Greetings all,

     My latest work has involved finding the speed response of my aeroelastic rotors when a step is applied to the motor current.  Because my robot heli is so small, we change thrust by varying rotor speed.  What's more, we change attitude by producing torques by varying the thrust of paired motors at the corners of the x-shaped frame.  As you might guess, getting fast attitude control is frustratingly difficult.

     For those of you who know control theory, I found that the speed step response was an underdamped two-pole system.

     I would normally have thought that simply speeding up a rotor would be a single-pole system:

     Ir * omega_dot = tau - Q

     Given the fairly small changes in speed, I'm not convinced that the aeroelastic stuff in my rotors is the explaination.  My suspicion is that it has to do with the momentum of the inflow and unsteady aerodynamic effects.

     Has anyone looked at thrust-vs-motor torque change before?  Can anyone point me to some references that describe dynamic inflow or dynamic rotor speed effects?

     -Paul