Thanks for the reply. The belts and chain are quite tense. There is also a lot of play at J2. By "constant weight" I meant that the arm is never perpendicular to the table - the gravity pulls it constantly downwards. I want to move some PCBs with the robot, so I'm far from 4 lbs. I'm 99.9% sure the play is coming from the gearboxes. Is there no other stepper alternative?