04-08-2011 17:50

ratdude747

Re: pic: 1675's REAL IRI Upgrade

Was this real or a joke?

04-08-2011 17:58

R.C.

Re: pic: 1675's REAL IRI Upgrade

For realsssss.

-RC

04-08-2011 18:30

Duke461

Re: pic: 1675's REAL IRI Upgrade

Chris,
You may have just started a massive debate.
Frightened,
-Duke

04-08-2011 19:11

BigJ

Re: pic: 1675's REAL IRI Upgrade

I wanted to try it on the practice field but the kids took the treads off and wouldn't let me.

04-08-2011 19:45

sgreco

Re: pic: 1675's REAL IRI Upgrade

That looks like a big improvement. Design truly is an iterative process. Too bad other mecanum teams of the past never thought of this.

04-08-2011 20:05

akoscielski3

Re: pic: 1675's REAL IRI Upgrade

honestly i wanted to do the same to our wheels...

04-08-2011 20:30

Sb28000

Re: pic: 1675's REAL IRI Upgrade

Very interesting. I would imagine that the driving style was changed to tank drive rather than the typical mecanum pattern, is this correct?

04-08-2011 20:36

Duke461

Re: pic: 1675's REAL IRI Upgrade

Unless tank treads now have the ability to strafe, i would say no.
Not hating on 1675 or anyone, but I'm not sure why everyone's praising this as if its a new design or a radically different/improved design, in comparison to a normal tank tread drive. Unless you can somehow strafe, the wheels are now no different than a normal tank tread drive--maybe even worse because the tread is zip-tied and not against a flat surface.
However, i would love to be disproven on this.
-duke

04-08-2011 20:44

ratdude747

Re: pic: 1675's REAL IRI Upgrade

no, its because a lot of people equate mecanums with dog poo. they point out things like "no bot on einstein has had mecanums" and things like that.

I consider the picture a DOWNGRADE. mecanums work if you do it right. gear them high and try to keep the weight semi-balanced.

I know there will be some angry replies to come from this from the "mecanum haters" out there.

04-08-2011 21:06

Chris is me

Re: pic: 1675's REAL IRI Upgrade

This "upgrade" was a friendly joke / prank from the kids on 1625. They obviously removed them, despite some of us friends teasing them that it was a big improvement. 1675 responded by hiding hundreds of mecanum rollers in 1625's tools.

Yeah, how dare we point out "facts" and stuff in an engineering discussion.

I think Einstein may not be the best sample for pointing out a correlation between traction drives and success, but I certainly can name far, FAR more top robots with traction drives. I certainly don't think the best teams are just too sucky at using mecanum drives to appreciate them!

04-08-2011 21:22

Duke461

Re: pic: 1675's REAL IRI Upgrade

Facts? Chief Delphi is not a place for facts chris.
Im curious as to how many top teams have actually tried Mecanum. Because its not that the people that dont use Mecanum are the top teams, its that the top teams seldomly use mecanum.
Chris, you seem to know every team , so whats one of the best teams you saw this year ( or any year) that used mecanum? Because im pretty sure the big name teams (71, 111, 67, 148, 233) have never used mecanum.
------
In other words, regarding tank v. mecanum, correlation does NOT imply causation.

04-08-2011 21:32

Chris is me

Re: pic: 1675's REAL IRI Upgrade

Not used mecanum in competition. That doesn't mean they've never used, tested, built a mecanum robot! It's an important distinction.

The best mecanum team this year was IMO 2826, which had an alternating drivetrain. If you go by FRC Top 25, not one team is "pure" mecanum. The best team probably to go pure mecanum was 2337, but I do think they would be just as good with a traction drive.

Yes, that's true, but it's not worthless either. I made a thread a few months back called "Video of Mecanum Drive Running Circles Around Traction Drives" asking for some footage. I'm still looking.

04-08-2011 21:43

Duke461

Re: pic: 1675's REAL IRI Upgrade

Yes i remember that thread. Excellent point, sir

04-08-2011 21:59

ratdude747

Re: pic: 1675's REAL IRI Upgrade

well, I am lookign for a video of a tank bot crushing a mecanum bot to bits against a wall. just like the video on your wish list, you won't see it because you are looking for too big of an advantage.

the reason a lot of top teams use:

traction: they have used it for so long and thats what they are used to and have plenty of spare parts for

crab: they have plentiful human and/or capital resources or they have used crab for so long they already know the drivetrain design before the beginning of the season.

i do recall a pure mecanum system being a division finalist. curie 2008. 2171 robodogs from crown point, IN. look at some of thier footage on thebluealliance from boilermaker regional... they had that crab drive rocking... and that was under the IFI system.

octanum sounds like a good offseason project but a waste of weight and expenses... the key to mecanum is speed... gear it high (stock toughbox nano will do) and go... you can have a scale-down button if it is too quick by itself.

04-08-2011 22:12

Chris is me

Re: pic: 1675's REAL IRI Upgrade

I can find you hours upon hours upon hours of traction wheels playing effective defense or offense around mecanum drives. There's video of some smart defense and plays by mecanum drives too, but certainly not entirely because of their wheels. If you're asking me to find a video of a bad frame being smashed to pieces by a traction drive, what does that have to do with anything? The strength of your frame isn't determined by your wheels.

I'm sure that's why some teams use traction drives, but really? Are you really trying to say that legions of good teams in FRC just make drivetrain decisions because they've never done anything differently? That's pretty awful engineering.

If you gear it high, how are you fundamentally different from a traction drive? High gearing implies traversing long distances. When you're doing that, a traction drive would certainly be able to go slightly diagonally to counteract losing strafing ability.

Now look, this was supposed to be a lighthearted thread where both sides would laugh about a prank everybody enjoyed...

04-08-2011 22:30

ratdude747

Re: pic: 1675's REAL IRI Upgrade

no, i was looking for tractions so powerful they crush stuff. the point is that you are looking for mecanums to be that much better. I will admit that it will not do circles around traction drive. however, it can score more efficiently when scoring involves more than just pushing things.

well, why not? if it works, do it. if you look thoguh history of things, breaking from a previous design that was successful has been a flop:

intel i860- was a RISC, not a x86 CISC cpu.
intel itanium- wasn't x86,
atari 5200/atari 7800- the 2600 was good enough, so there wasn't a need to upgrade
wankel engines- radically different than existing piston designs
microsoft bob- people liked the existing windows interface, no upgrade desired


there are more, but if there is no perceived need to change, why do it?

if what you have doesn't work or you are starting new, then that is a different discussion. point is that many top teams have been good for a long time and they never had a big reason to change (from their eyes).



If you gear it high, how are you fundamentally different from a traction drive? High gearing implies traversing long distances. When you're doing that, a traction drive would certainly be able to go slightly diagonally to counteract losing strafing ability.[/quote]

04-08-2011 22:32

Chris is me

Re: pic: 1675's REAL IRI Upgrade

Who was saying anything about crushing power?

If you really think the best teams in FIRST don't use a single minute of their 6 month long offseason to ever try a new idea, and that you are the enlightened one here, go ahead. I'd just rather we not endlessly debate in a humorous thread.

04-08-2011 22:35

NickE

Re: pic: 1675's REAL IRI Upgrade

In the 2010 SVR Finals, 675 (mechanum) played defense on 971 (traction). 971 almost literally drove circles around 675 and is able to easily push through them to score. Sorry that may not have been the video you were looking for though...

Match 1 | Match 2

04-08-2011 22:38

BigJ

Re: pic: 1675's REAL IRI Upgrade

Not quite hundreds....

maybe...

(we don't even know how many we hid, so they'll never know unless they empty all their containers!)

04-08-2011 22:47

ratdude747

Re: pic: 1675's REAL IRI Upgrade

it all comes down to implementation. a well designed traction will stomp a poorly designed mecanum.

I wish i had footage to back this up, but my team's bot this year was mecanum. we were the fastest bot that showed up to BMR. if our manipulator had worked better, we'd made eliminations (234 told us that had their alliance mate not disagreed, they would have picked us for a 3rd defense bot).

it also had no problems during the season either other than a spare practice gearbox having a defective gear from the factory (one stolen from a 2009 KOP gearbox fixed it).

whatever on this topic... people use what people use...

04-08-2011 23:05

Karthik

Re: pic: 1675's REAL IRI Upgrade

Your example of a noteworthy mecanum drive is one that didn't even make the elimination rounds at a 41 team event?

04-08-2011 23:06

Taylor

Re: pic: 1675's REAL IRI Upgrade

Holy Straw Man argument, Chris.
The "driving circles" challenge was certainly served and, to our knowledge, never met. It calls for (paraphasing) an inferior (mecanum drive) team defeating a superior (traction drive) team simply by virtue of its drive train. But then you state that only holistically inferior teams would use mecanums in competition in the first place.
As coach of our 2011 mecanum-driven bot, I noticed during practice and competition that it could perform maneuvers that a traditional (read: 4-wheel or 6-wheel, non-crab/swerve) robot could not. This maneuverability allowed us freedom of simplicity in our overall design, and the ways we implemented the mecanum drive were not evident in middle-of-the-field play - partly due to the limited access given to defending teams, partly due to the fact that we went to one event, and partly due to the fact that the only time we were actively defended, THAT ROBOT HAD MECANUM DRIVE TOO! (3487, who rode their mecanum drive all the way to St. Louis as Rookie All Stars).
Mecanum drive trains are not the optimal system for every challenge, but they do have merit. Swerve/Crab is undoubtedly better, but that arguably takes years of practice and refining to make decent. We had our mecanum drive running early Week 2 of build season, with no previous experience.
AndyMark does not make or promote sucky stuff they leave that to banebots. They've sure got a lot of iterated mecanum wheels, though.

To go back to the OP - it is pretty funny. As is the payback.

04-08-2011 23:19

apalrd

Re: pic: 1675's REAL IRI Upgrade

JVN disagrees with your statement. (And he says 148 hates mecanum).

I don't know what other teams do, but we don't look at drive systems first. We look at game strategy. We don't look at 6wd vs 8wd vs swerve vs mecanum vs slide vs nonadrive, we look at if the ability to translate sideways is a significant advantage, then factor that into our weighted decision matrix (the larger the advantage, the higher drive systems incorporating that will get more ranking points).

For us, the ability to train drivers to use a 6/8wd well has always led us to find the sideways translation to not be significantly helpful, except in the two years we convinced ourselves it was an advantages and built a swerve (and regretted it both times... One year we hated it so much we replaced the swerve pods with fixed wheels after the first competition)

04-08-2011 23:25

ratdude747

Re: pic: 1675's REAL IRI Upgrade

because the other half of the robot (read: manipulator and minibot) wasn't up to par. in fact, it really didn't work at all.

version 2 of the arm and minibot/launcher improved things in st. louis, but communication issues between myself and the head programmer led to code issues, the drivers didn't have enough practice with the final system, and a catastrophic failure ended it.

it proves that although a good drivetrain is good, it isn't everything.

Trust me, my years on 1747 taught me that equally well. In 2010, we could "glide" over bumps, push robots away from towers before they could hang, and some rowdy drivers of ours (not endorsing this) even disabled my current team's (2783) drivetrain in one match and flipped a rookie in another (anybody at buckeye regional that year knows about it). however, the kicker broke beyond repair, the vacuum didn't work, the roller to replace the vacuum was destroyed in the kicker failure, and the hanging device never worked. only this time, at boilermaker regional, we were picked by the 1st seed alliance (with 1501 and 1018) but lost in the semi finals in a close battle. by the way, it was a 2 speed traction drive (front traction, rear omni duals).

04-08-2011 23:31

Laaba 80

Re: pic: 1675's REAL IRI Upgrade

525

04-08-2011 23:36

Aren_Hill

Re: pic: 1675's REAL IRI Upgrade

I haven't found any recently.....hmm, remind to hide random swerve modules or something in your pit sometime

04-08-2011 23:38

XaulZan11

Re: pic: 1675's REAL IRI Upgrade

I think Ratdude actually shows an advantage of tank over mecanum. One of the reasons I want my team to use the same strong 6/8 wheel tank drive (or something similar) is that we can always play defense if we need to. Obviously, we always go into the year thinking we are going to be one of the best scorers at our events, things don't always go to plan and you need to adjust. Things break mid match or your scoring isn't quite as good as you expected, so you may be better served playing defense in some matches. This year at the Championship and IRI we played defense around half of the matches (depending on matchups), and got picked at both events because of our ability to play defense. I think there is no way we would have gotten picked if we had a mecanum drive. I don't recall seeing any mecanum drive play better than just 'ok' defense as they are just too easy to push around.

04-08-2011 23:40

Duke461

Re: pic: 1675's REAL IRI Upgrade

I didnt make any statement about Mecanum, i only asked if any big name teams used mecanums, and implied mecanums IN competition. I am still correct that 148 did not use mecanums in competition, right?
I guess i understand how one might interpret my statement as they havent bothered to try; that was not the intent. Rather, i was just curious for historical information.
-duke
P.S. There's really no point in arguing this guys; if this was battlebots, sure, argue away. But in a competition where there are many other aspects besides drivetrains that critically define your success, no.

P.P.S. You guys may disagree completely with me, and i'm not looking to make this an argument; however, i believe 100% that 254, 111, and 973 still would have won it all if they all had Mecanum drive trains.

04-08-2011 23:47

Duke461

Re: pic: 1675's REAL IRI Upgrade

I see your point, but i think mecanum can play defense. I really don't know how to explain it, at least in writing. if i had to verbally explain it to someone in person, i probably could. But, mecanum can play just as good defense, and avoid being pushed around at the same time. At BMR, 292 was scoring a solid 4-8 tubes every match, and we (461, with mecanum) played defense against them in their last Qualification match. We still lost because we didnt have that great of an outing offensively that match, but 461 kept them to i believe two tubes the whole match. again, i would probably have to write an essay to explain how/why, but i really dont feel like it, nor do i really feel like pursuing this argument

04-08-2011 23:51

Hawiian Cadder

Re: pic: 1675's REAL IRI Upgrade

that is a pretty excellent prank.

IMO, if the bumpers were made out of a fabric that was slippery, mechanum drives would have (maybe) a significant advantage as they could slide around the higher traction drives, however, because the bumpers sort of stick to each other, I think that most omni directional robots fall prey to the faster accelerating, more grippy tank drives.

we have built 2 mechanums and 2 tank drives since i have been on the team, and i would have to say that the mechanum prototype, weighing less than 40 lbs fully loaded (with battery), could probably drive circles around one of the tank drives (geared slower than it) and maybe the other (geared faster than it). However the full 120 lbs mechanum suffers too much loss of acceleration to out maneuver either of the tank drives.

04-08-2011 23:52

Taylor

Re: pic: 1675's REAL IRI Upgrade

Depends on the game and the strategies in place. In a year like this one, getting in the way constituted most of the defense, not pushing people around. Mecanum does well with that. In a game like Aim High, defense was pushing people around, and mecanum drive would be arguably a poor choice.

04-08-2011 23:55

Duke461

Re: pic: 1675's REAL IRI Upgrade

Agree completely. You've basically said what i was trying to say, i just couldnt think of the right way to say it.
thanks,
-duke

05-08-2011 00:04

ratdude747

Re: pic: 1675's REAL IRI Upgrade

two different bots, two different games, two different goals, and two different teams.

the mecanum was meant to be an offensive machine. the tank was meant to be a bump hopping defensive machine.

if you use your interpretation, then all it really proves is if your manipulator design is crap, then you will be stuck in defense.

may I ask how mnay defensive bots do you see on einstien? winning regionals? note that the tank bot lost in the semifinals. why:

1. 1018 was in the far back zone, we were middle, and 1501 was by the goal. this was so 1018 could use their 3 ball auto.
2. then 1018 and ourselves would switch places by crossing the bump. we would play defense and 1018 would feed balls to 1501 and score mid zone goals directly.
3. the failure was in the switch... the alliancein the semi picked up that if they blocked the bump, 1018 would be stuck as they were too tall for the tunnel. we were tied up getting them off the bump to let 1018 cross, so their goals were undefended, hence why we lost.

the fact that we were only good in one zone (defensive) was the kiss of death...

also, the reason why both designs in my last post failed was they same for both. we spent so much time screwing around with perfecting designs, trying to do everything, and over-complicating things that there was no time to troubleshoot and find practical bugs. both times the drivers only got 1 day of practice before competition.

so if you plan to have a manipulator that doesn't work, yeah, go tank since being able to score won't be on your agenda.

If you give your design a serious effort and get something for the drivers to play with with plenty of time to spare, then mecanum may be helpful.

05-08-2011 00:22

AlecMataloni

Re: pic: 1675's REAL IRI Upgrade

I don't think so. 973's defensive prowess definitely kept us ahead of the competition due to their awesome drivetrain (and drivers, of course). I remember many instances where all 3 of us had to weave through traffic and probably would've been out of luck if we had mecanums.

05-08-2011 00:23

XaulZan11

Re: pic: 1675's REAL IRI Upgrade

I believe there were 3 or 4 (not sure about 25) teams on Einstien who did not score a logo piece.

I think your idea that you only play defense if you plan to have a bad manipulator is very flawed. I'm pretty sure teams like 469, 71, 1625, 25, 973, 968, and 217 (all of which played defense more than once) thought they would have a good manipulator (and all did).

05-08-2011 00:24

Kevin Kolodziej

Re: pic: 1675's REAL IRI Upgrade

Aren, did you find all three types of rollers?? They weren't just in your main toolbox either...

I'd like to add to this little debate. Just information..do with it as you see fit.

Team 1675 has used Mecanum wheels in four years of competition:

2007: 8" wheel on slightly modified kit chassis (custom pillow blocks). We had a long center mounted arm that could reach in front and behind the robot to pick up and score, and score over opponents between us and the rack if need be. We decided that the strafing ability would be more beneficial to us when lining up away from the rack, even though we could get pushed away more easily. In most cases, the defender between us and the rack would be parallel to our strafing motion, meaning that we weren't going to get pushed away, just blocked, so in this case, advantage went to us. Disadvantage came when climbing partners ramps...or rather, attempting to. We only had success with lifting platforms. We were selected for elims in Cleveland, but not in Milwaukee or Atlanta. By the end of Atlanta though, we were consistently scoring 4-5 tubes per match.

2008: 6" wheels on custom 2x1 chassis. The 6" wheels were new that year and relatively untested. We encountered some initial problems with the plates warping and subsequently digging into the carpet. We solved this problem and newer generations of AndyMark's product have also addressed this issue. We had grand plans for a ball lifting mechanism that never were realized so we became a runner bot. Geared for speed, our bot was one of the fastest in Milwaukee and Chicago. We chose mecanum that year so that we could maintain orientation while going around the field (i.e. always have the robot facing us so we're ready to launch the ball as soon as we cross the lane divider). This became a non-issue when we abandoned the balls. Instead, we used mecanum to "change lanes" and eventually twisting of the frame actually allowed us to "powerslide" around every corner because of the rollers. The advantages we realized were not initially planned for, however, the planned for advantages were never needed, so it worked well anyway. We seeded 8th in Chicago, were picked by #1 in Milwaukee (lost due to mechanical issues), and were not picked in Atlanta or IRI.

2010: 8" wheels on suspension pods on custom chassis. The idea was to be able to manuever around defenders while using our ball magnet and be a top scorer. The ball magnet never worked properly (and was abandoned completely for NorthStar). Mechanical issues in Milwaukee prevented us from doing...anything...but things went well at Northstar and we were picked by #7 alliance. Did not go to Atlanta, were not picked at IRI. Mecanum allowed us to slide into the wall to retrieve missed shots, but otherwise didn't give us much advantage as it was geared to slow to evade. Unfortunately, not geared slow enough and thus was unable to climb bumps either...but this was solely a gearing issue and not a traction issue. This is the only year I would redo without mecanums if I could do it again.

2011: 8" wheels on custom chassis. Our most precisely crafted chassis led to our best functioning mecanum bot yet. The reasoning for using mecanum was simple: its quicker to move sideways to fine adjust with a stationary elevator than it is to back up, turn, and pull forward. We accepted the fact that defense would have their way with us most of the time (which, in reality, we did a pretty good job of evasion this year and there is one match in particular at St. Louis that we were able to spin around the defender while in full contact with them because of the rollers...traction wheels would have just stuck us there...quirky, but I'll take it...if I can find video, I'll post it), but were okay with that as we expected to be rarely leaving the scoring zone. The concept was sound, execution is where we failed. Tubes didn't always get to us, so staying close to the scoring rack didn't always happen, which led to being defended. Even so, we were top 15 in Milwaukee and Chicago, drafted by #8, and were the #8 captain in St. Louis, so I think we did something right. IRI we were usually the feeder/defender, which didn't work out so well for us. If I had to do this year over again, I'd use mecanums again without hesitation.

The biggest difference I see between a team like us (a team that has used mecanum wheels in multiple years, learned from mistakes, and developed designs and software to make proper use of mecanum abilities) and your perennial top tier teams (71, 111, 148, 254, 1114, etc) is practice. We have never built a second robot. We have old robots with mecanum drive still functional, but its not the same. Those teams I've listed, and many more, were extremely good at what they did this year because of the time their drivers put in. Their routes, routines, sitelines, alignments, etc. were nearly flawless by St. Louis (some well before that). Even though our robot this year was the most finished its ever been going into the crate, we still managed to miss all but one practice match this year, including St. Louis. We spent time at each event on the small practice fields, with drivers driving from an unusual viewpoint, and had one session on the practice field in St. Louis. Everything else our drivers learned came from in match experience. I have absolutely no doubt in my mind that if our drivers had a second robot and a rack to practice with at home, we would have been just as quick a scorer as 2826 or 111. We still would have been lacking in the minibot department though

I think I've said quite enough.

Kev

05-08-2011 00:36

BigJ

Re: pic: 1675's REAL IRI Upgrade

Something not mentioned: These treads were eventually used to make Greg Rupnick's Traction Hands to help him on his way to winning the IRI Mentor Minibot tournament!

05-08-2011 00:37

XaulZan11

Re: pic: 1675's REAL IRI Upgrade

I think you forgot a year, Kevin. The year you didn't have a mecanum drive and won a regional playing great defense.

05-08-2011 00:37

ratdude747

Re: pic: 1675's REAL IRI Upgrade

thats not what I was meaning. my point was if one wants offense and screws up the design, you will be stuck playing defense like it or not.

playing defense beacuse you elect to and playing defense because thats all you have left are not the same. all of your examples are elective defense moments, not forced (you said so).

I might also point out that not every bot on Einstein played defense at one point either. defense is not necessarily a "must have" to be successful. It all comes down to how one wishes to play the game.

bottom line: add defense if you want, just be aware that if you want more, design your manipulator carefully and remember Karthik's golden rules: don't bite off more than you can chew and its better to be good at one thing and poor at the rest than so-so at everything.

05-08-2011 00:41

BigJ

Re: pic: 1675's REAL IRI Upgrade

shhh Kevin hates defense

(the kids threaten to want to build a solely defensive bot every year to mess with him)

05-08-2011 00:47

Laaba 80

Re: pic: 1675's REAL IRI Upgrade

in 2010, 525 was able to defend me with mecanum drive. Its a little weird though, because in the entire match, they did not appear to strafe once. They were pushing the corner of our robot, and had me essentially pinned in the center of the field for around 10 seconds. In the end I realized our 6wd was faster, and used that to my advantage, but they put up a very good fight. They held me to 3 balls scored in the first match, and 4 in the second, compared to the ~6-7 i was averaging.

05-08-2011 01:01

Duke461

Re: pic: 1675's REAL IRI Upgrade

So you're saying mecanum's limit your ability to weave through defenses???

05-08-2011 03:26

Katie_UPS

Re: pic: 1675's REAL IRI Upgrade

I don't go on CD for a day, and you guys have interesting conversation without me..

During heated traction vs. Mecanum debate, this argument does not go over well (trust me, I know).

Speaking from experience as a spectator and one-event coach, most defensive motion is perpendicular to the motion of robot being defended (so if scoring robot is trying to move north, then the defensive robot is orientated to move east-west)*. Strafing is slower than typical forward/backward motion. A lot of robots are typically geared 12 fps**, our robot (this year) included. If my math is correct (basic geometry/trig)(someone feel free to correct me), a mecanum geared like ours (~12 fps) can only strafe at ~8.5 fps. Therefor, "weaving through defense" isn't as plausible as one would think.

Not to mention pushing, to which mecanums have little resistance to (the whole "non-powered rollers" thing).

However, a good driver can play fancy, and do some moves to mess with the defending driver... but that isn't the machine beating a machine, that's the driver beating a driver (although, as many of the greats will tell you, good drivers are just as -if not more- important than a good robot when it comes to winning matches).


EDIT: Also, Traction-Upgrades also make for some pretty spiffy belts



*Applying this defense to games such as Logomotion and Breakaway. This strategy was not as applicable in Overdrive/Lunacy, and I haven't focused on the defensive strategies in games before my time.
**excluding two speeds, but a lot of teams using two speeds are also not playing defense

05-08-2011 03:36

Chris is me

Re: pic: 1675's REAL IRI Upgrade

Absolutely. That's part of why no one has been able to ever produce a video of mecanum running circles around 6 wheel drives. People just seem to assume that sliding sideways is some kind of magic defender stunning motion.

05-08-2011 06:45

thefro526

Re: pic: 1675's REAL IRI Upgrade

I am an avid believer that using Mecanum wheels (alone, in a purely mecanum drive, and not some sort of octocanum (is that what you kids are calling it now?) drive) is one of the worst decisions a team can make.

How many times have we seen a machine with an awesome manipulator an mecanum wheels get shut down by a team with 6 wheels and roughtop treads...

Agree or Disagree, but the statistics don't lie.

05-08-2011 09:38

BigJ

Re: pic: 1675's REAL IRI Upgrade

These mecanum arguments never solve anything.

One side talks about how mecanum is suboptimal, and the other side white-knights mecanum until their keyboard breaks. Others bring in good information for the debate, but here's the thing:

There is no debate.

Driver skill matters, but physically there are properties mecanum has and properties traction wheels have. Nothing is going to change this fact.

Teams who want to use mecanum will use mecanum. Teams that don't, won't. I don't think anyone is going to have their opinions on the matter magically changed by arguing back and forth - they need to realize answers for themselves.

Team 1675 used mecanum this year because we believed before seeing the game actually played that the game and our design called for it. We believed that the Zone would be very crowded and that defenders would be willing to risk being right up on the zone, giving you limited room to move around once inside. We believed that having the fine positional control of a well-done macanum system was paramount. After all was said and done I believe we would have been fine with any drive system that could pivot.

Do I think we designed a bad robot just because it had mecanum wheels? No. In the future, I probably wouldn't lobby for using mecanum wheels unless the challenge specifically called for strafing or translation of some sort. However, I would hope that our team looks deeply at the game and our solution to the problems that don't involve movement and make a better guess on how the game will be played before deciding upon a drivetrain.

05-08-2011 09:51

Peter Matteson

Re: pic: 1675's REAL IRI Upgrade

177 won 2 regionals and Galileo in 2006 by only playing defense because we knew how to win by not playing the game as intended, and somehow everyone else was convinced else we were a good shooter. We intentionally kept the score low and won using the ramping and autonomous bonuses to win.

We actually caused a member of the GDC to lose a bet where he claimed no purely defensive robot would make it to Einstein.

FYI we were the 2 seed in Galileo that year and we rarely scored an offensive point.

OH, and we won Newton and the Championship in 2007 by using defense to distract everyone from the fact we had our partners splitting up the Rack to prevent long chains of tubes to keep the score low so we could win with ramping bonuses.

05-08-2011 09:51

Kevin Kolodziej

Re: pic: 1675's REAL IRI Upgrade

Oh, you mean the year we COULDN"T use mecanum (Lunacy)?? Yeah...we don't talk about that year. We only played defense because we had to, and while it worked out well at the regional level, did you see how bad we were in Atlanta and IRI?

I can't believe I lost my hair to a defensive robot...

05-08-2011 09:59

Kevin Kolodziej

Re: pic: 1675's REAL IRI Upgrade

Found the video I was looking for. Its not exactly driving circles around the defender, but its certainly a maneuver that would not have been possible without mecanum wheels: http://youtu.be/PDsq1sEVVKs?t=2m28s

05-08-2011 10:27

Jared Russell

Re: pic: 1675's REAL IRI Upgrade

I have to disagree on this one. To me, it looked like the defender got distracted by something else and gave up on their push. Had 2761 not stopped in their tracks, 1675 doesn't get a clean release into the scoring zone. A 6WD could have done the same thing (and probably resisted the original push better as well).

05-08-2011 11:09

Ryan Dognaux

Re: pic: 1675's REAL IRI Upgrade

After watching the clip about 5 times in a row, I disagree with this statement. 1675's only goal at that point was to get on the other side of the defender and get to the scoring rack. During the two-robot spinning motion, 1675 was on the opposite side and there was really nothing to stop them from translating away from 2761, as shown below -



I think what contributed to this motion was the mecanum wheel rollers being pushed from the side by 2761. The real trick would have been timing the translation correctly.

There's a lot of strong opinions about mecanum drive systems here - which is fine, everyone is entitled to their own opinion. The way I see it now with AndyMark selling mecanum wheels is that this gives teams an opportunity to have an omni-directional drive train with very minimal effort. So you have every team under the sun buying a set and trying them out, even if they aren't necessarily implemented correctly. More often than not, I see teams driving tank style with two sticks, completely ignoring the mecanum's translation capabilities.

So what does this come down to? Mecanum drives are inherently more difficult to control than a standard tank style drive. You can show someone immediately how to operate a tank style drive train and they'll understand it. They won't master it immediately, but I would argue that the amount of time that it takes to 'master' a tank style drive train is less than the time it takes to 'master' a mecanum drive train. No hard evidence to back up that claim either, just something that I've observed.

Most teams don't build second robots and don't have much driver practice time. So when they choose a mecanum drive, they are probably still trying to figure out how to control it out on the field. I think this adds to the perception that mecanum drive systems are a bad choice, when in reality the learning curve is just larger.

I agree that there are inherent disadvantages to using a mecanum drive, and that if your team has the time and resources to build a swerve drive system, then that is the way to go probably. But most teams don't. So they sacrifice some pushing power at the cost of omni-directional maneuverability.

One of our goals this summer has been to get students driving mecanum every week. We will see if it pays off next season - who knows, maybe we will finally be able to produce this fabled mecanum vs. six wheel video.

05-08-2011 12:30

Chris is me

Re: pic: 1675's REAL IRI Upgrade

"Healthy" debate about mecanum aside, I think it's ridiculous that we've gotten to the level of directly insulting 1675's machine and design decisions. They clearly had a pretty good robot this year.

05-08-2011 12:56

ratdude747

Re: pic: 1675's REAL IRI Upgrade

it depends on driver setup.

actually, the drivers got the drivetrain part down very quickly, as the way we set it up was just like the controls in video games like halo work. find a halo junkie and they will have mecanum down in a few minutes.

depends on the person i guess.

05-08-2011 13:05

Ryan Dognaux

Re: pic: 1675's REAL IRI Upgrade

Exactly. You can try to automate and control as much functionality as possible on your robot, but when it really comes down to it, it's up to the driver and operator to control the thing. Some teams just have better drivers than others. Better often means that they've had more practice and have had time to get used to how their machine drives and operates.

Anyway, back on topic - 1675's machine is legit.

05-08-2011 13:16

Duke461

Re: pic: 1675's REAL IRI Upgrade

This is why everyone needs to remember correlation does NOT imply causation, as i said earlier. Too many variables are in play. To name a few: Strategy during the match, driver experience, opposition, the game that year, skill of the robot in question outside of drivetrain, teammates, competition location, driver skill, control setup, speed, etc.

05-08-2011 14:59

Taylor

Re: pic: 1675's REAL IRI Upgrade

What is it about mecanums that make them so polarizing? The closest analogy I can think of is scissor lifts - they are generally frowned upon for competitive robotics use, but they don't carry nearly as much hatred (or love) as mecanums.
I've yet to see an "I love mecanums they're the best ever" thread; I've seen many "mecanums are the wheels of the devil" threads. Most teams that use them, do so as a bit of a situational compromise - sure, there isn't as much traction or speed as treaded wheels, but there is the gain of lateral maneuverability for minimal mechanical and programming difficulty, compared to swerve/crab drive.

So why the hatred?

05-08-2011 15:08

Ankit S.

Re: pic: 1675's REAL IRI Upgrade

It might be the way it was implemented. Teams that dislike mechanum drive may have had bad experiences with them, and rather than risk 400$ and try it again (or use those wheels again), they forsake it forever.

My team on the other hand used mechanum this year and we were very pleased with the result. We were able to weave around defense (atleast when our PWM's were connected). Also, the strafing helped us line up with the pegs.

All in all, teams that have had bad experiences w/ mechanum may forsake it, and teams with better experiences will probably stick with it. Due to the complexity and the relative novelty of mechanum, more teams have had bad experiences with mechanum, or better experiences without mechanum.

05-08-2011 16:04

ratdude747

Re: pic: 1675's REAL IRI Upgrade

This is what I was going to say but you already hit the nail on the head.

05-08-2011 16:11

Tom Bottiglieri

Re: pic: 1675's REAL IRI Upgrade

I don't understand this debate. What teams choose to incorporate into their robot is their choice and that choice is made under their value system. Yeah sure, 1114 has never used mecanum, but not every team wants to be 1114.

05-08-2011 16:43

Lil' Lavery

Re: pic: 1675's REAL IRI Upgrade

Open-field movement is not the reason to pick a mecanum, or just about any, omni-directional drive. The notable advantage is analagous to how these drive systems are used in the real world. The ability to translate in multiple axes without rotating the entire robot. This is particular useful in small, tightly packed spaces.

Think of how you parallel park in a car. Or, perhaps more of a direct analogy, moving from one normal parking space to the one next to it. That's not a very efficient or easy to execute series of actions in a FRC match. Strafing saves maneuvers like that in tight spaces.

Whether or not this is enough of an advantage to avoid the numerous drawbacks of mecanum systems is up to each particular team. I know that I won't support the selection of a mecanum system for teams that I'm associated with if FRC games continue to have a similar field lay-out and style of play. On the other hand, I probably carry a bias since an alliance partners' mecanum drive was a significant factor in ending my senior season in the Galileo semi-finals in 2007.

Sure it would have. "Bumper-locked spins" happen in FRC all the time. The real key to that maneuver was the open space where it was happening allowing for ~270deg of rotation. This type of maneuver is easily possible with a tank drive in a "side-impact" scenario like that. This isn't a perfect example, but it's one that was readily available and show the same principle being executed by a 6WD being defended by an excellent defensive machine who was on their way to Einstein.
http://www.youtube.com/watch?v=Bzpo3vVeGEY#t=3m45s
e; Another example in the same video.
http://www.youtube.com/watch?v=Bzpo3vVeGEY#t=4m48s

Notice how they escape from the spin move at the end, they don't translate directly away. They "spin off" the block, similar to how a tank drive would. Everything in that maneuver could have been executed by a tank drive, and similar situations frequently happen.

05-08-2011 17:13

lemiant

Re: pic: 1675's REAL IRI Upgrade

deleted

05-08-2011 17:20

ayeckley

Re: pic: 1675's REAL IRI Upgrade

We won Buckeye in 2010 (as alliance captain) using mechanums. During the balance of the season we never felt that we were at any real disadvantage against pusher-bots. In fact, we even successfully stuffed a reasonably-competitive 4WD tank opponent into the goal once. We put a lot of time, effort and $ into the control system to make driving as intuitive as possible however (closed loop on all four wheels, strategic assignment of user I/O, etc.). That, combined with a good driver and a practice bot made us successful, at least at the Regional level which was good enough for us. I don't think we would have been as successful with a traditional drive.

Just another data point...

05-08-2011 17:40

Hawiian Cadder

Re: pic: 1675's REAL IRI Upgrade

dunno if this is quite what you wanted Chris, but in this video 1318 litteraly drives circles around the defending robot in green, 3251. Although without any other drive-train details it is difficult to tell what really happened, this is an instance where i would say a mechanum robot definitely out maneuvered at least one non-holonomic defender with ease. Although this video says little about a mechanum driving circles around a defender like 973 (substantially more tenacious than the defenders in the video) I think that it shows the capability of a mechanum drive-train to use the ability to strafe to glide between defenders in a way that would be difficult for a tank drive to do.

http://www.youtube.com/watch?v=lwv9hZgw9r0

05-08-2011 18:15

XaulZan11

Re: pic: 1675's REAL IRI Upgrade

What I see in that video is 3251 playing defense solely on 3165 (the team with the white tube) and paying very little attention to 1318. I think it is relevant to note that 3165, with what looks like a mecanum drive, did not come close to getting past the defense of 3251. When 3251 did switch to 1318 at the end of the match, they let 1318 get away when they got ready to deploy.

05-08-2011 18:30

Andrew Schreiber

Re: pic: 1675's REAL IRI Upgrade

I'll explain my hatred of mecanums.

I don't hate them. They are a viable solution to a certain set of problems. Personally, I have not seen those problems as being prevalent enough in FRC to expend the resources needed to do mecum wheels. I evaluate this for every single game/challenge/project. If a mecanum wheeled system is the optimal solution to my problem then I will do it. I will also have criteria for why I chose those since I have to justify the expenditure. After the system has performed (usually end of season) I perform an evaluation of how effectively I solved the problem. Sometimes this comes back positively, and sometimes not so much.

The thing that I don't like about mecanums is not the wheels. It is the people that tout them as the Chuck Norris of FRC drive trains. They have downsides, some of them are quite serious (cost, added weight, added complexity, lack of traction, difficulty climbing ramps, requirement of keeping the CoG in mind, requirement of some sort of suspension...) . They also have some very serious benefits that you can't get using any other system. Too many times have I seen the comment that "mecanum wheel r better" espoused by some student. They aren't. But neither is a 6wd or a crab system or a nona-drive. None of them are inherently better than any other solution. Saying that is like saying that a laser cutter is better than an allen wrench. Yeah, if I am cutting out sheet parts (or birch like one of my EWCP friends) then the laser cutter is more effective for that job. But it won't help me if I need to bolt together my parts. My issue with them is that they are often held up as the solution to a problem rather than the solution to the problem at hand.

I've seen teams use the wheels to great benefit. I won't deny that there are benefits to using them. But if you need a hammer you use a hammer and not an oscilloscope.

I know that is probably a wall of text but just take away the next two sentences:
Evaluate how effectively all your options meet your requirements and choose the one that best fits your problem. Don't pick your solution and fit your problem around it.

05-08-2011 18:35

lemiant

Re: pic: 1675's REAL IRI Upgrade

I agree that this doesn't show an example of mecanum out maneuvering tank drive, but I have to say that the 1318 drivers do the best job of using mecanums that I have seen (in my limitted experince), using the strafing when and where it fits.

05-08-2011 19:38

bam-bam

Re: pic: 1675's REAL IRI Upgrade

This thread has been hijacked. Thank you for your time.

05-08-2011 19:40

Chris is me

Re: pic: 1675's REAL IRI Upgrade

I had no idea 1318 was being defended in that match. They also moved very slowly and aimlessly - not exactly running circles, unless you mean the literal circular path they take?

I honestly don't see why this thread had to turn into an argument. The reason the picture exists is because of two friend teams joking about their disagreement on design choices. They're clearly able to be light hearted about this. Why not us?

05-08-2011 20:13

AdamHeard

Re: pic: 1675's REAL IRI Upgrade

You certainly encouraged a non-light hearted debate early on in the thread.

05-08-2011 21:49

BrendanB

Re: pic: 1675's REAL IRI Upgrade

Wow another mecanum debate!

I have always been skeptical about mecanums but I wasn't solely set against using them until last year 2010 driving at an off-season event and realized how easy it is to push those wheels around the field (robot I was driving was 4wd: two pnuematic, two omni). Ever since realizing how easy it was to push them, I have zero desire to use them* unless there is a game that separates alliances from contacting each other. I could never justify a decision that would leave our robot so helpless under defense.

This year our team built a 6wd plaction robot with the mindset as rookies that we will build a robot that can simply play the game (low row + minibot that averaged a logo and a 1st place minibot at regional level. 12 for 12 deployments and 8 for 8 at STL). We knew we wouldn't be the best in most matches and designed our drivebase to be powerful on the field and pushed around many 6wd/8wd and some swerves too. Not matter how bad your upper assembly turns out, you should always design your drivebase to be one of the strongest on the field.

I have heard a lot of "they can out maneuver" or "strafe around opponents" but whenever I hear that I just want to see someone do it (and bad/stationary defenders don't count).

***no octocanums were mentioned in this post***

05-08-2011 22:37

Akash Rastogi

Re: pic: 1675's REAL IRI Upgrade

Why are so many people in this thread concerned about the merits of other teams' robots and feel the need to argue so passionately against mechanum drives? I can see plenty wrong with some of your own robots that I don't see in 1675's, for example. I won't call out case examples.

Fix your own robot's issues first, then maybe you'll have a valid enough stance on something to be allowed to preach to other people. (some of whom are mentors and also former world champion drivers)

+.02,
Agrees with Tom

05-08-2011 23:20

Andrew Schreiber

Re: pic: 1675's REAL IRI Upgrade

Show me the mentor who has never built a bad robot and I'll show you either a new mentor, a liar, or Andy Baker. One of the most important things one can do is learn from mistakes and this means that we have to make them. This means you can't discount someone's analysis merely based on the fact that they have screwed up in the past.

05-08-2011 23:34

Hawiian Cadder

Re: pic: 1675's REAL IRI Upgrade

the part about them driving a circle around 3251 was mostly a joke. I do think however, that 1318 utilized their mechanum fairly well. although they didnt do smooth lines around defenders, they were able to move through the crowd more effectively than most robots I saw at a regional level.

That is kind of what i was thinking too.

The circles was a joke, the robot did do a lap around a defender. I think that 1318 was able to maneuver better than most of the other robots on the feild, and a large part of that was their drivers ability to use the strafing effectively to move through the congestion, while it obviously says nothing about robot performance at the highest level, mechanums in this case proved to work very well.

06-08-2011 00:29

Katie_UPS

Re: pic: 1675's REAL IRI Upgrade

That's a little extreme. I mean, sure, we're not talking about the LOLz we got anymore; and, yes, there are already enough threads about Mecanum vs any other drive train, but the conversation has still been somewhat intelligent and hasn't degraded to people just yelling and blindly ignoring everyone else. Actually, this is one of the better threads I've read as far reasonably intelligent posts.

I'm really enjoying this discussion. I have yet to get annoyed by people just posting their opinions without reading what others have posted. Like I just said, this thread isn't really a bad thing... yet.

Thank you for the defense, however, as a member of said team, I'm not seeing this as people pointing fingers at our robot, but the drive train as a whole.

I didn't know that people actually knew that. 2 world championships, just to give him some more cred.

06-08-2011 00:40

XaulZan11

Re: pic: 1675's REAL IRI Upgrade

While I do not think it is right or fair to 1675 that they are signled out in the title and mentioned several times in this thread, debating other team's design decisions is nothing new on CD.

06-08-2011 01:29

Nemo

Re: pic: 1675's REAL IRI Upgrade

Definitely a funny picture! Hopefully everybody else who has read the mecanum vs 6WD threads enjoys it as much as I did.

I don’ t see too many people making huge generalizations in this thread, which is good.

Here is what I will add:

1) Mecanum is in some ways easier to drive than 6WD. This is because it gives you room for error. If you miss your route to a scoring peg by a bit, you simply correct it in 1-2 seconds by strafing. You don’t need to learn ridiculously complicated drive maneuvers – just drive it like a tank and strafe when appropriate. I’m not advocating sloppy driving– I’m saying that it probably takes more practice time to be a really effective 6WD operator, because it takes longer to adjust if you miss. This is relevant for teams that don’t have a practice robot / practice field or highly experienced FRC drivers. Know of any teams like that?

2) Mecanum is approximately even with 6WD in a few categories that I have seen occasionally cited as advantages for 6WD: complexity, cost, and weight. As a basis for comparison, I’m using “kitbot on steroids” as the 6WD, compared to 6” mecanum drive direct driven with with Toughbox Nanos. The mecanum drive costs about $300 more – not a giant amount when you spend $5000+ on the kit. The weight is about the same, and it’s not really any more difficult to assemble and program than a basic 6WD. The code is provided to everyone. You can bolt a mecanum drive to the kit frame in a week and then focus on the rest of the robot, just as you can with 6WD.

3) This year we had a relatively narrow scoring zone to share with our alliance partners, and the other team was not allowed to drive into it. A mecanum robot can spend most of its time in that protected zone if somebody is feeding tubes, which partially eases the vulnerability to pushing defense. We looked at that situation and went with mecanum, thinking it would help us score faster in tight quarters. One can look back at that reasoning and argue that we made a poor tradeoff, but we did have sane reasoning to go by. It is going a bit too far to generalize to the effect that there can never be a valid reason to select a mecanum drive.

4) At the regional level, mecanum drives held up pretty well. Plenty of teams have brought home regional banners using a mecanum drive along with solid manipulators / driving / etc. There’s nothing wrong with that.
_________________

Overall, I am more of a fan of 6WD after seeing how good the best of them looked on the field this year. I was surprised and impressed by how quickly and easily some of the 6WD drivers were able to hang tubes – essentially, their driving skill gave their 6WD robots the benefits we were looking for out of a mecanum drive. That was an eye opener. We are happy with our robot and our accomplishments from this year, but we’ve been playing with 6WD prototypes this summer and will probably bring some traction next year.

06-08-2011 02:19

Marc S.

Re: pic: 1675's REAL IRI Upgrade

I remember whatching 1675 returning the favor by generously donating 50 or so mecanum rollers to 1625.
By the way, did you guys ever find all of those?

06-08-2011 03:52

JohnSchneider

Re: pic: 1675's REAL IRI Upgrade

Im more curious as to where they got the colored tread

06-08-2011 12:15

Dillon Carey

Re: pic: 1675's REAL IRI Upgrade

Go to Mcmastercarr.com and search for inclined conveyor belting.

06-08-2011 12:46

Chris is me

Re: pic: 1675's REAL IRI Upgrade

***removed***

06-08-2011 13:35

EagleEngineer

Re: pic: 1675's REAL IRI Upgrade

Im pretty sure that 71 used mecanum this year in logomotion. Cause when i was watching the curie division finals 71 could move side to side, and im pretty sure i saw mecanums on their robot. See in the video how they move side to side. http://www.youtube.com/user/mckinley...49/mVCDScrUCsw

06-08-2011 13:40

Andrew Schreiber

Re: pic: 1675's REAL IRI Upgrade

I'm pretty sure they were a crab drive like they have been since 2005.

06-08-2011 14:31

apalrd

Re: pic: 1675's REAL IRI Upgrade

I am more than pretty sure, I'm certain that they have a crab drive.


@EagleEngineer:
Sideways movement does not indicate mecanum.

Mecanum, kiwi, slide, crab and nonadrives can all move sideways. I personally prefer crab or nona because they sacrifice little forwards power (with nona/slide you still can still put 4 CIMS to the forward direction, and add, say, two banebots to the slide wheel, with crab you can orient all wheels forward for maximum forward power)

(for those who don't known a Nonadrive is a 9-wheel slide drive, with articulating traction wheels. It was named by JVN, who is obsessed with the number 9. It was used by teams 148 and 217 in the 2010 seasons, and almost used by team 148 in the 2011 season (they pulled the slide wheel, but keapt the lifting traction/omni combos)

06-08-2011 14:36

ratdude747

Re: pic: 1675's REAL IRI Upgrade

agreed. i saw the bot up close during pit scouting. motor in pod crab.

06-08-2011 14:45

Andrew Schreiber

Re: pic: 1675's REAL IRI Upgrade

I know... The Beast has been crab drive every year that I can recall since 2005. This makes them one of the few top tier teams to have repeatedly used crab. The only ones I can think of other than them are 16, 111, and 1625. Many other top tier teams have experimented with crab and went back to other systems, these included (this isn't definitive, it is only what I can remember off the top of my head)

47 - 1998, 2000 - 0 Championships(to my knowledge they were the first crab in FRC)
67 - 2005 - 3 Championships (2005, 2009, 2010)
217 - 2002, 2003 - 2 Championships (2006,2008)
1114 - 2004 - 1 Championship (2008)
148 - 2008 - 2 Championships (2008 and 1993)
33 - 2005 (switched to 6wd halfway through the year), 2009 - 0 Championships
234 - 2010 - 0 Championships
469 - 2007, 2008 - 1 Championship (2003)
118 - 2005 - 2008 - 0 Championships

Just some extra data for the argument that simplicity is key. Every single one of these teams has since gone back to the tank style drive (6/8wd for most of them)

06-08-2011 14:58

apalrd

Re: pic: 1675's REAL IRI Upgrade

In 2005, we actually switched after our first competition, and pulled out the whole two crab-modules (two pods and a steering motor on a single removable block), and replaced them with four crab gearboxes mounted fixed (so we had a 4wd with pneumatic wheels, at less weight than the crab drive, and the cg offset of tetras on an arm allowed us to steer without too much bounce.) That non-crabbing robot went on to play on Einstein and win the IRI, but did not get picked at that first competition (the gripper was also partially to blame with that, but with the weight savings of loosing the crab, we could build a much better pneumatic one)


We don't talk about 2009. It sits in the basement and hasn't seen the light of day for about two years.


(47 also had a crab in 2000, FYI)

06-08-2011 15:02

Andrew Schreiber

Re: pic: 1675's REAL IRI Upgrade

I know, I remember that 2005 robot. I also remember tipping you guys at West Michigan that year...

I also know about the 2009 robot, I almost borrowed it for a class project but it turned out to be just too large to be safe for me to use for the experiment.

Thanks for reminding me what year 47 ran its second crab. I kept thinking 99 for some reason.

06-08-2011 17:55

EagleEngineer

Re: pic: 1675's REAL IRI Upgrade

I know, i just though i saw mecanums when i saw their robot on my tv. I must be mistaken, cause i knew mecanums could not be that effectient at moving side to side. So crab drive and swerve drive are the same thing right?

06-08-2011 18:22

Ian Curtis

Re: pic: 1675's REAL IRI Upgrade

Who initiated the slide drive? I've heard it called Buzz drive because 175 has used it several times, but were they the first?

06-08-2011 20:27

ratdude747

Re: pic: 1675's REAL IRI Upgrade

pretty much unless you get to the nitty gritty, where if you use your terms right, there is a difference.

06-08-2011 23:25

Kevin Kolodziej

Re: pic: 1675's REAL IRI Upgrade

47 did have a crab drive in 1999. There was a match at Great Lakes where they and 111 (on opposite alliances) both grabbed the puck and started going round and round. It was quite fun to watch!

06-08-2011 23:44

Andrew Schreiber

Re: pic: 1675's REAL IRI Upgrade

TIL...

07-08-2011 00:03

Tristan Lall

Re: pic: 1675's REAL IRI Upgrade

47 in 2001 was a crab too—except with treads. Each module was independently driven and steered.

http://www.chiefdelphi.com/media/photos/12374
http://www.chiefdelphi.com/media/photos/12290
http://www.chiefdelphi.com/media/photos/12291
http://www.chiefdelphi.com/media/photos/12292
http://www.chiefdelphi.com/media/photos/12293
http://www.chiefdelphi.com/media/photos/12736

07-08-2011 16:03

Ryan Dognaux

Re: pic: 1675's REAL IRI Upgrade

Correct - and I guess that would be a question for the driver and operator of 1675's robot, why didn't they translate away? It certainly was possible at that point, but it may have been just a heat of the moment kind of thing. It could also have something to do with they way their controls are set up. I've seen teams using two joysticks with a mecanum drive system, which seems counter-intuitive to me.

07-08-2011 17:53

BigJ

Re: pic: 1675's REAL IRI Upgrade

We use 2 joysticks. one is translation and the other does rotation on the x axis. Yes, this could be done with a 3-axis joystick but we didn't feel like buying a different joystick. Also tests with team member's personal 3 axis joysticks usually find the twisting in the direction of the arm can be awkward sometimes, especially if you needed to twist while translating in some directions.

07-08-2011 22:25

Taylor

Re: pic: 1675's REAL IRI Upgrade

We found the same to be true. We also found that it is very difficult to do a pure forward/backward, left/right, or cw/ccw twist and the driver would often do multiple moves at once unwittingly. For that reason, we have a 2-stick setup - one for forward and turning, one for strafing. Intuitive for laypeople, and workable in competition.

07-08-2011 23:13

Duke461

Re: pic: 1675's REAL IRI Upgrade

Also agree. Our joysticks at BMR got screwed up and i was forced to use a 3-axis joystick. granted, i had no experience with one and it was still a little screwy (shavings in jaguars we assume), but i absolutely hated it. I would love to hear as to why 2 joysticks is "counter intuitive"; i see no reason as to why it would/should be. In fact, i find a 3-axis counter intuitive.
Eventually we switched back, after much pleading, to using controllers like we did in 2010. Way better.

P.S. Although i prefer one for turning, one for strafing and forward/backward.

08-08-2011 00:16

ratdude747

Re: pic: 1675's REAL IRI Upgrade

sounds like halo style controls... left does all of your translations, right rotates. pretty standard.

3 axis style mecanum/crab is a mistake waiting to happen... when you try to translate left or right, you often rotate yourself as well...

some teams use tank-style controls where to strafe, you have to move both sticks left or right... never made sense to me... I am bad enough at tank controls, let alone that kind of horror.

08-08-2011 00:35

Molten

Re: pic: 1675's REAL IRI Upgrade

Since nobody has commented on this yet, what if they tried to strafe with the wheels like this? What would happen? Would they slowly drive out of the treads? or would it just sit there and put tension on the drive? Anyone know?

Just curious,
Jason

08-08-2011 00:37

Laaba 80

Re: pic: 1675's REAL IRI Upgrade

Its all about what the driver is comfortable with, it doesnt matter what anyone else thinks about it.

08-08-2011 00:41

Duke461

Re: pic: 1675's REAL IRI Upgrade

Well first off, the treads would probably slide off because they're not secured too well....but ignoring that, i would guess that it would barely strafe, and skip around like popcorn popping. What i want to try is to individually wrap each roller with tread. Nobody steal my idea unless 461 doesn't do that in 2012

08-08-2011 01:21

BigJ

Re: pic: 1675's REAL IRI Upgrade

Like I said, the kids didn't test it on the practice field like I wanted them to!

My guess is that without securing the treads to the mecanum hubs the diagonal force of the rollers would pop the treads off or tangle them in the wheel if it popped off diagonally.

If secured to the wheel it would just act like a lumpy traction wheel.

If secured to the wheel AND strafing was tried, the robot would be trying to pull itself apart and go nowhere.

08-08-2011 10:15

Dave Scheck

Re: pic: 1675's REAL IRI Upgrade

Nope, not us. 2009 was a Logitech gamepad. The left stick was the crab strick. You could think of it as a top view of the crab modules. Which ever way you deflected the stick, the module would go there. If you let go of the stick, the module would center. The right stick had multiple purposes. When the crab stick was deflected, only the Y axis was used, and it acted as the throttle. When the crab stick was not deflected, the right stick acted as a single stick tank drive. There were also a few gimmicks that we used such as having a button to angle the crab slightly (helped with picking up against the wall) and some special logic to tank turn while the crab wheels were not centered (standard tank turn logic doesn't hold true when the wheels are turned because the robot will try to pull itself apart )

08-08-2011 23:34

Laaba 80

Re: pic: 1675's REAL IRI Upgrade

Sorry about that. One of our mentors spoke with someone on your team about your crab drive, to get information about building our crab drive. Have you guys ever used, or tested out a 3 axis joystick for your crab drive? He was pretty convinced that a 3 axis joystick was the way to go after talking to you guys. The way he told us, the twist did the function that your left stick on the game pad did. Either he talked to the wrong person, or he confused himself.

09-08-2011 11:18

Dave Scheck

Re: pic: 1675's REAL IRI Upgrade

I don't think we ever experimented with a 3 axis joystick. We've always gone with the two stick approach. Back in the day, we just used the X-axis of the left stick for crab angle. I think 2008 was the first time that we used both X and Y to use the full circle of the stick for wheel angle.

I would think that the control that you described, where the Z axis of the stick determined the crab angle would be really hard to work with. I feel like you would lose a ton of resolution between the range of motion of the stick, and the physical dexterity required to twist the stick (as opposed to deflecting it). Like I said, I've never tried it, so if someone has had good success with that setup, more power to you.

09-08-2011 12:45

Jared Russell

Re: pic: 1675's REAL IRI Upgrade

We have tried 3-axis joysticks to control holonomic/strafing drive trains in the past, but always found that two sticks works much better.

It is simply too easy to twist when you only meant to deflect, and visa versa.

23-10-2011 09:58

O'Sancheski

Re: pic: 1675's REAL IRI Upgrade

Reported