View Full Version : Do garmin servos hold when AP is on?

09-11-2020, 02:36 PM
Do the garmin GSA 28 servos hold position when the AP is active? Or do they only energize and move when they are pushing on a control surface?

In other words, would the rudder servo hold my rudder in the middle when activated and straight or would they just remain disconnected until the system commands movement?

The airplane I'm building doesn't have nearly as much yaw stability when your feet aren't on the rudder pedals, so the servo holding the rudder still even when it's not actively moving it would make a significant difference.


09-11-2020, 03:20 PM

The GSA28 'Smart Servos' are brushless DC motors with an internal electronic clutch system. When disengaged there is no control system friction whatsoever and the the control arm on the servo moves freely.

When the GSA28s are engaged, the electronic clutch holds the control arm in a firm, fixed position until movement is commanded. So in your scenario above, the rudder servo would hold in a fixed 'middle' position when energized.

This is a popular YD (Yaw Damp) option on the experimental autopilot. With the YD engaged the GSA28 will keep a positive engagement and counteract any yaw tendencies while in flight. The YD can be activated without the rest of the autopilot system being engaged as well. Servo torque is user-configured so all flight axis servos can be overridden with pilot input - with no shear pins or mechanical linkages to break. The electronic clutches will slip at the specified torque with no damage to the servo.