Mecanum or Swerve?

[thefro526]

I thought a bit more on this Subject last night, and came to the realization that Swerve Drives are going to become more and more common in FRC. One of the biggest issues with Swerve Drives is that they're difficult to design and manufacture, and many teams could spend a whole build season doing this and not get it right. But, now that two types of swerve module are available as COTS items these two issues are almost non-existent, or no more so prevalent than in a Mecanum or Holonomic Drive.

If a team were to use the Commercially Available Team 221 Swerve Modules, then they'd really only have to build a frame in which to house them, and a system to steer them. From there, it's pretty much just a control issue, and I bet most teams could figure out how to get them working relatively easily. We've already seen a handful of teams use the Team 221 "Wildswerve" modules with some degree of success (11, 20, 234) and I've yet to hear of any failures.

The only downfall to using an off the shelf Swerve Solution like the Team 221 Modules is cost. A set of 4 Swerve Modules will set you back about $1k, whereas a set of Mecanum Wheels and 4 Transmissions should run you in the ball park of $700 or so. IMO, the cost premium is worth it, especially if you're a team that plans on using an Omni-Directional Drive to it's fullest potential.

Strangely enough, all of this thinking is leading me towards possibly pursuing a swerve drive for the 2011 season, should the game call for it, and I was always one of those "Why not just use a skid steer" kind of guys.

In conclusion, building a reliable and effective swerve drive, seems to be getting easier by the year.
(Sorry for the long post, I had a lot of thoughts to get out.)

[Chris is me]

Originally Posted by thefro526

We've already seen a handful of teams use the Team 221 "Wildswerve" modules with some degree of success (11, 20, 234) and I've yet to hear of any failures.

Both 11 and 20, despite building practice robots, had code glitches at their first regionals, and didn't really get their swerve drive code up to par until their second event. These are two teams with excellent programming teams as well. I'd be hesitant to extrapolate from there that "anyone" can do it; apparently control is harder than the build.

I'll let you know after I prototype something this summer

[ajlapp]

Swerve Drives are going to become more and more common in FRC. One of the biggest issues with Swerve Drives is that they're difficult to design and manufacture, and many teams could spend a whole build season doing this and not get it right. But, now that two types of swerve module are available as COTS items these two issues are almost non-existent, or no more so prevalent than in a Mecanum or Holonomic Drive.

This is the reason we wanted to introduce commercial swerve components to the market. There is always lots of discussion amongst the community about how to keep FIRST competitive....

I disagree with making the game easier or artificially leveling the playing field through other means.

I'd much rather see a large portion of teams building high quality robots by using off-the-shelf items when necessary to bolster an area of their team where they may not have the expertise.

That said, swerve is tough to pull off even if you start with pre-made transmissions. Cyber Blue is hosting a swerve discussion this week in Atlanta about the months they spent leading up to competition developing the technology.

[fritzdejongh]

I'd like to ask this question on swerve drives: From what I've read, they typically don't have completely independent control of all 4 wheels, and perhaps there are choices and trade-offs on how exactly to control them and how many motors to devote to steering. How smoothly do they end up turning in place or making a tight turn for example? Does this involve wheels slipping? What is the experience on what level of control is helpful?

My experience with Mecanum is that it can turn an average-resource team into a competent scorer and move them up to seeded range, at least for Breakaway. With the included holonomic, gyro, and PID VIs programming is easy, and implementing field-oriented steering and gyro stabilization is also easy.

[Tom Line]

Originally Posted by thefro526

I thought a bit more on this Subject last night, and came to the realization that Swerve Drives are going to become more and more common in FRC.

I would tend to disagree. Full mechanical designs for swerves (or the pictures to allow you to easily reverse engineer them) have been around for years. I believe 217 posted a cutaway of their serve from 5 or more years ago. Those teams are more than willing to lend help to anyone who needs it as well.

However, you still see a lot of teams who have already DONE swerve not using them going forward. Nearly every big name team has done swerve several times, yet most do not pick it as their drivetrain of choice.

Why?

1. Complexity. Both mechanical and programmatically.

2. Advantage gained. I would put forward that last year and this year are two of the biggest swerve-advantaged games so far. Yet if you look at the top tier of teams in OPR, the proportion of swerve teams comes no where near 50%. Swerve has a huge number of trade offs, and the advantages are actually questionable nearly every year. You'd have a hard time telling me that 67, 469, and 1114's lack of swerve this year is hurting them. I bet the choice not to do swerve HELPED them in a big way during the build season - it was that much more time to work on their ball handling systems.

3. Cost. Whether you purchase a turnkey system like the 221 one, or whether you build your own, there is no small cost in engineering, materials, and machining.

I keep pointing out and I will continue to point out that Swerve is cool, but most teams that build it realize they'd rather be spending their time solving the game rather than solving a drivetrain, and a 6-wheeled or 8-wheeled drivetrain will perform nearly as well in most applications, and better in many.

[Andrew Schreiber]

Originally Posted by Tom Line

I would tend to disagree. Full mechanical designs for swerves (or the pictures to allow you to easily reverse engineer them) have been around for years. I believe 217 posted a cutaway of their serve from 5 or more years ago. Those teams are more than willing to lend help to anyone who needs it as well.

However, you still see a lot of teams who have already DONE swerve not using them going forward. Nearly every big name team has done swerve several times, yet most do not pick it as their drivetrain of choice.

Why?

1. Complexity. Both mechanical and programmatically.

2. Advantage gained. I would put forward that last year and this year are two of the biggest swerve-advantaged games so far. Yet if you look at the top tier of teams in OPR, the proportion of swerve teams comes no where near 50%. Swerve has a huge number of trade offs, and the advantages are actually questionable nearly every year. You'd have a hard time telling me that 67, 469, and 1114's lack of swerve this year is hurting them. I bet the choice not to do swerve HELPED them in a big way during the build season - it was that much more time to work on their ball handling systems.

3. Cost. Whether you purchase a turnkey system like the 221 one, or whether you build your own, there is no small cost in engineering, materials, and machining.

I keep pointing out and I will continue to point out that Swerve is cool, but most teams that build it realize they'd rather be spending their time solving the game rather than solving a drivetrain, and a 6-wheeled or 8-wheeled drivetrain will perform nearly as well in most applications, and better in many.

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.

[Tom Line]

Originally Posted by Andrew Schreiber

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.

One very slight correction. 67's 2008 overdrive bot actually had rear-wheel-only pseudo swerve. If you watch their matches that year, it will suddenly dawn on your how they can turn their corners so quickly.

[Chris is me]

Originally Posted by Tom Line

One very slight correction. 67's 2008 overdrive bot actually had rear-wheel-only pseudo swerve. If you watch their matches that year, it will suddenly dawn on your how they can turn their corners so quickly.

IIRC from reading an old thread, the back wheels were unpowered, just turreted.

[Andrew Schreiber]

Originally Posted by Tom Line

One very slight correction. 67's 2008 overdrive bot actually had rear-wheel-only pseudo swerve. If you watch their matches that year, it will suddenly dawn on your how they can turn their corners so quickly.

Ah yes. I forgot that. This is outlined Here

[PAR_WIG1350]

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

[=Martin=Taylor=]

Originally Posted by Andrew Schreiber

....
...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.

Last time 111 didn't build a swerve they won both their regionals.

The same is true for 1625.

hmmmmm...

[artdutra04]

Originally Posted by Andrew Schreiber

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]

Originally Posted by artdutra04

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]

Originally Posted by StuMac

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]

Originally Posted by artdutra04

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.