Allow picking of btMultiBody, using a btMultiBodyPoint2Point constraint, with limited strength to avoid adding too much energy to the system (= blowup)
Add btMultiBodyJointMotor, it can be used in combination with joint limit (just add the joint limit after the motor, to avoid jitter)
The original version was written by Stephen Thompson.
I replaced Eigen math by Bullet LinearMath, and added a dedicated 6x6 matrix solver.
Also I integrated support for collisions/contact constraints between btMultiBody and btRigidBody, and de-activation support.
See Demos/FeatherstoneMultiBodyDemo/Win32FeatherstoneMultiBodyDemo.cpp for example usage.
There is currently only support for contact constraints for btMultiBody.
Next on the list will be adding support for joint limit constraint for btMultiBody.
The implementation is still experimental/untested, the quality will improve in upcoming Bullet releases.
