[ODE] Steering and rolling wheels

[Nate W]

On Thu, 13 Feb 2003, Sergio Casas Yrurzum wrote:

> My robot consists of the robot itself and three wheels, one front
> free-rotation wheel and two rear wheels that are (both) steering and rolling
> wheels at the same time.
> 
> The front wheel is joined to the robot with a BallAndSocket Joint, and works
> fine.

Actually, I'd wager that the ball joint does not work fine, and is in fact
the source of the problems you described.

If you're using a ball joint, the wheel is free to rotate on ANY axis.  
For that to work, the wheel would need to be spherical.  A flat-sided
wheel will rotate onto its side when you try to steer.  A cap-cyl wheel
might work OK, but it will probably bobble up and down as you steer.

Instead of the ball joint, try a hinge-2 joint.  Or two hinges with an
intermediate body - one hinge providing steering movement, the other hinge
allowing the wheel to rotate.  Two hinges is conceptually easy to
understand, but the hinge-2 joint does basically the same thing with less
computation.

-- 

Nate Waddoups
Redmond WA USA
http://www.natew.com