Mecanum Einstein this year
 

I know there alot of debate on this subject but I think this is the year we will see a set of mech's on einstein. I say this because were seeing a flat playing field so mecanums will be very effective. Plus mecanums and there drivers have progressed over the years in 2007 most teams made there own or they didn't know how to use them but this year we have great choices from andymark and our drivers have gotten very comfortable with the drivetrain, I think these are all good factors that might lead to a mecanum getting on Einstein

Re: Mecanum Einstein this year
 

I disagree. Mecanums can be easilly pushed around, which will be very detrimental this year. They will be very poor at defense, as well as slow(er) than other types of wheel base. Speed will be extremly important this year, unless you have someone ferrying you pieces. A good 6 wheel, 8 wheel, or treaded robot will have lots of fun pushing around the mecanums, away from their lanes, and away from their poles, as well as delaying them in the middle.

Re: Mecanum Einstein this year
 

All drive trains can be exactly the same speed, it all depends on gearing. I would actually expect the average mecanum speed to be faster than an equivalent tank drive due to the fact that a mecanum bot gains nothing from gearing slow, while a tank bot gains pushing ability.

As for the original topic, yes, mecanums stand a chance this year. Yes, one may make it too Einstein if it is driven effectively.

Re: Mecanum Einstein this year
 

The flat field is a good point, in that mecanums won't have issues with having to go directly perpendicular to the slope. More so than previous years, mecanums have a legitimate chance of making Einstein. With defense limited to central areas, mecanums will have much less of an issue scoring than in 2007 (maybe even an advantage over other drive systems, this year). That said, getting through the central deadlock without getting pushed around may be an issue. Quick mecanums that have lots of skill in scoring (don't need to ever play defense) may be some of the higher picks this season.

Re: Mecanum Einstein this year
 

I hope we will see a slide drive on Einstein, but other than that i don't think anything on Einstein will be mechanum, crab, or omni, simple reason: speed, although Mechanums can be geared to the same speed as a tank or other drive, 4 shifting gearboxes would be a little bit of weight. anyone who has a shifting gearbox up near 16+ feet per second is going to score more.

Re: Mecanum Einstein this year
 

I think there may be a decent chance this year. I think this year sets up best for mecanum since 2008. In 2008, three of the division finalist alliances had a mecanum robot (2171 in Curie, 842 in Archimedes, and 384 in Galileo...although I THINK each of those teams were the 3rd robot on their alliance). I don't think mecanum is that far off from making the biggest stage.

Re: Mecanum Einstein this year
 

There were plenty of successful mecanum bots that year (2337 in 2008 was Curie second seed, though were knocked out by eventual Einstein finalists). Maybe the flat field is the key? This year may be a good indicator.

Re: Mecanum Einstein this year
 

I don't think the teams that make it to Einstein this year will be because of the drive. I think autonomous and end game will define Einstein this year.
Mecanums naturally take more programming, so it takes away from developing a perfect autonomous. I think we may very well see a veteran mecanum( a team that has had mecanum since 09) but unlikely for a rookie mecanum (a team that hasn't done mecanum since 09)

Re: Mecanum Einstein this year
 

After watching our team's mecanum run for the first time, I'd say unlikely. I mean, it's not bad... It's just not what I thought it would be.

Re: Mecanum Einstein this year
 

By crab, I'm assuming you mean swerve. If memory serves me correctly, there has been at least one swerve drive on Einstein in 5 of the past 6 years, 67 in 2005, 71 in 2007, 16 in 2008, 111 in 2009, and 1625 in 2010. (I believe there was one in 2006, but I don't remember off the top of my head).

In any case, I doubt we'll see some sort of pure Holonomic or Mecanum Drive on Einstein just because more often than not, they aren't driven as well as most skid steers - though there are a lot more factors than just drive train that determine a teams success.

I wouldn't be surprised if we saw some sort of Octocanum, or other Hybrid drive on Einstein this year since some extremely high caliber teams are working with them, which means that they should have the practice, strategy and end effectors behind them to be successful.

On the subject of speed of omni-directional drive, Multi-speed Transmissions don't have anything to do with success, neither does top speed (assuming you're fast enough to be competitive, I'd say minimum of 9/10fps). You can have a top speed of 16fps, but the game will dictate if you can ever actually go that fast. Assuming the field is unobstructed - Which it NEVER is - the faster robot would always score more if all other things are constant. Add in some minor obstructions that need to be maneuvered around, and the top speed may as well be 12fps. (also, it seems that many people are underestimating "threading the needle" to get to the feeder station. It's not all that hard to do with some practice, I was able to do it at around 11/12fps after playing around after a minute or two, but there's no way you're flying in there at 16fps without rubbing the tower or wall.)

But, if multi-speed transmissions are truly the determining factor, then a multi-speed swerve, which isn't unfeasible (118 has built a few), would have some advantage.

Re: Mecanum Einstein this year
 

We debated this very subject at start of season and decided to stay with 8” Mecanum wheels. We played center zone last year and had no trouble pushing other teams around, inadvertently tipping several over while managing to hold our ground against 6 and 8 wheel drive Bot’s. In the off season we worked perfecting the degrees of freedom Mecanum wheels offer. It’ll be the skill of the drive team that plays and wins on Einstein not the type drive base, just like it was in 05.

Re: Mecanum Einstein this year
 

This.

The Breakaway on Einstein was intense. Seeing the robots score 2-5 balls in autonomous was absolutely amazing. That few point lead some teams got in autonomous did set the outcome of the game.

I still think that hanging wasn't worth enough points, though. Considering not many teams actually managed to successfully do it.

Re: Mecanum Einstein this year
 

Here we go again, yet another mecanum vs non mecanum thread.
Anyway our team is using 6" mecanum wheels and 9:1 banebots transmissions, our initial tests show speeds of 8+ feet per second.
Seeing as it seems that the last time mecanum drive really had a chance was 2007 I am not sure what will happen this year.

Re: Mecanum Einstein this year
 

Last year was the first year team 842 used mechanum. What we had that year in 2008 was 2 back wheels driven by super shifters with omnis in the front of our robot.

Re: Mecanum Einstein this year
 

Probably what he meant, but not the usual usage:

Re: Mecanum Einstein this year
 

The best most practiced drivers will make it to Einstein just like every year. It doesn't matter what kind of drive it is.

Re: Mecanum Einstein this year
 

If I were I betting man, I bet a lot of money that we won't see a mecanum bot on Einstein...

Mecanum's advantage is not in a flat field, it's in a tight area where you don't have room to change your orientation. FIRST never has a field with so many obstacles that you can't re-orient. Mecanum will be an equal the same this year as in past years. Mecanum serves no practical advantage on a FIRST field. Nothing has changed that this year.

Just like the past, we will not see a mecanum bot on Einstein.

Re: Mecanum Einstein this year
 

67 in 2005 had 3 wheels and did not swerve they drove their bot with a steering wheel and used the back wheel to "steer" their bot around.

Re: Mecanum Einstein this year
 

842's 2008 robot was 2 traction 2 omni.

I thought it would happen in 2010 not on merit but on sheer volume, yet the alliances with no mecanum robots consistently won.

I suspect 2011 may break the cycle, not because mecanums are at an advantage but because of luck and volume.


I believe all three wheels were turreted.

Re: Mecanum Einstein this year
 

67's 3 Wheel Swerve can clearly be seen in this picture:

http://www.chiefdelphi.com/media/photos/20540

Re: Mecanum Einstein this year
 

One of the few pictures in CD-Media that has a reasonably clean shot of their drivetrain: http://www.chiefdelphi.com/media/photos/21750 It looks like they had a mode that would make the robot 2WD plus one pivoting driving wheel--that shot seems to say they've got 2 fixed and one pivot.

But the better shot is http://www.chiefdelphi.com/media/photos/20540, before all that shielding went on. Definitely a 3-wheel swerve.

Fun fact: of the 5 swerve drives on Einstein, only 2 were standard 4WD swerves (71 and 111). 2 were 3WD (67, 16), and one was a 6WD swerve (1625). 2 won the event (67, 111).

I don't remember a single swerve on Einstein in 2006.

Re: Mecanum Einstein this year
 

Sorry about that. I knew you did them last year and looked at a pricture from 2008 and I guess I saw what I wanted to and expected to see.

Re: Mecanum Einstein this year
 

I am going to say that we will not see a mecanum robot on einstein.

Re: Mecanum Einstein this year
 

I am going to disagree with anyone making a blanket statement and say that, while it is more likely we will see a mecanum on Einstein this year than in previous years due to volume and increasing repository of good code/driving ability, we should reserve categorical judgment until Einstein actually, y'know, happens.

Re: Mecanum Einstein this year
 

I think there's a good chance we will see a mecanum on Einstein this year. Not because they have any inherent advantage in this game (they don't), but because out of the many teams that have chosen that drivetrain this year, there is a decent chance that one of them will end up in the 12 teams on Einstein. Their drive won't be the thing that gets them to that point though - it'll be on the strength of their other mechanisms.

Re: Mecanum Einstein this year
 

Figured I'd hunt this down to say: Nope

Re: Mecanum Einstein this year
 

Saw that coming

Re: Mecanum Einstein this year
 

Didn't 51 have mecanum this year?

Re: Mecanum Einstein this year
 

I believe it was a "slide drive", the no traction wheel version of a nonadrive, so 5 omni's

Re: Mecanum Einstein this year
 

I believe Aren's correct. Also, 2826 was VERY close to breaking the mecanum curse on einstein (although, they did use a jump drive to switch between mecanum and 6wd).

Re: Mecanum Einstein this year
 

i doubt we will see a purely mechanum drive on Einstein, ever. team with the maximum amount of experience and funds, who might be able to make it competitive enough to get there, would probably spring for swerve or crab drive. teams a teir down from that resource wise usualy stick to tank drive and shifters, a octumanium or nonadrive might fall in this tier. because mechanum is "an easier way to get 3 degrees of freedom" it involves trade offs, and to get to Einstein you really cannot have many trade offs.

Re: Mecanum Einstein this year
 

Agreed. I don't see the most competitive teams choosing mecanum anytime in the near future.

Re: Mecanum Einstein this year
 

I was gonna ask if Aren would have counted 2826's jump mecanums :p

Re: Mecanum Einstein this year
 

There was a robot on Einstein with CIMple boxes and no floor loading.

How's that for trade offs. Most of the robots on Einstein still used 6wd/8wd/skid steer tank, nothing complicated like swerve. Your logic is flawed. The drive bases on Einstein could have been produced by many "second tier" teams, the rest of the robot couldn't be though.

Re: Mecanum Einstein this year
 

i was very disappointed with Einstein this year, it seems like most years Einstein has the 12 most competitive robots giver or take, i felt like the powerhouse robots were not distributed amongst the divisions well, and alliance choosing was not the greatest. while the teams on Einstein were amazing, i did not think it was very balanced.

Re: Mecanum Einstein this year
 

Most of the teams on Einstein could take virtually any other robot at CMP, and with practice, still be on Einstein.

They win their divisions with what lies on the other side of the wall.

Re: Mecanum Einstein this year
 

I think that eventually we will see one in the next few years. I have seen several teams with mecanums who are programming their robots to give them a competitive edge. Granted there are trade offs but 1503 proved this year that trade offs don't hurt you when done right.

I have seen one mecanum robot from this year that can't be pushed easy and from knowing this team, they will build immensely on what they learned this year!

Re: Mecanum Einstein this year
 

Wow, seriously? 1503 was pretty clearly one of the best robots this year, and pretty much the steal of the Newton draft. Did you not see them put up 8+ tubes on Einstein?

Re: Mecanum Einstein this year
 

But Einstein is never the best 12 robots. It is the best 4 alliances. I've seen many years where the best robots don't end up on Einstein because they didn't pick well or they had bad strategy or mediocre drivers. I've said it dozens of times, a robot does not win events you have to have the whole package.

Re: Mecanum Einstein this year
 

yes, but i knew Galileo. would still win. in past years the championships winner was pre-determined, but barring major failure, i didn't think anyone had much of a chance against the alliance that still won.

Re: Mecanum Einstein this year
 

What do you think they did to make it so it couldn't be pushed easily?

Re: Mecanum Einstein this year
 

I can see what you are saying. At the start of championships, everyone knew that Galileo was the field with the best robots. But the other fields had equally as good of robots. You can't just jump to a conclusion based on who is on which field. I know there is the "Curie Curse" but everyone thought that 469 and 1114 were going to win championships last year. 67,177,and 294 pulled off an amazing victory with the odds favored against them. Galileo definitely deserved to win, but Newton gave them a run for their money in the Semi's and Archimedes gave them a pretty good run for their money in the finals. The only reason I think that Archimedes didn't reach the scores that Galileo did in the finals was because of the 3v2 that was happening.

Re: Mecanum Einstein this year
 

I can tell you what we did. We were geared near the wheel slip limit for mecanum wheels. We used 6" mecanum wheels direct driven with 12.75:1 toughboxes. Most of the time we could push defenders out of our way without too much trouble. We had a top speed of maybe 9 fps - we bet that our HP could get us game pieces so we wouldn't have to cross the field much. In my mind, two regional wins confirms that this was a legitimate strategy. Our weakness was not the drivetrain - it was our 2 second minibot.

EDIT: Also, the arrangment was very controllable - we were a perfect 11 for 11 hitting the double ubertube on Newton.

Re: Mecanum Einstein this year
 

To the post above: it was 67, not 254 last year.

Re: Mecanum Einstein this year
 

I think that the bad rep that Mecanum wheels have acquired is, in large part, due to their relative lack of experience. Mecanum drive simply has not been around for long enough for a large number of teams to really know how to "do it right." As a result, you see a lot of teams using mecanum wheels that don't execute well.

As always, there are outliers and exceptions...I personally know of a handful of teams that have built excellent Mecanum-drive robots, but few (if any) of the veteran teams have really experimented with Mecanum drive-trains enough to be willing to use them. I don't believe that Mecanum-driven robots have any sort of inherent advantage that always makes them a clear choice over other types of drivetrains; rather, I see Mecanum drive as a drive type that has its own strengths and weaknesses, just like six- or eight-wheel drives or swerve-drives. Those strengths and weaknesses must be evaluated by the team when deciding what drive type to use. At the same time, I don't see any inherent disadvantages that make Mecanum drives perpetually inferior to other types.

Mecanum wheels have their advantages and disadvantages; however, as with what has been said before: it's not the drive-train that determines how competitive a robot is, it is the whole package: drive-team, human player, end-effector, build-quality, reliability, etc.

EDIT: I think that in 2012 there is as good of a chance of a robot with Mecanum wheels on it making the trip to Einstein as any other year (unless the game turns out to be like Lunacy...in which case...well, we won't talk about Lunacy.)

Re: Mecanum Einstein this year
 

Out of curiosity, what drive trains did make it to Einstein this year?

Re: Mecanum Einstein this year
 

6 and 8WDs

Re: Mecanum Einstein this year
 

As of now, mecanum has been around for 6 FRC seasons. I really doubt teams have just not figured it out yet.

Re: Mecanum Einstein this year
 

And an "H" drive (51).

Re: Mecanum Einstein this year
 

Still, not a lot of teams have done it well. I don't think, either, that lack of knowhow is the culprit.

Re: Mecanum Einstein this year
 

Only 12 teams out of over 2,000 made it to Einstein this year. Lots of quality teams with 6WD and 8WD didn't make it either. A well done drivetrain of any type is just one part of a total robot / program that is required.

Good luck is also required. For example, one could argue that 148 suffered from a qualifying schedule that was too easy. They were third seed because their opponents didn't put up enough points. Had they been first seed, the entire alliance selection on Newton would have gone down differently - but this is nothing more than a bit of bad luck.

Re: Mecanum Einstein this year
 

Uhh, what? When has the championship winner ever be "pre-determined?"

Didn't everyone think that if 1114 and 469 got together they would win last year? How well did that work out?

And wasn't it supposed to be whoever won Newton in 2006? And wasn't Newton being written off in 07? And wasn't the Archimedes "super division" in 2005 supposed to create the division champion?

Given that AndyMark has been selling the wheels since 2006(?) and other teams, like 357, were making their own even before that, the book is pretty much out on how to do a mecanum drive correctly. The only really recent innovation in the drive has been the new introduction of "octocanums" and "jump drives," which had long been contemplated but never put on the field until recently.

The bad rep that mecanums get is acquired from... physics. High end teams don't like sacrificing ~30% of their power and a good chunk of friction.

Re: Mecanum Einstein this year
 

And weight/precision machining time. Mecanums require 4 gearboxes. 6/8wd requires 2 and even 51's H and 148's (2010) Nonadrive only really need 3.

Re: Mecanum Einstein this year
 

I think Hawiian Cadder is saying he didn't see much of a chance of beating the eventual champions after alliance selection. We can talk about relative divisional strength all we want, but ultimately it doesn't mean that much until we see which robots from that division actually get together. (And the first seed in Newton in 2006 did a great job preventing powerhouse alliances)


No arguing with that last point though.

Re: Mecanum Einstein this year
 

Has anyone compared to the percentage of teams that use mecanum to the percentage of 6/8 wheel drive? I wish I had my scouting notes from the past few years, but I think they would be surprisingly close. Its easy to look at the top teams (111, 217, 148, 1114, 254...) and say that barely anyone uses mecanum drive, but there are a lot of average to below average teams that use mecanum drive every year.

Re: Mecanum Einstein this year
 

The issue with mecanum drives at the high level of play is you are pretty much screwed against a decent defender. The idea of strafing out of the way, or dancing around a team that is actually playing smart defense (which is not what most average teams play in average qualifying matches) is just silly.

If you're the number two scorer on the alliance, it's not a hindrance (or if you're not playinh capable defense), but don't plan on being the top scorer.

Re: Mecanum Einstein this year
 

Do keep in mind though, the semifinals came entirely down to the minibot coin flip in match 1, and the finals were 2v3. While 254 / 111 / 973 was undoubtedly the better alliance, it was certainly not predetermined.

Re: Mecanum Einstein this year
 

It is true that defense can be tough on a mecanum robot. However, it is an exaggeration to say that mecanum is screwed against good defense.

I'll get one of my students to upload our videos, including the ones against 973. What you will see is a mixture of two things: 1) 973 wasting a good chunk of our time playing good defense, and 2) us getting around them some of the time. This is to be expected. 973 played what I thought was the best defense of any team I watched this year - they were able to stifle not just mecanum opponents but others as well. Yes, it is true that they were not only defending our robot, but that is also to be expected.

It's true that mecanum isn't going to "dance around" or "drive circles around" 6WD defense. But it is not true that mecanum is helpless against defense, either. It's also not true that 6WD is strictly better against defense in every regard. Notably, a mecanum driver can more easily fake out the defender and get them to start in the wrong direction and allow you to rather quickly get past them in the other direction. I'm not saying that works all the time, but it does work some of the time. And yes, mecanum looks pretty bad when the defense is working well and wasting 20 and 30 seconds at a time. Not denying that... I'm just saying that a defender is not able to guarantee this outcome. And do remember that good defense is also capable of wasting 20 and 30 seconds of a 6WD robot's time.

If one wants to argue that 6WD is better against defense than mecanum, then I can agree with that. 6WD is better at hitting the defender on their side near a corner, turning them some, and pushing past, which is a higher percentage play than trying to fake them out.

I don't think it is a liability to have one offensive mecanum robot on an alliance. It does get to be a problem when you have 2 or 3 mecanum robots and you lack a good 6WD to play defense or play some other strategy that requires pushing around. Not having those strategic options available (as 973 did when they switched over to defense after presumably playing offense all season long) is, in my opinion, the bigger downside to mecanum drive.

Re: Mecanum Einstein this year
 

If I don't miss my guess, Brendon is talking about the PVC Pirates (1058). They were able to lock the rollers of their Mechanums, basically changing them to a skid steer system, on the fly.

It was, IMHO, very impressive.

Re: Mecanum Einstein this year
 

Did they post any descriptions, pictures, or CAD drawings, do you know?

Re: Mecanum Einstein this year
 

Although mecanum cannot push around as other drives, I would argue that mecanum wheels can play good defense. Take for example Curie qualification match 110, where we helped save the match against arguably the fastest minibot on the field. We were on the red alliance, the robot with the folding mast who dropped their uber tube. http://www.youtube.com/watch?v=aEnahGGj9dY

I would argue,(as well as our driver) that if it wasn't for our mecannum wheels, we wouldn't have been able to slow down the team from scoring, block their way to the tower and swerve away at the last moment, ultimately making the minibot come in last. If that minibot would have gotten first, the results would have had a different out come.

Re: Mecanum Einstein this year
 

I wouldn't put too much weight on any videos of us from the quarters and semis. We were trying to play zone defense, and just were not very good at it (as we never had practice). We were quick to let teams go. In the division finals and on we tried man to man, which really worked out infinitely better for us.

Re: Mecanum Einstein this year
 

I agree and disagree. The 12 teams out of 2000 are not a simple random sample. The best teams make Einstein, and the best teams never have mechanum drives. The fact that the there is a consistent trend of simple 6WD's making Einstein and winning competitions speaks for itself. I don't think it's a coincidence by majority in numbers; it looks like a correlation to me.

(If someone has the number of mechanum teams in St. Louis, we could analyze whether the reality that they didn't make Einstein is statistically significant).

Re: Mecanum Einstein this year
 

Has anyone gone down the top 25 list and filled in the drivetrains? I'll start, but I don't know all of them:

254 - Skid Steer
111 - Skid Steer
1114 - Skid Steer
2016 - Skid Steer
217 - Skid Steer
987 - Skid Steer
148 - Skid Steer
1503 - Skid Steer
2056 - Skid Steer
233 - Skid Steer
67 - Skid Steer
33 - Skid Steer
1717 - Swerve
469 - Skid Steer
177 - Skid Steer
71 - Swerve
40 - Swerve
2054 - ???
118 - Skid Steer
330 - Skid Steer
16 - Swerve
51 - Slide Drive
27 - Skid Steer
2826 - ???
1538 - Skid Steer

Did I get all those right (off the top of my head)?

Re: Mecanum Einstein this year
 

2826 had mechanum and drop down plaction wheels.

http://www.chiefdelphi.com/media/photos/36224

Re: Mecanum Einstein this year
 

2054 was skid steer.

2826 had an "octacanum" drive.

The rest look right.

Re: Mecanum Einstein this year
 

They were able to lock their rollers with some special mods and with special programming they can realign/push back against defenders while retaining their position. I remember our driver bumping into them during a match with 6 plaction wheels and they didn't move.

Unfortunately for them they had mechanical/programming issues throughout the season but knowing this team they will be back and even tougher next year.

Re: Mecanum Einstein this year
 

I think the next trick to figuring out how complex drive trains should be is clarifying which of the D/T's on Einstein (or Top25) were:

• KOP (with perhaps sprocket gearing changes or different wheels, but all else the same)
• 1 or 2-speed
• Full-traction versus omni's on the corners
• Direct-Driven
• 4/6 motor
• etc

Speeds in high gear may be interesting to see, but really those are more about what a team's strategy is rather than 'best drive train'. I suspect we'd see a wide variety of skid steer designs in the top ranks.

Re: Mecanum Einstein this year
 

I know that Karthik's term "minibot coin flip" has become a popular way to describe the end game this year. I'm not a big fan of Logomotion's end game, and I think the description is true, to a point. But, eventually people have to recognize and appreciate greatness. 973 had the fastest minibot on Galileo and potentially the fastest minibot at Championship. 254 chose them to guarantee 1st place in the minibot race every match.

From now on, if you use the term "minibot coin flip" to describe our matches, know that our alliance was using a coin with two heads, we called heads every match, and won every toss.

Re: Mecanum Einstein this year
 

I agree despite my post before - I meant that from a spectator point of view it didn't look obvious who the winner was. The average FIRSTer didn't know 973 had the world's fastest minibot, and that was what locked up the championship with a very strong alliance. A lot of people thought it was over when 254 picked 111 - but 973 was what firmly locked it up.

Re: Mecanum Einstein this year
 

It may have been a coin-flip-minibot championship competition ... but 973's deployment was nothing short of lengendary in swinging the probability their way. That thing was ramp-style with 2 naturally-articulating degrees of freedom and 1 driven degree of freedom. It wasn't going to miss the pole by even half a degree, most of the time. I talked to them in the inspection line on Wednesday, and you could tell they put a very large amount of time into that thing before Champs.

It also didn't hurt that they had fastest drive train on the field this year (from what I saw), which gave them the advantage in getting around defense to the towers. The 254/973/1868 drive train in and of itself is an engineering marvel. The fine details of it would be appreciated by most. It's designed up against the edge of constraints in many cases and isn't replicable by most teams (since it probably couldn't be done on a non-CNC mill).

Re: Mecanum Einstein this year
 

177 used the latest revision on our 6wd that has gone through a lot of optimization over the last 6 years.

The stats:
4 CIMs
6x 4" AM performance wheels with roughtop tread.
AM shifter "guts" repackaged/repurposed and final ratios modified.
2 wheels are direct drive
~14 fps high gear
~5 fps low gear
Everything is packaged into a 2.5"x2.5" extrusion.

This year we used low gear so rarely that that our driver ocasionally forgot to shift when he got in a pushing match.

Re: Mecanum Einstein this year
 

What was your rationale for the small wheels?

I'm thinking 1) less gear reduction necessary and 2) lower center of gravity

are there other reasons?

Re: Mecanum Einstein this year
 

We (33) built a live-axle drive inspired by team 254. We made bearing blocks and cam tensioners out of 1/4" plate and cut them on a waterjet, but the bearing blocks were seriously just three holes in a line and not hard to make by hand. The shafts were lathed by hand (we used keyed shafts since they were easier to machine), and the wheels, hubs, and transmission components all came from Andymark. If you simplify the design, it isn't hard to make.

The Cheesy Poofs transmission, on the other hand, is quite difficult to replicate as basically all of the gears are custom-made by them.

33 robot stats (We were on the top 25, so that qualifies us?)
-8 wheel (6" wheels) live-axle DualDrive combining Plaction, KOP, and Lunacy wheels. Two wheels are actuated by pneumatic pistons, automatically.
-2-speed, 4-CIM transmission (5.5 and 12 ft/sec)

Re: Mecanum Einstein this year
 

The question I always ask the people at competitions who question are small wheels is, "Well, why do you use big wheels?".

Usually the answer is either they don't know, or they always have.

We use small wheels for a lot of reasons, but they mostly stem from two of ours teams primary design goals; less weight, and less friction.

Small wheels are physically smaller, which is less weight.
Small wheels require less torque to turn to achieve the same force on the ground, less force in the shafts/sprockets means smaller and lighter parts.
Small wheels need less reduction, which is both a direct decrease in weight, but also a decrease in friction losses as we can run less stages of gear reduction total.
Small wheels let you have a slightly longer wheelbase for all other factors the same.
Small wheels are cheaper for us to make, as it's a smaller diameter stock, and has much less wasted material.

Also, experimental data has shown that for rough top tread, smaller diameter wheels have more traction.

To summarize, teams with small wheels usually have done actual engineering and reasoning behind their wheel size choice. Many teams with larger wheels do not (although some do, and decide to use KOP or other COTS wheels of a larger size for some logical reasons (like 111)).

Re: Mecanum Einstein this year
 

1503 used 6X4" wheels, 1/8" drop. We used blue nitrile tread and didn't change tread once.

Our gearboxes were little innocent CIMple boxes with a secondary 12:18 sprocket reduction.

Fun fact about the CIMple boxes; if you didn't Loctite your motors in, they would work themselves loose after about two minutes of usage.

-Nick

Re: Mecanum Einstein this year
 

It's also worth noting that it's somewhat easier to use bigger wheels for newer teams.

Personally, I dig small wheels. 4 inch wheels are a biiiig weight cut when you add all the parts up.

Re: Mecanum Einstein this year
 

Any pics of your drivebase?

Re: Mecanum Einstein this year
 

Jim Zondag also posted their CAD in CD media.:)

Re: Mecanum Einstein this year
 

Adam pretty much nailed it below.

Historically we used the 4wd 2001-2005 (disclaimer: I haven't really looked at any of our robots older than this) with 6" pnuematic wheelchair wheels and 6" skyways in 2001 & 2003. In 2004 and 2005 we used 6" pnuematic and 6" omnis with a T-kats based 2 speed.

In 2005 we had a lot of drive issues, marking the carpet with our omnis and breaking KOP skyways when we switched over to them. That was the last year I let our team leader use the excuse "This is easy we've done it before." as a logical arguement in the decision of what drivetrain to use. In 2004 we had pushing power and the robot was designed to operate in the limited perimeter of the field. 2005 we were outgunned and spent the whole season fixing issues.

In 2006 we clean sheeted our drivetrain ideas and arived at going with a 6WD drop center with AM shifters an d 4" wheels. We made bearing blocks that bolted to a 1x1x1/16" box Al space frame. The performance was good for the way we played the game but we saw weaknesses in the design with the reliability, wheel alignment and maitenance. We used the brand new IFI wheels that year, which were good but did not reach the robustness of where they are now at that time.

In 2007 I designed the first parallel plate design that the Bobcats used as a way to keep the performance of the 2006 robot but improve the robustness of the 2006 design. This purpose of this was to improve mainenance, modularity, and reliability. In doing this we used AM shifters with custom output shafts and lost the outer steel plate from AM to shed weight and remove redundancy. We also made our own wheels because we wanted wide wheels in the corners(these can be seen elsewhere on CD). We never lost a chain, replaced a tread or had any issue with the drive. We still use this robot to practice although we probably need to replace bearings and motors at this point.

In 2008 we had to speed up the robot for the game, so we took the opportunity to improve packaging further and tighten everything up. At thispoint the drivetrain was mostly designed by another engineer on the team. We also narrowed our wheels because we did the math and realized the wider wheels didn't really do anything.

In 2009 we did our first live axle and cantilevered the wheels as well. We packaged the transmissions and all in a 2x2 box because we needed to package low and tight for our design that year. After this with the introduction of the AM hex bearings we hex broached everything.

Our 2011 drive was an evolution of the 2009 combined with our parallel plate system from previous years. We put the wheels and all inside the box this year combining the best of the 2008 and 2009 designs. This is what we planned to do for 2010 until we saw that game.

I hope this explains some of the thought behind how we got where we are as an example for other teams. I will openly admit we think there is another jump in highly mobile drive trains that teams are starting to go through right now and we think we have to put some work in to plan ahead for it.

Re: Mecanum Einstein this year
 

First, what Mike said.

Second, the real difference in Semi 1-1 was 254 missing an ubertube in autonomous, not the minibot (and given that 254/111/973 won in 2, there would still have been a second chance had 973 not taken first in the minibot race).

Re: Mecanum Einstein this year
 

Can we just agree that they outplayed us and leave it at that?

-Nick

Re: Mecanum Einstein this year
 

The "minibot coin flip" term is meant to refer to matches where the point differential on the rack became irrelevant, and was to be decided by relatively random nature of the minibots. However, there was nothing random about the minibot success of 973. They were consistently the fastest on Galileo. The minibot coin flip determined many matches throughout Logomotion, but it never really came into play for the World Champion alliance. They definitely didn't leave anything to luck.

Re: Mecanum Einstein this year
 

It's more about their overall design rather than the WCD-sliding blocks or their custom gears (which I suspect *could* be COTS gears if they chose).

3.5" wheels -- they can't go smaller because of the large gear on the shifting shaft
They can't make the first stage reduction greater because of CIM spacing (2.55 or 2.6" between CIMs) and the internal shaft spacing of the large gear on the first stage. The AndyMark super shifter runs into this same issue.
So they're 'stuck' with 18 ft/s, in a sense. All in the name of removing the 3rd gearing stage from the transmission to increase efficiency.

Then
- For any sort of decent acceleration, they need incredible efficiency on the overall drive train since it's only 4 CIMs (unless there were other motors hiding under the CIMs...)
- Weighing only 100 lbs + battery, bumper, lightweight minibot helps acceleration too

So their strategy, at 18 ft/s for an 'open field' where defense rules were constricting and effective "anti-flow" strategies forbidden, was actually a great idea in hindsight. 7 ft/s would help them get through the average defensive robot in a pinch, though the tradeoff was lack of torque -- which did get them into trouble once.

I'll admit, I didn't count gear teeth, and a bit of this is reverse-engineered estimation; so I don't know the true numbers for their gearing itself. Yet if you design a 2-reduction 2-stage gearbox (I tried the week after champs) you'll see that it's not quite as easy as slapping COTS parts together. So most of us wouldn't be able to do it quite like they do.

Re: Mecanum Einstein this year
 

Jesse - They could break 18FPS with bigger CIM pinions, however CIMs just so happen to take a massive acceleration hit right at the 18 FPS mark.

Re: Mecanum Einstein this year
 

All our gears are COTS in the sense that they're off the shelf products from either Martin or AndyMark.

This year we were forced to use more gears from Martin than we'd have liked and fewer from AndyMark. That required us to do a lot of machining to remove hubs, machine dog teeth, lightening pockets, and hex broach bores. In that regard the Martin gears are not truly COTS.

Re: Mecanum Einstein this year
 

Not to pick on you, but there are quite a few flawed assumptions here.

I can only speak for us, but I would assume 254 has the same reasoning.

We don't gear for top speed, but for a "sprint distance".

Low gear is well past traction limited. 254 was likely pushed in fm1 due to being underweight. There was no lack of torque. 99% of robots would not have been able to do that to them, 469 was really an edge case with their drivetrain.

Using the same geometry, you can easily gear to get a top speed in a smaller range (in 2010 we were 13.5 fps with LARGER wheels...). We're not stuck with 18fps.

Re: Mecanum Einstein this year
 

I get that 'sprint distance' concept; it's why I made my "gearing vs time" charts in my recent calculator. Other than that, a couple of things --

I was under the impression, from talking to kids on all 3 teams, that the drive train gearing between 254, 973, & 1868 were identical. Due to the collaborative nature of the machine shop setup (which is great, imo) I presumed many discussions and similar conclusions were made.

I'm having difficulty getting the geometry for less than 18ft/s correct by using 3.5" wheels, the 15:48 & 28:35 combos for the shifting stage, and 11:40 for the first stage; this is why the presumptions were made. It's easy to get less than 18ft/s after adding a 3rd stage, but that's extra weight/inefficiency. Increasing the 40T gear on the first stage interferes with the dog gear; decreasing the 11T pinion further to a 10T pinion without increasing the 40T gear causes the CIMs to touch (at least). For anyone wishing to use the COTS solutions from AndyMark without extra milling on the gears for the dog gear setup (such as my team), this is what we'd have to use.

So really, I have difficulty in understanding how you get the dimensions needed for 13.5 ft/s in the same geometry (2 stages of reduction); it doesn't work out for me.

Re: Mecanum Einstein this year
 

Although functionally the same, our drivetrains are very different at the part level. 254 makes no parts for us, and we make no parts for them. We're certainly buddies with 254 (and they/968/60 certainly inspired our design style), but we each run our own show.

What I meant by the same geometry, was the same overall gear setup. We don't use AM's stock shifter setup. We get dog gears custom cut each year per whatever ratio we need. It's a pretty simple operation for a CNC, so sponsors are willing to do it.

I also left this out of my previous reply, but it's possible to make this style drivetrain with zero CNC equipment (more parts on our current drivetrain are made on manuals than you would think); 973 did that from 2005-2008 (single speed through 2007, SuperShifters in 2008).