[ODE] Flywheels

Brian Clarkson brianclarkson at btconnect.com
Thu Nov 20 08:56:43 MST 2003

I don't think it would be difficult to keep angular momentum constant with
torque feedback. Like a servo system.


-----Original Message-----
From: ode-bounces at q12.org [mailto:ode-bounces at q12.org]On Behalf Of Gary
R. Van Sickle
Sent: 20 November 2003 03:29
To: ode at q12.org
Subject: RE: [ODE] Flywheels

> 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.

FWIUnderstand, it's not slowing down that's the problem, it's speeding up.
Conservation of momentum (at least angular) is not enforced in ODE, so it's
going to drift one way or the other due to integrator error or just
errors.  If you have a free ODE body spinning in space, it will gradually
up angular momentum (due to integrator issues IIRC) even though there's no
external source of angular momentum.  The problem is compounded by the lack
angular air friction.

Russ has mentioned several times that there was a simple and/or clever fix
this, but I'm not sure what he has in mind.  Russ, could you maybe point us
to a
writeup of what you're thinking of?  Maybe one of us can code something

Gary R. Van Sickle

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