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DFC90 - Sudden "Autopilot Disconnect" in Cruise

Do you have a pic showing the label on the motor, Alexis?

Administrator
Shoreham EGKA, United Kingdom

Unfortunately not, but will get it from Avionik Straubing, they have a second unit on stock

The state of that motor does suggests that the autopilot computer is going for a walkabout the whole time.

Admittedly the Globe motors are low quality motors, but somehow they got themselves designed into a lot of servos. It could simply be something which nobody else bothered to do e.g. a -65C or -55C lowest ambient temp spec, which almost nobody outside the top-end aerospace business will bother with, even if it isn’t a problem. I have seen loads of instances where a really unsuitable electronic component was used for something, and it turned out that it was the only one whose data sheet had the right temp range.

But DC servo motors should not wear at this rate. Also the soot suggests heavy arcing which is a symptom of being driven back and forth rapidly, and/or being fed with a primitive switching waveform which causes commutator arcing. I would not expect the servo designers to have worried about this or even noticed it, because the brush assembly is enclosed and the brushes can’t be seen.

Administrator
Shoreham EGKA, United Kingdom

Well, that’s interesting from an engineering standpoint. But you know this servo lasted almost 1000 hours …. acceptable to me. We’ll see how long it lasts with the new DFC90 autopilot …

Keep in mind that the servos spent >90% of their life (I assume) being driven by the analog S-TEC autopilot. You can’t really connect the DFC90 to their condition. I had my brand new pitch servo opened after ca. 50h with a brand new S-TEC and there was considerable coal dust in it.

Yes, that was what i thought too, yesterday! Te hplane has 900 h tt and has flwon with the 55 until 820 h!
Well, something else will break, I’m sure :-)

Somehow this sounds as if the S-Tec AP’s are not really a good variant to go with. Only what else to do retrofit.

LSZH(work) LSZF (GA base), Switzerland

S-TEC autopilots are rubbish from an engineering point of view. However, they are most often the only option available and do their job to some degree. If there are other options, I’d certainly avoid S-TEC altogether but is there anything else in the retrofit market? The DFC90 is without doubt the best unit you can get in the retrofit market (the only other good AP, the Garmin GFC700 is not available for retrofit) but unfortunately it can only be applied to a few airframes and as a replacement of S-TEC. Avidyne are working on their own servos and more STCs but you know how fast that goes…

I think it depends…
I have never evaluated the “engineering”, but the S-TEC 30+/GPSS in my Warrior works really very well. It has not failed once in 6 years, it is very precise and does all it should

Very old thread but @Flyer59 did you ever figure out what the root cause for the disconnects was?

EGSX
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