Continuous Joint

[daniel.honerkamp]

Hi, I’m trying to use a model of the PR2 robot in isaac sim. This robot has continuous joints in it’s arm. At the moment, these get converted from the urdf to the following joint:

        def PhysicsRevoluteJoint "l_forearm_roll_joint" (
            prepend apiSchemas = ["PhysxJointAPI", "PhysicsDriveAPI:angular", "PhysicsJointStateAPI:angular"]
        )
        {
            float drive:angular:physics:damping = 1000
            float drive:angular:physics:maxForce = 1800
            float drive:angular:physics:stiffness = 0
            float drive:angular:physics:targetVelocity = 0
            uniform token drive:angular:physics:type = "force"
            uniform token physics:axis = "X"
            rel physics:body0 = </pr2/l_elbow_flex_link>
            rel physics:body1 = </pr2/l_forearm_roll_link>
            float physics:breakForce = 3.4028235e38
            float physics:breakTorque = 3.4028235e38
            point3f physics:localPos0 = (0, 0, 0)
            point3f physics:localPos1 = (0, 0, 0)
            quatf physics:localRot0 = (1, 0, 0, 0)
            quatf physics:localRot1 = (1, 0, 0, 0)
            float physxJoint:jointFriction = 0
            float physxJoint:maxJointVelocity = 206.2648
        }

In Isaaac sim, the joint shows a joint limit of 3.4028235e+38 (as returned by self.get_dof_limits()). But it’s not actually possible to move it beyond a limit of -2pi/2pi, with the simulator throwing an error message of only supports target angle in range [-2Pi, 2Pi] and the joint not moving any further.

Is there a way to implement a continuous joint in Isaac? This is quite important to model our real world robots. I’m using isaac 2023.1.0.

Other threads unfortunately did not answer this question and were locked:

Continous joint limit issue

Hi @floodsung, Can you clarify what was an issue? It looks like an expected behaviour - continuous joints don’t have limits, this value 3.4028235e+38 is the default value automatically set in the joint properties, but as continuous joints don’t have limits it doesn’t mean anything. When you switch to the revolute joint, they now have limits and if you manually don’t provide and set them, lower and upper limits would be set to the default values - the largest allowed limits for the revolute join…

How can I make a revolute joint rotate continuously near the +-pi?

Hi. I want the joint to spin continuously at point ±pi using position control. But now, the controller can’t find the shortest route and turn the other way around by 2pi. (please see my video) When I use IsaacGym, which supports the PhyX3 engine and hinge joint, There was no problem. Here is my input example-> [3.1, 3.12, 3.14, -3.14, -3.12, -3.1] rad this shows continuous rotation in the real world. How can I make it rotate without any malfunctions? added 1) The joint has no joi…

Your help is much appreciated!