jremington, thank you for the response and diligence. In the control system hierarchy, the 9DOF AHRS provides orientation input in quaternion-space. At this point, I am aware of a variety of control techniques that will operate the plant to achieve a user-specified setpoint (such as PID's), however, I am not familiar with how the control system achieves this when all values are in the form of quaternions.
A simplified one-loop example: 1) read user-established setpoint 2) read AHRS input 3) calculate error between setpoint and input 4) controller adjusts plant output for a known reaction 5) delay by time step and repeat loop
Using the above pseudocode it is possible to achieve stability for a Cartesian system by correcting for error vectors. Will this method likewise work to correct for errors between quaternions?