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I have created an sdf file in drake with 3 links and 2 joints, which looks similar to a 2R manipulator. The first link is the base while the second and third links are just long box rods. The 2 joints are revolute and are on the same axis.

However, when I try spinning the far-most joint, the first joint starts moving. (Probably because of inertia).

Is there a method in drake where I can make the joints move independently from others and not be affected by other joints in motion? I wouldn't want to just increase joint friction or inertia parameters of the first joint. I would like the first joint to completely stay still while the second joint is moving.

Thank you

Yuki
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  • Do you have code that reproduces the movements that you don't want? I'm not sure if I completely understand what you mean by "when I try spinning the far-most joint" - are you applying a torque? As for decoupling motion among your joints, you'd most likely want either (a) inverse dynamics with trajectories to physically control the links (if you are simulating with dynamics) or (b) do things in a purely kinematic way (I'll have to look into how to do that in the simulator if that's what you want). – Eric Cousineau Feb 26 '20 at 15:55
  • Drake also has a utility called "geometry inspector" that you can use to exercise individual joints in a model. That's under drake/manipulation/utils. – Sherm Feb 26 '20 at 16:25
  • @EricCousineau Yes, it will be purely kinematics so I wouldn't want to implement extra dynamics if I won't be needing it. I apply an acceleration at the joint to move the link. – Yuki Feb 26 '20 at 20:21

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