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Joints not independent

I am trying to set the PID position controller on my 7-DOF robotic arm using ros-control. However, the joints are not behaving independently. For instance when I move joint 2, joint 4 moves a bit as well. This makes the PID tuning complicated. How can I make the joints independent of each other so that I can set each joint's PID separately? Do you think that the problem is because of the inertial values?

Also, when setting one of the joints (which is on a horizontal plane) as revolute, the link starts moving even when the set position is 0, however when changing it to continuous joint it behaves correctly. Why is this?

Thanks

Joints not independent

I am trying to set the PID position controller on my 7-DOF robotic arm using ros-control. However, the joints are not behaving independently. For instance when I move joint 2, joint 4 moves a bit as well. This makes the PID tuning complicated. How can I make the joints independent of each other so that I can set each joint's PID separately? Do you think that the problem is because of the inertial values?

Here is a video showing this behavior. I am giving a reference angle (position) to the last joint (the wrist joint). However as can be seen, the joints before are also moving even though I tuned the PID values of each joint. Also, when increasing the damping value, sometimes the link starts vibrating a lot.
https://youtu.be/GnTFysoRYjk

Also, when setting one of the joints (which is on a horizontal plane) as revolute, the link starts moving even when the set position is 0, however when changing it to continuous joint it behaves correctly. Why is this?

Thanks