Check out Sabbatani's new brakes, they are using a liquid magnetic polymer that turns to a solid when a voltage is applied. The hub is non rotating and by using complex castings and insulators, the wheel rotates about the hub and has vanes inside the fluid. When Sabb' uses the brake lever he applies a voltage to the polymer and the vanes are progresively slowed by the thickening polymer! The higher the voltage the thicker the polymer becomes, this has been experimental stuff for some years now but it was only a matter of time before someone came up with a use for it.