Q: I've used R/C servos to control my registers/dampers, just as you said, together with controllers that you told me to, but the servos growl even when they don't move!
A: Three causes are possible (ordered by probability):
- Power is insufficient at the register/damper location, wiring is too weak. Run a 16 gauge speaker wire to it, and put a 470μF electrolytic capacitor from ground to power at each servo, this worked for me.
- Register/damper is too tight for the servo you used. Either loosen it up mechanically and lubricate well, or use a higher torque servo.
- Servo is getting old. Old setup I used to run 2001 to 2003 had no problems, but the same servos I used back then growl today, even though they haven't been used for last five years.
A: Control signal is too weak, servo doesn't recognize it as such anymore. Google up a "servo booster" (there are too many around to recommend anything specific) and install it at servo.