Testing

*To view our full testing report, follow the "lab report" link at the bottom of this page.*

Background:
    Unfortunately, our drone was unable to compete on the 4/30/2016 competition. This was due to our Sabertooth H-Bridge motor controller frying due to large voltage spikes from our alternator. We determined this would be a perfect failure mode to investigate for the Mechanical Lab portion of the course. 
    An alternator works by rotating an iron rotor within a stator. The iron rotor has copper windings around the entire rotor, which produces a field current from the voltage regulator. This field current directly correlates with how strong the magnetic field is around the rotor. When rotated, the magnetic field of the rotor flows across the three separate copper stators producing an A/C current. Alternators can produce more and less voltage than its specified voltage. In automobiles, an alternator will produce more voltage than specified. This is due to multiple systems running off one battery, i.e. headlights, radio, dash lights, and electric windows. If all the systems are running simultaneously, the battery will have a large dissipation. To ensure the battery never drops below 12 volts the alternator will over charge the battery at approximately 14 volts, or for a 24-volt system an alternator will overcharge to around 28V to compensate for the extra dissipation.
    The small batteries we were using dissipated very quickly due to the high load from the Ampflow motors. Thus, the alternator compensated for this by sending large voltage spikes to the motor controller. Using an oscilloscope, we were able to determine that the alternator was producing spikes up to approximately 40 volts. Our motor controller is designed to run at 24 volts, so these large spikes are likely what caused it to fail. Further testing determined we would have been able to mitigate this by using a voltage step-up. With the voltage step-up installed, the results showed that the voltage spikes were approximately 27 volts. 
    
Subpages (1): Lab Report