Sunday, May 4, 2008

Trackbot part 2

Power supply/Motor drivers

On the same board as the motor driver I put the power supply. A simple design based around a 78L05 regulator. Again a smaller, lighter version of the 7805, but only rated to 100mA. Various filtering capacitors were used. I used recycled capacitors as much as possible as part of my recycling design philosopy. Also I had a few small 6.3V rated capitors from computer mice. Tiny and light, just want I needed. Because I needed a 3V power supply for the motors I went for two battery packs. A 9V battery to supply the main 5V regulated circuit and a 3V (2 x 1.5V AAA) battery pack just for the motors. The 3V supply only had one filtering capacitor on it. But this did mean I had to have two battery connectors on the power board, so two plugs, etc. Small things like this slowly add up to more weight. Finally on the power board went the power switch, some jumper connectors so I could disable either the 3V or 9V power lines (for testing) and various molex connectors (power input, motor connections, power output to main board, relay control input).

With the power/motor board done I was ready for some testing. For the AAA batteries for the 3V supply I was using rechargable batteries (NiMH) so was only getting 2.4V. However Trackbot went well, the speed was good and the climbing ability was excellent. Trackbot would almost go up walls. Shorting the 5V output line to a relay contact would kick a motor into reverse and Trackbot would spin around quite nicely. One issue was the rubber tracks would sometimes come off as they would stick to the carpet a bit too much. Plus I have found over time the rubber has stretched a little.

Next time the main board...

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