PxJointAngularLimitPair invalid limit equivalence?

Gaming and Visualization Technologies APIs Physics Modeling (closed)
1

The issue I am seeing is in version 3.3.4 but looking at the documentation for 3.4 it looks like it’s probably still applicable.

I have configured a PXD6Joint which is locked in all axes except twist and is limited in the twist axis. I would like my joint to be able to twist from 0.8 radians to 3.6 radians. According to the documentation for PxJointAngularLimitPair my limits can go all the way from -2pi to 2pi but my lower must be less than my upper so I set lower=0.8 and upper=3.6. This works perfectly at the lower limit but as I rotate towards the upper limit my system explodes when my twist angle hits exactly pi. I haven’t totally stripped down my system to the simplest possible case but I believe I’ve removed all joints connecting the two actors except my twist joint.

Next I observe that 0.8 radians is the same angle as -5.5 radians and 3.6 radians is the same as -2.7 radians so I change my limits to lower=-5.5 and upper=-2.7. This still satisfies the -2pi to 2pi range and lower is still less than upper. As far as I can see this should give the exact same behavior as before but this setup explodes immediately.

My question then are:

  • Is there a difference in expected behavior when setting up a twist joint with lower=L and upper=U vs lower=L-2pi and upper=U-2pi provided L, U, L-2pi and U-pi are all in the range [-2pi, 2pi]?
  • Are there further undocumented requirements on the values provided to PxJointAngularLimitPair?
  • Is my joint expected to go crazy in this way when transitioning twist from pi to -pi?
2

The documentation is incorrect here - the limits must be specified in range (-Pi,Pi) rathber than the documented limits.

Releases > 3.4 will support the (-2Pi,2Pi) range but if you are on 3.4 or earlier then the supported range is actually (-Pi,Pi)

3

Thanks for your reply. That’s very useful to know.

So how would I express that I would like my joint to range from 0.8 to 3.6? Should I set the limits to Lower=0.8, Upper=-2.6? Is the bit about the lower being required to be less than the upper accurate?

If not then presumably I should adjust the local constraint frames such that the twist range is easier to work with?

thanks again

4

Yes, you will need to adjust the local frames so that your min and max sit inside the range (-Pi,Pi).

Cheers,

Gordon

5

great. I can do that. Thanks for the assistance Gordon.