# Bikes

Nine Continents Hub Motor repair https://www.youtube.com/watch?v=vrUjPNIs348

https://en.wikipedia.org/wiki/Variable-frequency_drive for non permanent magnet motors

Schlumpf geared bottom bracket (Mountain Drive)

"Drag increases by the square of the speed, not the cube. Power required goes by the cube, though...

The power required to overcome the aerodynamic drag is given by:

Pd = Fd.V = 1/2 rho v(cubed) A Cd

Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power."

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