Another chapter to the 6WD vs. Mecanum debate
 

So here is my question, If a Mecanum robot and a 6WD robot come in contact and the mecanum strafes out of the way and heads forward can the 6WD catch up after it starts strafing?

Re: Another chapter to the 6WD vs. Mecanum debate
 

It all depends on how fast your 6wd base is and how good your drive is. I would imagine that the average 6wd would have no problem catching up to the mecanum robot. I think it would be a cool project to get a 6wd robot and a mecanum robot in the same area and see who can out maneuver the other. I still have my money on the 6wd.

Re: Another chapter to the 6WD vs. Mecanum debate
 

There are a lot of variables here that depend on both robots and their respective drivers....

But in general and in my opinion - yes. A mecanum can't get past a 6WD just by going sideways for a second.

Re: Another chapter to the 6WD vs. Mecanum debate
 

We are going to put them head to head and get a video up by sat. i will post it back here

Re: Another chapter to the 6WD vs. Mecanum debate
 

From experience, a 6WD will push right through a robot with mecanum drive. A good driver could just clip someone with mecanum trying to slide to the side and throw that robot off target.

Re: Another chapter to the 6WD vs. Mecanum debate
 

6WD isn't that much more powerful than a mecanum drive. Of course 6WD is more powerful, but you are exaggerating quite a bit.

The argument pretty much boils down to who the drivers are and what they do. Certain 6WD teams will destroy certain mecanum teams, but certain mecanum teams will run circles around certain 6WD teams. It all depends on the team, the strategy, and the execution. The wheels themselves are unimportant.

Re: Another chapter to the 6WD vs. Mecanum debate
 

Is he? Do you have anything to back this claim up?

Re: Another chapter to the 6WD vs. Mecanum debate
 

Well, there is "a 6wd", and then a 6wd with high traction wheels, 4 CIMs, and shifting.

One of them is anywhere from mediocre to good, the other is great. The great one will beat a mecanum any day of the week.

Re: Another chapter to the 6WD vs. Mecanum debate
 

I would argue that shifting is not an absolute requirement to build a great 6WD. Other than that, completely agree.

Re: Another chapter to the 6WD vs. Mecanum debate
 

A very solid base can happen without shifters, but if you take two 6wds equal in all but shifting, the shifting is superior. It will push harder (while drawing reasonable current) and drive faster.

Re: Another chapter to the 6WD vs. Mecanum debate
 

True...but if the decision is 6 drive motors w/o shifting vs. 4 with shifting, then things get more interesting.

Re: Another chapter to the 6WD vs. Mecanum debate
 

[quote=Colin P;1004786]6WD isn't that much more powerful than a mecanum drive. Of course 6WD is more powerful, but you are exaggerating quite a bit.[quote]

Yes it is.

Mechanum inherently wastes ~30% of it's power just in slipping its rollers. That is pure waste of energy that translates to nothing in the terms of pushing force/traction.forward motion. That's not exagerating that's physics.

All else being equal you start yourself at a disadvantage with mechanum.

Re: Another chapter to the 6WD vs. Mecanum debate
 

No, it's not physics. It's a myth. There is almost no loss of power at all during forward motion.

When a mecanum drivebase is traveling perpendicular to the axles of the wheels, as if it had traction wheels, the slipping of the rollers is almost nonexistent. There's a teeny bit of roller motion that happens on a compliant surface like carpet, but 30% is a huge exaggeration.

What you do give up with mecanum wheels is maximum pushing force. Because the individual force vectors are in different directions, the sum of the magnitude of the forces on the carpet is greater than the magnitude of the sum of those forces on the robot. The wheels will slip at the same wheel/carpet force as any other wheel having the same surface, but when using mecanum wheels that happens when there is less total force on the robot than when using traditional traction wheels.

Re: Another chapter to the 6WD vs. Mecanum debate
 

Emphasis mine.

Because a mecanum drive has less total usable force at any given speed than a 6wd, and power = force * speed, does this not mean that mecanum drive has less available power than a 6wd?

If my interpretation is correct (please correct me if I'm wrong), the power loss in mecanum comes from the force vector cancellation during straight-line driving, not from frictional losses in the rollers.

Re: Another chapter to the 6WD vs. Mecanum debate
 

Yes. But that's a power limit, not a power loss. This may seem like nitpicking, but it's an important distinction.

The "force vector cancellation" does not cause any power loss unless you are operating on a very resilient surface at high vehicle force levels and speeds. And then it's not a fixed 30% number but rather a function of the force and speed.

Once a mecanum's wheels break traction (start slipping), then any additional power supplied to the motors is wasted in scrubbing the wheels on the floor.

Re: Another chapter to the 6WD vs. Mecanum debate
 

That makes sense, and I'm all about nitpicking distinctions, otherwise ambiguity would prevail.

This makes sense too.

Thanks for the input!

Re: Another chapter to the 6WD vs. Mecanum debate
 

Depends what you mean by beat. A pushing match? Probably so. A test in maneuverability? I'd disagree with that. If your driver knows how to truly utilize the strengths of the mecanum drive, then you can juke 6 wheel drive robots all day long.

Picking one of them revolves entirely upon your team's strategy for this year's game.

Re: Another chapter to the 6WD vs. Mecanum debate
 

I've literally never seen a mecanum "juke 6 wheel drives all day long". Not saying it can't be done... just saying I really, really want to see video of it. Partly for "proof" and partly because it would be really cool to watch.

Re: Another chapter to the 6WD vs. Mecanum debate
 

You will see a difference in pushing performance due to the traction capabilities of the wheels used, not so much the power available.

The mecanums are usually a hard roller material, which will not provide much "grip" into the carpeted surfaces. Assuming the 6WD is using some sort of treaded wheel it will have more traction onthe carpet.

Think about walking across the playing field in your slick soled dress shoes. You can move, you can run, but you can also push your foot out to the side and it will slide across the carpet. In a pair of softer soled athletic shoes, you can also move and run, but if you try to push your foot out to the side it will take more force to do so.

The mecanum is like the dress shoe, the treaded wheel is like the athletic shoe.

Re: Another chapter to the 6WD vs. Mecanum debate
 

As previous leader of the 449 Drive Team for two years, I'd like to put in a few good words for mecanum.

First off, there is almost no power loss in forward/backward movement in a mecanum drive - the rollers do not move unless you are strafing. The fact that mecanum is "less powerful" is a common misconception - mecanum is *not* omni holonomic, and the only difference in power is the difference in coefficient of friction with the floor between the roller material and the material of your six wheel drive wheels. Mecanum's only real weakness with respect to being pushed is from the side, which in this game isn't all that important as the other robots are not allowed to interfere with your goal scoring. Last year during the DC regional we had some issues with ball manipulation that forced us to change our strategy during the quarterfinals to "go into the front zone and push the defensive bot out of the way," which we were able to do with no problems at all.

Secondly, strafing is *amazingly handy," especially in a game like this years in which staying lined up with a goal is crucial to success.

Thirdly, it is not particularly complex. One your team invests in writing/acquiring decent drive code, building a mecanum drive is as trivially easy as building a normal four wheel tank drive. Well, perhaps a wee bit more, as you need to have one gearbox per wheel.

Fourthly, mecanum is also fairly robust - we have lost rollers and drive belts and still been able to play the game fairly well, as even a mecanum missing the strafing capability can turn better than a standard 4wd. You really don't even have to adjust that much for it on the controls. We were able to traverse the bump last year as well as any other robot at the competition without mucking up our drive in the slightest.

And finally, I am amazed at how AndyMark's mecanum wheels have improved over the years. We had very few maintenance problems with our rollers last year, and the main issue we had (difficulty in adjusting the connection to each roller) seems to have been fixed on this years generation of 6'' mecanum wheels.

Re: Another chapter to the 6WD vs. Mecanum debate
 

or rotating.

Mecanum is fully holonomic if properly coded. All three degrees of freedom can be executed simultaneously with no skidding of the contact patch.

If by "power" you mean "maximum force" this is not correct. Even with the same material on the mec and the 6WD, the mec will have less maximum pushing force, as explained in many posts here on CD.

Re: Another chapter to the 6WD vs. Mecanum debate
 

This is not true.

Also not entirely true - it's worth noting a mecanum drive more or less necessitates a lower traction roller.

It can also be pushed from the front more easily due to those spinning rollers.

Keep in mind just because there's no "at the goal" defense doesn't mean there is no defense.

Re: Another chapter to the 6WD vs. Mecanum debate
 

I'm with you Chris. If Mecanum Drives could outmaneuver traditional Traction Drives so well, wouldn't we see them at the higher levels of competition much more often? (Think Division Finals, Einstein)

Now a Swerve Drive can Juke 6WD's all day long - and that's cool to watch.

Re: Another chapter to the 6WD vs. Mecanum debate
 

It does not necessitate a lower traction roller. A properly coded mec is fully holonomic and there is no skidding of the contact patch... only rotating of the patch, like swerve.

Re: Another chapter to the 6WD vs. Mecanum debate
 

My mouth got ahead of my brain again - I meant that mecanum drives more or less will always have less max pushing force ("lower traction") than a 6wd wheel, even if both were coated with roughtop tread.

Re: Another chapter to the 6WD vs. Mecanum debate
 

Would mecanum even work with the kind of tread that AM sells for traction wheels?

Re: Another chapter to the 6WD vs. Mecanum debate
 

Based on what Ether said two posts earlier I would say yes.

Re: Another chapter to the 6WD vs. Mecanum debate
 

Making a roughtop mecanum wheel would be an award-worthy feat, indeed.

Still, in a roughtop vs. roughtop pushing battle, the 6WD would STILL always beat the mecanum drive...because maximum tractive force for the mecanum drive IS influenced by the fact that there are passive rollers. Read Ether's white papers - they explain it all.

Re: Another chapter to the 6WD vs. Mecanum debate
 

By "omni holonomic" I was referring to the drive system of four omni wheels placed in square or diamond configuration. If that's not what the term means, then I'm sorry, that's what it's always referred to in our team.

No, I don't mean maximum force. I know mecanum wheels do start skidding before 6wd drive, but honestly I *rarely* see a pushing match actually reach that point in competition, and with the pinning rules in place it's even more of a nonissue now than it has been in previous years.

And yeah, the rollers turn while rotating, but it's not as if someone hitting you from the side will cause you to start spinning.

I've had to push against 4wd and 6wd drive robots with mecanum before, and not once have I seen the rollers spin - try it yourself, you'll notice that the difference is not nearly as big as most people make it out to be. Yes, there's a lower cap before mecanum wheels start skidding, but how often have you seen wheels skid in a FIRST pushing match? It's not exactly a common occurrence - in my time in FIRST I really can't recall ever seeing our mecanum wheels skidding on the carpet. In my experience, the idea that "mecanum drive gets pushed around a lot" is almost entirely a myth.

People put way too much store in "If we end up exactly head to head and are pushing each other, my robot will win out." That's not a realistic situation. In the context of an actual competition, in which your goal is not to push head to head with other robots, mecanum is not at a significant disadvantage in terms of being pushed. Take into account the fact that defense isn't allowed to push you while you're scoring, and the best way to get into the scoring zone will probably be dodging the defensive robot rather than pushing it (in fact, are you even allowed to push another alliance's robot into your scoring zone?), and I really don't see what the benefit of a 6wd is.

Re: Another chapter to the 6WD vs. Mecanum debate
 

2006 Boston Regional Finals Matches 1 and 2 come immediatly to mind for me. Every thing you say you have never seen occur happens in those matches and the drive train on the defensive bot was not that good, it was a poorly executed 4wd design.

I have seen Mecanum drives pushed directly backwards by a 4 or 6 wheel drive despite trying to push forwards. There is definitely a disadvantage to mecanums whenever there is pushing.

I think the advantage to 6wd is pretty obvious and pretty much common knowledge, it is simple, reliable and easy to manuever. There is a reason that the majority of teams on Einstein every year seem to be 6 or 8wd

Re: Another chapter to the 6WD vs. Mecanum debate
 

Of course, 469 in 2010, with their shifting, was no ordinary machine: both really quick and incredibly powerful. But if you check out the below video, you see them put a really nice move on our driver, then just shove us out of the way. It was really impressive to see, and I almost applauded..

youtube.com/watch?v=qAMlb2iugUs

Re: Another chapter to the 6WD vs. Mecanum debate
 

I think that's probably because the majority of teams in FIRST don't use mecanum. Walk around the pits at regionals if you don't believe me.

Mecanum is unequivocally more maneuverable than 6wd, and mechanically it's no more complex (and you can get working drive code online, I believe our team has published ours), and it's perfectly reliable - our team has never had a major drive failure (one which made our drive unusable or even less maneuverable than a 4wd) due to the mecanum wheels.

I encourage you to build a mecanum bot and push against a 6wd with it. I think you'll be surprised at how hard it is to actually get the mecanum to skid.

Re: Another chapter to the 6WD vs. Mecanum debate
 

Maybe that's because it's not as good - the VAST majority of the best teams in FIRST don't use mecanum, and it's not because they're stupid.

Is it? Honestly? I think 6wd maneuverability is quite underrated - there's a reason there's literally never been a mecanum on Einstein.

We've pushed plenty of mecanum bots no problem (and yes, the rollers spin)

Re: Another chapter to the 6WD vs. Mecanum debate
 

Yes 6WD can push harder than Mecanums. So? I did not catch Dean saying this year's main goal was to push around other robots. In fact I see there is a rule against pinning and contact during certain match times.

Next year, when the goal is simply to push each other I will be on my way to northern Minnesota for these:

http://www.mattracks.com/

Good luck to all, have a safe build season!

Re: Another chapter to the 6WD vs. Mecanum debate
 

When the Blue Alliance comes back up, watch matches with team 40 in 2006. They had a mecanum drive with a drop down "traction plate" to stay in place when they wanted to. When they were on the mecanum wheels, they got pushed all over the field, when the traction plate was down, teams rammed them until their angle was off and with the mecanum wheels they couldn't fight back for their initial position.

Mecanum wheels have strengths that traditional skid steer drives do not. Pushing is not one of them.

Re: Another chapter to the 6WD vs. Mecanum debate
 

I feel a little bad using this as an example because I think you did a great job on 469 and had a great robot last year, but I see too many mecanum drives like this one in this match. In theory mecanum can work welll, butt too often teams don't strafe or take advantage the 'ability to drive circles around slow 6 wheel drives' (which I'm still waiting of a video of, btw).

I think mecanum can be an effective drive system but 97 times out of 100 6 wheel is just better. The best utilization of a mecanum drive I've seen was 2171 in 2008, but their drive still wasn't as good as 1114 and the other 6 wheel drives that year. I think there is a reason none of the elite teams have used mecanum drives.

Re: Another chapter to the 6WD vs. Mecanum debate
 

I feel like mecanum bots will do pretty well this year. We also used mecanum in 2007. We resurrected our 2007 chassis and put the electronics from last years robot to do prototyping/let software have more then 6 hours with the robot. I just don't see a well designed mecanum bot having problems out-maneuvering a 6wd bot.
Here are our 2007 drive tests:
http://www.youtube.com/watch?v=v_vUYyJAkCc
http://www.youtube.com/watch?v=YbluSr2Mf5Q
http://www.youtube.com/watch?v=W0XN6iSvCXo
Here are a few more:
http://www.youtube.com/watch?v=L01Ok-6AMhM
http://www.youtube.com/watch?v=RXGbo3tQapE
http://www.youtube.com/watch?v=ZnoMhVEqx1c
http://www.youtube.com/watch?v=oamC4esbGfI
http://www.youtube.com/watch?v=KfOLERgWQrU
http://www.youtube.com/watch?v=fdS8BmQom58&NR=1

Re: Another chapter to the 6WD vs. Mecanum debate
 

Every fall I do the drive train presentation at FIRSTFare, our FRC technical conference in Portland. I go through all of the teams who were either division winners or finalists at the championships and try to determine what basic system they used for their drive train. Obviously the game has a lot to do with what works but here are the results from 2008 and 2010:

2008 Championship Division Winners and Finalists
14 Six Wheel with traction wheels all around
2 Six Wheel with omnis
2 Four wheel with omnis
2 Mecanum
2 Crab Drive
1 Four wheel rack and pinion.

2010 Championship Division Winners and Finalists
2 Four Wheel
5 Six Wheel
10 Eight Wheel
2 Nine Wheel (148, 217 partnership)
1 Mecanum
3 Crab Drive
1 Treads

I left out 2009, the Lunacy year, because there the drive train was more or less determined by FIRST. I might have gotten a few of these wrong because I'm just going by what I can observe from the team's website and Blue Alliance video.

What you can see is that very few Mecanum drives make it to the top levels of competition. How much of that is because many of these elite teams have a drive base they've developed over the years that they are happy with and how much of it is because Mecanum doesn't readily translate into a competitive advantage FOR THOSE GAMES is something we won't know. This might well be the year that Mecanum breaks out...or not.

Re: Another chapter to the 6WD vs. Mecanum debate
 

No, I think there are plenty of teams who have never tried it - I know that 449 had never used mecanum until '07, and since then we've used it in both games which allowed it. There's a lot of stigma around mecanum based on this myth that it gets pushed all over the place - anyone who has had experience driving a mecanum bot will tell you that this is nowhere near as big an issue as you think it is.

No, the rollers do not spin unless your wheels are already skidding - the physics of this has been explained multiple times earlier in the thread. As has been mentioned earlier in the thread, the only power difference mecanum suffers is the fact that the wheels skid sooner than traction wheels. You will never start pushing a mecanum bot and see the rollers immediately start spinning - it's the same reason that acceleration of mecanum drive is identical to that of a traction drive.

Yes, it is unequivocally more maneuverable. You turn just as well, you accelerate just as well, and you have an extra axis of movement. If that's not unequivocally more maneuverable, then nothing is.

Re: Another chapter to the 6WD vs. Mecanum debate
 

I'm going to throw a wrench into the works.

Back in 2005, 330 had this debate a bit ourselves. We decided to work a compromise: We'd build our frame to run both (quite easy to do) and rig it with 6WD and rig our kit frame with mecanum (6" fully nylon wheels, KOP trannies from that time frame--single speed, single CIM). At that time, our 2003 robot was still operational, so we decided to test against that (4WD, 2-speed, drill motor transmissions).

We could not beat the 4WD in speed. We could not get around it for shooting a gap between two goals. I distinctly remember the mecanum losing a push test, and after the first 5-10 seconds, it wasn't a contest! If we'd been hit trying to cap, we'd have lost position, every time we took a hit. We had trouble strafing with an off-balance load (tetra on a pole). If I had video, I'd post it. Just on motors, we should have been able to push the 2003 robot, 4 CIMs versus 2 drill motors, roughly equal weights.

The 6WD stayed on the competition robot. To this day, 330 has not done a competition mecanum. Not because we're scared to, but because the GDC has yet to give us a game where it's an advantage given our play style. The only competition omni-directional drive we've ever done was a 6WD rotational drivebase on our 2009 robot, because it fit a key part of our game plan (avoid getting pinned if possible).

Oh, and one other thing: At that point, we had two years of experience with small-scale mecanum, both programming and hardware.

Re: Another chapter to the 6WD vs. Mecanum debate
 

I think it should probably be noted that declarations about how rare mecanums were on Einstein don't really mean much till after 2007. At least.

2007 was the first year andymark offered mecanum wheels. So pre-2007, the only teams attempting this would be teams with the time and patience to make their own wheels and try them out.

Even then, I think it's a little arguable that they've had much of a chance at shining since 2007. Look at the run down:
2007: Debut of AM mecanums, with all the first-run, low volume problems.
2008: Mecanums arguably weren't much of an advantage.
2009: Lunacy, slicks only
2010: Bumps and plywood under the field reduced the effectiveness of mecanums.

So I don't think there have been all that many years where mecanums were both commonly available and obviously useful for that year's game. Now that may be because they just aren't ever going to be useful to the game, but I'd want a few more games to actually make that call.

Re: Another chapter to the 6WD vs. Mecanum debate
 

How much power-loss is there strafing sideways with a "normal" mecanum drivetrain?
Specifically -- how much current draw is there on a single motor?
How fast can you gear up the drivetrain before that "sideways" current draw becomes undesirable?
If you gear to a safe speed (without undesirable current draw), will you be making a tradeoff on forward/backward speed (i.e. would you have geared faster otherwise?)

In a game which emphasizes full field sprints, I think the "safe" gearing for a mecanum is just too slow -- but that is just my opinion... (one which is founded on calculations and engineering analysis, plus some anecdotal evidence on the side... yes, 148 build a mecanum drive this fall, and we hated it).

If you're a team debating between 6WD or mecanum my opinion is you should go 6WD. I promise you won't regret it.

However -- The most important thing is that whatever you do, you get it built quickly, get your mechanism on it, and start testing and improving as soon as possible! The more testing and driver practice you get the happier you'll be.

-John

Re: Another chapter to the 6WD vs. Mecanum debate
 

I compiled this information on a thread a while ago....It's not entirely complete, but if it means anything to this conversation I have the drivetrains of the winning alliance members of the championships.

2010
67 – 8 WD
177 – 8 WD (articulated is sets of two, front and back)
294 – 6WD

2009
67 - 6WD wide
111 - 4 wheel crab (non-coaxial), wide
971 - 6WD wide

2008
1114 - 6WD long
217 - 6WD long
148 - three-wheeled crab (coaxial), nonagon-shaped robot

2007
177 - 6WD long
987 - 6WD long
190 - 6WD long

2006
217 - 6WD long
522 - Treads, long
296 - 2WD long, Omnis in front

2005
67 - three-wheeled crab (non-coaxial). Flop bot.
330 - 6WD long
503 – 4WD long, omniwheels in rear


2004
71 - 4WD long
494 - 4WD long
435 - 2WD long, with casters in front

2003
111 - Four-wheeled non-coaxial crab (with dropdown skid for turning)
469 – 4WD Long
65 - 4WD Wide

2002
71 - 4WD flop bot with casters in front
173 - 4WD long
66 – 4WD long

2001
71 - ?
294 - ?
125 - ?
365 - ?
279 - ?

2000
255 - ?
232 - ?
25 - ?

1999
176 - 4WD long w/ Omnis in front
1 - tank treads, long
48 – 4WD, long

1998
45 – 4WD long with Omnis in front.

1997
71 - ?

1996
73 - ?

1995
100 - ?

1994
144 - ?

1993
148 - ?

1992
126 - ?

Important to note that mecanum wheels have not been available to first teams for this entire time, but the numbers are stacked in favor of skid steers. From 04 to 05 the dimensions changed from 30x36 to the current size, 28x38, so there are fewer 6 wheel bots as you go back before 2005.

I've had people argue that the reason skid steers win more is baecause they are more common, but I prefer to view this as "the best teams win, and by no coinsidence, they are skid steer bots." So basically they are winning because they are good, not because they are greater in numbers. They are simple, intuitive to drive, and comparatively pretty light, which leaves weight for an affective manipulator.

Re: Another chapter to the 6WD vs. Mecanum debate
 

We are building a mecanum drive. We feel it's best for our strategy.


BUT!!!!

We are also building into our drive the ability to quickly change to 6 wheel drop center. The holes are already cut into our frame. Add a nano box and a little chain and off we go.

Our first regional is week three, if we were week one I doubt we would attempt the mecanum setup. If we didn't have the ability or funds to build a second robot for practice and testing we wouldn't try mecanum.

Re: Another chapter to the 6WD vs. Mecanum debate
 

Our team decided on mecanum drive day 2 of build season, we had resurrected our 2007 chassis into a driving mecanum proto-chassis by the end of week one. We have 1/2 our chassis done now (waiting on more brackets from 80/20) and because we are making most of our robot from 80/20 we will probably make a practice chassis. I think that because 2007 was the introduction of andymark mecanum wheels that it seems they havnt had a decent chance to prove them selves since then, this seems to be that year.

Re: Another chapter to the 6WD vs. Mecanum debate
 

As a team that does not have the space to create a full field for practice purposes, I can say that the biggest advantage mecanum gave us last year is one reason the team was enthusiastic about using it this year:

It controls exactly like a first person shooter, so kids good at these types of videogames have an inherent knack for mecanum controls that they do not for skid steering.

That, and nostalgia. 2010 was a great year for us, and that mecanum drive had a lot to do with it.

Re: Another chapter to the 6WD vs. Mecanum debate
 

AndyMark's mecanum wheels have certainly improved over the years.

The '08 6'' mecanum wheels were pretty bad - the plate was far too thin and would bend in on the rollers. Still, even with this problem our '08 bot was one of the most maneuverable at ever regional we attended; it was a nightmare to maintain, though (especially as I was the one fixing them in the pit between matches...ah, the memories).

No mecanum in '09, sadly.

The '10 6'' mecanum wheel were a vast improvement - thicker plate, better rollers. They still had occasional problems with sticky rollers, so you'd have to play with the lock nuts between every match to free them. Much less of a pain than '08, though. They also, like the '08 wheels, were manufactured to allow the rollers to be reversed, which while good in theory did get in the way of maintaining them a bit. Overall I'd give them a B - they did their job, and were certainly an improvement.

A quick glance at this year's generation of 6'' mecanum wheel seems to reveal that they've fixed most of my problems with the previous generations - they have removed the generic plate in favor of "left" and "right" wheels, which has allowed them to fix the access problems. The bolts seem to protrude a lot further out, as well, which makes it much more unlikely for you to unwittingly loosen them enough during maintenance to lose a roller in a match (this happened to us once or twice last year). The plate is nice and thick, too - they're claiming it supports a 400 pound load per wheel, which is great.

Unfortunately, having graduated and now being in Colorado means I won't get to see them in person, but I'm hoping they've finally worked all the kinks out of the design this year. They're certainly heading in the right direction, if nothing else.