constraint instability

[Jiri]

Hi,

I need to connect two bodies by a 6dof constraint. The heavier body is lifted a bit and its gravity acts on the lighter body through the constraint, see the attached file (for simplicity "only" p2p constraint is used). I use double precision. If the constraint is not used, everything is stable. But if I use it, there are two problems which worry me.

1) If I use small coordinates, the constraint exhibits slight instability approx. every 5s (you have to zoom in).

2) And what concerns me even more - in my application I have to use really large coordinates, see the position_offset in the code. Using the large coordinates the constraint is even more unstable.

I would like to ask, if somebody has an idea what should be done to avoid this.

I expect there might be two problems. One is that the heavier body effectively lies on the lighter one. However, the mass ratio is reasonable.
Another problem might be that some part of the code related to constraints is very sensitive to precision. I would actually like to understand the code where the constraints are solved and analyze it myself, but I am lost there although I understand literature dealing with constraint solving. Is there a good reference with apparent correspondence to the code?

Thanks a lot!