An imported robot arm "never moves" in simulation: the IK solver returned success with a 0.2 mm residual in five of six directions, but the arm's links overlap 4.4 to 13.8 mm at every joint so the collision query dropped every solution; on top of that the URDF declares 1.0 Nm of joint friction and a placeholder effort of 1 Nm, so the joints couldn't beat their own friction, and each joint moved 2 to 46 percent of a 0.2 rad command.