Anyone had an S-Tec pitch or roll servo overhauled lately?

[bcg]

My Alt hold has been erratic recently so I ohmed the pitch servo across pins 3-4 and got 60 ohms.  It should be about 4 so I connected it to 12v to deglaze the motor and it ran for a minute or so before just shutting off and now it's ohming open so, I think it's time for an overhaul.  Anyone had this done recently?  How much was it and how long did it take?

[Fly Boomer]

6 minutes ago, bcg said:

My Alt hold has been erratic recently so I ohmed the pitch servo across pins 3-4 and got 60 ohms.  It should be about 4 so I connected it to 12v to deglaze the motor and it ran for a minute or so before just shutting off and now it's ohming open so, I think it's time for an overhaul.  Anyone had this done recently?  How much was it and how long did it take?

I'm not familiar with deglazing a servo, and my initial search didn't turn up anything.  Where can I learn about that?

[bcg]

55 minutes ago, Fly Boomer said:

I'm not familiar with deglazing a servo, and my initial search didn't turn up anything.  Where can I learn about that?

There's a really old newsletter from S-Tec from 1996 that talks about it. Give me an email address and I'll forward it to you.

Edit - I went ahead and uploaded it here.

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STec Newsletter Troubleshooting Oscillations.pdf

[MikeOH]

Are these servos brushed DC?  I suppose the commutator could be 'glazed' but, depending on how many hours, I'd suspect the brushes.

[Rwsavory]

Yes, they are dc motors with brushes.  For overhaul expect about $1500 and 3 weeks. 

[mike_elliott]

Run the motor in both directions for about a minute to clean off the armature and rid yourself of the stiction that causes put h ocillations or wing rocking . 

Those itty bitty motors may cost about $10 ea if they didn't say Stec and need legal coverbutt, and that should have been known and taught prior to first soloing

The Stec doc will have the sub D connector pins you'll need. I think they are 234&7, but I'm old and to lazy to go look at my pigtail I made up back in 2000. In any event, if you put the juice to the wrong sets of pins, it should be no harm, maybe you'll activate the clutch or something

[N201MKTurbo]

You can send the motor to globe motors and they will overhaul the motor for about $150.

[bcg]

Run the motor in both directions for about a minute to clean off the armature and rid yourself of the stiction that causes put h ocillations or wing rocking . 
Those itty bitty motors may cost about $10 ea if they didn't say Stec and need legal coverbutt, and that should have been known and taught prior to first soloing
The Stec doc will have the sub D connector pins you'll need. I think they are 234&7, but I'm old and to lazy to go look at my pigtail I made up back in 2000. In any event, if you put the juice to the wrong sets of pins, it should be no harm, maybe you'll activate the clutch or something

That's what I was doing

It's 1 and 34 for pitch, 33 and 50 for roll.

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[bcg]

You can send the motor to globe motors and they will overhaul the motor for about $150.

Brilliant, I should have thought of that. I'll do exactly that if I can't get it cleaned up and running. Thank you!

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[MikeOH]

28 minutes ago, N201MKTurbo said:

You can send the motor to globe motors and they will overhaul the motor for about $150.

Probably where S-Tec sends 'em

[N201MKTurbo]

A friend brought me his STec trim servo. I disassembled the motor checked the bearings and the brushes and couldn’t find anything wrong. It would barely turn at its rated current with no torque. I told him that the armature was bad. He called Globe to see if he could buy a new armature, they said they didn’t make that model any more, but if he sent the motor in they could rewind his armature. So he sent it in. They returned it in less than a week and it worked perfectly. Repair charge was very reasonable. 

[bcg]

A friend brought me his STec trim servo. I disassembled the motor checked the bearings and the brushes and couldn’t find anything wrong. It would barely turn at its rated current with no torque. I told him that the armature was bad. He called Globe to see if he could buy a new armature, they said they didn’t make that model any more, but if he sent the motor in they could rewind his armature. So he sent it in. They returned it in less than a week and it worked perfectly. Repair charge was very reasonable. 

There's really not all that much to the motor. If it wasn't something for an airplane, a replacement would probably be $30 or so. New brushes would probably solve my problem.

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[N201MKTurbo]

36 minutes ago, bcg said:

There's really not all that much to the motor. If it wasn't something for an airplane, a replacement would probably be $30 or so. New brushes would probably solve my problem.

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The brushes in those motors are massive and all I’ve looked at (2) had a few thousand hours on them and the brushes looked almost new. It’s not the brushes.

[Rwsavory]

OK folks, now I am no expert on autopilots and not a mechanic or Avionics tech. However, when you’re talking about taking apart these servos and tinkering with them, sending them out to various places for DIY repairs, I do know something. And that is that the manufacturer of the autopilot, (and the FAA) would probably look dimly upon that unless you have the training and certs to do it. The risk you run is that you mess things up, send it back to STEC, and they say no way. Now what are you left with? A very expensive door stop.
 

Suck it up and have it done right. You can make up the money you spend by looking for quarters under the FBO sofa cushions.

[bcg]

15 minutes ago, Rwsavory said:

OK folks, now I am no expert on auto pilots and not a mechanic or Avionics tech. However, when you’re talking about taking apart these servos and tinkering with them, sending them out to various places for DIY repairs, I do know something. And that is that the manufacturer of the auto pilot, (and the FAA) would probably look dimly upon that unless you have the training and certs to do it. The risk you run is that you mess things up, send it back to STEC, and they say no way. Now what are you left with? A very expensive door stop.
 

Suck it up and have it done right. You can make up the money you spend by looking for quarters under the FBO sofa cushions.

The reason Globe was suggested is because they're the original manufacturer of the motors.  S-Tec doesn't build those themselves, and likely sends them to Globe for repair as well.  I don't think even the FAA would have a problem with a repair made by the OEM to original specs, as long as the appropriate logbook entries are made and signed off on.

This is kind of a funny conversation in that it only exists because the Mooney is certified.  If the was the Vans forum, I could go down to the local Hardware Store or Radio Shack and buy any motor I wanted to off the shelf and modify it however I needed to make it work.  That simple fact makes me believe that a lot of the FAA rules aren't really about safety.

Honestly, most of the parts in an airplane aren't all that complicated to work on, even the avionics.  I mean seriously, an electric motor is an electric motor, there's not something magic that happens to it when it gets put into an airplane part.  There are a lot of people that could do as good of, or probably even better, work as many A&Ps that aren't allowed to only because they lack a piece of paper.  It would be nice if the FAA had a limited cert to allow an owner to work on their own plane, like Canada does.  I don't expect it to happen anytime soon though.

[Rwsavory]

Yes, I get it. It’s frustrating. Simple parts. Etc. We all know that doesn’t matter. Plus, the manufacturer does not publish its current service data. 

[bcg]

Not that I'm going to do this, nor would I recommend anyone else doing so, but I thought this was really interesting just because I like to know how things work.

 

[N201MKTurbo]

18 hours ago, bcg said:

There's really not all that much to the motor. If it wasn't something for an airplane, a replacement would probably be $30 or so. New brushes would probably solve my problem.

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Those motors are very well made. I have been in the R&D world for about 35 years, with a lot of motion projects. A motor like that probably sells for a couple of hundred bucks.

[N201MKTurbo]

4 hours ago, bcg said:

Not that I'm going to do this, nor would I recommend anyone else doing so, but I thought this was really interesting just because I like to know how things work.

 

The motor in the servo is way better made that that cheap piece of crap. Yes, they work exactly the same, but you are comparing a Timex to a Rolex

[bcg]

The motor in the servo is way better made that that cheap piece of crap. Yes, they work exactly the same, but you are comparing a Timex to a Rolex

I didn't think I was inferring that they were the same quality motor. I just thought it was interesting to understand the internal components and how it functioned. I certainly didn't mean to trigger you so...

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[EricJ]

5 hours ago, N201MKTurbo said:

The motor in the servo is way better made that that cheap piece of crap. Yes, they work exactly the same, but you are comparing a Timex to a Rolex

Kinda fun to see somebody hand re-winding the armature on a $10 hobby motor, though.    

[MikeOH]

3 hours ago, EricJ said:

Kinda fun to see somebody hand re-winding the armature on a $10 hobby motor, though.    

Wow!  And to think I thought I was a CB

[Philthe123]

Great website.  Thanks for all the knowledge and wisdom.  Having some issues with Trim Servo.  Can someone give a contact or link to Globe Motors.  Thanks, Phil T.

[bcg]

Great website.  Thanks for all the knowledge and wisdom.  Having some issues with Trim Servo.  Can someone give a contact or link to Globe Motors.  Thanks, Phil T.

They won't sell you the part, many have tried, all have failed. You can either get a used one off eBay or something or, you can get an authorized dealer to send yours back to S-Tec.

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[Philthe123]

I was actually asking to find out where to send it for a rewind.   Hopefully this is still a possibility.