I wanted to improve the power supply for the Raspberry Pi to remove all the adapter cables and to allow the Pi to be powered without arming the motor. These aims have been achieved by adding a USB socket and a LiPo balance connector socket to the existing Battery Eliminator Circuit (BEC).
I cut the socket from a 3S LiPo balance connector extension and soldered the two outer wires to the BEC input. Although the two centre wires are not used, I left them in place to provide some strain relief when unplugging the socket from the battery. With the BEC powered from the balance connector, the Pi can be powered independently of the flight motor, but still from the same battery.
I wanted to use a right angle Micro-B USB cable to connect the power to the raspberry Pi. The original straight plug stuck out too far and the bare wires were not very sturdy. To use this I soldered a USB A Socket to some copper strip board. The middle two data pins do not line up with the 0.1 inch hole spacing so needed a little adjustment to fit the board. I also needed to enlarge the holes to take the sockets fixing legs. The board was left long and tapered to match the width of the BEC.
The BEC output wires were cut and soldered to the 5V and ground tracks on the board. I kept the servo connector to power the GPS boards separately from the Pi to bypass the Pi’s internal power limitations.
Everything was lined up as compact as possible and then bound together using heat-shrink tube.
The final item turned out neat and compact.
The stripboard provides a nice flat surface for some velco to attach the unit inside the aircraft. The 30 cm USB cable is just long enough to reach the Raspberry Pi on top of the wing.