The Rasa hydrogen fuel cell car developed by Riversimple has been attracting a lot of attention with its innovative design and impressive performance. A key feature is its four in-wheel electric motors which directly drive the vehicle's wheels.
The thin, powerful pancake motors were developed for the UK company by Printed Motor Works, and had to meet a number of demanding requirements. One of these was the need to include an integral mount for the brake disc while maintaining the motor's external rotor design, which is necessary to produce the high torque required.
Further constraints were the use of conventional, externally mounted disc callipers, a low target weight and the need for the whole package to fit within a 15" wheel rim.
The XR32-11 in-wheel motors allow the Rasa to use regenerative braking, recapturing over 50% of the kinetic energy, and using a bank of supercapacitors in the front of the car to store the electrical power...