EBike Torque Arms
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Torque arms or other torque controll devices are generally required on any hubmotor that has more than a few hundred watts of power. The motor design typicaly has an axle that is larger than the standard 10mm round axle on a bike. The axle then has two flat sides machined into it creating a flat 10mm wide axle.
The flat sides keep the axle from rotating within the bike frame dropouts. At some point, the motor will have enough power to bend steel bike frames dropouts, and crack aluminum frames. Then the wheel may leave the bike, possibly while moving fast.
Torque arms are used to add more strength to the bike frame, so the motor axle will not rotate damaging the frame. Often they are designed primarily for front hubmotors, but some designs fit both front and back, or may be easily adapted. Made of thick metal,they fit tightly on the flat sides of the axle, and have a long "arm" portion that gives it a wrench like leverage. The arm is attached to the frame with bolts or clamps preventing unwanted rotation of the motor axle.
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