the gear and the plate are not concentric. there is a teeth on the plate which will move the gear to rotate. The effect to simulate is that the plate will rotate in a constant speed. when the teeth touch the gear, it will push the gear to rotate. when the teeth is departed with the gear, the gear should stop rotating. I set up the contact between the gear and the plate. But the strange thing is, although the gear will start to rotate when the teeth touch it, but it will not stop rotating when the teeth is departed from it. see the video. How to simulate? Thanks a lot!