Solar Vehicle Electric Motor Design
I am currently overseeing a small team of three students to design and manufacture a brushless permanent magnetic motor prototype for CalSol, UC Berkeley's solar vehicle team. This is a work in progress and developments will be updated as they come, but our work thus far is shown here.
Motor Modeling in MATLAB
After first recognizing that we wanted a 3-phase, axial flux (a.k.a. pancake), coreless dual-rotor motor, I worked with Richard Malueg (RMI Systems, Inc., chief engineer) to model motor efficiency, weight, and other characteristics in MATLAB. The results indicated the characteristics of the motor required (e.g., number of poles, air gap, wire thickness, etc.) for optimized efficiency and weight.
Mechanical Design in SolidWorks
With fundamental electromagnetic properties determined, we were able to begin designing the mechanical components of the motor. The uppermost images above show the integrated result of the separately designed components of the rotors, stator, and coils. Major design challenges include:
- securing the coils to the axle shaft to minimize displacement, twisting, or flexing to prevent coils and magnets from touching
- bearing the ~1000 lb. load created by the attractive force between the two magnet arrays
- interfacing metals of different coefficients of thermal expansion (i.e., steel for the bearings, backiron, and axle; aluminum for the rotor bodies) to reduce motor weight
- housing bearings such that they can be variably pre-loaded and such that the motor is possible to assemble
- providing sufficient heat conduction/convection paths for coils to dissipate heat
Motivation
Solar vehicle racing is an energy game, and a winning car requires an electric motor of the highest efficiency. Commercially available motors for solar vehicles, however, are outdated, extremely costly, or overpowered and heavy. Very few teams tackle the challenge of building their own motor due to the difficulty of design and manufacture, but the benefit, in theory, is an electric motor (or motors) that has a weight, efficiency, size, power, etc. optimized for their particular vehicle. It is also, of course, an exemplary opportunity for college students to participate in hands-on and team engineering.