[emeraldstorm]

Originally Posted by Paul Richardson

When you think about turning scrub (the resistance to turning from friction), it helps to look at the path each wheel will take when the robot pivots, because this determines the friction force you'll see.

To start simple, imagine a Segway rotating in place about its center. If you traced the path of the wheels, they would draw a circle, right? If you looked at the wheels at any point along that circle, they would be pointing tangent to the curve. In other words, in order to follow the curve, the wheel just needs to roll forwards as the Segway rotates, and there is no sideways movement (which would cause friction). So you can see that the center wheels of a robot have almost no contribution to turning friction.

However, if you switch to a 4/6/8 wheel robot and imagine the circle traced by the corner wheels, you see that the wheels are not tangent to that curve. The corner wheels can't just roll along, they have to slide sideways, too. This is where nearly all turning resistance comes from.

That's some interesting information. On my way to redesigning my concept drivetrain due to this; Thank you! (is it ok to mention that I repped?)