Autopilot wandering in Trk and Nav mode.

[JohnH]

RV-7 with AP74, D100, EMS D10. Latest 5.4 software works really well on altitude hold. This plane has always wandered around the Hdg, Trk and Nav.

After sorting out issues with the 5.4 upgrade, some test flights revealed a serious wandering or up to 20 degrees either side of the Hdg or Trk. No difference was noted with either Trk or Hdg modes. In itial setup atefr installation took some time tio get these functions working better, so settings of 100% on the torque and 6 on sensitivity seemed to work best but not cure the problem.

After reading the forums etc. as well as carrying out the Dynon service on the servo with the play in the shear bolt, things were slightly more improved, but not cured.

Today while trying it out with sensitivity set as high as 25 no cure could be found at all. I suspect that the original problem of the play in the servo drive shaft and arm are the real culprit here again.

Is there any permanent cure for this without buying a new servo?

 

[dynonsupport]

Turning down the turn rate can improve things for some people, so the AP makes gentler turns. Also, are you getting any servo slipping? That's indicated by the roll axis mode indicator changing to a yellow backlit annunciation.

But alternatively, and maybe try this first: a lot of people find that using the alternate roll mode (described in the latest manual, but details coming up) helps with these issues. To enable it, simply set the turn rate to 0, and make sure bank angle is set to a reasonable value (20-30 degrees, perhaps). When set this way, the AP uses a completely different set of control laws that doesn't use turn rate, instead favoring a method where it uses more bank to correct for larger heading/track corrections.

 

[DBRV10]

Also check these two things, The middle hole is used on the servo arm and that the shear screw has not broken.......

 

[JohnH]

Thanks for the information, I do get servo slippage when the sensitivity is set over 18 or 20. The response to any bank angle is very slow, but I have not tried setting the bank angle to 0 yet. I will do so as soon as I get another opportunity.

I will also check the servo arm, shear bolt and which locating hole on the arm is used.

 

[BigJohn]

Forgive me for suggesting something you have probably already checked. My D180/AP74 wandered a lot but it turned out NOT to be an AP problem. I had incorrectly set up and calibrated the mag compass. See: http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1306854939.