"Just had another thought. Since you are wanting to use collective pitch control instead of just relying on the speed of the different rotors for control of elevation and yaw, why not just add a teeter hinge to control yaw? It would only require 2…"

"fair enough"

"all this talk about using a series hybrid setup; Gas, nitro, diesel ICE combined with an alternator/generator to power electric motors for the rotors. Has anyone thought of using small form factor Hydrogen fuel cells in place of the ICE/genny setup?…"

"You'll also have the ability to autorotate in the, hopefully unlikely, event of a 2 engine failure. Probably won't help much, given the low mass of the props, but it's something."

"Another out of the box option that comes to mind is a horizontal flywheel. Stationary when no yaw adjustment is needed, spin it up to counter-rotate for yaw. With the size of this copter a couple pounds of extra weight shouldn't have a whole lot of…"