How to determine how fast a part is spinning?

Quite a simple question but couldn't find any way of answering it.

I tried checking the RotVelocity property, but it didnt work. It was always 0,0,0

I really don't like the idea of welding a part to the edge of the wheel in order to check the angular velocity.

I've also tried using the AngularVelocity constraint to check it, but i couldn't figure it out either.

Anybody help??