equivalent constraint

[gdlk]

Hi!

I have a question more related to physics than bullet probably. Currently I have a constraint between two spheres, so one can do a oscillation movement respect the another one (in other words, a pendulum). If the sphere are called A and B, the frame parameters when the constraint was created was: sphere A -> identity; sphere B -> local position to A CoM.

I was thinking in change the way the constraint was created, so the frames will be: sphere A -> rotation to align Y axis with direction AB; sphere B -> rotation to align Y axis with direction AB

The question is, that would be equivalent in behaviour? or one approach is better than the another? or both are bad? (the final idea is build a rope)

Thanks!!

[Basroil]

Construction wise they should be similar, but their motion is going to be very different in one key situation due to sampling differences.

Take for instance a cable vibrating with a certain velocity such that nodes rotate opposite of the adjacent nodes. Now imagine that the frequency and vibration strengths is enough that the axis of each body goes from +c to -c each simulation frame. In this particular case, the second option you stated would have all nodes rotate in place (perfect standing wave with all nodes), while the first method would produce a standing wave where the nodes themselves move.

Which is better is up to you, though you'll find that your first method might be a bit more stable if you include collisions while oscillating.

[gdlk]

It take me a time to see that you say, but I think I finally got the picture in my head

Thanks!! =D