Power Issues

We determined that speed would be a significant advantage in the tournament.  Therefore we looked into increasing Doyle’s motor voltage.  This was done, by making a simple modification to the handyboard.  A break was made in the supply trace to the two motor driver chips.  The new power supply we used consisted of 16 AA NiCads (i.e. to 9.6 V packs) for a nominal voltage of 19.4 V and a current rating of 650 mAh.  The positive side of the new supply was then connected to the motor chip side of the break in the trace and the negative side was connected to the same ground plane as the handyboard’s 9.6 V supply.  Doyle’s maximum speed was now greater than 40 inches/s.  However his speed vs. applied duty cycle function became even more non-linear than before.  Because of this our code used a lookup table, which took the values provided by the feedback control and came up with a linearly proportional duty cycle.  As a note on charging the NiCads, we used a DC power supply with a current limiting capability.  We charged the 9.6 V packs separately by setting the voltage to somewhere between 11.5 and 12.0 V and limiting the current to about 65 mA (10% of the battery capacity).