Constant Torque Spring Mechanism Explained

A constant torque spring is a special type of flat spiral spring designed to deliver nearly uniform torque throughout its rotation. Unlike ordinary springs that get harder to pull the more you extend them, a constant torque spring maintains almost the same rotational force from start to finish.

How the Constant Torque Spring Mechanism Works

A constant torque spring is mounted between two spools:

  1. Storage Spool (inner drum): The spring is naturally coiled here when at rest.
  2. Output Spool (outer drum): The spring’s outer end is attached in the opposite direction.

When the output spool rotates, it winds the spring backward, forcing it to wrap tightly onto the output spool. As soon as the external force is removed, the spring begins to unwind smoothly, pulling torque from the output spool back toward the storage spool.

Because of the spring’s geometry and material properties, the torque it generates remain almost constant, rather than increasing sharply as the spring tightens.

This makes constant torque springs ideal for mechanisms that need steady, predictable rotational motion rather than rising resistance.

Note: Constant Torque Spring vs. Constant Force Spring Mechanisms

Note: Constant Torque Spring vs. Constant Force Spring Mechanisms

  • Constant force springs provide steady linear pulling force.
  • Constant torque springs provide steady rotational torque.

Both use the same basic winding principles, but the motion they create and their applications are different.

Where Constant Torque Springs Are Used

Constant torque springs support are widely used in devices that require steady, controlled rotary movement:

  • Automatic Cable Retraction

Ensures smooth rewinding in vacuum cleaners, badge reels, power cords, and cable organizers.

  • Counterbalance Mechanisms

Helps offset gravity in display panels, medical equipment, adjustable arms, or lids that need smooth lifting and stable positioning.

  • Mechanical Power Sources

Provides rotational energy for small motors, timers, instruments, or systems requiring repeatable, uniform torque.

Advantages of Constant Torque Springs

  • Stable, Consistent Output

Delivers nearly uniform torque throughout the rotation, unlike conventional springs, where tension increases with deformation.

  • Counterbalances Gravity Effectively

Helps create controlled, effortless lifting or lowering in devices that need balance or assisted movement.

Partner with Teng Yao for Constant Torque Spring Solutions

Constant torque springs can greatly improve the smoothness, safety, and reliability of rotary mechanisms. Teng Yao specializes in flat spiral springs engineered for stable performance and long service life.

If you need customized torque values, compact spool designs, or material options, our team can help. Contact us to develop a spring solution tailored to your product’s needs.