Pulling it all together!

 A few more late nights working to assemble my robot. Thankfully the CAD model went together pretty well, with just some minor filing of parts to make them fit together well. I used hot melt threaded inserts in several places which makes it very quick to assemble (and more importantly take apart) when things go wrong.

Here you can see the lower chassis with the Motor2040 board mounted at the front with the battery tray in the middle between the wheels (the battery slides into this). The UBEC sits on top of the middle battery and the USB-C battery pack is on the back, held in place with velcro straps.

The 3D printed Raspberry Pi 5 case sits on top, screwed onto a pair of bars. The screws come up from below and hold the case together, so need to be fitted before the bars are screwed down onto the robot. You can just see the Motor2040 board below the Pi here with an IMU plugged into the QWIIC socket. It was at this point that things started to go wrong. See the yellow wire which has snapped off the IMU board where I had soldered it straight to the PCB. Then I realised my Motor2040 board has no servo headers. I have nowhere to plug in the servos on my grabber!

Some frantic study of the Motor2040 board documentation and schematic revealed no broken out pins from the GPIO. There were some analogue inputs, but it turns out these are for a seperate ADC chip and not the RP2040. Then I spotted the UART pins labelled RX and TX on the board. Looking at the schematic these are directly connected to a pair of GPIOs on the RP2040, and I was not using them for serial communications as I am using the USB socket for that! I clipped my PicoScope probe ground to the USB plug (the only accessible GND point with my board mounted) and found a simple servo driving example for MicroPython. Setting the RX and TX pins as the 'servo outputs' in the example I was able to confirm the PWM output on these pins on the PicoScope. The day was saved!