Does Your Servo Need a Brake? Probably Not, Unless This
Most servos don’t need a brake. The motor holds position fine under power. But I’ve seen enough vertical axes drop their load when someone hit the E-stop to know when you actually need one.servo with brake
Here’s the thing people miss: holding torque disappears when power cuts. Standard servo holds a robot arm in place by pushing current through the windings. Breaker trips, cable snags, someone slams the emergency stop — no more current, no more holding. Brake? Gone. Gravity? Still there. Load drops.
A servo with a mechanical brake clamps the shaft with a spring. Power holds the brake open. Lose power, spring slams it shut. Simple. The motor doesn’t fight gravity, the brake does.
Where a brake is mandatory:
Vertical loads. Anything gravity can yank down if power dies. Z-axis lifts, robot shoulder joints, elevator stages. No brake means whatever’s up there is coming down.
Safety valves. Steam line, chemical feed, fuel supply. Power goes out and that valve better fail closed, not slowly drift open because the motor lost holding torque. A brake locks it in the safe position.
ISO 13849 compliance. If a moving part can hurt someone during power loss, a brake is probably on the checklist. Your safety auditor will find it if you don’t.
Where you don’t need one:
Horizontal motion with nothing to drop. AGV steering on a flat warehouse floor stops wherever it stops. Fine. Conveyor slows down and coasts. Fine. Pick-and-place where the gripper retracts on E-stop anyway. Fine. Don’t add a brake you don’t need.
What to check when you do need one: spring-applied, power-off-engaged. Not the other way around. Brake torque rating higher than your worst static load. And ask about engagement time — some brakes lock in 10 ms, some take 50. On a Z-axis holding 50 kilos of tooling, those 40 milliseconds are measurable droop.
Our S9150D and S9750 industrial servos come with spring-applied brake options. Fail-safe isn’t optional on our heavy line.
Not sure if your application needs a brake? Contact XQ-Power and tell us what happens when your power cuts.