Autopilot Question

[INA201]

I have a Century 2B that I have never fully gotten to work reliably.  Ive had the amplifier, roll servo, and other components rebuilt by Bevan-Rabell.  Bevan is came highly recommended.  Anyway all was well until a week after the last annual.  I discovered that when engaging the autopilot the roll servo motor just makes a spinning sound while the visible gear on it doesn't move.  Does anyone know if I should just pull the motor and send it off?  Is it possibly an adjustment issue?  Can I have my local IA just pull out the motor and still fly while it is removed?  Any other suggestions would be great.  Has anyone had their Century autopilot working reliably for an extended period? FWIW I have the Gad29B and GTN 750 hooked up to it.  Any SE shop recommendations as well if that should be the course of action.  Thank you guys!  I know GFC 500, but I am not fully funded for that......YET.

[KSMooniac]

I would talk to Bevan again, especially if it hasn't been a long time since they serviced the servo.

Sent from my LG-US996 using Tapatalk

[N201MKTurbo]

Your servo has two circuits. one that runs the motor bidirectionally. The other powers the engagement solenoid. It sounds like your engagement solenoid isn't working. I would suspect wiring and connectors more than your solenoid. It is unlikely to fail.

Have your mechanic disconnect the connector by the servo and put a meter on the wires from the plane. Two of the wires should go to battery voltage when the autopilot is engaged. The other two should go from about -10 to +10 volts depending on where the roll knob is set.

[INA201]

1 hour ago, N201MKTurbo said:

Your servo has two circuits. one that runs the motor bidirectionally. The other powers the engagement solenoid. It sounds like your engagement solenoid isn't working. I would suspect wiring and connectors more than your solenoid. It is unlikely to fail.

Have your mechanic disconnect the connector by the servo and put a meter on the wires from the plane. Two of the wires should go to battery voltage when the autopilot is engaged. The other two should go from about -10 to +10 volts depending on where the roll knob is set.

Sounds like this could be the issue to me. Thank you for the information. 

[Jake@BevanAviation]

If the drive motor is running (pins C and D) the solenoid is on (pins A and B).  A simple voltage check with the servo connector with a multi-meter will show where the issues is.  With the meter on the ship side  pins A and B  (ground) when the roll rocker is pushed up the solenoid should get buss voltage. You can also test the servo with power-supply if needed.  The 4 pin connector are notorious for being intermittent.  If you are still having issues just give me a call and I will help with troubleshooting as much as possible.

[N201MKTurbo]

4 minutes ago, Jake@BevanAviation said:

If the drive motor is running (pins C and D) the solenoid is on (pins A and B).  A simple voltage check with the servo connector with a multi-meter will show where the issues is.  With the meter on the ship side  pins A and B  (ground) when the roll rocker is pushed up the solenoid should get buss voltage. You can also test the servo with power-supply if needed.  The 4 pin connector are notorious for being intermittent.  If you are still having issues just give me a call and I will help with troubleshooting as much as possible.

Thanks for the pinout!

[carusoam]

Great post, Jake!

Best regards,

-a-

[Bob Weber]

1 more for Jake, if you see engage voltage wiggle the connector while the system is engaged and watch for the solenoid to engage. Century Flight Systems has had a bulletin out for the little blue connectors for a long time, they told us about them when I was training there in 1989. My favorite weapon is a 45° snap on pick, slightly flatten one half of the socket to create more tension.

[cliffy]

Nothing better than people here willing to offer suggestions and help. People who REALLY know what they are talking about- 3 cheers!

[INA201]

Just an update. We isolated the issue as the wire that powers the clutch is defective. I still haven’t had time to meet up with the avionics guy to get a new wire run to fully make the repair. 

[INA201]

Got the autopilot operating.  Now on to dialing in the mild oscillating behavior.  I would also like to tighten up the blue connectors.  What is the best trick and tool for tightening these up?  I saw the pic of a "Pick."  Thank you guys for the help.

[jetdriven]

You can replace the split pin female connectors with a solid barrel connector then you don’t have to worry about tightening  it up occasionally

here they are.  Cooper 126 series 

https://www.alliedelec.com/view/search?keyword= Cooper 126

 

Edited October 26, 2019 by jetdriven

[INA201]

7 hours ago, jetdriven said:

You can replace the split pin female connectors with a solid barrel connector then you don’t have to worry about tightening  it up occasionally

Does that require new male connectors as well? Any recommendations or direction for acquiring these connectors?

Thank you for the help. 

[Jake@BevanAviation]

Winchester connectors used to have a machined 4 pin female connector that worked great but I have not been able to locate the connector for some time.  Using a small pick you can push the female split pins back together.  Sometimes this will fix the intermittent issues that are connector related.

[Bob Weber]

13 hours ago, INA201 said:

Got the autopilot operating.  Now on to dialing in the mild oscillating behavior.  I would also like to tighten up the blue connectors.  What is the best trick and tool for tightening these up?  I saw the pic of a "Pick."  Thank you guys for the help.

I can get you the part number of the pick in the pic if you would like. What kind of oscillations are you seeing?

[INA201]

12 minutes ago, Bob Weber said:

I can get you the part number of the pick in the pic if you would like. What kind of oscillations are you seeing?

Sure!  Thanks

In heading mode or GPS mode the plane will slowly turn two or three degrees right and then correct it by turning left overshooting the desired heading and then the process starts over again.  @jetdriven gave me some insight on turning the threshold adjustment screw counterclockwise which has begun too work but I think I was being too conservative.  He said to make a full turn of the screw and watch effectiveness and then another turn as needed until it dials out. Also, it was a 20 turn adjustment pot.  I was only doing 1/4 turns and waiting a minute or so but was slowly seeing improvement.  Any other advice is greatly appreciated.

Is there a way to tighten up the connections to the amplifier or is just cleaning them up the best option there?

Great help on this and thank you!

[Jake@BevanAviation]

So the best way to adjust the roll threshold is to max out the pot until it produces a slight roll oscillation and then back it off until the oscillation stops. There is a product that Bob has suggested to me and I have started using that works wonders with connector pin issues.  Stabilant 22, you can find it online.  I have been using it for about a year and had great results.

[INA201]

I looked up Stabilant 22 and a lot of audiophiles seem to use it as well.  So just paint it on and plug it all back up? Thanks for more insight.  

[Bob Weber]

SG3ASH45B Snap On part number for the probe. Stabilant 22 by all means on the connections. A health check of the servo motor should be done as well.

Give a call if you would like, visit WebairConsulting.com then call 616 822 1999

Edited October 25, 2019 by Bob Weber

[INA201]

Just wanted to put a link for the Stabilant 22 on this thread .  "Parts Drop" is a listed supplier on Stabilant's website and looks like the best option and pricing available.  The product looks like it solves a myriad of connection issues.  Thank you guys for the heads up on this!  Looking forward to trying it.

https://www.ebay.com/itm/Stabilant-22-Liquid-Semi-Conductor-5-mL-kit-Electronic-Contact-Enhancer-/381762729543

[jetdriven]

There is also a chemical called Deoxit that works pretty well.

[philiplane]

On 8/20/2019 at 6:32 PM, INA201 said:

I have a Century 2B that I have never fully gotten to work reliably.  Ive had the amplifier, roll servo, and other components rebuilt by Bevan-Rabell.  Bevan is came highly recommended.  Anyway all was well until a week after the last annual.  I discovered that when engaging the autopilot the roll servo motor just makes a spinning sound while the visible gear on it doesn't move.  Does anyone know if I should just pull the motor and send it off?  Is it possibly an adjustment issue?  Can I have my local IA just pull out the motor and still fly while it is removed?  Any other suggestions would be great.  Has anyone had their Century autopilot working reliably for an extended period? FWIW I have the Gad29B and GTN 750 hooked up to it.  Any SE shop recommendations as well if that should be the course of action.  Thank you guys!  I know GFC 500, but I am not fully funded for that......YET.

Roll oscillations are caused by:

1-Using a narrow track width setting when in GPS mode, as in 0.3 mile setting instead of 2 mile setting in cruise flight

2-dirty slip rings on the roll servo. This can be tested by using a precision power supply hooked to the servo. The servo is supposed to start moving with less than 3 volts applied. If it takes more, the brushes and slip rings are dirty, so the computer will keep sending power until the servo responds. This causes overshooting. Pilots virtually never do the autopilot pre-flight check, which by itself will keep the servo clean through exercise. With a recent rebuild, this shouldn't be a problem, but it should be checked to rule out excess resistance.

3- loose bridle cable, allowing the servo to move excessively before the ailerons catch up.

[jetdriven]

Ideally, you want servo startup voltage below 1V.  Mine was it 2.5V and I just had it overhauled, it fixed a lot of the slow response or non-responsiveness I had. 

[Jake@BevanAviation]

Ideal startup voltage after overhaul or cleaning and bearing replacement is around 800mvDC.  Typically anything above 2VDC is getting in the area of high startup voltage especially on a 14v system.

[INA201]

1 hour ago, Jake@BevanAviation said:

Ideal startup voltage after overhaul or cleaning and bearing replacement is around 800mvDC.  Typically anything above 2VDC is getting in the area of high startup voltage especially on a 14v system.

I recall my avionics shop running 1.5 volts  to the servo and it wouldn’t kick in. He then went to 3 volts and it engaged. We pulled the amplifier and servo and sent it to you guys.  It has functioned just fine in the past three years and I’ve always tolerated the mild oscillating behavior and connection issues.  Now that I’m planning more IFR adventures I’d like to get it totally tightened up if at all possible.  Is there an easy way to test startup voltage while the servo is mounted. 
 

Thank you guys for all of your insight. This is a lot of fun figuring all of this out. Really good information.