[ODE] Possible solution to unstable rotating bodies problem

Russ Smith russ at q12.org
Thu Apr 7 11:41:41 MST 2005

if you do this then any freely rotating body will always spin along the
same axis, regardless of how asymmetric it is. that extra torque term
causes the rotational axis to wobble around in asymmetric bodies (e.g.
long thin planks). but like you say, this is really just an accuracy
issue. many users will not even notice the difference - in fact at
mathengine we shipped an early release where this torque term had the
wrong sign - the torque was completely backwards - and nobody noticed.


Russ Smith

On Wed, 6 Apr 2005, Erin Catto wrote:

> In my engine I don't include the inertia torque term: cross(omega, I*omega).
> Without this term you get conservation of angular velocity rather than
> conservation of angular momentum. This leads to greatly increased stability
> at the cost of decreased accuracy.
> I wrote about this in my GDC paper.
> Erin
> http://www.gphysics.com
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