Limits on btGeneric6DofSpringConstraint not working?

[hogius]

Dear all,

My friend and I try to simulate a metal wire using a chain of btCapsuleShape connected by btGeneric6DofSpringConstraint. However, it turns out to be very 'wobbly', i.e. shows a lot of bending and displacement even if we set all limits to zero (which should result in one solid rod). Has anyone an idea what to do about that? Any help and new ideas are welcome

Best Regards,
Chris

[Erwin Coumans]

They should be stiff, unless you use large differences in mass. Can you try making the masses involved more similar?

Otherwise, try reproducing it in the Bullet/Demos/ConstraintDemo and attach a zipped reproduction case,
Thanks,
Erwin

[hogius]

Hey,

thank you for the fast response! The masses are exactly the same. I modified the "ragdoll"-demo and attached it. Please let me know if you prefer a modification of the "constraint" demo. The interesting part beginns at line 480.

Thank you for your time and effort,
Chris

[Erwin Coumans]

Ah, I missed the 'spring' part. Using springs in combination with a fixed degree of free doesn't work well. Not sure how to simulate a wire in the best way, you might want to try the soft body ropes, with some settings too (and attaching rigid bodies for the collisions).

Make sure to not use too small body/shape sizes, and the bodies should not overlap. Attached is a slightly modified demo with bigger shapes that don't overlap.
Thanks,
Erwin

By the way, I also create a .bullet snapshot. You can create such .bullet snapshot by pressing on the '=' key in the Bullet 2.76 demos. Such .bullet file can be opened in the work-in-progress Bullet physics editor, see http://bullet-physics-editor.googlecode.com