Help! I need a Century III autopilot servo.

[mschmuff]

Does anyone know where I can get a roll servo rebuilt? Or a new one for an M20F.

[jetdriven]

Autopilots Central in Tulsa OK

[John Pleisse]

Call Todd at LNS Avionics. They have all things Century. They make no apologies for price, just fyi. They are close by.

[N201MKTurbo]

The little hanger faries went through mine and it has worked perfect ever sense.

[N201MKTurbo]

Why do you think you need a new servo?

 

Do you have access to a 0-10 DC regulated powersupply? The best way to evaluate the serve is to measure the minimum voltage where it starts moving, in both directions. The rule of thumb is it needs to move at less then 5V. After the hanger faries got done with mine it moves at 0.5 volts. They had to polish the commutator and brushes to a mirror finish to get it that low.

[jetdriven]

Century specs are startup voltage less than 2V.  It if takes more than that to get the motor moving (clutch not applied), then it needs attention.

FWIW it takes a grand to overhaul the servo. If your brushes are bad and you keep running it, it takes more.  The downside, the shops  never met a servo that didnt need overhauled.

[N201MKTurbo]

I haven't looked at a lot of these, but it is hard to imagine the brushes getting warn out. Mine had 4000 hours on it as far as I know, I could check the logs again to see if it was ever overhauled, but the brushes are massive for such a small motor and mine looked like new. Maybe they prefer to replace them instead of polishing them if the surface gets rough. If I were selling brushes, I would write the service instructions to mandate replacement.

 

The motor has a four stage planetary reduction drive that must have a gear ratio of about 1000:1 and it has huge strong gears for such a small motor. The problem is that after 30 years or so the grease dries out. Cleaning and re-greasing got it to 2V, polishing the commutator and brushes got it to 0.5V. There are four ways to assemble this motor two of the ways make it go the wrong direction and one of the ways that it goes the correct direction is not to print. And the parts have no markings as to orientation. If you are not familiar with small motor design and construction I would leave this to the professionals. If you put it back together with it turning the wrong direction and put it back into your plane, your plane will try to do a barrel roll when you turn on the autopilot.

[mschmuff]

Update - went to West Aero?? At W29 - Bay Bridge,MD.  They charged me $270 to diagnose the issue - "Bad Servo" needs to be rebuilt.  $1600.  "And it will take us about 5 hours to remove and 5 hours to reinstall"! So for almost $3000 they can get me back in the air.

I thought that sounded insane so I picked my plane back up paid the $270 and took it back to my mechanic.  I called Bevan-Rabel in KS and they said they would take a look at it.  I had my mechanic remove it (45 minutes).  Bev-Rab rebuilt it for $635 and my mechanic reinstalled in 1.25 hours. So for $1,000 I'm back in the air and it is working the best / smoothest it has ever worked!

Huge shout out to Bevan - Rabel for saving me $2000!!!

[carusoam]

Doing you own leg work for $2k in savings sounds pretty good!

Best regards,

-a-

[Alan Fox]

I haven't looked at a lot of these, but it is hard to imagine the brushes getting warn out. Mine had 4000 hours on it as far as I know, I could check the logs again to see if it was ever overhauled, but the brushes are massive for such a small motor and mine looked like new. Maybe they prefer to replace them instead of polishing them if the surface gets rough. If I were selling brushes, I would write the service instructions to mandate replacement.

 

The motor has a four stage planetary reduction drive that must have a gear ratio of about 1000:1 and it has huge strong gears for such a small motor. The problem is that after 30 years or so the grease dries out. Cleaning and re-greasing got it to 2V, polishing the commutator and brushes got it to 0.5V. There are four ways to assemble this motor two of the ways make it go the wrong direction and one of the ways that it goes the correct direction is not to print. And the parts have no markings as to orientation. If you are not familiar with small motor design and construction I would leave this to the professionals. If you put it back together with it turning the wrong direction and put it back into your plane, your plane will try to do a barrel roll when you turn on the autopilot.

Did you learn this from experience!!!!

[N201MKTurbo]

Did you learn this from experience!!!!

 

I tested it on the ground before I flew it. All you have to do is turn the roll knob, if the yoke goes the wrong way you did it wrong.