I got an old drone, first thing I've tried to do is to connect to it's JTAG and try to hack/debug it. Unfortunately, It was not that successful. Instead of buying a new drone (like most people will do) I decided to connect two technologies I love Bluetooth and Drones. 

I didn't want to waste money on remote instead I've used smartphone as remote and it's Bluetooth capability to transmit. It will not work for long distances but it's really nice idea.

The I could not find any documentation of the old MCU, so I've trashed it. I've left the mechanical part. Printed new PCB with Nordic BLE MCU, Gyroscope and some MOSFET to power on the engines and viola! 

With one engine 

With all of them:

You can find source code for Nordic BLE MCU:

https://github.com/CUDAHEAD/nRF_ble_quad_copter

And the beautiful (not really) UI for Android based remote:

https://github.com/CUDAHEAD/joystickQuadCopterControl