Help needed: Servo buzzing

 Hi all, I'm new to the Arducopter and am having an issue which I have been unable to resolve on my own that I am hoping this community can help with. I'm planning to use the APM2.5 to control a custom vehicle which uses Hitec HS-50 servos (relatively small ones, ~6g). All of my testing has been performed on a bench being powered through the APM power cable, and I've also tried powering my servos through an ESC with the JP1 jumper moved appropriately. In each case I believe I am getting a clean 5Vs. I am able to connect to the APM through the mission planner software and also have been successful modifying the code to send custom MAVLINK messages. I have not connected any RC equipment, only the servos, ESC, and telemetry radio.

 The problem I am having occurs when I try to plug in my servos. I know they are not fried because I can control them using the DemoServo script provided, and I've tried different HS-50s as well. When I plug them in, they make a loud buzzing sound, like the servo is being driven at a very high frequency. Applying a little torque to the servo by hand indicates to me that it is being commanded, but again I believe the servo is being burned out by the way in which it is making noise, and know it is not normal behavior. I've tried writing custom commands in loop(), of the form APM_RC.OutputCh(CH_1,1500) to no avail, the buzzing continues.

 Can anyone make a suggestion as to what I should check? Thank you for your help!

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Replies

  • I'm not a technical expert on the APM board circuitry, but from my experience of various autopilot and microprocessor-based products, they're not cut out to power servos directly. The main problem is that servo load can change dramatically and hence the current draw on the board will spike at this time. This is a recipe for a burn out, or at best a brown out.

    On my rovers I use an H-bridge based servo/encoder IO board with a separated power rail (5V/3.3V out so I can power a microprocessor board off it). There are plenty of off-the-shelf boards out there; I'm sure you could find one for your purposes.

  • T3
    Where do you have them plugged in? Also did you configured your APM to control your servos? If you did you may have an issue that the APM is not level and it's trying to move the servo to get it leveled. Just guessing? Be warned about how you power your servos. If it comes from APM you might get a brownout on the APM. The APM can't power to much stuff and servos take a lot of APMs.
  • Servos under load will buzz. Digital servos buzz - sometime loud - even under no load. But since HS-50 are analog, I guess they're under some load. Or I miss something.

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