[Ken Leung]

How much friction force you can get out of the wheels is pretty much determined by the weight and coefficient of friction. The friction force pretty much comes from static friction between the wheel and the carpet. Fs =< uN

This means you can exert a force of uN (or less) from the wheel onto the ground without slipping. u is coefficient of friction, which is a constant for whatever wheel you are using. That's why teams add other material around wheels to have a bigger coefficient of friction.

N is just the normal force from your robot. The heavier your robot is, the bigger the normal force the wheel and carpet will feel. That is why teams concentrate their weights on the powered wheels, and try to get to robot as heavy as possible.

With bigger u and N, your robot can push harder without the wheels slipping as easily. So, say, you are not lifting up goals. Fs is about 130u at most. If you lift one side of one goal, and put the weights on powered wheels, then Fs become about (130+90)u (lifting goals on one side is about supporting half the goal's weight). This add about 69% more possible friction force you can take advantage of from the wheels.

If you were pushing, say, 100 lbs before your wheels slip, now, you can push 169 before they slip.

Lifting two goal would mean adding 180 lbs on your robot, making Fs (130+180)u. 138% more possible friction force you can take advantage of. Now you can push 238 lbs before your wheels slip.


Traction isn't the only factor in your drive train, there are also motor power and current limit... With tons of traction, your robot will probably stall before your drive train slips on the carpet...

But, having more traction will still help out a lot if you are going to gear your drive train really strong, or add more motors.


I am curious, were the carpet damaged a lot at this last two regionals? Was there any Disqualification due to damaging of the carpets from wheels?