The Sparkfun AVC 2011 is coming up and this year I might enter a hovering robot. Quad rotors are all the rage now, but I’m not into high disc loadings. So I’m thinking about entering a robot that hovers on one rotor and uses control vanes to cancel the rotor torque and maneuver. This configuration is unstable, so I’ll have to close a few control loops. Once you get a stable platform, the navigation is simple: You just pick waypoints far enough away from the Sparkfun building and a do carrot and stick control law. Simple.
Anyhow, how much power does it take to hover? Momentum disc theory to the rescue. The result is (derive it yourself. It’s easy!)
T is thrust, rho is the density of air, and A is the rotor area.
Here are some curves for 1 kg and 0.5 kg vehicle.
I’ll double these numbers and pick a motor. It looks like a 300 W motor and prop bigger than 8 inches will do the job. Something like this motor
fits the bill nicely. Notice that the motor is rated for 333 W and 3D aircraft up to 2 lbs. That’s consistent with my numbers.