system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we use four or more rotors on drones, but only maximum two on regular helicopters? Why are we not making full size quadrocopters?

Is one more efficient for the size than another? More powerful? "We just alyways did it this way"?
gpt
The most difficult part of making a helicopter is transmitting power from the engine to the rotor. For small quadcopters, the rotors are driven directly by electric motors. This works well enough for short flights and small payloads. But battery density is not to a point where an electrically powered full-sized helicopter would be competitive with petroleum powered helicopters. And since internal combustion engines and associated transmissions are quite heavy, it does not make sense to put four of them on a helicopter.