Electronics

Surprisingly all the electronics needed to build the prototype already exist.  All that's needed is (1) a quadcopter flight controller which can be controlled by a mobile device over WiFi, (2) a GPS module*, (3) four micro brush motors and ESCs, and (4) a micro-servo for actuating the rotors (5) 1S Lipo pack along with 5V voltage booster to power everything.

• For the electronic flight controller the Openpilot Mini CC3D should work. It supports a GPS module, has been shown to be controllable over WiFi, and has an active user community. Moreover, the firmware and ground control station software supports plugins which should simplify software development? 

• To GPS or not? The sole reason for having a GPS module is to allow the Droket to automatically return the launch point; however since the CC3D transmits telemetry data, then I think it should be possible to allow the mobile device to return the Droket using only Inertial Navigation? Not having to use a GPS module should save on weight and cost.

• WiFi - UART Module.  This is the part of equipment that is the most confusing to select.  Essentially this device acts as a transparent bridge between the WiFi signal of the mobile device and UART signal from the CC3D. Simple right? Will there are a number of really low-cost boards based on the ESP8266 which do amazing things, except none of them seem to just do the basic operation of acting as a transparent bridge. Well, I found a custom firmware which seem to allow the needed functionality. Next step is to do some testing.

• Four micro brush motors and accompanying ESCs will be used.  The main issue there is the cost of the ESC, with each costing about $10 US each, versus $8 for the micro motors and propeller set. 

• For releasing the stored rotors then a sub micro servo or will likely be needed?