Usually, the traction motor is mounted between the wheel frame and the driven axle. This is called a "nose-suspended traction motor". The problem with this mounting is that some of the motor's weight is on the axle. This causes the track and frame to wear out faster. The "Bi-Polar" electric locomotives built by General Electric for the Milwaukee Road had direct drive motors. The rotating shaft of the motor was also the axle for the wheels. 