AUtopilot Disconnects

[Donmyoung]

We are having a random problem with the AP74. Some days it works great, then the next flight it will engage for few seconds and disconnect. We have flown with the autopliot for up to 3 hrs straight. The next day it wouldn't stay on for more than a few seconds. We have a disconnect button on the stick in addition to the disconnect on the AP74. Then we have 2 breakers for the servos and AP74. Do you think it might be a grounding issue? Or should I look else where?
Thanks in advance

 

[Dynon]

Are you saying that the autopilot itself actually disconnects? Or does the AP74 just fail to control it (the AP74 itself is actually just a set of buttons and lights).

If the former, I'd chase the disconnect switch and its wiring. If the latter, what are you seeing on the lights on the AP74 when it can't control the autopilot? Is the backlighting on or off? Does the EFIS give you any error messages?

 

[Donmyoung]

When I push the button on the AP74 to engage the autopilot, the light comes on the AP74 and the Efis shows the autopilot engaged. After a few seconds, the light on the AP74 goes off, and the efis shows "offff". It just will not say engaged. The next time I fly it may work perfectly.

 

[Dynon]

Can you press the AP74 AP button to re-engage it right away, or does the AP74 stop responding to button presses entirely. Or, can you change the armed modes (get HDG/ALT/TRK to light up) but not engage the AP again when it turns off?

If there are no error messages being generated by the EFIS, this sounds like a disconnect switch that's getting grounded ("pressed") when you don't think it is.

 

[jakej]

Is it possible you have an NC (normally closed) as opposed to an NO one ? Just thinking ......

I had that happen once, someone 'borrowed' a ptt switch & accidentally replaced it with an NC version :

Jake J

 

[Donmyoung]

As the autopilot has worked for as much as 2 1/2 straight, I don't think it is the wrong switch. However, it could be a ground issue.

Also, when I flew the other day, I could press the AP74 button to reengage, and it would engage for just a second or two. I could change the armed modes and they all light up when pressed, as they should for pre-arming.

My partner in the plane flew yesterday. See his comments below.



On the trip down, once established in a cruise climb and relatively on course, I engaged the AP. It held the GPS course and, per its programming, climbed to the desired 5500 foot altitude where it dutifully leveled off. Without any input from me and without any reason that I can gather, a little over an hour into the flight it shut off and refused to come back on for more than a second or two.



On the return flight, it refused to work at all. In fact, it quit working altogether. By that, I mean that when I was relatively stable and on course and at a constant altitude, I attempted to engage the AP in HDG, TRK and NAV mode and it would stay “on” for no more than a second or two and then disengage.



Several times, after it disengaged and I tried to power it “on” again, I got a funny screen. See Image2 attached. Look at the bottom left of the screen. As you can see, the AP is “OFF/OFF” As that is the case, there should NOT be anything appearing at the bottom right of the screen, but you can clearly see “305/4480FT” This portion of the screen should only display this information when the autopilot is ENGAGED.



During several tried of turning the thing back ON after it simply switched itself OFF, I got an error message on the EFIS screen which said something like “Autopilot Error”. And then, regardless of what buttons I pushed or however many times I attempted to reset the AP74 unit, all I got was what you see in image1, “ERR/ERR.” Interestingly enough, when I pulled the breaker for the AP74, the D180 gave me a bus error telling me that the AP74 was not online. So, the EFIS sees the AP 74 and apparently sees the servos but still shows ERR/ERR.



Houston, we have a problem. I don’t know if it is in the AP74, a Servo, the Efis itself, or what…….

 

[Dynon]

So given what you're describing, it sounds like something is causing the servos to disconnect, which is more likely to be in the servo or its disconnect wiring than the AP74 itself, given what you're experiencing. You'd see ERR/ERR is if the servos have either the lost power going to them, have become disconnected from the DSAB, or if there's something wrong with one or more servos. So those are a few places to look. One thing you could try is to physically disconnect one servo at a time to see if you could isolate it that way. Also try removing the AP74 from the system electrically too - you can still control the AP via EFIS. Essentially, narrow down where the problem is coming from device-wise, and then figure out what the issue with the device is.

 

[ploucandco]

What about an intermittent CWS/disconnect button?

 

[Dynon]

It's not impossible, but that doesn't describe the error condition that you're seeing on the servos. That's more indicative of them not being there at all, either on power or DSAB.

 

[Kregster]

I have experienced the same thing. Just started happening with no reason at all.... Did this ever get resolved?

 

[Donmyoung]

Update: we haven't been flying much due to weather. We went back and did the setup all over again, from scratch. Seems to be working much better. Still get the occasional disconnect, but have logged a couple of 2 1/2 hour flights with no problems or just one or two random disconnects.

So, don't really have a clue what caused the issue, or why we are still getting the occasional disconnects. However, it is usable at this point.