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Unread 04-01-2010, 21:45
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Where'd my wrench go?
AKA: Michael Baker
FRC #0675 (Tech High Phantom Robotics)
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Re: crab drive vs. mecanum drive system

Quote:
Originally Posted by Andrew Schreiber View Post
Won't work, Mecanum requires having 2 motors per side.

Personally I have always liked 6 wheel drive machines w/ a drop center wheel. It may not be as flashy as a 3 speed swerve drive but it is reliable. In my book reliability beats everything.
^ Words of sense.

Mecanum is simple to build (well, compared to Crab/Swerve), but the more complicated programming and driver training is one turn off, and the lack of traction is another. If somebody pushes your bot, it doesn't have the friction of normal traction wheels to prevent you getting pushed around everywhere. Add that in with the higher cost, and; though a cool system, there will be simpler, more reliable, and better ways to do it.

Crab, while you get a lot more traction, is even more complex and cost-prohibitive than Mecanum; and it can't be switched to a traditional skid-steer setup with a simple change of the wheels and a little hacking of the code.

I'm a fan of simple skid-steer 2, 4, or 6wd bots, especially "dropped center" bots since it helps them gain some agility while turning in place. 2wd drop-center 6-wheel bots are especially cool imo, as far as turning agility is concerned, since there's less drag to overcome from the "skid".



Quote:
Originally Posted by Chris is me View Post
I think the bigger issue with 2 CIM mecanum isn't torque but that you can't independently control 4 wheels with 2 motors. Well, with any amount of reasonability.
You would need a forward/reverse gearbox, with matching ratios, and a clutch so the gearbox could disengage and switch to forward or reverse. And to be able to do so quickly and effeciently would be a ridiculous engineering task considering the engineering experience (or lack thereof) of the Students, as well as financial and time limitations.

So yeah, it's unreasonable.
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