Coasting Stop (Coast)
The form of stopping obtained by turning off all switches in the H-bridge and leaving the motor terminals open. No electrical torque is applied to the motor; the motion is damped only by friction, bearing drag and the load. It has the longest stopping times and the lowest mechanical stress of the options.
In a coasting stop the current path is broken, so no heat is produced on the driver side and no energy flows back into the supply line. Mechanically it is also the gentlest option: gear backlash closes without impact, belts and chains are not tensioned, and a suspended load swings less.
When it is preferred:
- When position is not critical: Fans, mixers, freely rotating mechanisms.
- When the mechanics are delicate: Transmission elements with fine gears or plastic parts that a hard stop would stress.
- With self-locking gearboxes: A worm gearbox already stops the load, so electrical braking is unnecessary.
On the other hand, a coasting stop is not safe with a high-inertia or back-drivable load; the load keeps moving and can even accelerate under gravity. In that case the correct order is to reduce the speed with a ramp first, then apply dynamic braking, and engage a mechanical brake if needed.
Where this term is used: DC Motor Driver Selection Guide