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Unread 17-10-2005, 03:32
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Tristan Lall Tristan Lall is offline
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Re: realistic friction constants.

I think that this will clarify things with regard to the types of friction.

As for friction coefficients, just a note; rolling friction is actually static, not kinetic, because a point on the circumerence of a wheel (or any rolling element) is instantaneously stationary relative to the ground. In fact, this is what allows a drive wheel to put power to the ground—the frictional force effectively moves the robot. If the wheel were sliding (like a skidding car with the brakes locked), the kinetic coefficient of friction is used, since there is relative motion between a point on the wheel and the ground. Sometimes you see the frictional losses at the axle counted in a wheel's rolling friction, but strictly, they're separate.

Common coefficients of friction for tread materials vary greatly; I'd estimate around 0.6 for Skyway smooth wheels, or around 1.2 for most rubber/polyurethane ridged treads. These are very rough figures, though, because many factors influence the coefficient of friction, including tread bias, carpet bias, tread wear, cleanliness of tread, etc.. Also, if your normal force varies (e.g. the weight distribution of the robot shifts from front to back), the friction at a wheel will vary.

Last edited by Tristan Lall : 17-10-2005 at 03:38.