Problems Faced

Current Draw from Components

When we first moved all the components to the mobile unit we realized that the battery pack was going to be insufficient to operate the different components.  The microprocessor itself requires xxx amps and the battery pack was not going to provide the necessary amperage.  To solve the problem we moved to two different power sources.  One source consisted of two parallel packs of 3 AA batteries.  This gave us a 5V source with the necessary amperage to drive the atmel microprocessor.  The second source consisted of 4 AA batteries hooked in series to make a 7V source.  This second voltage source was used to drive the Stepper Motor.  With the additional packs we were able to provide sufficient current to all the components.

Limitations of the Stepper Motor

The Stepper Motor really turned out to be a disappointment.  We initially thought that it would provide sufficient torque to drive the car because of our previous experiences with it balancing a beam.  At very low RPMs it did provide enough torque to move the car, but anything faster than a crawl and the Stepper Motor would stop turning.  Basically this is a characteristic of a Stepper Motor.  At slow speeds there are small steps and plenty of time to push current through the inductors.  At faster speeds there is less time for current to pass through the inductors and consequently less 'push' on the shaft.  The result:  our car would only move at very slow speeds.