Failing Servo

A failing servo may move erratically during flight - this could be a problem with the electronics or (more likely) a broken gear (to protect your servos, consider making the [[servo saver modification]]). When that happens, the chain of events may look like the following:

• During normal movement, the servo suddenly “skips ahead” to a position further than commanded.
• The rapid change in servo position is transmitted to the swashplate, which causes the helicopter to roll.
• The FBL electronics react by moving the other two servos to counteract the uncommanded roll.
• The net effect is as if you changed the collective pitch, since all three servos have moved in the same direction.
• The helicopter moves rapidly up or down, depending on which direction the failing servo jumped.

This might happen during a hover, or it might happen when you’re getting the helicopter light on the skids, so that it suddenly “hops” into the air.

Eventually, if the failing servo gets worse, it will begin to move so far that the FBL can’t compensate, so that the helicopter consistently rolls or pitches in one direction while gaining or losing altitude.

I’ve found that this problem will tend to worsen rapidly - the first time it happens, the heli will jump just a bit, and you’ll be left wondering if you imagined it, or it was a gust of wind. While you’re thinking that through, it will happen again, stronger. If you wait much longer, you will likely lose control - you need to land ASAP and look for the failing servo!