Hmn, Actually, I think it is working. I had a bodge elsewhere for controling the roll, after taking that out it is much better.

Still wondering, though, in kg*m^2 is "m" the diameter? This was a wild guess. Initially I thought it would be mass, but kg is the same thing, isn't it?

Anyway, I appear to be on the right track, because my entities bounce around okay, though they all finish on funny angles because they think they are spheres.