First Time Sawppy the Rover Rolled On Its Own Power

Once the serial bus servo wiring harness was soldered (twice, once for each side) they were examined with a multi meter for obvious mistakes: First to make sure there’s continuity across all the terminals that are supposed to be connected, and make sure the bits that are supposed to be separate are indeed independent. After that was verified, it was time to hook everything up and try it for real. All we needed was a Raspberry Pi 3 to run SGVHAK rover’s software (modified to command Sawppy’s serial bus servos) and finding an old two-cell lithium ion battery pack to power it all.

Once everything powered up, the rover could move but in a haphazard uncoordinated fashion because the steerable wheels weren’t pointing in the correct directions. Before it can move well, we needed to find and record their actual center position. In theory there shouldn’t be any work necessary because a servo knows its center position and all we need to do is line up with it. In practice, each servo has a tiny bit of error, each 3D-printed shaft coupler has a little bit of error, etc. Overriding all these little errors is the fact these steel steering shafts were cut by hand on a poor man’s lathe so the set screw detents on either end of these shafts don’t line up at all. All these sources of error add up and they’re why we needed the ability to adjust steering center position.

Once center positions were established, Sawppy was able to roll around on its wheels. There was still a lot of work to do but it was exciting to cross this threshold.

Servo Rover

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