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Unread 13-04-2014, 21:33
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themccannman themccannman is offline
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AKA: Jake McCann
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Re: Swerve Drive vs Mecanum Wheel drive?

Quote:
Originally Posted by Ether View Post

Jake,

I agree that if you assume there are no differences between "good" and "bad" mecanum bots then there will be no differences between them. I just think that's a bad assumption, in practice.
I'm not assuming there's no difference, I'm assuming that every team has the capability to at least assemble their wheels correctly.

Quote:
When you said "The rollers on mecanums ... will always spin slightly unless you are going perfectly perpendicular to their direction of rotation" I read that to mean that the only time the rollers on a mec wheel on a mec vehicle would not spin is when said wheel was going in a direction perfectly perpendicular to the direction of rotation of the roller presently touching the ground (i.e., going in the direction of that roller's axis). If that is what you meant, it is not correct. If that is not what you meant, could you please clarify what you did mean?
That is exactly what I meant. When a wheel is traveling on a surface perfectly perpendicular to it's axis of rotation there will be no net force causing it to spin. Since a mecanum wheel only has two directions (one axis) of rotation and neither of those directions is perfectly perpendicular to the axis of rotation of the rollers; it is not possible to drive a mecanum wheel on a surface with friction in a manner that will cause a net zero force on it's rollers in their axis of rotation.

Quote:
In practice it is possible to build a mecanum vehicle which, when operated in the forward (or reverse) direction on a hard surface, will exhibit virtually no motion of the rollers. In other words, spinning rollers in the forward/reverse direction is not an inherent property of mecanum wheels: it is a mostly due to roller axial free play and operating on a compliant surface.
We're not talking about a hard surface, we're talking about robots on a soft carpet. Even so however, I don't buy that. I don't think that you can build a vehicle on mecanum wheels that will exhibit near-zero roller motion under hard acceleration forwards or backwards. With very slow acceleration of course it's possible have very little roller spin, however with the acceleration we see in FRC, I don't believe that.
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