[ODE] problems with redundant constraints?

Erin Catto erincatto at sbcglobal.net
Mon Feb 21 23:06:36 MST 2005

I'm guessing that the global or stop CFM is too large. Try reducing them.
Also make sure the ERP is not too large.

Setting a maximum torque on the driver motor might achieve the effect you
want without the extra joint.


-----Original Message-----
From: ode-bounces at q12.org [mailto:ode-bounces at q12.org] On Behalf Of Graham
Sent: Monday, February 21, 2005 9:32 AM
To: ode
Subject: [ODE] problems with redundant constraints?

Hi!  I want to simulate a wheel that has some torsional "give" to it. 
What I did was connect the drive motor (a Hinge joint) to a "hub"
body, and then connect the hub body to the wheel body using a second
Hinge joint, which has a histop and lostop set to 0.0, and has a
stopCFM and stopERP set up to simulate the torsional springiness. 
Problem is, ODE wigs out completely, flipping the wheel around various
axes when I try to drive the thing on a ground plane.  It's as if the
redundant constraint axis has interfered with the solver.  I am using
WorldStep.  I seem to recall reading about this kind of solver
requiring very careful selection of constraints, so that the degrees
of freedom are known precisely... so what I'm asking is, is there any
way at all to simulate what I'm trying to simulate?  Or, is there any
way to modify ODE to automatically determine the degrees of freedom? 
I've had issues with redundant constraints when buiding suspension
rigs as well.  Thanks!

- Graham Fyffe
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