Well, I got to thinking about the Variable Pitch quad problem. I don't really have time to work on a project like this right now but I thought I'd throw this out there in case someone else was interested. A small hydraulic motor and pump could be used using one electric motor to drive all 4-6-8 whatever variable pitch rotors. It would get rid of the gearing for sure and the motors would all be controlled by the bypass valve and all spin at the same speed. The attitude control would then be controlled by variable pitch rotors. Just a crazy thought.
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Would the wieght and mechanical complication of the fluid, lines, actuators, tank and pumps (or pump and servo's) be less than four direct servos ?
You could possibly get away with three servos if you use a swash plate setup, and the movement required for -15º to +15º of pitch would need at least 10mm of smooth and precise movement with very little force.
Can hydraulic motors be efficient enough? I always thought they were pretty bad.