I spent a number of years designing outer-runner direct drive permanent magnet motors for industrial equipment and I've got some questions.<p>Cheifly, bearings. They're not shown in any of the oh-wow images, but these will likely be the most expensive component of each motor. Big bearings are expensive, and to accept the loading of normal wheel operation, these will have to be pretty beefy. That's not even discussing operational life and maintenance.<p>After you've stuffed a pair of angular contact roller bearings into this "wheel", you're going to want to keep salt water and road grime from entering those bearings, so what do you use as a seal? Whatever you use is going to be big, expensive, and suck up huge amounts of power due to the large contact surface.<p>Finally, once you've got big ass bearings and big ass seals, how do you have enough room to put a decent amount of copper in there? Power in these things always amounts to maximizing the amount of copper in the space, and I just don't see room for it.