I recently wrote my thesis on the topic of using feedback control to provide a vertical position autopilot for an RC helicopter. I used a Gaui EP100 on a test-rig to test the control techniques. The control theory has been designed so that it can be applied to a helicopter of any dimension/number of blades. It is presented in this 26 page document. I hope this can be of some use to someone!
The video below shows me performing some basic disturbance rejection tests.