The drive motor is currently the most expensive item in the solar car. It is over half the cost of the entire system at $4100 (see cost and weight budget). The drive motor needs to be about 30hp and under 100lb. There are very few applications of light electric motors with this much power so finding a used motor is difficult. I have only been able to find very expensive motors from specialized electrical car conversion companies. Most electric cars have drive motors that are much bigger than what is required in the solar thermal car. They are often around 100hp. These electric cars accelerate quickly and have top speeds over 150km/h. The solar thermal car however will be travelling much slower to conserve it's solar energy.
I am still looking for a good used drive motor. Golf cart electric motors can get as high as powerful as 10hp. It would be possible to use 3 of these motors but this could be difficult.
I am still looking for a good used drive motor for the solar thermal car. The motor size is really between small motors and larger electric vehicle motors.
The speed control is also very expensive. I could build an inexpensive resistive speed control. This would increase resistance in the controller to decrease the power to the motor. The problem with this controller is that at low speed most of the power is concerted to heat in the controller.
An efficient speed control can reduce the power used by the motor without adding resistance and wasting extra power. I am working on a speed control using the Arduino controller's PWM function to control the drive motors speed. The PWM (Pulse Width Modulation) increases the duration (width) of “on pulses” to control the power. The pulses are so fast the the motor only receives the average power between the pulses and is very smooth. The Arduino's PWM signal can control a small transistor which can then be used to switch a powerful solid state relay. I am still looking for a solid state relay that can switch fast enough and can handle the high power of the drive motor. A smaller battery back and drive motor will be tested with the solar thermal car large speed control in the electric bicycle, electric drive test unit. If the speed control is sized for the solar thermal car drive motor and works well with the smaller electric bike motor it should be ready for testing in the one mirror trailer test unit with the full sized battery and drive motor.