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-   -   Autopilot pulsating (http://www.vansairforce.com/community/showthread.php?t=175789)

togaflyer 10-05-2019 07:47 AM

Autopilot pulsating
 
I have a Garmin set up with the G3X Touch, Garmin servos, and the 307 autopilot control head in my RV 10. I used the recommended setting, that Garmin provides, for the AP configurations. I keep getting a pulsing one per, a small pulsing about a second or two apart on the pitch Servo. I can see the edge of the elevator slightly pulsating. When I press the CWS the pulsating stops, so I know it is coming from the pitch Servo. I checked and everything is tight and secure with the servos. I sent an e-mail to Garmin, but since it is the weekend I figure I would reach out to see if I should change something in the configuration. The AP captures and holds the altitude perfectly. No seeking or wandering issues. Just getting that little continuous pulsating.

BlackhawkSP 10-05-2019 10:26 AM

Quote:

Originally Posted by togaflyer (Post 1378065)
I have a Garmin set up with the G3X Touch, Garmin servos, and the 307 autopilot control head in my RV 10. I used the recommended setting, that Garmin provides, for the AP configurations. I keep getting a pulsing one per, a small pulsing about a second or two apart on the pitch Servo. I can see the edge of the elevator slightly pulsating. When I press the CWS the pulsating stops, so I know it is coming from the pitch Servo. I checked and everything is tight and secure with the servos. I sent an e-mail to Garmin, but since it is the weekend I figure I would reach out to see if I should change something in the configuration. The AP captures and holds the altitude perfectly. No seeking or wandering issues. Just getting that little continuous pulsating.

I would start with lowering the Pitch Servo Gain. Check in the G3X install manual around page 32-73 ish (REV-AA).

M McGraw 10-05-2019 11:42 AM

Check your elevator stiffness
 
I had the same issue with my G3X autopilot. I thought my elevator was smooth and free until I tested a couple other RVs. Your elevator should flow with very very little friction. I adjusted my hinge points and now my autopilot is solid and steady with no pulsating.

togaflyer 10-06-2019 05:41 PM

I checked the flight controls and very smooth with no resistance. I was going back over the configuration section in the install manual. On page 34-89, the section for the fine adjustment amount and fine adjustment time both states "if the installer notices the aircraft doing very small oscillations, the fine adjustment time and fine adjustment amount can be used to correct this" It just doesn't say how, so I sent the Garmin folks all the info. Sounds like I need to change the setting either higher or lower. Thanks for the feedback, got me motivated to research deeper.

scrollF4 10-06-2019 08:31 PM

Check the pitch trim
 
Rich,
Try one more thing. With my Skyview, if I don't have the pitch trim pretty close to center, the autopilot will fight it with a pulse about every 1.5 to 2 seconds. When this happens, I disconnect the autopilot and discover right away the nose trying to drop or rise...I had my pitch trim just far enough out of null for the autopilot to have to nudge against it. I'll trim it out myself, then reengage the autopilot...smooth sailing.

I hope that helps, Sir.

rvator10 10-07-2019 07:53 AM

please let me know what Garmin has to say, my 14A does the same thing.
i have tried to fine tune the trim first with no help. its almost like the servo is bouncing between two positions driving the airplane to go up and then down, the servo steps need more granularity? :confused:

Walt 10-07-2019 08:05 AM

Quote:

Originally Posted by M McGraw (Post 1378100)
I had the same issue with my G3X autopilot. I thought my elevator was smooth and free until I tested a couple other RVs. Your elevator should flow with very very little friction. I adjusted my hinge points and now my autopilot is solid and steady with no pulsating.

I have 'fixed' a few AP's with the above (14 included), if the surface doesn't fee-float it needs to be adjusted. The surface should return on it own to its natural resting place after being deflected.

togaflyer 10-07-2019 06:23 PM

The Garmin folks got back, this is what they sent me:

Why don’t you also try flying in PIT mode with pitch = 0, and VS mode with VS = 0 and see if you feel the pulsing in other than ALT mode.

Lot’s of RV-10s are using the same settings (before you changed them), so it doesn’t seem like it should require a gain change.

They also mentioned it could be an installation issue, yea, that answer is no. But he did say to set the trim to the default of zero, which I will try. Walt, I will also check the response after it is deflected. Good suggestion. Heading to Petit Jean this week so I will get a chance to play with the AP a bit more while en route

Walt 10-07-2019 06:33 PM

Quote:

Originally Posted by togaflyer (Post 1378564)
Walt, I will also check the response after it is deflected. Good suggestion. Heading to Petit Jean this week so I will get a chance to play with the AP a bit more while en route

I'll be at PJ fri-sun also, grab me and I'll take a look, see you there!


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