Quote:
Originally posted by Andrew
(Note: you can only effectively have six wheels on the floor if you use a suspension.)
Could you elaborate?
|
Any support system that has more than three points of contact is indeterminate. Think of the crappy table at the restaurant where one leg is too short and the table rocks back and forth between two different determinate conditions.
If you have six wheels, for instance, the platform has to be exactly machined and the surface flat (or compliant) in order for all six wheels to be on the ground at once.
If the tires wear or the frame gets bent or the surface changes such that the there is about 1/16" to 1/8" difference between the highest tire and the lowest tire, the machine will settle on a support of three or four tires.
The way to avoid this is to put all six wheels on a suspension where the wheels have 1/4" or more travel. The spring in the suspension will allow the tires to accommodate to the variations in wheel diameter and surface.
Technically, the carpet is a "suspension" in that it has a surface springiness. Also, unless the robot frame is really, really stiff, there is some compliance in the frame. This is usually enough for the four wheeled robots to have all four tires on the ground.