Project Years: 2022-2023
Contributors: Matthew Thomson
Altium365 Project: https://americas-starr-university-of-alberta.365.altium.com/designs/3D787631-1535-445B-B7B4-8C9FE7C40575#design
Github Repo: UASTARR/power-distribution-boards
The GPS Power Delivery Board was STARR’s very first custom PCB to fly on a rocket. Its job was to take a 1S LiPo battery, route it to a Featherweight GPS tracker, and control the flow of power. The board was designed around an STM32WB15CCU microcontroller, and ran a very simplistic Bluetooth Low Energy server. It had a single characteristic that allowed the user to control the arming state, which was changed through an BLE testing app provided by STMicroelectronics. Power was controlled by dedicated IC switches, and the PCB used a patch+chip antenna combination. It successfully performed its role on Ringo II, where it was used to disable power to the Featherweight GPS tracker in the nosecone to conserve battery power on the pad while other arming issues were resolved.
While the GPS PDB fulfilled its job perfectly, it was an extremely challenging project for a group of students who had never designed a PCB or even worked with a microcontroller before. Seriously, it was a miracle it worked the first time, and that was only because obsessive reviewing caught all the minor errors that could have killed the design. It was shelved for three reasons:
In retrospect, the hardest to overcome is learning RF design which basically needs to be self taught. The software for the STM32WB15’s BLE state machine is very clunky, but makes sense with experience coding in C and working with microcontrollers.
While it is true any power distribution board (or really any COTS design) can be a point of failure, it’s important to understand that with sufficient engineering design rigour, testing, and plethora of KISS (keep it simple, stupid) will minimize the chance of failure. For example, a thoroughly tested, flight-proven COTS WAS could reasonably replace a screw switch, for example.
Although future revisions to the WAS were shelved until 2025, wireless arming remains a potential avenue for arming our rockets in the future. The main roadblock is working around our carbon fibre airframes, which block RF communication.