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Unread 09-12-2009, 23:23
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FRC #1197 (Torbots)
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Re: crab drive vs. mecanum drive system

Quote:
Originally Posted by superbotman View Post
My team is debating on the drive system we want to use and I thought I would ask what has worked well for other teams.

1. Crab drive works best

2. Mecanum drive with each wheel having its own motor wins.

3. Use mecanum drive with one motor per side.

4. don't do any and use some other drive system
Crab is tough to build, though there are now swerve modules available. Needs a customized frame and coding. Also note that there are two types: coaxial and non-coaxial, each of which has its own unique challenges.

Mecanum drive is simpler in the frame (KOP frame works), but you need to make sure the wheels are tuned right. I'm going to have to disagree with daltore on the diagonal, though--we never saw anything when we tested our set back in 2005. A MAJOR pro here is that if it doesn't work, you grab 4 wheels from the parts box and slap them in, then remove the sideways code, and you have 4WD.

Mecanum with only one motor per side is impossible. Omnidrive (4-wheel) gives one motor per wheel, one wheel per side, or something of that sort.

Many teams use a 6WD with either a dropped center wheel or omnis on one end or the other. That's the simplest, and the KOP frame is set up to handle it already.

At this point, though, you're about out of time to prototype anything other than a 4WD or 6WD, unless you get an order in to AM immediately.

There is one other consideration, however:
We don't know the game yet, and you're choosing a drive to use for the game. Stop. Think about it. You could be investing hundreds of dollars in a system that won't fit the game at all. Or something like happened this year, where mecanum wheels and omni wheels couldn't be used.

If you go ahead and try any of these systems, do it as a prototype in the offseason (the month left of it, or the next one) to get the hang of it, then build it for the competition season following that when you actually know what you're doing. Can you do it during the build season? Probably. Can you do much else? Probably not.

I know that when 330 tried their set of mecanums during build season, we already had a couple of years of small-scale testing under our belts, and a full-size backup that we could literally swap in a few minutes. (I'm talking VEX scale here--the EDUbot was great for that!) We had code, we had wheels made after Kickoff, we had the Kit frame rigged for mecanum pretty quickly, and we had a 6WD drop center on the competition frame. Last week of build, we had a decision meeting, did some final testing, and the mecanums lost to the 6WD drop center. If we ever try mecanums again, we'll be almost ready to go. That's why you prototype. But if you lock into a drive now, you might not be able to change when you realize that being able to dodge around opponents isn't going to help you this year, or that you really want that extra maneuverability, or this, or that. Seriously, don't lock in now.
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Past teams:
2003-2007: FRC0330 BeachBots
2008: FRC1135 Shmoebotics
2012: FRC4046 Schroedinger's Dragons

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