❝ Electric motors are round. Wheels are round. It’s a pretty natural impulse to combine the two. No lesser automotive luminary than Dr. Ferdinand Porsche did it first, inventing the wheel-hub motor in 1897. He mounted two of them to his front-driven battery-electric prototype “Lohner-Porsche.” Three years later he invented the gas-electric hybrid by fitting four hub motors to his elaborate four-ton “Mixte” coach. The one tiny rub: Those 14-hp motors weighed around 320 pounds. Each.
Modern materials and engineering have enabled dramatic improvements. For about seven years, Protean Electric has been selling a 100-hp hub motor that weighs just 68 pounds. So why do all volume-produced EVs still mount their motors inboard? To minimize unsprung weight for optimal ride quality.
❝ Enter Silicon Valley inventor and serial startup founder Marcus Hays and co-inventor Scott Streeter. They wondered if it might be possible to develop a wheel and motor system that weighed no more than a conventional aluminum wheel…Without the gear reduction of a body-mounted motor, a hub motor needs high torque to act through the 1-foot lever arm from the hub to the contact patch. Wheels then need hefty structure to transmit these acceleration, braking, and cornering forces between the hub and the rim.
Hays’ radical solution: do away with the hub entirely and power the rim…
❝ Mass, cost, and rotational inertia instantly plunge with this approach. Mounting the motor so that it drives a rim-mounted ring gear…lowers the required torque to get the wheel spinning. It also greatly increases the electric motor’s top speed. And guess what? Motors wound for high rpm instead of high torque, like those on a drone copter, can deliver the same power as high-torque motors using vastly less copper and hence weighing one-twentieth as much. Bam — a cost- and weight-savings twofer.
RTFA. Reanalysis of how and why electric power can be delivered to the road for transit – private or public-size vehicles – much more efficiently.