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Norcalrv7
02-14-2018, 01:17 AM
Would anybody be willing to share their gain settings for a grand rapids autopilot setup? I've experimented with mine quite a bit, and can't seem to get rid of a slight oscillation in both pitch and roll. It's almost if the smallest possible movement by the servo is still too much. In my upcoming condition inspection, I'm going to try and change the geometry of the servo arms in order to allow for finer movement.

Or am I being too picky?

Norcalrv7
02-14-2018, 01:47 AM
Just found something in the servo manual that suggests changing the linkage length slightly. It sounds that the stepper motor might be at a "dead area" right around neutral controls

YellowJacket RV9
02-14-2018, 05:54 AM
I'd be interested to see if that helps. I have, occasionally, a very slight roll oscillation in level fight in smooth air, at altitude. I can usually temporarily fix it by hand flying for a minute and then re-engaging the A/P. Lowering my roll gain setting seems to have no effect.

Chris

Isaac
02-14-2018, 10:35 AM
Any chance your GRT AP issue could be related to the problem that GRT fixed with an update to their Adaptive ADAHRS software. A description of the problem (see below) on the GRT autopilot forum appears to be similar to what you are describing.

Two customers reported ?small roll oscillations? or ?loose autopilot performance? recently. An investigation revealed that changes to the AHRS calculations that affected yaw axis appear to be responsible. This may be more likely when certain (normal) magnetometer errors were present. The problem was eventually duplicated in the company test airplane (an RV-6A), which will be used to validate the fix.

A software fix is being pursued that will be made available by February 28, 2017. This fix will be identified on the website. Operation of the autopilot when exhibiting this roll oscillation is not dangerous, but could result in degraded ride quality.

YellowJacket RV9
02-14-2018, 01:58 PM
Any chance your GRT AP issue could be related to the problem that GRT fixed with an update to their Adaptive ADAHRS software. A description of the problem (see below) on the GRT autopilot forum appears to be similar to what you are describing.

Two customers reported ?small roll oscillations? or ?loose autopilot performance? recently. An investigation revealed that changes to the AHRS calculations that affected yaw axis appear to be responsible. This may be more likely when certain (normal) magnetometer errors were present. The problem was eventually duplicated in the company test airplane (an RV-6A), which will be used to validate the fix.

A software fix is being pursued that will be made available by February 28, 2017. This fix will be identified on the website. Operation of the autopilot when exhibiting this roll oscillation is not dangerous, but could result in degraded ride quality.

I have the latest version software, but could be a good thing for the OP to check.

Chris

lr172
02-17-2018, 04:09 PM
I have always thought my GRT AP was too aggressive in it's adjustments and could never get it to be as smooth as I would like fully with gain settings. On a cross country flight, I can watch the nose move as it adjusts. I have always felt that the servo had too course of a resolution, especially in pitch. I have considered changing the throw to see if that would help (I believe it will), but haven't gotten around to pulling the baggage bulkhead to do it.

If I were to venture a guess, the GRT test plane has it's mounting to the elevator bell crank in a non-standard location and therefore providing a less aggressive throw and why they don't see the issue. In the 6, this installation is a builder effort and there is no guidance from Van's on where to put the hole. Only recommendations from the AP providers.

Larry