Chief Delphi - Mecanum or Swerve?

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Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- Technical Discussion (http://www.chiefdelphi.com/forums/forumdisplay.php?f=22)

- - Mecanum or Swerve? (http://www.chiefdelphi.com/forums/showthread.php?t=85182)

PAR_WIG1350

13-04-2010 20:50

Re: Mecanum or Swerve?

The closest we've come to swerve was last year when our rear wheels were mounted on a small powered turret.

artdutra04

16-04-2010 13:46

Re: Mecanum or Swerve?

Quote:

Originally Posted by Andrew Schreiber (Post 953367)

What is of most interest to me:

217: Swerved in 2003. Hasn't done it again. (Nonadrive is the closest they've come)
67: Swerved in 2005. Hasn't gone back. (This was a cool flop bot swerve though)
1114: Swerved in 2004. Hasn't gone back.
33: Swerved in 2005, switched to different drive train halfway through the season. Again in 2009: Maybe?
71: has been using swerve since 2005. (Of particular interest: Hasn't won a Championship since 2004)
111: even I don't know how long.
68: 2008,2009,2010. This year their swerve drive was too much of a technical undertaking for them.
148: Swerved in 2008. Hasn't gone back since.

So many veteran teams have tried swerve and gone back to traditional 6wd/8wd machines. 2009 was not a FULL swerve, only 2 wheels actuated as far as I can recall.

67, 6wd the last couple years. 8wd this year.
1114, 6wd. 8wd this year
33, 6wd.
217, 6wd (excepting this year)

I know correlation does not imply causation but I have a hunch that there is a reason why none of these teams have gone swerving again. It may be a cool thing, and definitely a design every team should have in their arsenal, but in most cases it is not the most efficient design.

I disagree. The first year 228 did swerve was the first year we won a regional.

StuMac

16-04-2010 14:33

Re: Mecanum or Swerve?

Quote:

Originally Posted by artdutra04 (Post 954220)

I disagree. The first year 228 did swerve was the first year we won a regional.

correlation != causation.

Just because your team won their first regional with a swerve design, doesn't mean that it's a good system. There are way to many variables that also have just as major effect on your regional win. The quality of drivers, your opponents, other mechanisms on your robot, the game itself, luck. There is simply too much room for other explanations.

That said, I've very little interest in swerve or mecanum drives. Sure, they're cool to prototype, but unless a team has many years of experience driving one (read: practicing with a swerve bot in the off-season), has the machine shop and hands to build it near perfectly, the coders to ensure it's working flawlessly, the pit crew to ensure it's maintained constantly, and a host of other things, I just don't see them as that great an asset. Sure the occasional team like 111 or 71 will make swerves work, but honestly, is it really worth the upkeep? Some may say yes. I say go with what's solid, can be easily maintained, can be easily adapted, and doesn't require two joysticks to control. And that, is a 4 wheel, 6 wheel, or 8 wheel drive. Let the creativeness show in how you play the rest of the game with your manipulator.

Ether

16-04-2010 18:22

Re: Mecanum or Swerve?

Quote:

Originally Posted by StuMac (Post 954227)

Let the creativeness show in how you play the rest of the game with your manipulator.

That's certainly one point of view, and perhaps held by many teams and individuals.

There is another valid point of view however, a point of view which puts less emphasis on the "game" and puts more focus on learning. There is so much math and physics and engineering to be learned and so much creativeness and discovery can result from striving to understand and build a swerve or mecanum drive. Torques and force vectors, vector addition, trigonometry, bevel gears, software algorithms (closed-loop position control for the steering, closed-loop speed control for the wheels, how to properly adjust each of the wheel speeds - and directions for swerve - to reduce scubbing and maximize efficiency), the list goes on and on. So even if you don't win the game, you may come out ahead :-)

~

sgreco

16-04-2010 19:06

Re: Mecanum or Swerve?

Quote:

Originally Posted by artdutra04 (Post 954220)

I disagree. The first year 228 did swerve was the first year we won a regional.

Correct me if I'm wrong, but from what I understood you locked your swerve modules in place and skidded in elims at WPI.

I did the math last year about swerve percentages, but there have been 4 teams to win the championships with a swerve. (111 twice). In total 42 teams have won nationals. That's 9 percent to win with swerve. People often question "more teams compete with drivetrains other than swerve, so the odds are swerve won't win as much" but in reality, the best teams win, or at least really good teams do. If swerve teams consistently dominated skid teams, it would reflect in the stats, and they don't reflect that.

I'm not saying swerve is bad, I'm just suggesting that the advantages it appears it have on paper aren't quite the same as on the field.

Andrew Schreiber

16-04-2010 23:22

Re: Mecanum or Swerve?

Quote:

Originally Posted by joek (Post 953482)

then they must be using Fisher Price motors to drive, because we're only allowed 5 cims

Yes, many teams use the FP through an AM planetary to mesh with a CIM motor.

Quote:

Originally Posted by artdutra04 (Post 954220)

I disagree. The first year 228 did swerve was the first year we won a regional.

There are exceptions, for some teams swerve works really REALLY well. Their drivers just get the hang of it.

Just to share a bit of a conversation I was having the other day, the problem with swerve drives is that the wheels are never in the direction you want to go. There is a slight delay. If the driver is aware of this and does not try to correct for it you will be fine. Otherwise you end up going in a bit of a circle. It takes some getting used to. Not a downside just a fact. If you decide to go with a swerve drive robot you need to build a practice bot so your driver can get the hang of it.

ALTrammell818

17-04-2010 08:50

Re: Mecanum or Swerve?

Quote:

Originally Posted by Tom Line (Post 952862)

No - at least not by our scouting methods. Mecanum robots are immediately removed from our defensive pic list, as are robots with slick wheels / omni wheels. A decently geared robot with traction wheels will have no problem moving a robot with slick/omni or mechanum out of their way and scoring.

Mechanum are a neat idea (as are omni wheels), but once you bring robot to robot contact into the equation, I'd much rather have robots with traction that won't get pushed out of the way easily.

Regarding any lag time with swerve modules: If you have it programmed correctly, your swerve modules should never have to turn more than 90 degrees from any given point. When you keep in mind that a tank drive has to "turn" before it drives forward, there really is no lag in a well-done swerve drive when compared to a tank drive. When you take into account acceleration time, there really isn't any lag in a swerve compared to a mechanum either.

You may want to note, however, that except for a few teams, most teams do NOT do swerve every year. Even teams that have done swerve, generally don't repeat it much. That's because it takes so much time, machining, programming etc to make it work well.

Swerve is that thing that every team has to try at least once. They try it, they may win a couple engineering awards with it: then most teams rarely do it again.

Have you not seen the number of Mecanum drive bots this year with unbelievable pushing power? Back in Detroit the only bot with more push than us was the Juggernauts.

artdutra04

17-04-2010 11:27

Re: Mecanum or Swerve?

Quote:

Originally Posted by sgreco (Post 954294)

Correct me if I'm wrong, but from what I understood you locked your swerve modules in place and skidded in elims at WPI.

That's an interesting and one hundred percent wrong rumor.

Quote:

Originally Posted by StuMac (Post 954227)

correlation != causation.

Actually, in this case our swerve drive was the reason for our success. Our alliance had two strong offensive robots (230, 20) and we were the strong defensive robot in the opponent's home zone. Without a swerve drive, we would never have been able to defend two robots simultaneously by constantly strafing, out-maneuvering, and out-pushing them.

Ether

17-04-2010 13:07

Re: Mecanum or Swerve?

Quote:

Originally Posted by Tom Line (Post 952862)

Regarding any lag time with swerve modules: If you have it programmed correctly, your swerve modules should never have to turn more than 90 degrees from any given point.

Hi Tom,

Is this true only for swerves with unlimited steering rotation, or is it also true for swerves with limited steering rotation?

Quote:

Originally Posted by Tom Line (Post 952862)

When you keep in mind that a tank drive has to "turn" before it drives forward,

Could you please explain what you meant by the above?

~

buildmaster5000

17-04-2010 19:14

Re: Mecanum or Swerve?

For us, the reason we wanted to build a swerve drive is that we had trouble with our 6wd drop center wheel this year, so we wanted something that would offer more mobility without suffering in traction. We also had considered getting the 221 modules at the beginning of the year, but decided that our ONE programmer was going to be busy enough so we would wait for the offseason. I am personally more and more convinced that we should do swerve, and that we should be able to mount our modules on the bottom of our frame from this year after we take the kit wheel brackets off. It is interesting how different teams use swerve then never use it agian, but I agree with whoever said that driver practice, and lots of it, is how to get comfortable, and therefore good, with swerve.

steelerborn

17-04-2010 21:18

Re: Mecanum or Swerve?

I really like the swerve drives over mecanum drives.
I am working on a cad of an offseason swerve system right now.
It should be posted soon.

buildmaster5000

17-04-2010 21:43

Re: Mecanum or Swerve?

Quote:

Originally Posted by steelerborn (Post 954645)

I am working on a cad of an offseason swerve system right now.
It should be posted soon.

If you could PM me when its up, that would be great!! We have been stuck with the 221 modules because we lack the resources to design one ourselves

ADHDassassin

17-04-2010 23:33

Re: Mecanum or Swerve?

Quote:

Originally Posted by =Martin=Taylor= (Post 952867)

In my six years of competing in FIRST I don't remember a single mecanum robot ever dominating a competition.
.

I'm not exactly sure how my team did this year but we dominated FIRST Overdrive in 2008 with a mecanum robot, before FIRST Nationals we had a 30-1-0 record and two regional victories. It was an incredible design for turning around that track as we could essentially rotate around are front left wheel to make incredibly sharp turns. It also helped that we had a driver that also flew RC planes at a national level.

I understand that Lone Star and Bayou are considered to be "easier" regionals but we controlled that competition from our very first match. At nationals we had some code and design issues that prevented us from success... We gave in to the temptation to fix something that was already working.

But overall I love the mecanum drive train and watching one work is a beautiful demonstration of force vectors :)

TEE	18-04-2010 11:19

Re: Mecanum or Swerve?

Quote:

Originally Posted by sdcantrell56 (Post 953491)

We're using 8wd tank drive with 6 motors this year (4cims and 2 FP's)

Any team only using 2 cims in the drive this year is seriously hurting themselves

This year, we had a tank drive with 2 omni's in the back, so the robot would turn around its front (where the ball is), and we only used 2 cims. We could have added two more, but two seemed to be working fine; we could push well, and we could move around okay. We didn't end up adding two more because of the added weight (which would slow our hanging down).

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