Coil length isn't the only thing that matters. And as Nick said, a picture isn't going to do anything to help him even as far as coil length goes. He would need full measurements of the coil and the gap, and as he pointed out he would also need to know the geometry of the motor and suspension. Long story short, the easiest way for them to do it would be with the physical driver in hand, including soft parts. And chances are good, reverse engineering the driver probably isn't something they really want to get into anyways. It would be fairly time consuming on their end. If you really want something from Fi, recone the driver with PSI parts, sell it and use the $$ to buy a Fi driver.