Monday, March 28, 2011

The Bridge and engine room

The Bridge is meant to be the control center, like the bridge on a ship. It carries the Logomatic, the inertial and magnetic sensors, a LiPo battery to power this all, and plugs for the GPS and BlueSmirf.

The bridge board is a custom PCB designed with Eagle and made through BatchPCB. It is exactly the same size as the Logomatic board, and is designed to sandwich the sensors between itself and the Logomatic.

Due to an unfortunate choice of pinouts on the Logomatic, only one PWM is available to control the motors. I need 4. Search, search, what do you call a part which takes I2C input and produces multiple PWM outputs... Oh yeah! Arduino!

So, there is a second board called the Engine Room. This board hosts an Arduino Nano, an opto-isolator, a quad half-bridge circuit for the tail rotor, and a pair of beefy MOSFETs and diodes for the main rotors. The engine room board is cleanly split into two parts: One for the low-power electronics, and one for the motor controls. Only an opto-isolator bridges the gap. No Electrons Allowed Past This Point, in either direction. The low-power part was designed to run on power supplied by the bridge, while the motor part runs on the 11.1V high-discharge motor battery which came with the helicopter originally.

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