Trutrak servo growls – Normal or Not?

C

Crak

Filing Flight Plan
Joined
Jan 12, 2024
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Eckbert
Hi everyone,

I’m in the process of bench-testing a TruTrak (now BendixKing) autopilot servo and noticed something I’d appreciate some experienced insights on.

When I engage the autopilot and the servo begins to move, it produces a distinct clicking or growling noise — almost like a rhythmic “click-click-click” as it adjusts. Once the servo stops moving, the noise disappears entirely. Functionally, the system seems fine:
  • The servo holds position firmly when engaged.
  • It responds smoothly to both fast and slow pitch/roll changes.
  • Voltage is stable (tested with a Sorensen DLM bench supply), and no unusual heat or vibration is present.
From my research, including Dynon’s test videos and old forum posts, this could be normal behavior for stepper-driven servos, where micro-steps and load changes create audible mechanical noise during operation.

Still, I’d like to confirm:
  • Is this noise considered normal for TruTrak/BK servos?
  • Could it be gear/clutch wear or a sign of a problem?

I’ll be sharing a YouTube video shortly (I need 3 more post to put links) to illustrate exactly what I’m hearing.

Thanks in advance for your insights!
 
Here’s the video he’s referencing

 
Mine does this as well. Unsure if it's normal or not.
 
Hey all,

I sent a video of the noise from my TruTrak servo to BendixKing support, and they confirmed that it's normal behavior. They mentioned the servos are just noisy units and the clicking/growling sound is expected during operation.

I wasn’t expecting an answer, but thought I’d share this for anyone else who might be concerned about similar noise.

Hope this helps!
 
Crak said:
Hey all,

I sent a video of the noise from my TruTrak servo to BendixKing support, and they confirmed that it's normal behavior. They mentioned the servos are just noisy units and the clicking/growling sound is expected during operation.

I wasn’t expecting an answer, but thought I’d share this for anyone else who might be concerned about similar noise.

Hope this helps!
Click to expand...
I appreciate it! Always wondered about it. First time I fired it up in the hangar without the engine running definitely startled me. I assumed it was normal but the affirmation is nice.
 
The Aerocruze 100 autopilot has some pretty hefty servos. We have only installed 1 system, but they seem to be built well and there have been no complaints for the customer.

We have installed multiple STEC systems with complaints nonstop about product performance.
Aerocruze > STEC
 
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