- how does the engine generate enough excess torque to turn the props?
To proced the explanation.
If the two pistons do same work,have same friction and underside pumping and the two propellers are equal but mirrored, generators will take no power but Will continiously compare voltage and phase and try to be in step.
If piston masses are the same there will be no mass forces or torques coming out as they cancel.
Problem is the propellers.We can either separate them so far that they do not intefere but it takes mass space etc.When a propeller blade goes into the common zone as shown on picture it will be unloaded that is try to accelerat more than sister prop that has all three blades doing full work.Next moment Sister send one blade into the zone an unloads by accelerating but is running the opposite direction.As said before the first order torque reactions will cancel but the propeller blade number order will not and be unpleasant..The electronic saving can be to take Power from one side and offer to the other three times per engine rev and the we will have turbine smoth power from a single cylinder two stroke even if it misfires s such creatures sometimes do.