A friction motor is a simple mechanism to propel toy cars, trucks, some trains, action figures, and similar toys. The motor consists of a large flywheel which is connected to the drive wheels of the toy via a very low gear ratio, so that the flywheel revolves faster. The flywheel's axis is perpendicular to the direction in which the toy faces and moves. When the toy is pushed forward the drive wheels engage the flywheel. Pushing the car forwards repeatedly spins this flywheel up to speed. When let go, the flywheel drives the car forwards. The flywheel stores the kinetic energy of the initial acceleration and propel the toy after it is released.
As the flywheel, unlike the spring of a pullback motor, is continuously rotating and not held, the motor may be "pumped up" by pushing the car repeatedly forwards. Some used a zip cord pulled from the vehicle body to accelerate the flywheel directly. Another system was the Turbo Tower of Power (TTP) in which air expelled from a hand-operated pump pushed turbine blades on the flywheel's rim.
These toys were especially popular in the 1960s to 1980s.
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