Hi I have built a gear drive for robotic arm that uses a worm set (worm gear +worm) at stage one. Worm (wheel) is of bronze and worm gear is steel haing a lead angle of appx 8 deg. This set is further coupled to a spur gear set that further increases the torque such that the over all gear ratio is 1: 320. Now ideally the gear drive can be rotated from the output shaft as the lead angle is greater than 4 deg. However for some reason this mechanism is exhibitoing self locking in a way that even applying 40 kgs of load at the output shaft, the input does not rotate. can any one explain this? The literature suggests these lead angles should not indicate self locking.