Requesting Physists Help With Friction

[jgannon]

Though it's not exactly related to the topic at hand, this seems like a good place for "my mind is being blown by friction" questions. Can someone explain why there is a twofold difference in the friction coefficients quoted for the inline and transverse directions on the rover wheels? I'm having a lot of difficulty understanding exactly what mechanic comes into play to make that happen, since the material is smooth and appears to be essentially uniform.

[Bongle]

Originally Posted by jgannon

Though it's not exactly related to the topic at hand, this seems like a good place for "my mind is being blown by friction" questions. Can someone explain why there is a twofold difference in the friction coefficients quoted for the inline and transverse directions on the rover wheels? I'm having a lot of difficulty understanding exactly what mechanic comes into play to make that happen, since the material is smooth and appears to be essentially uniform.

My only guess is that once the rover wheels get scuffed up by spinning a lot, the grooves along the wheel (in the direction it spins) will have an effect on its grippiness sideways. So perhaps the numbers they gave us are correct only for sufficiently scuffed wheels. We ran our lightly-loaded kitbot on a somewhat dirty hardwood floor, and the wheels picked up some dirt and scuffs. I suppose with enough running with a heavy enough robot, they'll develop substantial grooves.

As for the actual question, surface area CAN affect friction if the surfaces deform. You don't see race cars with skinny tires because the bigger tires allow for more stickiness, and you don't see skates with large surface areas because it wouldn't generate enough pressure to melt the ice and create the layer of water that you actually skate on.