Joints depend on other joints

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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