Beening serious for a moment you boffins with spinners will know if this will work. Its just an idea but as it seems that a method for limiting spinners is undecided I thought Id mention it. If you attached a G-Force meter on or near to the blade of the disc and span it very slowly (a known rpm) and hit a solid object that stopped the disc could you calculate the energy of the impact? If so you could then recalculate this for the top speed of the disc. A simple Accelerometer (Spelling) such as those used in Car Airbag systems could be used and are relativly cheap.