Be wary of those, the weights look like they're press fit on, they may not be removable without damaging the motor. The one's that look like discs are completely enclosed and I don't think it's practical to modify them as normal rotating motors, I've never taken one apart though as I only have one, and it makes too nice of a vibrating motor to destroy. Keep in mind, the voltage and RPM rating on these motors can be highly variable and they are NOT ment for high speed constant use.