Engine spring

The motor spring or (in clockwork) spring barrel is a spring enabling to store energy when it is tensioned, and to restore it during the trigger. Most of the time it is a metal strip of hardened steel wound on a wheel. The energy returned is transmitted by a set of gears . In some applications, the system is regulated by a rotating vane (air friction attenuates variations in speed) or by an exhaust system .

In general, the spring is reloaded by a knob (the crown of a watch, called crown ) or by a removable key (clocks, toys).


  • current
    • Watches
    • Mechanical pendulums
    • Music Boxes
    • Measuring tape
    • Self-retracting cable reels (eg in vacuum cleaners , chainsaw and lawnmower engines )
  • Ancient
    • Telegraph apparatus (motor for driving the paper web)
    • Toys
    • Turntables
    • Camera


  • If we say “up” a watch to recharge the spring, this comes from the “reassembly” of the weights of a clock. Indeed, prior to the invention of the motor spring, they were weights which actuated the clocks thanks to gravity, and they had to be reassembled when they were at the end of the race.

Advantages / disadvantages

  • The motor-powered device is perfectly autonomous and can operate indefinitely without input using the technology (battery, plug, fuel). On the other hand, it must be reassembled regularly.
  • The restituted energy varies according to the more or less raised state of the spring, which makes it difficult to obtain a regular velocity. A rocket corrected this irregularity on very old watches. At present, the reassemblies are called “automatic”, operating thanks to an oscillating mass.
  • Noise of the transmission or regulation system.
  • Weight / size


  • Invention before 1400.

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