Just ran across some old photos of motors I rewound back in the mid 1980's. This motor was from work. The windings were stripped out, and the motor was rewound for more RPM and more current. It eventually got up to about 20 Amperes at full power, on 12 RC2400 Nicad cells. That's about 250 watts. That contact slider on top of this motor was a two position unit, first to open up the folding prop, second was to run at full power. The motor brushes were made from an automotive alternator set, since the original brushes were only good for about two amps.
The gearbox was made with a drill press, and a file. It did get a number of flights on it in a sailplane with about 100 inch wingspan. The power system would get it up to about 300 feet before the batteries went flat. Guess the efficiency of the setup was not very good.
Like a dumb idiot, when we moved to a new home, that thing got thrown out. Should have kept it as an old memory.
Shortly after that, I picked up one of the Astroflight Cobalt Geared motors that had far more power than the unit I built.
The second photo is a Astroflight 90 with a home made gearbox. This unit ran on 38 RC2400 Nicad cells, and turned a 20X10 wood prop at about 5700 RPM. The circuit board on the side is a home made microcontroller controlled speed control that I built. It's rated at about 40 Amps at 100 Volts DC. That went into a 10 foot wingspan Piper Cub that had three years of flying on it before it was sold.
It's interesting, my Hacker A60-16M turns that same exact propeller at 7300 RPM. That is double the watts, at about 1/2 the total power system weight. And they both had about the same flying time.
So now, when you pick up your cheap powerful 500 watt motor from the Internet, you've got some idea on how some of this stuff started.