MGL Avionics User Forum

Hello, I have just spent two months on site to install an autopilot on my plane and I’m turning crazy. I have a servo that makes an abnormal noise and does not move. I swapped this one side roll to pitch and the problem moved to the other side. So I think that's a servo problem. The importer checked this one and told me that it works normally… I can’t share a video (because it’s .mov) but we can see that during the test phase roll side servo does not move unlike the other side (pitch). What do you think ?

Here is the video (servo placed roll side)

https://we.tl/t-UWy7UBS5j1

This will be almost certainly because the servo arm position moves 'through zero'. It's a top secret problem and is deliberately set to keep you guessing, that's why it's not mentioned in any of the books. The old forum had some information on it but that was useful (like the screen designing thread), so is no longer available. Me, cynical about MGL documentation; surely not!

It's been quite some time since I set mine up, so my memory is going to be a bit shaky. If you go into the servo test screen you should see, at the bottom, some numbers that represent the position of the servo arm (presumably across the CAN bus). I can almost guarantee that when your stick is moved from one side to the other that the number goes through zero. What you need to do is ensure that the number stays above zero so, for instance (with totally made up numbers) at full left the number says 643 and full right it says 2120. The best thing to do is disconnect the rod from your servo arm and remove the limit screws, so the servo arm can rotate through 360 degrees. Then turn the arm one way, so the arm is now pointing up i.e. stick central. Move the arm one way and then the other and check the numbers stay above zero. If it doesn't then move the arm the other way until it does. This is simple to do and should only take a minute or so. Reattach the rod to the servo arm and do and servo set up and test. Reinstall limit screw etc.

An alternative is to remove the grub screw, take off the servo arm and turn the servo spindle to achieve the same as above. Make sure you remember to reinstall the grub screw.

There may well be better ways of doing it but that should work.

This message will self destruct after 2.3 hours to ensure the 'Zero Mystery' remains a secret.

PaulSS is correct.
I recently set my servo back for a firmware upgrade and during the servo setup screen on my Discovery I watched the servo position numbers as it proceeded thru it's range of motion and passed zero I also remembered the old posts and corrected it.

Glenn

Thank you for your reply. From what I remember from the setting, the values ​​were above zero. In addition I changed position of the servo (pitch to roll) and the arm is turned 90° with always the same problem. I'll check again tomorrow though.

Hello,
I checked today and the values are between 3000 and 3700 so it doesn’t move throught zero, it’s another issue…
The arm does not move at all

Is the spindle able to move if you remove the rod? Could the grub screw have come out so the spindle is moving and the arm is not? What LED indications are you getting?

Led is flashing red.
I have twice sent the servo back to the importer who does not want to replace it, and gives no explanation or solution. I am desperate I equipped all my plane in MGL and the highlight was the autopilot and now I can not do anything. All arm attachments are normal
Here is a link to a video. The servo pick up the position and does’t not go through zero, but doesn’t move… what can I do ?
https://we.tl/t-6wIoywymtJ

Problem finaly fixed. Defective product repaired internally by the importer. Great!