This video shows me flying a Syma X5C quadcopter, with the factory closed-source flight controller replaced by a Quanum Pico 32-bit brushed FC. I followed the directions in the "Visible Drone" chapter of this excellent new book, but, lacking the eye/hand coordination required to do surface-mount soldering, I used a Quanum Pico instead of the Teensy-based FC shown by the author.
A simple 3D-printed mount allowed me to attach the new controller with some 3M VHB tape. 1.25mm picoblade connectors, available cheap on ebay, connect the FC to the brushed motors on the Syma. I flashed my own firmware on the board, using PIDs from a 3DFly/Pico vehicle I'd built.
In addition to having a Spektrum DSM receiver onboard, the Quanum Pico has built-in Molex connectors for attaching I^2C and UART devices. So I'm hoping to use the modded Syma drone to experiment with proximity sensing, optical flow, and the like.