My Actuator Drifts or Won't Hold Its Position — What Should I Do?
Linear actuators should hold their position when power is removed, provided the load is within spec. If yours drifts, creeps, or slowly retracts under load, here are the most likely causes and solutions.
Backdriving: The Most Common Cause
Backdriving occurs when the load force on a stopped actuator is strong enough to push the lead screw backward, causing the rod to move without motor power. Most PA actuators use a self-locking lead screw that physically prevents backdriving under rated static load. Drift almost always means one of:
- Load exceeds static load rating— The static rating is the maximum weight the actuator can hold stationary. Overloading this causes screw creep.
- Wrong actuator type— High-speed actuators (like the PA-15) trade self-locking for speed. If you need the load to hold, select a standard-speed model with a confirmed self-locking screw.
- Damaged lead screw or nut— Worn internal threads from overloading can reduce the screw's locking force.
- Relay or switch leakage— In rare cases, a faulty relay with small leakage current can cause slow creep. Test by physically disconnecting power wires from the actuator — if drift stops, the control circuit is the cause.
How to Fix or Prevent Drift
1. Verify load against static rating
Check the actuator datasheet — compare your actual load to the listed static load rating (not dynamic). Static ratings are typically 1.5–2× the dynamic rating. If you're exceeding it, upgrade to a higher-rated model.
2. Confirm screw type
Check your actuator's datasheet for "back-drivable" or "self-locking" note. Acme lead screws are typically self-locking; ball screws are back-drivable. If your application requires static holding, ensure you have a self-locking screw type.
3. Add a holding brake (if needed)
For dynamic loads that require absolute position holding (e.g., vertical lifts with passengers), add an external motor brake relay that mechanically locks the motor shaft when power is removed.
⚠️ Do not use a drifting actuator for safety-critical holds If an actuator is drifting even within its rated load range, it may indicate internal damage. Contact PA Support — a unit drifting under rated static load is potentially covered by warranty.