HingeJoint Problem

[edualbu]

Hi,

I recently started using bullet for robotics simulation project. I was testing hinge joints to see if they can be used to simulate actuators in a robotic arm and I noted some strange behaviours.

When I apply some torque for some time in a Rigid Body with no damping and no gravity, it gains some angular velocity and keeps rotating forever with the same velocity as expected. That's ok. Also, if i apply torque forever, the velocity keeps increasing to infinity.

However, if I apply the same torque for the same time in the same Rigid Body now attached to a HingeJoint, it gains some angular velocity, but, when I stop applying it, the Rigid Body starts getting slower and slower, losing energy. That's not right. Also, if I keep applying more torque forever the velocity reaches a limit and then stops increasing.

Is that behaviour normal? Do I need to change any parameter? Or, maybe, change the solver?

Thanks for the help

Eduardo

[Erwin Coumans]

The behavior is normal, there are various reasons why energy is not preserved in the constraint solver. For robotics you might want to use the btMultiBody/bt, which is based on the Featherstone Articulated Body Algorithm. Again, there might be some energy preservation issues, due to various issues.

Improving the quality and energy preservation is an area that I am working on, but it will take time.