[ODE] Flywheels

Brian Clarkson brianclarkson at btconnect.com
Tue Nov 18 18:03:29 MST 2003


I thought the bendy wheels problem was associated with the hinge constraint.
I don't plan to use a hinge. I was going to set gravity at zero and let the
flywheel (gyro) spin on what ever axis it needs. This would mean I don't use
any joints not even for collision. Well maybe one ball joint would be
needed. I am favouring a scalling of the rotation speed. This needs to be
selected relative to the rpm of the flywheel. I think the 90 deg point is
critical for precession. This is where it has most effect. I think scalling
is not as easy as I am thinking. Is the radius of gyration a function of rpm
or is it constant. I can't remember.


-----Original Message-----
From: Martin C. Martin [mailto:martin at metahuman.org]
Sent: 18 November 2003 15:51
To: Brian Clarkson
Subject: Re: [ODE] Flywheels

Brian Clarkson wrote:
> Martin
> Then any movement
> forces  would be applied as world angular and linear forces. This should
> produce the gyroscopic processional behaviour
> that you refer to as the "won't move the obvious way". Its this behaviour
> that would be useful to have handled by ODE.

Well ODE will certainly give you that, but maybe not at 180 deg per
timestep.  I'm not sure, you'd have to experiment.  And remember the
"bendy wheels," you may get a similar problem.

> You say that ode does not conserve angular momentum. This is not my
> observation. When my rigid bodies are in free fall and are spinning they
> don't appear to slow down. i.e. when they fall of a shelf or a ledge. Are
> you referring to something else here.

In free fall yes, but try it while applying forces/torques that cause
gyroscopic precession.  I'll bet that angular momentum will change
slowly over time from what it should be.

- Martin

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