My grandson bought one of those cheap 110V. rotating 'color-spot' balls. After I hung it from the ceiling for him, I noticed I could reverse direction of the rotation by stopping it with my hand and nudging it the other way. That seems to imply I could do the same thing with a fan or other A/C motor, but I doubt that's possible. What's happening with the ball? TIA
It probably uses a shaded pole induction motor. These have a shading coil around a part of the stator pole face to provide some torque when the motor is at standstill to get it turning in a preferred direction (well, really to get it turning at all).
Once the motor picks up some speed, the current induced in the spinning rotor reinforces the torque. However, if the rotor is initially given an initial rotational velocity opposite that produced by the shading coil, when the stator is energized, the resulting torque produced by the rotor currents will reinforce that direction of spin instead.
That is probably a shaded pole motor. The "shade" that decides which way it is going to go is pretty soft. On a regular induction motor there is a start winding and a capacitor that kicks it over. Usually you can swap a couple wires to nudge it over the other way. If you have a centrifugal switch cutting the cap out it would run either way if you disconnected the cap, but you would have to nudge it over yourself to get it going.
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