Pulling the car backward (hence the name) winds up an internal coil spring. When released, the car is propelled forward by the spring. Once the spring has unwound and the car is moving, the motor is disengaged by a clutch or ratchet and the car then rolls freely onward.
Most of these cars are otherwise free-rolling. Winding them up requires them to be pushed downwards, engaging the clutch. As the motor is only engaged for winding whilst held down, the complete winding must be completed in one pass, unlike the flywheel motor. A few motors have an internal one-way clutch that allows winding with a back-and-forth motion.
Some pullback motors, usually intended for racing in pairs, have used a catch and release mechanism to retain their springs. These may be wound separately, then launched together by releasing their spring triggers. Darda use such a mechanism for their Stop'n'Go motor. This is pre-wound, then releases automatically when shunted from behind. This allows relay races to be set up with multiple cars.
The very simplest of these motors may use a stretched rubber band as a linear spring, rather than a coil spring. These are bulky and less powerful but require little manufacturing sophistication: coil springs, although apparently simple, demand a highly developed steel metallurgy. For this reason these toys are usually home- or crafts-made.
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