Right now I want to build my own robot arm. I have done the most part of robot arm. The only problem is that when I insert my gripper to the top level assembly, the gear mate doesn't work. The left and right sides of gripper seem to be locked and two pieces will rotate towards the same direction rather than the opposite direction.
I searched some related issues but couldn't find a solution. My assembly are all float in the top level. No one is fixed.
Thank you for any help in advance. The attachment is the pic of my robot arm. Please let me know if you need any files to reproduce the problem.