Joint error: can i add joint for only one link?

[weidh21]

Hi everyone, I’m trying to create a task, in which my robotic hand can push the cube to the desired position. To do this, I attempt to create a primitivistic joint(named “PrismaticJoint1”) to the base link of my hand. However, the joint can not be got by the function

self._hiro_hand_idx_5 = self.hiro_hand.get_dof_index("PrismaticJoint1")

and the error is：

 File "d:\isaac\ku\isaac_sim-2022.2.1\exts\omni.isaac.core\omni\isaac\core\articulations\articulation_view.py", line 264, in get_dof_index
    return self._dof_indices[dof_name]
KeyError: 'PrismaticJoint1'

So I was confused about how to set a joint to the base link, so that I can control the base link to move?

Thanks for any suggestions and your kind help!

[AlesBorovicka]

Could you please share some simplified USD scene?
If you try to create articulation with just one joint - being prismatic joint, I think this wont work for fixed articulations. There is expected a fixed joint and then a prismatic joint. You can try to add a dummy body in between that you connect with a fixed joint.
Anyway if you can confirm that its this case, I will try to fix this for next release.
Thanks, regards,
Ales

[weidh21]

thanks for your reply. my usd scene is shown as follow:

[weidh21]

I plan to add a body and make it fixed, then connect the body to the base link that I wanna drive.

[AlesBorovicka]

Right, as said currently for this to work, there has to be one more body with a fixed joint, this is a limitation I am trying to fix, but there are some technical obstacles.
articulation_test.usda (6.9 KB)

I have attached articulation chain that should resolve what you are trying to achieve. Note that there is one more additional body that is connected with a fixed joint. This is currently necessary.

Regards,
Ales

[weidh21]

Thanks a lot