[archiver]

Posted by Patrick Dingle at 03/21/2001 10:25 PM EST


Coach on team #639, Red B^2, from Ithaca High School and Cornell University.


In Reply to: wheelchair wheel just aren't going to cut it
Posted by Ken Leung on 03/20/2001 3:10 PM EST:



I agree with you completely... but have a couple comments to add. Torque is important, but torque doesn't mean anything if your robot can't grip the carpet! What we're dealing with here is static friction. Static friction tells you the maximum amount of sideways (perpendicular) the wheels of your robot can exert on the field before they slip. This maximum force is equal to the coefficient of friction multiplied by the "normal force" (the force of the robot on the ground). So there are two ways to increase the maximum amount of force your robot can exert without slipping:
1) a heavier robot
2) increasing coefficient of friction

There are many ways to increase the coefficient of friction... grooves, "wonder wheels", etc... However, there is a maximum grip that you can possibly get on carpet, and you can't do much better than grooved wheels. Therefore, if you've already grooved the wheels and stuff, and still have trouble, then you most likely have a light robot, and you can't do too much better with increasing coefficient of friction... unless you go to treads.

Another point: power all wheels. Unpowered wheels is just a waste of traction & torque.

Anyway, enough physics from me!

Patrick

: Good call about the traction...

: Usually when people are thinking about a drive train, they usually only think about how much gear ratio the motors have, or how much speed/torque do the motors transfer onto the wheels.

: However, that's only part of the problem. The over all goal of a drive train is to transfer one form of energy into another, and one form of an motion to another. Although motors take care of turning electrical energy into mechanical energy, you stil