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 Post subject: autopilot servo question
PostPosted: 27 Aug 2010, 10:19 
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Location: KFOK Westhampton, NY
Aircraft: 1978 V35B
I had someone tell me that the servos in my KFC200 system are not rebuildable/able to be overhauled, etc. Anyone know if this is so?


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 Post subject: Re: autopilot servo question
PostPosted: 27 Aug 2010, 10:42 
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Company: Emergency Medicine
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No, Mine have been OH, I need to get my Pitch trim servo worked on again, Autopilts Central did the work in Tulsa OK.....

Jay

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 Post subject: Re: autopilot servo question
PostPosted: 27 Aug 2010, 11:02 
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Username Protected wrote:
I had someone tell me that the servos in my KFC200 system are not rebuildable/able to be overhauled, etc. Anyone know if this is so?


Jim

We work on them all the time.

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 Post subject: Re: autopilot servo question
PostPosted: 27 Aug 2010, 20:23 
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Username Protected wrote:
I had someone tell me that the servos in my KFC200 system are not rebuildable/able to be overhauled, etc. Anyone know if this is so?


I have this directly from the Kansas City FSDO. Technically they cannot be OH as there is no OH manual published. They however can be "cleaned". My avionics shop "cleans" them the exact same way that they used to OH them.


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 Post subject: Re: autopilot servo question
PostPosted: 27 Aug 2010, 22:22 
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They can be repaired and issued an 8130 tag to reflect such repairs.

And when we are writing our work orders, we are never to use the term "overhauled" or "rebuilt."


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 Post subject: Re: autopilot servo question
PostPosted: 28 Aug 2010, 20:21 
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Jim: I had some servo problems the end of last year and there was a point where some avionics shops (I was traveling when it happened), had difficulty getting replacement servos under warranty. That may be what you're hearing. My home shop, Flite Electronics, didn't have that issue.

I had some voltage spiking they couldn't find the source of and went through three sets of servos in about 9 months. They traced all power to the servo, scoped it and did bench tests. Bill Hale on Beechlist helped us find a solution if that's what you're running into.

Best,

Dave

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 Post subject: Re: autopilot servo question
PostPosted: 29 Aug 2010, 11:38 
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Company: Emergency Medical Associates
Location: Huntsville, Al KMDQ
Aircraft: F33A
The guy I bought my plane from said he had the servos cleaned on my KFC 150 . I was wondering about this. Can someone tell me exactly what they do. Are they opened up and "dusted off, oiled?"
Is this something that should be done every 500 or 1,000 hours?
Russ


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 Post subject: Re: autopilot servo question
PostPosted: 29 Aug 2010, 17:10 
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Are the KFC200 servos the same ones as the KFC225 i.e. KS270C, KS271C and KS272C?

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 Post subject: Re: autopilot servo question
PostPosted: 29 Aug 2010, 17:24 
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Dash numbers or flavor numbers vary from airframe to airframe for things that vary like full drive rpm.


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 Post subject: Re: autopilot servo question
PostPosted: 29 Aug 2010, 22:10 
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Username Protected wrote:
The guy I bought my plane from said he had the servos cleaned on my KFC 150 . I was wondering about this. Can someone tell me exactly what they do. Are they opened up and "dusted off, oiled?"
Is this something that should be done every 500 or 1,000 hours?
Russ


I think having your avionics shop do a check of the servos every 1000 hrs would be reasonable. Maybe 500 if you fly a lot of IFR and tend to rely on your autopilot. My 1991 A36 has a little over 3000 total hours on it. I think the KFC 200 was put in about 2500 hrs ago. I had my avionics shop "clean" all of the servos and a do a bunch of other things with the autopilot etc.... I told them that I wanted it working like new. Spent about $3000. They told me that the servos were in serous need of maintenance.


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 Post subject: Re: autopilot servo question
PostPosted: 29 Aug 2010, 22:49 
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Company: Clayborn Lab
Location: Truckee Ca
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I have had an S-TEC 50 in my baron for 24 years. The servos began to act up 12 years ago. I have experience with with armature based rotating components. I was told that my model servo was no longer re-buildable. I thought I would give them a go prior to spending $4K. The motor was full of brush dust and no new brushes available. I serviced the commutator (emery clean-up), cleared the mica insulation between the bars. I got the tec specs from the factory and one of the servos would not meet the first motion voltage threshold. I found another servo on E-BAY and after the clean-up it did meet the spec. They still work to this day. If a shop is willing to "clean and restore" I would give it a try.


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 Post subject: Re: autopilot servo question
PostPosted: 29 Aug 2010, 23:27 
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There are 2 models of servo; one is a "dash" version of the other. There were problems in th earlier ones where power would get applied to both directions at the same time and fry the power transistors that switch the current off and on to the motor. The newer versions correct that issue. And no, the older servos can't be upgraded.

Lancaster Avionics, Lancaster PA does a really good job with the KFC 200.

Lorne


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 Post subject: Re: autopilot servo question
PostPosted: 30 Aug 2010, 08:54 
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What does cleaning mean?

That depends. Okay, enough of being a smart @$$. Something that happens with autopilot servos is that over time they get dirty, but not in the way you would think. Tarnish, or carbon, or whatever causes high resistance between contacting points on motors and resolvers and whatever else may move and flow current is the problem.

Good shops or Autopilot guys will check for breakout voltage or force on the motors and resolvers. For an example of what I'm taking about here is a description and possible causes. Again, there are several such causes and effects that all require "Cleaning" in their own way.

So what is breakout force as I'm describing it? Simply, the voltage or force that is applied to the motor to make it overcome forces holding it still so that it will begin to run. This goes with resolvers or motorized pots also used in some of the airline equip. such as cabin pressure. So as the brushes get worn or have buildup, or maybe an armature, you get the idea, it takes more voltage to get a movement to happen. As soon as the dumb thing starts to move it takes much less voltage to sustain it and the motor overshoots it's intended goal or it moves radically giving a rough ride or porpoise if in the altitude axis. Hardened grease in gears or on shafts cause mechanical resistance and shows up in the winter months or during high altitude flights. This is a no kidding statement. I have seen hundreds of problems similar to this fixed by putting iso. alchohol, or some other solvent to loosen up old grease and then doing nothing else. This is true in autopilot servos, mechanical counter gear assy's, even in airliners such as mode control panels, cabin pressure selector panels, and on and on. So by cleaning you are removing high resistance electrical connections that would cause an overvoltage to make movement happen, or old grease or debries that would make a mechanical resistance to to movement. Any combination of this will cause you problems. As an example, I'm only talking about 20 or 30 millivolts difference in the breakout voltage to cause problems. It doesn't take much.


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 Post subject: Re: autopilot servo question
PostPosted: 30 Aug 2010, 09:36 
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Bryan Wood...thanks for the post. Very informative. :cheers:

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 Post subject: Re: autopilot servo question
PostPosted: 30 Aug 2010, 13:48 
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Joined: 07/20/08
Posts: 1365
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Location: KFOK Westhampton, NY
Aircraft: 1978 V35B
Username Protected wrote:
What does cleaning mean?

That depends. Okay, enough of being a smart @$$. Something that happens with autopilot servos is that over time they get dirty, but not in the way you would think. Tarnish, or carbon, or whatever causes high resistance between contacting points on motors and resolvers and whatever else may move and flow current is the problem.

Good shops or Autopilot guys will check for breakout voltage or force on the motors and resolvers. For an example of what I'm taking about here is a description and possible causes. Again, there are several such causes and effects that all require "Cleaning" in their own way.

So what is breakout force as I'm describing it? Simply, the voltage or force that is applied to the motor to make it overcome forces holding it still so that it will begin to run. This goes with resolvers or motorized pots also used in some of the airline equip. such as cabin pressure. So as the brushes get worn or have buildup, or maybe an armature, you get the idea, it takes more voltage to get a movement to happen. As soon as the dumb thing starts to move it takes much less voltage to sustain it and the motor overshoots it's intended goal or it moves radically giving a rough ride or porpoise if in the altitude axis. Hardened grease in gears or on shafts cause mechanical resistance and shows up in the winter months or during high altitude flights. This is a no kidding statement. I have seen hundreds of problems similar to this fixed by putting iso. alchohol, or some other solvent to loosen up old grease and then doing nothing else. This is true in autopilot servos, mechanical counter gear assy's, even in airliners such as mode control panels, cabin pressure selector panels, and on and on. So by cleaning you are removing high resistance electrical connections that would cause an overvoltage to make movement happen, or old grease or debries that would make a mechanical resistance to to movement. Any combination of this will cause you problems. As an example, I'm only talking about 20 or 30 millivolts difference in the breakout voltage to cause problems. It doesn't take much.


Bryan, just so I understand ,a servo is not disassembled, bushingins/wear parts replaced? Is it just "soaked" in a solvent and retuned to service ?


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