Single Axis Stability in QuadCopter

The Masters student working on the QuadCopter stability system had their final seminar last week. They have been hampered over the past year with an overly complex system design that I put together for them, language skills and lack of time due to coursework commitments. In spite of all this they managed to get a pretty good understanding of the electromechanical system, produced system models and controllers in simulink. The basic code is now up in 3 modules on google code - adelaide quadcopter project.

The final controller they ended up using was a basic Proportional-Derivative (PD) controller. The integral part leads to tighter approach to the set point, but is not always necessary. There being 4 degrees of control the quadcopter can be stabilized in yaw,pitch, roll and height. Basically a fully stable system should be able to hover. Linear motion on X and Y can be achieved by dropping it into an unstable state. This can be implemented as a state-space control, a multidimensional extension of the PD.

The single axis stability is not too bad as it comes out here, could be better though. There is an unstable region with +/- 18 Degrees oscillation. At times given low damping the oscillations tend to build up.