com/forums/showthread.php?p=1397442#post1397442)

[KrazyCarl92]

In my experience, I have only competed with 2 robots that stick out in my mind as having implemented a mecanum drive in a fashion that in some way improved their overall strategic design and were executed well: Team 230 in 2010 and Team 58 in 2012. Both of these teams had creative ways to use their mecanum drives to do something that a standard tank drive could not (or at least not as simply or with the same resources). 230 used theirs to strafe sideways once atop the bumps in the field so they could engage their hooks and climb the tower, knowing they were lined up as they did so and not having to climb as far. 58 used their mecanum drive to position themselves against field elements in auto, moving along multiple axes to ensure they were in the proper location to consistently score their 10 point autonomous.

I often ask a team with a mecanum drive in the pits what their drive train allows them to do that the kit drive train cannot achieve. If the answer is a blank stare or simply "strafing" for no well thought out reason, then I am obviously going to deem their drive as a disadvantage when I see them using it to no advantage on the field. This is because there are then plenty of things that an all else equal robot with a traction drive CAN achieve that this mecanum drive robot cannot. Even the two teams mentioned above did have their limitations owed to their mecanum drive trains, but at least their mecanum gained them something (hey look, points). I'm sure there are more examples of this, but for most mecanum bots I am left thinking that the robot would be at least as effective with a traction drive.

TL;DR consider the marginal gain of your mecanum drive. If one does not exist, why bother?

[Electronica1]

I'm curious, do people move octocanum drives lower on their list/ automatic dnp in a similar fashion to mecanum drives?

[RonnieS]

When we go through our picking process, the first thing is always going to be the best robot in the category we seem.to need first will be brought up first for discussion. After that, we will look at the limitations that pick would have for our alliance and the strategy we want to play. Unfortunately, I will say I hate most mecanum bots because they almost always lack the driver experience needed to make them affective. Granted, there is always that occasional team but not often. Through my experience, I have always been able to find a better robot with some sort of traction setup. Even if that team with traction capability had not shown much, I would feel more confident for example sticking them in the corner and leaving them their for the whole match to inbound and spit out and not move. Where if I had a mecanum bot, I couldn't believe as much that they wouldn't be pushed out of position. (Examples from Arial assist; obviously will vary upon game). I am typing from my phone so excuse any errors haha.

[Karthik]

There are a lot of people dealing in absolutes here, which we should all know is dangerous (https://www.youtube.com/watch?v=wgpytjlW5wU). (Frankly, the only reason to issue an absolute blanket Do Not Pick rank on a team is for a demonstrated pattern of dishonest and unethical behaviour. This is an absolute that even a Jedi would get behind.)

I echo many of the thoughts said by others in this thread. Each team should be evaluated on a case by case basis, on how their design and level of demonstrated functionality would complement your own robot and your desired elimination strategy. From my own personal experiences, I would say that most mecanum robots we've competed with have not been fit to be included on a picklist. Sometimes this is because their drivetrain makes them easy to defend against or unable to defend others. Other times it's been because the robot is just not generally very good. However, this is not an absolute. In 2010 at GTR, we were very close to picking a mecanum robot (Team 188) over a team who has never lost a regional (Team 2056), and ended up winning the event with a mecanum robot as our third alliance member (Team 1547). So it's not impossible for teams to use mecanum wheels with a great degree of success, albeit the frequency seems to be much lower. As for any talk of an inherent bias against mecanum wheels that isn't precipitated by actual robot performance, this is just dumb. The only inherent bias I've seen from teams when it comes to alliance selection is a bias against inferior robots, which is exactly what the picking process is based around.

[Monochron]

There are a lot of people dealing in absolutes here, which we should all know is dangerous (https://www.youtube.com/watch?v=wgpytjlW5wU). (Frankly, the only reason to issue an absolute blanket Do Not Pick rank on a team is for a demonstrated pattern of dishonest and unethical behaviour. This is an absolute that even a Jedi would get behind.)

I echo many of the thoughts said by others in this thread. Each team should be evaluated on a case by case basis, on how their design and level of demonstrated functionality would complement your own robot and your desired elimination strategy. From my own personal experiences, I would say that most mecanum robots we've competed with have not been fit to be included on a picklist. Sometimes this is because their drivetrain makes them easy to defend against or unable to defend others. Other times it's been because the robot is just not generally very good. However, this is not an absolute. In 2010 at GTR, we were very close to picking a mecanum robot (Team 188) over a team who has never lost a regional (Team 2056), and ended up winning the event with a mecanum robot as our third alliance member (Team 1547). So it's not impossible for teams to use mecanum wheels with a great degree of success, albeit the frequency seems to be much lower. As for any talk of an inherent bias against mecanum wheels that isn't precipitated by actual robot performance, this is just dumb. The only inherent bias I've seen from teams when it comes to alliance selection is a bias against inferior robots, which is exactly what the picking process is based around.

Super duper ditto.

[/thread]

[Rangel(kf7fdb)]

I'm curious, do people move octocanum drives lower on their list/ automatic dnp in a similar fashion to mecanum drives?

I think we would actually move octoncanums higher on the list with of course overall performance of the robot taken fully. That drive definetely isn't that simple and takes a lot of effort and machining. More often than not, if a team can do a good octocanum, the rest of their bot is probably pretty solid. Of course this is just speculation and I do not have any statistics to back this up.

[Jonathan Ryan]

Team 145 has made it to the finals at FLR and TVR respectively the last two years with mecanum wheels.

I think the driver has a lot to do with it also. If the mecanums help you avoid getting pushed or pinned then they are an advantage.

[Citrus Dad]

In our experience the teams that are able to execute highly maneuverable drive trains build swerve drives, so we don't see top-end mecanum drive trains. So we're left choosing our second robot and the mecanum drives haven't been as well executed as the available tank drives for the specific roles we're looking for.

[Botsup]

Friends don't let friends drive mecanum. Enough said...

[EricH]

My take on this is simple. A well-executed mecanum, including driver practice, is not something to overlook/automatically DNP. A poorly-executed mecanum is something to be aware of in terms of "we don't want to pick them unless they offer some other benefit", same as any other poorly-executed drivetrain.

Therefore, drivetrain shouldn't matter, the execution of that drivetrain's capabilities on the field should.


Unfortunately, many mecanum teams haven't figured out how to build and operate that drivetrain properly yet. Therein lies the perception problem. There are teams out there that are more consistently successful with a mecanum drivetrain than with a tank drive. They are a minority...

[PayneTrain]

I don't think it's much of a stretch to say that while you can't say the mecanum as a drive system is dead on arrival, it seems to be invariably used by teams who are "in too deep" and would have more than likely struck gold with a 6-wheel tank instead of mining for limestone.

One time mecanum user, first time caller: never again. There were some minor maintenance kerfuffles at Alamo this year with an experimental drive train* but it pales in comparison to the constant retooling of the mecanum wheels and code to get the dadgum thing to drive 4 years ago. Finalist trophy, tell the haters to buzz off and whatever, not worth.

15 years later and we're finding plenty of fun ways to retool the 6WD in new and exciting ways to tailor our team. If you want to drive a mecanum, your call. You want to change drive train design on your team from the ground up annually or bi-annually? Ok.

If it a) goes out and executes a valid strategy and b) an alliance captain sees your valid strategy meshing well with theirs, then there's no reason to not do it.

The fact still remains that seeing a well-executed strategy being driven on 4 mecanum wheels isn't something that comes up too often in the history of FRC, and smart people in FRC love their FRC history. If you want to do a case study on wildly successful mecanum drives, go check out the fantasy section of the library because it's as wild a tale as Dean Kamen in a tux (well, not that wild (http://www.chiefdelphi.com/media/img/71f/71f574407c5756c973686c4a577e0d52_m.jpg)).

*(but Wil, why did your team run an experimental drive train at an official FRC regional? GREAT QUESTION! (http://i.ytimg.com/vi/6674ozx16D0/0.jpg))

[who716]

in my own personal opinion as the driver and alliance selector, I avoid mecanum wheeled robots all together. I don't see the use for them. They are too easy to block and push around. and with no real advantage, I don't see our team using them any where in the near or distant future.
we were the number one seed at an event this year and the pick list was given to me with a tie for my first pick, I went over to both teams discussed examined there robot ext. and when it came to picking the main reason I picked the team I did was they had hi grips while the other had mecanums.
it turned out that in the next event they had swapped there wheels out for hi-grips and were able to play more aggressively on the field. just my opinion.

[who716]

Friends don't let friends drive mecanum. Enough said...

boooya

[Zaque]

Has anyone considered picking a mecanum robot after talking to the team about switching the wheels to traction for eliminations? Or do you think the lack of drive practice would offset any benefits from the traction wheels?

[who716]

Has anyone considered picking a mecanum robot after talking to the team about switching the wheels to traction for eliminations? Or do you think the lack of drive practice would offset any benefits from the traction wheels?


that could end up being a lot of work

[Zaque]

that could end up being a lot of work

True, WCD has spoiled me in terms of pit repair/wheel replacement.

[EricH]

Has anyone considered picking a mecanum robot after talking to the team about switching the wheels to traction for eliminations? Or do you think the lack of drive practice would offset any benefits from the traction wheels?

I'd say that the lack of drive practice would effectively disqualify that option. Along with:

--You now have a 4WD all-traction setup. Generally speaking, those don't turn easily. (With the shorter wheelbases we've seen the last couple of years, though, that's less of an issue.)
--You really need to make a major change to the programming, like eliminating the sideways motion part. Otherwise the robot will act really funny on the field. (Alan Anderson has a story about that somewhere...) But changing the program requires some testing, which you probably won't have time to do...

In short, not a good option. Either you take a mecanum robot as a mecanum robot or you leave them for someone else to take.

[Abhishek R]

It's interesting to see that different regions may have different takes on drivetrain choices. I noticed a lot more mecanum robots in Orlando than I did in Texas (it seemed like 1/3 of all the competition used mecanum).

I figure this might have to do with the mentality of the teams. Again, this is just from my observation, and it's not a blanket statement. But in Orlando, it looked like everyone is more focused on outscoring the opponent rather than denying points from the opponent (which isn't bad, as long as your alliance has more points at the end is all that matters) - in short, offense > defense. For many teams, this was their first regional, yet the finals saw scores around 180 on both sides.

At our first regional, Alamo, the finals never saw a score above 100 points. I attribute that towards a more defensive focused play in Texas, rather than offense. While teams still build and gear towards scoring points, when it comes down to strategy, there's an emphasis on locking down the opponent so they can't score any more points.

Because of this, and the reputation most mecanum driven robots have for getting pushed around, it seems teams in our region stay away from them, and instead focus on tank drives or, even further, butterfly drives to escape pins more easily.

[thatprogrammer]

It's interesting to see that different regions may have different takes on drivetrain choices. I noticed a lot more mecanum robots in Orlando than I did in Texas (it seemed like 1/3 of all the competition used mecanum).

I figure this might have to do with the mentality of the teams. Again, this is just from my observation, and it's not a blanket statement. But in Orlando, it looked like everyone is more focused on outscoring the opponent rather than denying points from the opponent (which isn't bad, as long as your alliance has more points at the end is all that matters) - in short, offense > defense. For many teams, this was their first regional, yet the finals saw scores around 180 on both sides.

At our first regional, Alamo, the finals never saw a score above 100 points. I attribute that towards a more defensive focused play in Texas, rather than offense. While teams still build and gear towards scoring points, when it comes down to strategy, there's an emphasis on locking down the opponent so they can't score any more points.

Because of this, and the reputation most mecanum driven robots have for getting pushed around, it seems teams in our region stay away from them, and instead focus on tank drives or, even further, butterfly drives to escape pins more easily.
This may have to do with Alamo being earlier, and teams not being sure about offensive strategies at that point in time. By world champs, teams scored over 250 points even during the finals, due to solid offensive strategies being made over the 6 weeks of comp.

[PayneTrain]

It's interesting to see that different regions may have different takes on drivetrain choices. I noticed a lot more mecanum robots in Orlando than I did in Texas (it seemed like 1/3 of all the competition used mecanum).

I figure this might have to do with the mentality of the teams. Again, this is just from my observation, and it's not a blanket statement. But in Orlando, it looked like everyone is more focused on outscoring the opponent rather than denying points from the opponent (which isn't bad, as long as your alliance has more points at the end is all that matters) - in short, offense > defense. For many teams, this was their first regional, yet the finals saw scores around 180 on both sides.

At our first regional, Alamo, the finals never saw a score above 100 points. I attribute that towards a more defensive focused play in Texas, rather than offense. While teams still build and gear towards scoring points, when it comes down to strategy, there's an emphasis on locking down the opponent so they can't score any more points.

Because of this, and the reputation most mecanum driven robots have for getting pushed around, it seems teams in our region stay away from them, and instead focus on tank drives or, even further, butterfly drives to escape pins more easily.

I attribute that more to about 8 teams at Alamo knowing how to play the game and about 5 or 6 of them actually able to play it.

[Sam_Mills]

I don't think mecanum wheels are a great drivetrain. That said, I think a lot of teams who choose mecanum wheels also make other poor choices for their robot, and that is the real reason they aren't on Einstein.

The Einstein level teams pick teams who have high quality and reliable robots, which are generally made by teams who don't use mecanum wheels.

That is not meant to be a blanket statement, but my general view and opinion.

I would assert that it is safe to say this is not a view or an opinion, but an objectively observable trend. Of course the only way to prove this; You need a database directly comparing average win/loss ratio of different classes of robots by drivetrain.

This is not likely to happen any time soon, but that doesn't mean we can't recognize that it is true that robots of similar ability level have similar qualities. Mecanum robots historically are not as good as non-mecanum robots. We don't have to like it, but that is how it is.

I think I may coin a term "mecanum-apologist"...

[Max Boord]

It's interesting to see that different regions may have different takes on drivetrain choices. I noticed a lot more mecanum robots in Orlando than I did in Texas (it seemed like 1/3 of all the competition used mecanum).
49 tank, 10 mecanum, 2 jump drives and 1 swerve.

I figure this might have to do with the mentality of the teams. Again, this is just from my observation, and it's not a blanket statement. But in Orlando, it looked like everyone is more focused on outscoring the opponent rather than denying points from the opponent (which isn't bad, as long as your alliance has more points at the end is all that matters) - in short, offense > defense. For many teams, this was their first regional, yet the finals saw scores around 180 on both sides. This is why you see mecanum drive in Florida. Defense is not played nearly as much as in other places and most alliances go for the outscoring strategy. Just look at QF 2-2 at South Florida in 2013. The match had 3 mecanum drive robots, no defense and a 149-103 score.

[Abhishek R]

This may have to do with Alamo being earlier, and teams not being sure about offensive strategies at that point in time. By world champs, teams scored over 250 points even during the finals, due to solid offensive strategies being made over the 6 weeks of comp.

Right, but I know it was the first regional for most of the teams there. Our alliance ran the same strategy that we ran at Alamo (2 assist cycles, the 3rd robot being focused on defense) yet the scores were significantly different.

Again, just an observation.

[who716]

I believe that it is very well known New England is where some of the heaviest defensive play occurs. watching events all over the US I noticed that in the west its offense offense offense. even in Texas the robots were made to play a purely offensive games, example 148 118, yes they play defense but there robot designs were more offensive. therefore I believe its true that mecanum wheels would be more common in those areas then up in new England.

[Anthony Galea]

Sorry to go a little off-topic here, but these are questions I had relating to this thread.

1) An add-on to the question for those who said automatic DNP: Instead of pick list, if you are a top 8 seed and a team with mecanum wheels above you picks you, do you automatically decline, or is it dependent on performance?

2) Are the same penalties made towards teams with:
a)4WD Omni
b)Slide/H Drive
c)Kiwi Drive

[AllenGregoryIV]

Sorry to go a little off-topic here, but these are questions I had relating to this thread.

1) An add-on to the question for those who said automatic DNP: Instead of pick list, if you are a top 8 seed and a team with mecanum wheels above you picks you, do you automatically decline, or is it dependent on performance?

2) Are the same penalties made towards teams with:
a)4WD Omni
b)Slide/H Drive
c)Kiwi Drive

It depends on performance. I don't think to many teams were declining 33 this year even though they were a 4WD omni robot. However, I assume that their drivetrain choice was a consideration when teams were putting together pick lists.

[Max Boord]

Sorry to go a little off-topic here, but these are questions I had relating to this thread.

1) An add-on to the question for those who said automatic DNP: Instead of pick list, if you are a top 8 seed and a team with mecanum wheels above you picks you, do you automatically decline, or is it dependent on performance?

2) Are the same penalties made towards teams with:
a)4WD Omni
b)Slide/H Drive
c)Kiwi Drive

1. It would depend on the team.

2.
A: Until a larger amount of teams use them I shovel them into the same pile as mecanum. that being said, i would pick 33 at just about every opportunity.

B: mecanum pile.

C: DNP. it can not push and has a smaller wheel base.

[indubitably]

Right, but I know it was the first regional for most of the teams there. Our alliance ran the same strategy that we ran at Alamo (2 assist cycles, the 3rd robot being focused on defense) yet the scores were significantly different.

Again, just an observation.
Strategy can also describe how the 2 assists are obtained such as utilizing the human player and in which zones.

[EricH]

1) An add-on to the question for those who said automatic DNP: Instead of pick list, if you are a top 8 seed and a team with mecanum wheels above you picks you, do you automatically decline, or is it dependent on performance? If a mecanum robot is in the top 8 and picking, either they are that good or they got a good schedule. If they are consistently in the top 8, they're that good. Therefore, automatically declining them--to me at least--is a really bad move unless the team's strategy does not mesh well with my team's strategy. (OR if they're playing scorched-earth and I know about it, in which case, I may decide to accept anyways...)

2) Are the same penalties made towards teams with:
a)4WD Omni
b)Slide/H Drive
c)Kiwi Drive
I'll take 'em based on performance. Again, it's not the type of drive you have, it's how you use it.

[AmoryG]

"Quarterback X is the worst quarterback ever"

"Why?"

"Their completion percentage is crap if you include all the practice games they played in"

See the problem with including all data?

Of the teams that completed 7 cycles DURING THE COMPETITION SEASON not a single one of them was mecanum wheeled.

Why is this? If they are touted as more mobile why were these "inferior" drivetrains able to accomplish something that they were not?

What did 2052 do after the season to be able to accomplish 7 cycles? Why did they not accomplish it during the season?

I don't think you can really compare off season professional sports games to off season FRC competitions. For example, in NFL preseason games teams avoid playing their starters and when they are on the field they don't always play at 100% to avoid risking injury. In FRC off season events teams compete with one robot and they usually give it their all since injury/damage is not nearly as big a concern. Off season FRC events can be just as competitive as events that are "for real", so I don't think you should ignore the data.

[PayneTrain]

For example, in NFL preseason games teams avoid playing their starters and when they are on the field they don't always play at 100% to avoid risking injury.

You don't see teams making many groundbreaking additions or non-critical upkeep on the machines and there likely isn't a lot of scouting either.

However, your example meant to provide contrary evidence of an FRC offseason event being comparable to an NFL preseason game cites something that happens consistently at FRC offseasons: teams don't put in their top drive team for every offseason match of every event they attend.

[pntbll1313]

What did 2052 do after the season to be able to accomplish 7 cycles? Why did they not accomplish it during the season?

2052 had another 6 hours of unbag time (Minnesota teams must bag their entire robot after their last regional of the season, they are then allowed 6 total hours to work on it out of the bag prior to the Minnesota State Tournament). During that time our driver got more driving practice, along with fixing an issue that caused jams in our hopper. If we had made a practice robot, had a practice field using real carpet, another event, or had just finished the robot sooner we did during the build season, I am confident we would have been at that level of driving earlier. Our driver that season was amazing, but he definitely got better every competition with practice. We went from 3 cycles in our first regional, to 4 at our second, to 6 at worlds during eliminations, and 7 at State. Mostly thanks to driver practice. Mecanum also helped us line up at the feeding station as we had one of the narrower loaders out there.

teams don't put in their top drive team for every offseason match of every event they attend.

Clearly everyone is not familiar with the Minnesota State Championship. Teams from Minnesota earn points at their first regional they attend, with point amounts being similar to how teams qualify for the Michigan State Champs. I assure you everyone in Minnesota takes this event extremely seriously, and all teams brought their best drive teams, and their A-game.

[AmoryG]

You don't see teams making many groundbreaking additions or non-critical upkeep on the machines and there likely isn't a lot of scouting either.

However, your example meant to provide contrary evidence of an FRC offseason event being comparable to an NFL preseason game cites something that happens consistently at FRC offseasons: teams don't put in their top drive team for every offseason match of every event they attend.

I would actually argue the opposite. Teams have greater freedom to modify their robot during the off season because the rules are more relaxed and the robot isn't in a crate so you can make changes more easily. Teams can also put the competition into perspective and make a much more competitive robot.

Also, I'm talking from experience and I remember my team put a lot of effort into off season events. Maybe not all teams do, but my team competed like it was any competition and I'm sure many other teams have a similar mindset. Also I know some off season events are taken very seriously. IRI is the first one that comes to mind.

[DampRobot]

You don't see teams making many groundbreaking additions or non-critical upkeep on the machines and there likely isn't a lot of scouting either.

Sounds like you haven't been to a Cali offseason then.

[PayneTrain]

I would actually argue the opposite. Teams have greater freedom to modify their robot during the off season because the rules are more relaxed and the robot isn't in a crate so you can make changes more easily. Teams can also put the competition into perspective and make a much more competitive robot.

Also, I'm talking from experience and I remember my team put a lot of effort into off season events. Maybe not all teams do, but my team competed like it was any competition and I'm sure many other teams have a similar mindset. Also I know some off season events are taken very seriously. IRI is the first one that comes to mind.

More professional sports analogies:

LeBron James can take the opportunity to retool the starting 5 he plays on when he calls up 9 of his closest contemporaries on the court for a rousing game of basketball at his house. While ESPN may want to carry the feed, the Elias Sports Bureau probably has better, more official things to do.

Even the FIBA Gold Cup is an event held by a major sanctioning body, but Anthony Davis' FIBA stats aren't coming up in the NBA books.

You want to bring up IRI? MLB doesn't count any statistics in official books for their all-star game either, even if some people walk home with special hardware.

If you want to challenge my anecdote of "not everyone is going out there with every resource they can muster to win the Alliterative Offseason of the week" with "my team does", that's your prerogative. Still doesn't make any of these events FRC-sanctioned events with any official meeting, which is the point Andrew was making earlier.

What was this thread about again?

[PayneTrain]

Sounds like you haven't been to a Cali offseason then.

I live in Virginia and am a full time college student. I'd appreciate it if you can fly me out to Chezy Champs :)

[cmrnpizzo14]

The way that our team operates in terms of picking is that the first pick will be based primarily on ability. If a team complements our strategy of play well and will put the most points on the board then they will be the first pick regardless of drive train (usual caveats for reliability, etc). The first metric that we use for our second pick is drivetrain. We essentially just want a strong drive( traction wheels, 2 speed preferred) and then after that we will look at their scoring potential.

For us drive train can certainly brake a second round pick but it is highly situational. If we are an 8th seed or a similar position where we need to take risks and try a robot with a huge upside then we might go with a mecanum robot for the second pick to try and outscore the higher alliances.

[DanBrowne]

The issue I see with mecanums is that a lot of teams don't drive them like mecanums. They drive them like tank and don't take advantage of the omni-directional capabilities of the wheels. If mecanums were driven correctly (like Team 126 and 58. They know how to drive!), then I think we would be having a different discussion.

It's the same for all configurations. Omnis should be driven like Team 33 did. Swerve. Well if you made a swerve then you know how to drive it correctly because your that smart!

The key to a well driven drivebase is taking advantage of your drives strengths and weaknesses. Tanks shouldn't get t-boned because they can't get out of it. Mecanums shouldn't stay in corners to long because they can't push their way out if they get defense.

In my book, go tank! Only use mecanum if you drive it right and don't waste your time. Unless you want to try something new. Then go for it with gusto and lots of patience!

[T^2]

Tanks shouldn't get t-boned because they can't get out of it.

Yes, they can.

[RunawayEngineer]

This year in particular, Mecanyms = DNP for the simple reason that most of the game is spent in contact with other machines - either playing defense or under defense.
In another year where 6 machine pile-ups aren't common and defense isn't as critical, mecanum bots will be back on the table.

[MARS_James]

This year in particular, Mecanyms = DNP for the simple reason that most of the game is spent in contact with other machines - either playing defense or under defense.
In another year where 6 machine pile-ups aren't common and defense isn't as critical, mecanum bots will be back on the table.

I gotta ask, why did your team say yes to 2152 in South Florida then? The competition wasn't that deep I admit but you were next up in the pick order so the difference would have been negligible.

EDIT: Also 21 your other alliance partner ran mecanum this year, did your team try to talk 2152 out of it or no?

[AmoryG]

More professional sports analogies:

LeBron James can take the opportunity to retool the starting 5 he plays on when he calls up 9 of his closest contemporaries on the court for a rousing game of basketball at his house. While ESPN may want to carry the feed, the Elias Sports Bureau probably has better, more official things to do.

Even the FIBA Gold Cup is an event held by a major sanctioning body, but Anthony Davis' FIBA stats aren't coming up in the NBA books.

You want to bring up IRI? MLB doesn't count any statistics in official books for their all-star game either, even if some people walk home with special hardware.

If you want to challenge my anecdote of "not everyone is going out there with every resource they can muster to win the Alliterative Offseason of the week" with "my team does", that's your prerogative. Still doesn't make any of these events FRC-sanctioned events with any official meeting, which is the point Andrew was making earlier.

What was this thread about again?

I agree with that point, I just don't agree that we should completely ignore what a mecanum wheeled robot did just because they did it at an off season event.

[Lij2015]

Our first pick and our second pick(1533 and 2068) at Virginia had mechanum wheels as well as our number one robot on our list at Chesapeake(1629) picked us and our second pick also had mechanums(623)

I'm personally not the biggest fan of them, but at both our regionals we were the only bot on our alliance to not have mechanums, so I'd say as long as you can use them they don't affect anything haha.

[Kevin Leonard]

I've seen one exceptional implementation of Mecanum wheels in all of FRC ever- and that is Team 2052, KnightKrawler, as has already been mentioned in this thread.

I've also seen a few robots where the ability to strafe gives them a marginal benefit over a traction drive- 126 2013, 58 2012- where the ability to strafe gives them an ability they wouldn't have had otherwise.

I think all of these robots, barring perhaps 2052, would have been just as good or in some cases better with a traction drivetrain. However, it depends on the strategy and role your robot intends to play on an alliance.

If you were a cycler in 2013, a Mecanum drivetrain can be fine, sometimes even a good thing.

If you were a full-court shooter in 2013, where your entire strategy revolves around reaching a location and staying there for the match in order to score points, you should have a drivetrain that allows that.

In 2014, any robot that could get easily pushed across the field moved down the picklist, purely because that makes it more difficult for them to score. If you drove that same robot like 33, you move back up the picklist because your driving is fantastic and makes up for that to a degree.

If your robot exhibits negative qualities in a match, it will get penalized- not because it specifically has a certain mechanism on the robot, but because the robot doesn't do what needs to be done, and that could cost my team the regional.

[BBray_T1296]

If your robot exhibits negative qualities in a match, it will get penalized- not because it specifically has a certain mechanism on the robot, but because the robot doesn't do what needs to be done, and that could cost my team the regional.

Quoted for truth

[evanperryg]

Our alliance did this at Panther Prowl last year. We could not have been more pleased with the outcome.

At crossroads this year, my team picked 2 mecanum drives (2358, 4085) as the 8th seed. These robots were very strong as defenders because they were maneuverable and tall enough to block the other alliance's shooter. It's about picking a good alliance, not good robots.

[RunawayEngineer]

I gotta ask, why did your team say yes to 2152 in South Florida then? The competition wasn't that deep I admit but you were next up in the pick order so the difference would have been negligible.

EDIT: Also 21 your other alliance partner ran mecanum this year, did your team try to talk 2152 out of it or no?

I can't go into specifics, but there was a lot going on in regards to Alliance Selection at SFL that we (I especially) left to chance and the gamble didn't pay out in the brackets. I learned a lot and will be making adjustments for next year.

[MamaSpoldi]

In my experience, I have only competed with 2 robots that stick out in my mind as having implemented a mecanum drive in a fashion that in some way improved their overall strategic design and were executed well: Team 230 in 2010 and Team 58 in 2012. Both of these teams had creative ways to use their mecanum drives to do something that a standard tank drive could not (or at least not as simply or with the same resources). 230 used theirs to strafe sideways once atop the bumps in the field so they could engage their hooks and climb the tower, knowing they were lined up as they did so and not having to climb as far. 58 used their mecanum drive to position themselves against field elements in auto, moving along multiple axes to ensure they were in the proper location to consistently score their 10 point autonomous.


Yup. In 2010 our robot had mecanum wheels and we definitely used them to our advantage. It was a great season for us winning 1 Regional, finalist at the other, and we made it to the semi-finals at Championships.

I believe that it is very well known New England is where some of the heaviest defensive play occurs. watching events all over the US I noticed that in the west its offense offense offense. even in Texas the robots were made to play a purely offensive games, example 148 118, yes they play defense but there robot designs were more offensive. therefore I believe its true that mecanum wheels would be more common in those areas then up in new England.

Although I agree that New England has some of the heaviest defense, I believe it is still possible to use mecanum to your advantage. We won the WPI regional and were finalist at the Connecticut regional (both in New England) in 2010 because we used the mecanum as a specific feature... and also because we had a very sturdy and well implemented control system.

I also agree that using it just for the perceived maneuverability and without gyro stabilization and other optimized control software can be a recipe for poor performance.

[JesseK]

At least in the Capitol Region, many of the teams who did Mecanum drives 2010-2013 had magnificent and beautiful looking drive trains, followed by piecemeal and somewhat functional mechanisms. This tells me that while the Mecanum drive probably works well, the drive team probably had very little practice with using the drive train and mechanisms together. 623 was typically a good example of this, yet in 2014 they pulled it together and found a very lucrative role they could reliably fill, winning them Chesapeake.

It's tough to write off a Mecanum drive just by itself, IMO. It's far better to see how a team uses the Mecanum and how well the robot performs a role relative to other robots that perform the same role.

BTW, to me this wording is as hilarious and ironic as a license plate that says "Epic Fai" - I just may have to change wording in some of my drive train presentations:
... there are a few moments when they cause noticeable forced lateral motion of an opposing robot.

[Sam_Mills]

Originally Posted by DanBrowne
Tanks shouldn't get t-boned because they can't get out of it.

Yes, they can.

Source? We all know there are little tricks like deployable omnis or ball casters, choice of bumper fabric, etc., but if it was as simple as "yes they can," then RUSH would not have won MSC this year.

*Yes, there are methods of escaping a pin faster than others, but "yes they can," implies that T-bones are no more an issue for tank drives that other drive systems.*

*Edit: Rudeness + accuracy

[Chris is me]

Source? We all know there are little tricks like deployable omnis or ball casters, choice of bumper fabric, etc., but if it was as simple as "yes they can," then RUSH would not have won MSC this year.

If you were going to site "spin out of it," or "a good driver can get out of it no problem," then you should go on TBA and watch some high level play.

I am reasonably confident that 1678 probably knows a thing or two about handling defense... He isn't saying that T-bones are easily beatable, he's saying it is physically possible for a tank drive robot to escape a T-bone pin. This happens all the time, just not quickly or reliably enough to satisfy many teams.

[AdamHeard]

If you were going to site "spin out of it," or "a good driver can get out of it no problem," then you should go on TBA and watch some high level play.

I'm pretty sure they got to see some high level in play after back to back Einstein appearances as the #1 seed.

[Sam_Mills]

I'm pretty sure they got to see some high level in play after back to back Einstein appearances as the #1 seed.

There was no indication on the information visible in the post that he(she?) had been a part of 1678. I am very aware of how highly they perform, so I am actually pretty surprised that he/she would simplify friction pins as "yes, you can drive out of them."

When you consider that they play on the same field as 254 and 971, this comment is even more surprising, because if it was as easy as driving out of them, then 254 would not bother with their extensive testing of bumper materials, and 971(unless it is for envelope reasons) would not bother with an octagonal drivetrain. At some level you must know you cant just drive out of them either, as you too are updating your 2014 robot with a different bumper shape.

In the bulk of situations, the premise is wrong, regardless of who says it or what team they are from.

Edit: Although I will admit, my comment was unnecessarily rude. I am sure I am not the only one who gets tired of misinformation on CD.

[Kevin Sheridan]

There was no indication on the information visible in the post that he(she?) had been a part of 1678. I am very aware of how highly they perform, so I am actually pretty surprised that he/she would simplify friction pins as "yes, you can drive out of them."

When you consider that they play on the same field as 254 and 971, this comment is even more surprising, because if it was as easy as driving out of them, then 254 would not bother with their extensive testing of bumper materials, and 971(unless it is for envelope reasons) would not bother with an octagonal drivetrain. At some level you must know you cant just drive out of them either, as you too are updating your 2014 robot with a different bumper shape.

In the bulk of situations, the premise is wrong, regardless of who says it or what team they are from.

Edit: Although I will admit, my comment was unnecessarily rude. I am sure I am not the only one who gets tired of misinformation on CD.

With our new bumpers we can literally just drive straight out of a t-bone. No special maneuvers necessary. We did extensive tests using 971's practice bot, which is t-bone machine (Austin used that robot to t-bone our robot with the old bumpers until the batteries died), and we were able to escape t-bones in under 5 seconds every time.

[Sam_Mills]

With our new bumpers we can literally just drive straight out of a t-bone. No special maneuvers necessary. We did extensive tests using 971's practice bot, which is t-bone machine (Austin used that robot to t-bone our robot with the old bumpers until the batteries died), and we were able to escape t-bones in under 5 seconds every time.

Was this using the sailcloth covers? I bought some to do some testing with but have yet to get the chance to actually try it.

[Kevin Sheridan]

Was this using the sailcloth covers? I bought some to do some testing with but have yet to get the chance to actually try it.

Yes. We also had new pool noodles that were significantly harder than our old ones. A "downside" is that is also became really hard to play defense with the new bumpers. Our driver could no longer rely on friction pins and had to learn how to stay in front of robots better since it became really easy for other robots to "slide" past the bumpers.

[T^2]

When you consider that they play on the same field as 254 and 971, this comment is even more surprising, because if it was as easy as driving out of them, then 254 would not bother with their extensive testing of bumper materials, and 971(unless it is for envelope reasons) would not bother with an octagonal drivetrain. At some level you must know you cant just drive out of them either, as you too are updating your 2014 robot with a different bumper shape.

Tank drives such as 254's, 971's, or 1678's can get out of pins precisely due to clever use of bumper shape and material selection. One may even go so far as to say, as others in this thread have done, that the ease-of-use of such drivetrains allows teams to funnel more resources into other aspects of the robot, such as the aforementioned bumpers. Then again, even though I was part of team 1678 for the past two years, I didn't see a single one of our division qualification matches, so what do I know?

[Chris is me]

Yes. We also had new pool noodles that were significantly harder than our old ones. A "downside" is that is also became really hard to play defense with the new bumpers. Our driver could no longer rely on friction pins and had to learn how to stay in front of robots better since it became really easy for other robots to "slide" past the bumpers.

Did you guys try leaving the front and back noodles "squishy" and the side noodles "firm"? Seems like the best of both worlds there; obviously most T-bones don't involve the front of the robot.

[Kevin Sheridan]

Did you guys try leaving the front and back noodles "squishy" and the side noodles "firm"? Seems like the best of both worlds there; obviously most T-bones don't involve the front of the robot.

We did not have time to test different set ups for front/back and the sides. The bumpers were barely finished before SVR because Colin tested several different fabrics after Waterloo so we had little time to make the new set of bumpers. We also havent had time to revisit bumper testing this offseason because of Chezy Champs.

[c.shu]

So according to the poll as it is right now, ~40% of teams would either move you lower on their list or not pick you at all for having mecanum wheels.

[Sam_Mills]

Tank drives such as 254's, 971's, or 1678's can get out of pins precisely due to clever use of bumper shape and material selection. One may even go so far as to say, as others in this thread have done, that the ease-of-use of such drivetrains allows teams to funnel more resources into other aspects of the robot, such as the aforementioned bumpers. Then again, even though I was part of team 1678 for the past two years, I didn't see a single one of our division qualification matches, so what do I know?

I am very aware that some of the best teams in the world are able to get out of friction pins pretty quickly (which is a relative term, meaning the average time to get out of friction pins is anything but quick), this is not what I was addressing. I was addressing the other 2700+ teams that have to decide every year what drive train they want to use. Most of them will not do extensive research, and many will be making their bumpers on practice day. Accounting for this, if for some reason not getting T-boned is their number 1 priority, then tank with traction wheels is undeniably the worst decision they can make.

Tank drives are great and I would probably never willingly field anything else, but relative to other drive trains they are the most susceptible to friction pins. Outlier cases can be misleading, but perhaps my statement was too. Of course the teams that can get out of t-bones the best are some of the highest level teams, but just because something is possible doesn't make it likely.

I will concede however, that I should not have been so rude, and I apologize.

[efoote868]

So according to the unscientific poll as it is right now, ~40% of people represented on CD would either move you lower on their list or not pick you at all for having mecanum wheels.

Fixed it for you.

Going to quote myself to save some effort


This statement has always irritated me. Mecanum drive trains were extremely rare before AndyMark manufactured them, while swerve drive trains were (relatively) much more popular. The first year I remember AM mecanum wheels was in 2007; before that it took teams significant resources to manufacture them. If I recall correctly, two teams had them in 2005, maybe a half dozen in 2006, maybe a few more in 2007.

2008 didn't lend itself to mecanum drive trains (successful robots were geared 18fps+ with 2 stage transmissions). 2009 mecanum wheels were illegal, 2010 a large segment of the teams automatically ruled them out ("can't traverse the bump!"), similarly with 2012 ("can't balance on the bridge!").

Even now they're still taboo due to all the misinformation floating around.


In my opinion, "never made it to Einstein" has no place in this discussion because it ignores the wheel's history, as well as game designs and strategies. Until there is a year in which a large segment (say 20% or more of teams) in the FRC population uses mecanum wheels, I'm going to give no credit to that statement. After all, 100% of the robots on Einstein in 2009 had hard plastic wheels for their drive train.

In my humble opinion, the game this year did not lend itself to a strictly mecanum drivetrain. The field was wide open, the position of your robot mattered (favoring high traction drives), and quickness and speed mattered (in both short distances and cross field - something that benefits multiple speed transmissions).

If next year's game saw upwards of 30% of teams choosing mecanum drivetrains, and [I]still none of those teams make it to Einstein, there might be something to that statement.


Excluding robots based solely on their style of drivetrain isn't too intelligent; one would do better to look at the complete package as well as how the robot's functionality and performance could fit into a prospective alliance.

[pntbll1313]

If next year's game saw upwards of 30% of teams choosing mecanum drivetrains, and still none of those teams make it to Einstein, there might be something to that statement.

That's a good point. I would be interested in knowing the total number of teams that chose each drivetrain. I don't think a CD poll would ever be a good way of finding this out, as more advanced drive trains would be over represented. (new teams that don't follow CD and used the kit bot would be under represented, where great teams that pick swerve may have 5 members following CD and all select that option in the poll). We would need to look at real scouting data for the answer to that. For example in my division at Champs, Galileo had 10 mecanum bots that I know of based on my scouting. They went 8-2, 8-2, 8-2, 3-7, 6-4, 2-8, 4-6, 6-4, 5-5, and 3-7 in qualifications, for an overall 53-47 record. In Galileo at least, it looks like mecanum drive performed more or less on par with the rest of the field based on that overall record.

Knowing the overall percent of teams that choose each drivetrain, their percentage of making it to champs, and their winning records, would all be pretty interesting information. That probably isn't pertinent to this discussion though as I think you need to judge the robot on individual performance. The difference between a good swerve and bad swerve may be the difference between moving in a match or not, so you obviously can only take these generalizations so far. Assuming you have a functioning drive train I still feel driver practice is the single most important aspect with any drive train.

[c.shu]

Fixed it for you.

Sorry I was not specific enough for your liking. I will try to be much more descriptive next time I make a simple observation so as not to be criticized for the lack of detail.

[AdamHeard]

Fixed it for you.

Going to quote myself to save some effort




In my humble opinion, the game this year did not lend itself to a strictly mecanum drivetrain. The field was wide open, the position of your robot mattered (favoring high traction drives), and quickness and speed mattered (in both short distances and cross field - something that benefits multiple speed transmissions).

If next year's game saw upwards of 30% of teams choosing mecanum drivetrains, and [I]still none of those teams make it to Einstein, there might be something to that statement.


Excluding robots based solely on their style of drivetrain isn't too intelligent; one would do better to look at the complete package as well as how the robot's functionality and performance could fit into a prospective alliance.

Statistically it doesn't really matter what percentage of teams run a certain drive, it's what percentage of competitive teams are running a certain drive.

I don't really care what n% of teams run, as it's reasonable to state that for whatever reason n% aren't a top team.

However, the decision making process of the proven competitive teams provides much more insight. The top teams, far more than any other, are constantly assessing things for competitiveness. They are also generally the most willing to COMPLETELY contradict historical beliefs (of the public, or their own) because something has value to them.

To me it speaks volumes that more top teams don't run them. I'd wager a fair number of top teams have tested mecanums in private, and chose to not use them. I won't say that we are or aren't a top team, but we tested mecanums (this is the first time it's public knowledge) and were not happy with them versus a fast and well tuned Nwd.

[efoote868]

To me it speaks volumes that more top teams don't run them. I'd wager a fair number of top teams have tested mecanums in private, and chose to not use them. I won't say that we are or aren't a top team, but we tested mecanums (this is the first time it's public knowledge) and were not happy with them versus a fast and well tuned Nwd.

Top teams don't run mecanum drives because they don't have to. When they choose to use a holonomic drivetrain, they have the resources and can afford the added complexity of swerve or butterfly - they engineer out the known deficiencies.

To me, the beauty of AM's mecanum wheel is that it makes easy holonomic drivetrains available to low resource teams.

IF we see more field layouts like 2010 (with tight areas to maneuver and precision driving required), I suspect we'll see more teams chose holonomic drivetrains, which will mean more mecanum drives.

[Andrew Schreiber]

To me, the beauty of AM's mecanum wheel is that it makes easy holonomic drivetrains available to low resource teams.


I'm going to disagree with this notion because, as it's written, it's missing a key point.

(Keep reading after it, I do clarify it significantly.)

It makes BAD holonomic drivetrains available to low resource teams.

You know, I can go out and buy a swerve module too? I'd make the exact same statement about a drive with them. Why? Because the hard part about holonomic/omni directional drive systems is they are hard to control. The mechanical aspects of things are hard (yes, even mecanum wheels) but building a reliable, tuned, and intuitive method of controlling them is HARD.

So, let's take team number 4xxx. They are your average semi experienced team. Some resources but not enough to build a second bot. Enough resources to build a solid manipulator and put it on a KOP drive train. Maybe even get a couple hours of driver practice.

Now imagine they put mecanum wheels on that KoP drive (because it's not hard. Costs about as much as adding shifters which is another system this logic CAN apply to). So, I've added some extra work beyond implementing simple skid steer drive. I guess I can use the WPILib's Mecanum implementation. But my robot turns as it strafes because my CG isn't perfect, what do I do? It's either something the driver has to get used to or it's something I have to invest more of my most limited resource (manpower) into fixing. So, now my manipulator has lost an iteration or small tweaks? For what gain?

Most teams don't think of problems this way. But they should.


Mecanum wheels are a solution to a problem. But they aren't as simple as slapping them on and using the WPILib Mecanum Drive class. That's a great way to build a crappy omni directional drivetrain. If you want it to be world class you need to develop and test a reliable and intuitive user interface. And you need to understand how it changes how you can interact with game objects and the field. It needs to be built into your greater strategy. And your driver needs to understand the limitations and benefits of your drive system.


Omni Directional drivetrains ARE inherently difficult. Nothing is ever going to make them easy to do. COTS parts simplify the mechanical issues with them. But the hard part is always going to be the UX.

[efoote868]

I agree that a team needs to build their robot for a strategy. In recent years, the ability to strafe hasn't been high on my priority list.

But if a low resource team were to come to me, and tell me that they must have a holonomic drivetrain for their strategy, and they wanted a recommendation, I would recommend mecanum 9 / 10 times.

In my experience, mecanum drive trains are simple to implement, can be robust with just a gyro for field centric control, and when all else fails you can swap out 4 wheel chair wheels.

I agree though, strategy trumps drivetrain.

[AdamHeard]

But if a low resource team were to come to me, and tell me that they must have a holonomic drivetrain for their strategy, and they wanted a recommendation, I would recommend mecanum 9 / 10 times.


I would tell them their strategy is likely flawed and they don't need holonomic movement.

[Jared]

I would tell them their strategy is likely flawed and they don't need holonomic movement.

So true. There has yet to be a game that really requires holonomic drive to win.
(WildStang 2003 may be an exception)

[AdamHeard]

So true. There has yet to be a game that really requires holonomic drive to win.
(WildStang 2003 may be an exception)

Well, I'd buy the argument that in some games holonomic makes sense in some ways.

However, for a team with presumably not the same resources as a top team, when you factor resources into strategy, mecanum in my opinion is never the option.

If you're at that level, there are likely other areas of the robot that would have a greater payout for the same resource investment.

[efoote868]

I would tell them their strategy is likely flawed and they don't need holonomic movement.

If they wanted to be a lap runner in 2008, or they wanted to quickly clear soccer balls from a zone in 2010, or they wanted to strafe in front of the racks in 2011, or they wanted to strafe sideways to quickly catch a truss shot and release a ball in 2014, or they want to move in an L shaped fashion without changing orientation in 2015 then a holonomic drivetrain might be the correct fit for them.

You cannot know the best implementation to a strategy without knowing the strategy, and you cannot know the strategy without knowing the game rules.

[AdamHeard]

If they wanted to be a lap runner in 2008, or they wanted to quickly clear soccer balls from a zone in 2010, or they wanted to strafe in front of the racks in 2011, or they wanted to strafe sideways to quickly catch a truss shot and release a ball in 2014, or they want to move in an L shaped fashion without changing orientation in 2015 then a holonomic drivetrain might be the correct fit for them.

You cannot know the best implementation to a strategy without knowing the strategy, and you cannot know the strategy without knowing the game rules.

You're not reading what I'm saying.

I agree those features are cool, and all have some arguable utility...

My argument is that if the same amount of resources put into that were put into something else, the net competitiveness of the team would be higher.

[MARS_James]

If they wanted to be a lap runner in 2008, or they wanted to quickly clear soccer balls from a zone in 2010, or they wanted to strafe in front of the racks in 2011, or they wanted to strafe sideways to quickly catch a truss shot and release a ball in 2014, or they want to move in an L shaped fashion without changing orientation in 2015 then a holonomic drivetrain might be the correct fit for them.

You cannot know the best implementation to a strategy without knowing the strategy, and you cannot know the strategy without knowing the game rules.

Speaking from experience in those games, in 2008 unless you were small (like 148) lap running would not give you a significant advantage for it to be a reliable strategey since the field got very cramped. 2010 was a horrible year for mecanum bots in florida because the cramped quarters actually made for viscous defense so clearing soccer balls would have been a challenge. 2011 as a team that ran mecanum for the exact reason you listed I wish my team would have gone another way, sure we were an alliance captain but the draw backs it gave us were not worth it especially come eliminations. 2014 from my observation the best catchers did not have mecanums this year, the 2 best catchers in our state, my own robot and its twin 1251, ran 8 wheel drive.

There will be a day when the best solution for a game is a well designed holonomic drive, unfortunately for most teams that will mean upper level teams running swerve, mid level teams running octanum, and mid-low level teams with pure mecanum. That game will have a mecanum wheel make it to Einstein, and touch the carpet, but swerves will rule.

[efoote868]

You're not reading what I'm saying.

I agree those features are cool, and all have some arguable utility...

My argument is that if the same amount of resources put into that were put into something else, the net competitiveness of the team would be higher.

I'd maintain that the amount of man hours required to build a decent mecanum drive are not that much more than the amount of man hours required to build a decent tank drive, and the difference in man hours is minimized compared with any other holonomic drive.

[EricH]

I'd maintain that the amount of man hours required to build a decent mecanum drive are not that much more than the amount of man hours required to build a decent tank drive, and the difference in man hours is minimized compared with any other holonomic drive.

Mechanically, yes. The amount of man-hours required to build a tank drive and a mecanum drive will be very similar from a mechanical standpoint. 2 more gearboxes, possibly wheel assembly, that's probably under a typical meeting for 1-2 people.

HOWEVER, to truly calculate the time, you need to factor in programming. A tank drive can be as simple as mapping two joystick axes to two PWM (or CAN) outputs (in teleop, anyway). A mecanum drive requires three joystick axes mapped to four PWM/CAN outputs, and the outputs can all be different (in theory at least, in practice it'll more likely be two and two, but which two changes a bit...). Sure you can use the pre-done stuff and adapt it--but you are going to want to tweak it to match your system, which may or may not be more trouble than it's worth.

That extra time may be the difference between a so-so vision code or so-so automode and a good or great vision or automode.

[Kevin Sheridan]

Mechanically, yes. The amount of man-hours required to build a tank drive and a mecanum drive will be very similar from a mechanical standpoint. 2 more gearboxes, possibly wheel assembly, that's probably under a typical meeting for 1-2 people.

HOWEVER, to truly calculate the time, you need to factor in programming. A tank drive can be as simple as mapping two joystick axes to two PWM (or CAN) outputs (in teleop, anyway). A mecanum drive requires three joystick axes mapped to four PWM/CAN outputs, and the outputs can all be different (in theory at least, in practice it'll more likely be two and two, but which two changes a bit...). Sure you can use the pre-done stuff and adapt it--but you are going to want to tweak it to match your system, which may or may not be more trouble than it's worth.

That extra time may be the difference between a so-so vision code or so-so automode and a good or great vision or automode.

I would even argue that mechanically there is a pretty big difference too. The tolerances are a lot tighter when machining and assembling the frame for mecanum, otherwise you could end up with only 3 wheels on the ground and a really bad drivetrain. 6WD tank is much more forgiving in regards to bad machining.

[donkehote]

I would tell them their strategy is likely flawed and they don't need holonomic movement.

QFT

[Andrew Schreiber]

I would even argue that mechanically there is a pretty big difference too. The tolerances are a lot tighter when machining and assembling the frame for mecanum, otherwise you could end up with only 3 wheels on the ground and a really bad drivetrain. 6WD tank is much more forgiving in regards to bad machining.

Oddly, for mecanum you want a floppy chassis. Rigidity is your enemy. It's one of those small things most teams miss when building mecanum and then get confused when they lift a corner on a mounting plate under the carpet and their bot gets all squirrelly.

But I wouldn't know this unless I've built a handful of omni directional drives (kiwi and a handful of mecanums) and fielded them. It's NOT as simple as people think.

[Max Boord]

I would even argue that mechanically there is a pretty big difference too. The tolerances are a lot tighter when machining and assembling the frame for mecanum, otherwise you could end up with only 3 wheels on the ground and a really bad drivetrain. 6WD tank is much more forgiving in regards to bad machining.

My team has run varying degrees of "floppiness" and pretty conclusively showed a rock solid chasis with properly tuned PID loops preforms about the same or worse than a floppy frame running the default WPI holonomic code. The difference also increases as the robot goes through more and more events.

EDIT:
CG has far more of an effect than frame rigidity. Even 2 metal pneumatic tanks on one side caused strafing to deteriorate noticeably.

[jwfoss]

After further thought, I believe my first post was not blunt enough.

In reality, if mecanum wheels are the answer, I have found that I have asked my self the wrong question. There has not been a single game in my opinion where mecanum drive (or any omni-directional drive for that matter) has presented a significant enough advantage to justify the development of such a drivetrain. It goes against a fundamental rule that anything new in a drivetrain must be tested in the offseason.

Remember the three most important parts of a robot...

[Nemo]

That extra time may be the difference between a so-so vision code or so-so automode and a good or great vision or automode.

Maybe our team is just "challenged," but we have repeatedly failed to get vision processing to work, whereas adding gyro feedback to a mecanum drive was not a big deal.

We can get vision processing code to work in the shop, but we haven't ever gotten it to work on a field with venue lighting and bandwidth limitations. We've also had communications issues with the camera and program lag with the camera turned on. These are solvable problems, but we have run out of time in the years when we tried to make it work.

[Max Boord]

We can get vision processing code to work in the shop, but we haven't ever gotten it to work on a field with venue lighting and bandwidth limitations.

Have you ever tried going out to the field on thursday durring lunch/ after matches end and tuning it then? I know orlando lets teams do this if for some reason practice matches are not being run.

Also, adding gyro feedback for field orriented drive is incredably simple until it starts to drift.

[efoote868]

Also, adding gyro feedback for field orriented drive is incredably simple until it starts to drift.

In my experience, this isn't a problem in the 2 minutes required to run a match.

[Monochron]

In my experience, this isn't a problem in the 2 minutes required to run a match.

You may want to qualify that with "in my experience with very low drift". I have seen large amounts of drift absolutely ruin a robot's ability to move reliably. Like always, strict tolerances are needed for a control system like this.

[efoote868]

You may want to qualify that with "in my experience with very low drift". I have seen large amounts of drift absolutely ruin a robot's ability to move reliably. Like always, strict tolerances are needed for a control system like this.

Both years using field-centric drive utilized the kit gyro, and as far as I know the drivers never needed to reset the orientation.

I do recall a problem one time shortly after installation, but that was because we'd accidentally hooked to the temperature output.




Does anyone know off hand what expected drift is over time?

[Jared Russell]

Does anyone know off hand what expected drift is over time?

It's...complicated. Drift happens because you are taking an angular velocity measurement and integrating it over time. Small errors in velocity measurements add up to big errors in position given sufficient time. There are many sources of errors, some of which are random and others of which are systemic:

1) Bias drift. MEMS gyros are sensitive to temperature...and they self-heat when powered. Several minutes after booting your cold robot, the gyro will think it is spinning because the null voltage when it was calibrated with has changed. Leaving your robot on for several minutes prior to match start (and recalibrating the gyro soon before the match starts) helps somewhat.

2) Axial misalignment. If your gyro is not perfectly level with the field, you will accumulate small errors over time. Aligning the gyro to your frame is one thing; going over a bump or doing a wheelie on the field is another.

3) Saturation. If your gyro measures up to 250 deg/s rotation and you spin faster than that, you will underestimate your rate of turn and drift will accumulate quickly.

4) ADC discretization and conversion noise. Your analog measurements lose some precision during the conversion to a digital measurement. Carefully selecting the bandwidth to use during sampling helps somewhat, though narrower bandwidth may limit your ability to sense rapid turns.

5) Cross axis sensitivity. Unfortunately, it turns out that gyros only MOSTLY measure angular velocity...they also pick up linear accelerations (typically <1% of cross axis sensitivity, but every little bit counts when integrating).

6) Thermomechanical noise. Unfortunately, even if you perfectly compensate for all of the other factors, Brownian motion occurs within the gyro and will add up over time. There is nothing you can do about this one other than to buy a more expensive gyro.

Various specs for all of these factors are available for most gyros. Turning this into a "degrees per minutes" position drift estimate is possible using complex math; for the KOP gyro (http://www.usfirst.org/uploadedFiles/Community/FRC/Game_and_Season__Info/2010_Assets/ADW22307_RevE.pdf) from a few years back (which I believe is still the gyro available through FIRST Choice as of last season), about 200 degrees per hour is the quoted drift rate. Drift in position occurs exponentially, so in about a minute you would expect ~.05 degrees of drift...IF you perfectly account for the accountable factors above (which is almost never the case in FRC). In my experience, a degree or two of position drift per minute is more achievable (as long as you don't spin too fast and stay on a flat and level field).

[efoote868]

In my experience, a degree or two of position drift per minute is more achievable (as long as you don't spin too fast and stay on a flat and level field).

If you observed drifting of more than 10 degrees per minute and the robot wasn't saturating or shaking the gyro, what would you think? Would that be typical of the FRC gyro, or would that indicate a bad sensor?

[Tom Bottiglieri]

If you observed drifting of more than 10 degrees per minute and the robot wasn't saturating or shaking the gyro, what would you think? Would that be typical of the FRC gyro, or would that indicate a bad sensor?
We have not seen any of the recent kit provided gyros net that bad of a drift. I think bullet point #1 in Jared's list is the biggest culprit to gyro drift in a typical FRC match. Competitions are usually held in cold arenas and your robot won't start moving until a minute or two after you turn it on. We map a button on our operator console to reset the gyro calibration, and print out the current integrated angle so the driver can assess if they need to reset it. Ideally this is something we do automatically next year.

[efoote868]

One thing I would like to test is driving a field centric drive with a very large gyro drift (say +/-10 degrees).

If the driver can see the robot, I don't think a drift that large will matter (in tele-op). An interesting question would be, "How long can someone drive a field centric drive before performance suffers from gyro drift?"

I'd hypothesize that you wouldn't see a big difference in performance until drift reached ~15 degrees.


Coming back around to my questions, if performance doesn't suffer with 10 degrees of drift, I don't think gyro drift should be a concern preventing teams from using field centric drives.

[Max Boord]

One thing I would like to test is driving a field centric drive with a very large gyro drift (say +/-10 degrees).

I tried. Its impossible. Also, its not even the problem of a set drift. Its when it starts to drift several degrees per second. then, when robot not moving (to inbound, shoot, whatever) and you try to drive again you can not tell where is forward.

Once you realize the problem exists things don't get much better. Your robot will start driving in ever shrinking circles when you press forward.

If the driver can see the robot, I don't think a drift that large will matter (in tele-op). An interesting question would be, "How long can someone drive a field centric drive before performance suffers from gyro drift?"
2 degrees fixed is noticeable. 10 feels very weird. 2 degrees per second is enough to make a robot impossible to drive.


Coming back around to my questions, if performance doesn't suffer with 10 degrees of drift, I don't think gyro drift should be a concern preventing teams from using field-centric drives.
The main reason I think field-centric control it is not used more is fear of a delicate piece electronics being trusted to control a drive train. In addition, robot-centric is not that hard to understand.

[efoote868]

I tried. Its impossible. Also, its not even the problem of a set drift. Its when it starts to drift several degrees per second. then, when robot not moving (to inbound, shoot, whatever) and you try to drive again you can not tell where is forward.

Gyro drift occurs when the gyro has very small errors in the rotation value it is reading (turning at 1 degree / second versus reading 1.001 degree / second).

When you integrate the error of rotation, you get an error in position.

What was discussed was that after the gyro runs for sixty seconds, the cumulative error is about 2-3 degrees, not 120 to 180 degrees.


Yes, a field centric robot that is off by 2-3 degrees per second is going to be difficult to drive, but I'd say something is fundamentally wrong with the system you're referencing (gyro not calibrated, pin out is wrong, code is wrong).

[Chris Hibner]

We have not seen any of the recent kit provided gyros net that bad of a drift. I think bullet point #1 in Jared's list is the biggest culprit to gyro drift in a typical FRC match.

I agree with this assessment. We always throw out the WPI library and do our own bias calculation and integration. Our method is simple: big moving average for the bias calculation up until the instant the FMS switches from disabled to auto - then we freeze the bias and start integrating.

[Max Boord]

Gyro drift occurs when the gyro has very small errors in the rotation value it is reading (turning at 1 degree / second versus reading 1.001 degree / second).

When you integrate the error of rotation, you get an error in position.

What was discussed was that after the gyro runs for sixty seconds, the cumulative error is about 2-3 degrees, not 120 to 180 degrees.


Yes, a field centric robot that is off by 2-3 degrees per second is going to be difficult to drive, but I'd say something is fundamentally wrong with the system you're referencing (gyro not calibrated, pin out is wrong, code is wrong).

Interesting. with the KOP gyro my setup would accelerate up to 20 degrees per second in some cases while in others would only move 1-2 degrees per minute. The drift would also change direction so I do not think it was a calibration issue. I even tried it on a spare CRIO and got similar results to one encased inside a driving competition robot.

[thegnat05]

My team had mecanum drive train for Ultimate Ascent and that was the season that our team actually performed the best. We were alliance captains and made it to semi-finals at our regional. We also won the quality award. In my opinion mecanum is a valid choice for a drive chain and when used on the right robot, can be very effective.

[Gdeaver]

Allot of post on this subject. My take on it is that going forward any team that is considering a omnidirectional drive system should evaluate the performance of that system compared to the six cim tank drive. The new standard. The power of 2 additional cims changes the game. Low resource teams can purchase Cots 3 cim gear boxes and have a very good powerful drive train easy now. This year with swerve we found that when we went up against the best we were too slow and at the same time did not have enough traction. We as a team realize that our current 4 cim swerve is not enough going forward. We as a team are working on taking swerve to the next level by adding more power and easier driver control. We've built a tribot and have been testing it. We have a 6 cim swerve module designed but not built for it . There are allot of positives on the drive ability of it but also negatives for the shape. For a 4 swerve module we have built a quasi cvt 1 cim module and are designing a 4 cim 4 mini cim drive. At the same time we're working on methods to make an omni directional robot easier to drive. Yes, there is a drive train arms race. Keep up or get nuked next year. Mecanums may have been relevant in the past . There utility in the future is very questionable. In my opinion.

[cjl2625]

About the gyros:
In our swerve drive, sometimes I'll turn on the robot and the gyro might start drifting at 3 deg/sec at times. Even when it doesn't drift this bad, it accumulated quite a bit of error in a match. This seems inevitable; we've replaced the gyro many times.

We have a gyro reset button, and I end up calibrating the gyro many times in match. Even with the reset, I sometimes find myself driving with 25+ degrees of error.
Somebody above said that this was impossibly disorienting, but I find it manageable.
I got used to gyro inaccuracies after some practice.

Nevertheless, we're determined to improve the system. We are going to try using two gyros, one mounted upside down. 1717 does this and says it helps a lot.

Even if I had to deal with gyro drift forever, if still greatly prefer field centric over robot centric

[Chris Hibner]

About the gyros:
In our swerve drive, sometimes I'll turn on the robot and the gyro might start drifting at 3 deg/sec at times. Even when it doesn't drift this bad, it accumulated quite a bit of error in a match. This seems inevitable; we've replaced the gyro many times.

We have a gyro reset button, and I end up calibrating the gyro many times in match. Even with the reset, I sometimes find myself driving with 25+ degrees of error.
Somebody above said that this was impossibly disorienting, but I find it manageable.
I got used to gyro inaccuracies after some practice.

Nevertheless, we're determined to improve the system. We are going to try using two gyros, one mounted upside down. 1717 does this and says it helps a lot.

Even if I had to deal with gyro drift forever, if still greatly prefer field centric over robot centric

I don't think you need two gyros or non-kit gyros. We have seen similar problems with the WPI gyro code, which is why we do our own bias calculation and integration - see my above post. If you need more details, let me know.

[cjl2625]

I don't think you need two gyros or non-kit gyros. We have seen similar problems with the WPI gyro code, which is why we do our own bias calculation and integration - see my above post. If you need more details, let me know.

Hmm, that's interesting.
Yeah, I'd love to know the details of how you guys calculate that.

[Chris Hibner]

Hmm, that's interesting.
Yeah, I'd love to know the details of how you guys calculate that.

This is going to be a long post. I'm trying to target this post at relative newbies, so if any of this is old news feel free to skip to the good parts.

(Since this got long, I'll break it into two posts: the first will be explanation (the "why), and the second will be the "how" part.)

The vast majority of gyro "drift" is usually due to a poor voltage bias calculation.

What is this "bias" that you speak of? The sensor outputs a voltage relative to the angular rate (these devices are angular rate (speed) sensors, not heading sensors). The voltage when still (angular rate = 0) is typically around 2.5V for a 5V sensor, but in reality that can vary for many reasons. Therefore, the software always needs to calculate the voltage bias before using the angular rate to compute a heading. The bias is used by subtracting it from each sample before computing the heading. Thus, after the "bias subtraction", the sensor output is transformed from 0 - 5V to approximately -2.5 - +2.5V.

How is the bias typically calculated? The bias is calculated by averaging a number of samples when the software thinks the gyro is still. The WPI gyro software performs this calculation as soon as the software begins to run. Any movement of the robot just after power-on until the bias calculation is finished will cause your bias to be bad, and you will get a large gyro drift. "When is the WPI code finished calculating it's bias so we know it's safe to move the robot?" you ask. Good question. I don't really know, which is one of the reasons we don't use it. Another reason we don't use it is because we find it nearly impossible to keep the robot perfectly still immediately after power on.

Can the bias of the gyro drift? The short answer is yes. If you calculate a good bias, and then the bias changes, your heading will drift over time. That's not good.

What causes the bias to drift I don't want to repeat a good post: see Jared Russell's post above. One important I'll repeat: the bias is likely to drift as the gyro warms up. Therefore, in an ideal world you would like gyro to be at its steady-state before calculating the bias. The WPI code does this immediately after power-on so the likelihood of bias drift is much higher than if you could wait.

Ok, then in your opinion when should the bias be calculated There are 3 main criteria for me: 1) The robot MUST be PERFECTLY STILL; 2) The gyro should be at steady state; and 3) The bias calculation should be performed as close as possible to the time your are going to start using it (in other words, a bias calculation from 5 minutes ago is much less likely to be accurate than a bias calculated 1 second ago).

So when do YOU calculate the bias? Simple answer: the instant before the match begins. This ensures it satisfies all three criteria: 1) the robot will be perfectly still since all humans have to be off the field or someone is getting DQ'd; 2) The gyro should be at steady state since it has been a few minutes since power-on; and 3) the instant before the match starts is as close as you can get to when you start using the bias.

What are the disadvantages of your method? The WPI gyro code can't be used, and you have to write all of your own software.

[Chris Hibner]

So, how do you actually do it?

First, we throw out the WPI gyro library and just use the analog input library. You'll need to know the sensitivity of your gyro (in deg/s/V), but if you don't know that you can make a guess and figure it out with some testing. We always do the tests anyway to characterize the sensor we're using.

You need a few things in your code:

1) An array of gyro voltage readings so you can calculate a moving average. This moving average will be stopped once the match begins and this average will become your gyro bias.

2) A variable to indicate that your robot has become enabled once during this power cycle. Why is this important? Because you don't want to resume calculating the bias in that short disabled period between auto and teleop. You may say, "but you said a bias calculated as close to the the current time possible is better, so wouldn't it be good to calculate it again just before teleop?" The answer is no, because then you have a good chance of violating the most important criteria: the robot MUST be still. There is a decent chance that either your robot was still in motion as power was cut to end autonomous, or some other robot runs into you at the end of autonomous. Either way, the safe bet is to just use the bias from just before auto mode starts.

3) An integral to calculate the heading from the angular rate samples. (If you don't know what that is, it's a fancy term for area under a curve, which is a big sum. Look it up on wikipedia.)

So here it goes with the code:

(note: caveats apply. a) I'm doing this by the seat of my pants, so there may be a bug or two; b) this is more intended to be pseudo-code rather than copy-and-paste C code; c) this is intended to provide a general idea - not a final solution - see (a) and (b))

(note 2: I'm going to assume you have a typedef.h file and use descriptive types. f32 = 32-bit float, u8 = unsigned 8-bit integer, s16 = signed 16-bit integer, etc.)

defines and global variables

#define GYRO_BIAS_SIZE 32
#define GYRO_ANALOG_CHAN 1
#define GYRO_SENSITIVITY 0.025 /* in deg/s/V */

f64 gyroBiasArray[GYRO_BIAS_SIZE];
f64 gyroBiasSum;
u8 gyroBiasIdx;
bool visitedEnabled;
f64 gyroHeading;
f64 currentTime;
f64 previousTime;


In your "init" function

gyroBiasSum = 0;
gyroBiasIdx = 0;
visitedEnabled = FALSE;
gyroHeading = 0;

for (u8 i = 0; i < GYRO_BIAS_SIZE; i++)
{
gyroBiasArray[i] = 0;
}


In your fastest periodic loop


f64 gyroV;
f64 gyroDPS; /* in deg/sec */
static f64 gyroDPS_prev = 0; /* deg/sec previous sample - used for trapezoidal integration */

if ((getFMSMode() == AUTO) || (getFMSMode() == TELEOP))
{
visitedEnabled = TRUE;
}

previousTime = currentTime;
currentTime = getTickCnt_ms() / 1000;

/* sample the gyro voltage */
gyroV = getAnalogVoltage(GYRO_ANALOG_CHAN);


/* calculate the bias if we have not yet been enabled */
if (FALSE == visitedEnabled)
{
/* compute the moving average by first calculating a moving sum
the moving sum is computed by first subtracting the oldest
sample in the bias array, then add the current sample. Then
replace the oldest sample in the bias array with the newest sample. */
gyroBiasSum -= gyroBiasArray[gyroBiasIdx];
gyroBiasSum += gyroV;
gyroBiasArray[gyroBiasIdx] = gyroV;
gyroBiasIdx++;
if (gyroBiasIdx >= GYRO_BIAS_SIZE)
{
gyroBiasIdx = 0;
}
}
else
{
/* if we're here, it means we've been enabled. Therefore, we need to
be calculating the heading instead of the bias. */

/* first, subtract bias voltage and convert to degrees/sec */
gyroDPS = (gyroV - (gyroBiasSum / GYRO_BIAS_SIZE)) * GYRO_SENSITIVITY;
/* Now, compute heading using trapezoidal integration */
gyroHeading += ((gyroDPS + gyroDPS_prev)/2) * (currentTime - previousTime);
gyroDPS_prev = gyroDPS;
}


And there you have it.

I would highly recommend characterizing the sensor you're using rather than just using the sensitivity from the data sheet. Not only can the sensitivity vary from part to part, but the sensitivity can be reduced if the gyro isn't mounted perfectly flat. Here's how we do it:

1) make your best guess at the gyro sensitivity (use the nominal sensitivity in the data sheet if you have it).

2) Place the robot flat up against a wall and start your code.

3) After sufficient time to allow a good bias calculation, enable your robot into teleop mode.

4) Rotate your robot 180 degrees and place the robot flat against the wall again (so you ensure your robot rotated as close to exactly 180 degrees as possible).

5) Write down the computed heading.

6) adjust your gyro sensitivity in your code using the following calculation: NewGyroSensitivity = OldGyroSensitivity * ActualRecordedHeading / 180

7) Repeat the procedure until your recorded heading is VERY close to 180 deg.

Last note: we actually use LabVIEW. I can post that as well if you don't do textual programming.

If there are any questions, let me know.

[cjl2625]

Wow, thanks for posting this!
I'll share this it my team.

What exactly do you mean by the "init function"? Do you mean to put that in Begin.vi? (We use LabVIEW too)
How fast do you run that periodic loop?
And you just reference the gyro heading in tele/auto by using a global variable, right?

[Chris Hibner]

What exactly do you mean by the "init function"? Do you mean to put that in Begin.vi? (We use LabVIEW too)

Correct. However, for LabVIEW it's much easier than the C version I posted. You don't need much in Begin.vi other than wire a FALSE into the visitedEnabled global (if you choose to make it a global - we make it global because we use it in a few places).

Download "The Secret Book of Labview v1.0" here (http://www.chiefdelphi.com/forums/showpost.php?p=1336294&postcount=21) and go to page 25 (page numbered 20, page 25 of the PDF) and try to implement the "boxcar filter" - that will be your moving average that you need for your bias calculation.

How fast do you run that periodic loop?

I don't have the code in front of me, but it's either 5 or 10 ms. We've been doing most of our control code in a 25 ms loop, but we have one really fast loop just for this.

And you just reference the gyro heading in tele/auto by using a global variable, right?

Correct

[Pault]

What are the disadvantages of your method? The WPI gyro code can't be used, and you have to write all of your own software.

Although I have never done this before, I would imagine this only holds true for LabVIEW users. One of the benefits of Java and C++ is that you can change pretty much any of the high level code in the WPILIB. In this case, just extend the gyro class and rewrite whichever part of it calculates the bias.

Edit: There is a convenient int in the Gyro class (Java) called m_center. All you would have to set that variable to voltage of the analog channel at the start of the match. Unfortunately it is set at the default access level without a modifier method, so you would have to extend the gyro class (or just make a slight modification to your version of the WPILIB).

[Joe Ross]

One of the benefits of Java and C++ is that you can change pretty much any of the high level code in the WPILIB. In this case, just extend the gyro class and rewrite whichever part of it calculates the bias.

It's not quite so easy (in Java at least). The method that calculates the gyro bias is private, so it can't be extended. You have to patch WPILib.

[Pault]

It's not quite so easy (in Java at least). The method that calculates the gyro bias is private, so it can't be extended. You have to patch WPILib.

As I said in my edit, you don't have to modify that code. Just overwrite the m_center variable at the start of the match. Good catch though.

[Tom Bottiglieri]

Edit: There is a convenient int in the Gyro class (Java) called m_center. All you would have to set that variable to voltage of the analog channel at the start of the match. Unfortunately it is set at the default access level without a modifier method, so you would have to extend the gyro class (or just make a slight modification to your version of the WPILIB).
Kind of, but that's not really how the gyro works under the hood. The FPGA onboard the cRIO has a hardware accumulator which can integrate a signal coming from the ADC at a specific sample rate. This is used for the gyro as the timing is really precise and fast. In software, there is a memory mapped interface to the FPGA used to configure and view state on the various subsystems (accumulators, counters, etc.). The code in initGyro does the following:
1) Reset and init an accumulator on the channel the gyro is plugged in to.
2) Wait 1 second
3) Turn on the accumulator
4) Wait 5 seconds
5) View the 'value' of the accumulator (a 64b long) and the count of samples taken to get there.
6) Find the average voltage per sample, set that as the new 'center' for the accumulator.
7) Reset the accumulator

When you ask for an angle reading, it just reads the current 'value' out of the accumulator and scales it to a human understandable value.

m_center holds a local copy of what got written into the FPGA's accumulator as the 'center'. It is just a cached value used to convert the last few average samples on the ADC to a measurement with correct units in getRate. (Remember, the accumulator is doing the heavy lifting for measuring position). Writing to m_center won't really help here.

I don't know why WPILib chose to wait for 5 seconds to denoise the sensor. It seems like this can be done in WAY less samples (like, 10ms).

[Tom Bottiglieri]

It's not quite so easy (in Java at least). The method that calculates the gyro bias is private, so it can't be extended. You have to patch WPILib.
So long as you put your subclass in the edu.wpi.first.wpilibj package you should be able to poke around at the accumulator object, so you can just build a new init method. Which is dumb.

[Gdeaver]

I don't think drift is all of the problem. This year we used the KOP gyro for autonomous. Drift is no problem for this short period. Back in 2012 we never got an acceptable field centric working. 2 weeks ago the programming team developed field centric code again. Put it on the robot with the kop gyro and with some adjustments in code it works fairly well. Most of the testing was done at low velocity checking rotations and stuff. Yes, there was drift but, not excessive. Would be fine for a 2 minute match. Last wed. The drivers tried the field centric code and when the robot is driven hard the the way swerve should be, The gyro goes nuts. Large 10 15 20 30 40 degree swings in 10 to 15 seconds in both rotational directions. The drivers where practicing figure eights. Had to put robo centric back on for the rest of the night. This has to be some thing other than drift. Acceleration affecting the gyro rate? We have some other digital gyros to test. Just have to figure out and program them into the c-rio. We need a rock solid orientation to use field centric in competition. Is this a swerve issue, how do other teams do it.

[efoote868]

Could the gyro have been saturated?

[Greg McKaskle]

Just to pile onto a thread that was once about mecanum robots.

The LabVIEW WPILib code is just as open as C++ and Java, and is in fact even easier to modify or use as a template to write your own stuff.

By the way, it is highly likely that the WPILib code will be modified to incorporate better calibration for 2015. The implementation in WPILib is simple, but not entirely incorrect. If your team relies heavily on the gyro, you can better characterize your sensor and customize the calibration to your setup.

Greg McKaskle

[Alan Anderson]

Acceleration affecting the gyro rate?

Yes, that's a real thing. I remember seeing a value of 0.2 degrees per second per g of acceleration. That doesn't sound like much, and a properly mounted yaw rate sensor with good mechanical isolation shouldn't give you significant problems. But remember that vibration is also detected as acceleration, and it's possible that having the sensor rigidly mounted to the robot frame can yield false readings when the robot is in motion.

Consider also the possibility that you have an electrical issue. Signal noise picked up from motor wiring on the gyro analog signal will be accumulated as errors in the gyro angle. Make sure your sensor wiring is not running alongside power wiring.

[cjl2625]

if ((getFMSMode() == AUTO) || (getFMSMode() == TELEOP))

Is there an easy way to do this in LabVIEW?
Or do I have to put something in auto and tele that wires true to the visitedEnabled global?

[Chris Hibner]

Is there an easy way to do this in LabVIEW?
Or do I have to put something in auto and tele that wires true to the visitedEnabled global?

Like this:

Actually, we usually just wire a TRUE constant into visitedEnabled in Teleop and our Auto code. That makes it much easier.

(EDIT: Sorry for the issues. The site is having attachment problems. I should be able to post it in the morning unless the site problems persist.)

[Chris Hibner]

Here we go: