Original poster: David Speck <dave@xxxxxxxxxxxxxxxx> Jon,There are several ways to do this. One approach uses a transducer like a magnet moving inside a coil attached to the spinning device which is constrained so it can move only up and down, for example. The zero crossing on the induced voltage will correspond to the instant when the oscillating mass starts to reverse direction. A zero crossing detector can trigger a strobe light and show you the orientation of the rotor at the instant when the heavy side is up (or down, depending on the way the machine is set up). Other systems use piezo sensors to do the same function.
HTH, Dave
Do remember the elements for the balancing machine? I've been thinking of constucting one of these, and would appreciate any insight as to how one is put together. So far, all I can think of is mounting the motor on a table with springs and marking where the spinning rotor goes high. Thanks, Jon