[bluescrn]

The electric motors used can change the speed of 4+ independent propellers extremely quickly.

This is hard to do with petrol engines, without costing a lot of extra weight or mechanical complexity, in a system where any single failure means a crash

[scotty79]

I wonder if there's some simple variable transmission that could be electronically controlled to deliver power from the motor to the propellers in highly controlled fashion.

[ahartmetz]

A generator and four motors. Efficiency would probably be around 70%. It's about 90% in diesel-electric locomotives where more weight and money is spent on efficient conversion hardware.

[scotty79]

That adds weight of 4 beefy electric motors to the system.

There's differential based continous variable transmission that varies according to resistive torque on a control shaft: https://makezine.com/2012/08/10/lego-continuously-variable-t...

This might enable electronic control witout using any motors just one simple coil per propeller. Energy generated through this way of control could be stored to power onboard devices.