[Joe Johnson]

If it is used as a sensor and it is done safely, I assume it would be legal.

The question referenced above specifically says you can buy and use a tachometer and you can use a KOP motor as a tachometer. Note that it does NOT say that non-KOP motors cannot be used as a tachometer.

A tachometer is a device that provides a voltage proportional to rotational speed.

Many tachometers are just fancy motors. A motor is really just a simple tachometer.

As long as you are using the motor as a tachometer, I can't imagine that it is not legal.

Now, if you are using the motor as a motor, then that is another matter. Just as if you bought a tachometer and used it as a motor you'd be afowl of the rules.

Callin' 'em as I see 'em.

Joe J.