Setting up a BulletConeTwistConstraint

Scripting Issues
1

I am attempting to simulate a gimbaled rocket nozzle using a ConeTwistConstraint. This is how I set it up:

self.cone = BulletConeTwistConstraint(self.rocketNP.node(), self.rocketNozzle.node(), frameA, frameB)
self.cone.enableMotor(1)
self.cone.setMaxMotorImpulse(1)
self.cone.setDamping(100)
self.cone.setDebugDrawSize(2.0)
self.cone.setLimit(20, 20, 0, softness=0.1, bias=3.0, relaxation=8.0)
self.world.attachConstraint(self.cone)

This is how I control the motor every frame:

force = Vec3(0, 0, 0)

if inputState.isSet('forward'): force.setX(1)
if inputState.isSet('reverse'): force.setX(-1)
if inputState.isSet('left'):    force.setY(-1)
if inputState.isSet('right'):   force.setY( 1)

force *= -20.0/180.0*math.pi

self.rocketNozzle.node().setActive(True)
force = rot.from_euler('zyx',force).as_quat()

self.cone.setMotorTarget(LQuaternionf(force[0],force[1],force[2],force[3]))

Controlling the motor seems to work fine. However the nozzle quickly starts jittering around and won’t st, especially when trying to go back to the center position. I tried to smoothen the movement by adjusting the dampening, the max motor impulse and by adjusting the limit parameters, but I don’t really understand how they work. I imagine MaxMotorImpulse to define the strength of the motor and dampening to - well - dampen the movement of the joint but when playing with the values I cannot make out any changes in its behaviour.

And I couldn’t find any info on how softness, bias and relaxation work, I don’t quite understand them from palying around either. It would be nice if you could tell me more :slight_smile:

Thanks in advance!