[ODE] Servo to reach a target position

[Nate W]

On Thu, 10 Apr 2003, David Whittaker wrote:

> Truthfully, my thoughts are that once we get back to ODE, and away from a
> general PID algorithm, I and D both lose all value.  

That's been my experience with Juice.  In fact, the same proportional gain
and force parameters work for most joints in most models.  What little
tuning I've needed to do has been always been accomplished with
proportional gain alone.

> Since the joints are implemented as constraints, and the entire
> purpose of the solver (dWorldStep) is to find a configuration that
> satisfies all the constraints, you really do have a "perfect" system
> to work with from the outside.

IIRc, Russ even went so far as to say that it's better than perfect - it
can effective "see" one time-step into the future.

> A final note: the more I think about it, the more I realize that a
> (non-powered) joint with stops is already a pretty decent controller.  
> You can set the Low and High stops to the same setpoint, then adjust
> StopERP to act (exactly) like a Kp parameter.  FMax keeps things from
> happening way too fast.

I don't think FMax applies to the joint stops, though.  Does anyone know
for sure?

-- 

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