The KKmulticontroller is a flight control board for remote control multicopters with 2,3,4 and 6 rotors. We get it to stablise the aircraft during flight. It takes the signal from the three gyros on the board (roll, pitch and yaw) and feeds the information into the Integrated Circuit (Atmega IC). This then processes the information according the the KK software and sends out a control signal to the Electronic Speed Controllers (ESCs) which are plugged onto the board and also connected to the motors. Depending upon the signal from the IC the ESCs will either speed up or slow down the motors (and tilt the rear rotor with a servo in a Tricopter) in order to establish level flight.

The board also takes a control signal from the Remote Control Receiver (RX) and feeds this into the IC via the aileron, elevator, throttle and rudder pins on the board. After processing this information, the IC will then send out a signal to the motors (Via the M1 to M6 pins on the board) to speed up or slow down to achieve controlled flight (up, down, backwards, forwards, left, right, yaw) on the command from the RC Pilot sent via his Transmitter (TX). In the case of a Tricopter, one of the pin connectors (M4) will control a servo to achieve yaw authority.

The v.5.5 has an Atmega168 chip on board and an ISP header which gives users the option to tweak and upload their own controller code.

other source
KK multicopter flash tols is a tool to easily upload a firmware to your KK multicopter board. It is designed to support the users that never have flashed a firmware to a micro-controller before. You just have to select your programmer and your board or controller type. Afterwards you have the possibility to flash a firmware file from your PC or directly from the internet by selecting from a list of latest available firmwares. The tool is saving some settings on the exit of the tool. So that you don't have to set-up everything on the next launches of the software.