Its design for a 20second operation. Pass decades, it working perfectly ok. However, lately, sometime after an operation, it rotate the other way, and then for the next turn, it rotate perfectly again... :(
You have a worn winding. As the arm holding the worn winding rests in exactly the wrong place, the arm behind it holds a greater magnetic potential and so the motor goes into reverse. if it bothers you, you will need to replace or rebuild.
Depends on the motor. Some small motors have a cam that prevents reverse rotation if this is the case maybe it has stuck possible a bit of grease in the wrong place.
Electric motor? DC or AC? The direction of spin of an electric motor is determined by the polarity of the current used to drive it. In DC, if the motor is running off a circuit board and it is reversing spin the likely culprit is a burnt diode on the board. Otherwise a dead short in the motor. In an AC motor, 3 wires determine the direction of spin - 2 live wires and a neutral. Depending which wires are powered determines which way it spins. When weird stuff like this happens to equipment that has been running fine I always ask What changed recently
confusing step look into in yahoo and bing that will will help
