Autopilot "Wallowing"

[jaustinmd]

I have the XTreme mini-EFIS driving the MGL servos for bank and pitch. Both in the "bugs" and "wpt" modes, my Zenith 750 STOL "wallows" or in other words, rolls left for a few seconds and then rolls right. It tracks the heading OK, but this "wallowing" is uncomfortable! It also holds altitude quite well. The Zenith STOL 750 is a high wing plane and is very stable hands-off and I also try to trim up the plane well before engaging the autopilot. The bank servo is quite rigidly mounted so I don't think there's a problem there or with the linkage.

I've tried about every combination of torque, response, and magnitude but nothing seems to help. Could this be a function of the slow speed of the plane? Since it is a STOL, it only cruises at about 82 kts. I once had a Cessna 206 with the factory-installed autopilot and it would "wallow" also at speeds less than 100 kts (it cruised at 142 kts).

John
N750A

[krhea]

Mt RV7 does the same thing. I had an Enigma at first and i only used the autopilot once but it was rock steady. I upgraded to the IEFIS and have done everything imaginable: Including: Changing the shape of the aileron trailing edges, replacing all standard hardware in the aileron and elevator controls to precision, double,triple checked the Set screws on the servos ( Grub screws). Moved the AHRS around and remounted about 4 different times, reset AHRS Several times with longerons "0.0°", recalibrated the Compass several times. About ready to buy Garmin or Dynon. software is latest too. Another person over in Colorado RWarre with an RV7 has the same or similar issue.


Keith Rhea
RV7, +600 hrs

[John H]

I have a RV9 with the older Odyssey and full AP. After takeoff and trim for cruise, the AP is absolutely rock solid and stable. Can fly totally hands off. I do believe if I had a servo on the throttle and engage a intercept for my destination runway the Rv just might land by the AP. IMHO as good as if not better than a Trutraack AP.

[rainier]

The AP will not use the compass except in the case where the GPS is not working. With compass heading it is less stable due to lag but still tracks well (just cannot correct as quickly as when flying on GPS).
Does this happen in dead calm air ? If yes how does it behave in turbulence ? I can tweak it is a bit if needed, but have to be careful with that - it tends to fly a wide range of aircraft very well and its extremely easy to much that up.

It's also not too concerned about your AHRS - it is not too interested in your attitude, rather just in attitude changes...

[rwarre]

I still am fighting a pitch issue. Sometimes the ap pitch will hold for a long period while other times it will porpoise going up 500 fpm and down the same amount or more. So the altitude hold does not work as expected. The bank isn’t an issue and works fine.

[Piterval]

Hola a todos, yo tuve ese mismo problema que comentan todos y encontré el problema en el montaje de los sensores sp6 sp7. Los había colocado sobre una superficie de aluminio demasiado blanda y tenía vibraciones, por consiguiente el horizonte y el compás no eran estables ,entonces el autopilot copiaba todo lo que hacía la pantalla.Hice un montaje más sólido y todo cambió para bien. También puse unas esponjas a las salidas de los conectores ya que las plaquetas al parecer vienen como sueltas adentro de las cajas, no se cual será la razón de eso. Yo lo he solucionado de esa manera y me funcionó bien. Lugo de que logre hacer funcionar todo se me rompió el maldito servo de banco, ya hace más de 2 meses que estoy esperando que me lo lleven por la garantía ya que estoy en Argentina. Todavía no puedo creer que se haya partido un engranaje de plástico y un pasador de acero que tiene adentro. Lo peor es que solo tiene 2 horas de uso. Realmente deberían tener un mejor control de calidad. Saludos.

[sparxfly]

I still am fighting a pitch issue. Sometimes the ap pitch will hold for a long period while other times it will porpoise going up 500 fpm and down the same amount or more. So the altitude hold does not work as expected. The bank isn’t an issue and works fine.

I had a similar problem with one installation- pitch control would be fine for a while, then go haywire with major excursions and overshoots of the flight director/AP.
In that case the problem was a slightly loose grub screw that locks the collar to the servo shaft.
The shaft has a flat machined on it for the grub screw to lock- but it only requires some slight looseness of the grub screw for the collar to rock on the shaft.
If the trim was such that the pitch servo was holding some correcting force, alt hold would work as the grub screw was up against the 'rock' limits on the shaft flat.
Nicely trimmed out and the pitch control was loose as a goose.

Fixed it with some shaft/thread locker and seriously tight grub screw, but I would prefer the shaft to have a drilled indent for the grub screw to engage in rather than a flat. Much more positive locking.

[krhea]

Hola a todos, yo tuve ese mismo problema que comentan todos y encontré el problema en el montaje de los sensores sp6 sp7. Los había colocado sobre una superficie de aluminio demasiado blanda y tenía vibraciones, por consiguiente el horizonte y el compás no eran estables ,entonces el autopilot copiaba todo lo que hacía la pantalla.Hice un montaje más sólido y todo cambió para bien. También puse unas esponjas a las salidas de los conectores ya que las plaquetas al parecer vienen como sueltas adentro de las cajas, no se cual será la razón de eso. Yo lo he solucionado de esa manera y me funcionó bien. Lugo de que logre hacer funcionar todo se me rompió el maldito servo de banco, ya hace más de 2 meses que estoy esperando que me lo lleven por la garantía ya que estoy en Argentina. Todavía no puedo creer que se haya partido un engranaje de plástico y un pasador de acero que tiene adentro. Lo peor es que solo tiene 2 horas de uso. Realmente deberían tener un mejor control de calidad. Saludos.

Hello everyone, I had the same problem that everyone comments and I found the problem in the mounting of the sp6 sp7 sensors. I had placed them on an aluminum surface that was too soft and had vibrations, therefore the horizon and the compass were not stable, so the autopilot copied everything that the screen did, I made a more solid mount and everything changed for the better. I also put some sponges at the connector exits since the platelets seem to come loose inside the boxes, I don't know what the reason for that will be. I have solved it that way and it worked well for me. After I managed to make everything work, my damn bench servo broke, I have been waiting for more than 2 months for them to take it to me for the guarantee since I am in Argentina. I still can't believe a plastic gear and a steel pin inside it broke. The worst thing is that it only has 2 hours of use. They really should have better quality control. Greetings.