Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 12-12-2014, 01:27   #1
Registered User
 
american's Avatar

Join Date: Feb 2011
Location: Shanghai, China
Boat: 1986 Tosca 36'
Posts: 113
Send a message via Skype™ to american
Question Auto Pilot Stuck Servo

For a few months now I've encountered an odd issue with my auto pilot system. The control unit is a standard Raymarine. Steering is connected to a custom-made chain-quadrant, driven by a Yaskawa brand 12v servo (?) motor.

The issue is this: Leave the boat for a few weeks, come back to it, the auto pilot servo is engaged, steering at the wheel is locked-out.

Temporary solution: Turn on power to the boat, toggle auto pilot power (hitting auto/manual on the control interface), and wiggle the wheel - the servo will eventually disengage. This can take 5~10 minutes - wouldn't want to try this during an emergency where steering is required ASAP!

(I am thankful I always check steering before backing out of my slip! So is the guy who owns the catamaran parked behind me!)

My question for you all... I would like to understand how/why a mechanism that requires 12v to engage would mysteriously engage when sitting idle without any power applied.

My slip is not atop an ancient indian burial ground.

I don't suspect this is an issue with anything other than the innards of the servo motor. The motor (and system) were installed by the boat's previous owner. He told me these motors, "...are frequently found being used for auto pilots on Japanese fishing boats." There are four wires going into the motor - 12v +/- and two wires for servo control signal from the autopilot brain.

The motor looks something like this:



Which appears to be a "print motor."

Anyone have experience with this sort of thing? Suggests on diagnosing and troubleshooting the issue?

Unless advised to the contrary, I'm hoping to open up the motor and see if it might just need cleaning in-and-around the engaging mechanism.

Thanks, in advanced for any feedback or advice!
__________________

__________________
-american
http://sv-synchronicity.com/
american is offline   Reply With Quote
Old 12-12-2014, 06:27   #2
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Auto Pilot Stuck Servo

When locked, take an ohm meter and see if the windings are shorted together.

Mark
__________________

__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 12-12-2014, 06:43   #3
Registered User
 
transmitterdan's Avatar

Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,028
Re: Auto Pilot Stuck Servo

My guess is that there is a brake inside the motor. If so, the brake is engaged and disengaged by the autopilot. The brake is used to hold the rudder between movements. My second guess is that the brake is sticking maybe because some small amount of water got inside the motor at some time in the past. Usually a motor with a brake will have a cover that can be removed with just a few screws to access the brake and it's electrical solenoid. The trick is knowing which screws. The brake is held in the off position by one or two springs usually. Maybe a spring is broken too. Also, the bearings of the motor might be damaged by salt water.
__________________
transmitterdan is offline   Reply With Quote
Old 13-12-2014, 05:49   #4
Registered User
 
american's Avatar

Join Date: Feb 2011
Location: Shanghai, China
Boat: 1986 Tosca 36'
Posts: 113
Send a message via Skype™ to american
Re: Auto Pilot Stuck Servo

Transmitter Dan,
I opened the motor and took it apart completely. Suspect the issue is the brake, but it looks more like a sort of spring operated clutch. Thing is, it's made of two dissimilar meters and appears to have welded itself together.

Assuming this is the correct diagnosis, question is now this:

How does one unweld two bits of metal? Appears to be copper or brass on one side, steel or iron on the other.

Kill it with fire?

Sent from my HTC M8w using Cruisers Sailing Forum mobile app
__________________
-american
http://sv-synchronicity.com/
american is offline   Reply With Quote
Old 13-12-2014, 07:45   #5
Registered User
 
transmitterdan's Avatar

Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,028
Re: Auto Pilot Stuck Servo

In the original post you said that toggling the A/P on and off will eventually disengage the brake. The brake is probably held in one position by a spring. I assume your A/P runs on 12V. If you can find the 2 wires that operate the brake then momentarily applying 12V to these wires should try to move the brake to the other position. I don't know if the brake is locked with power on or off. It may be that the spring keeps the brake engaged with power off. Application of DC power a few times might get the brake to release.

Pictures might help.
__________________
transmitterdan is offline   Reply With Quote
Old 20-12-2014, 20:52   #6
Registered User
 
american's Avatar

Join Date: Feb 2011
Location: Shanghai, China
Boat: 1986 Tosca 36'
Posts: 113
Send a message via Skype™ to american
Re: Auto Pilot Stuck Servo

Problem solved. Thank you for feedback provided here. Apologies for slow reply, but I was out sailing and far away from an internet connection.

So the problem ended up being this bit:



Which, before removing from the servo and cleaning looked like this:



If you are interested in the full gallery of images, follow this link:
Auto Pilot Troubles - Imgur

Details of the issue and the fix: It's a Japanese-made "print motor" being driven by a standard Raymarine auto pilot unit. The offending gear-bit in the first image is made of two dissimilar metals (appears to be brass and steel?), mounted on the drive shaft. The geared end connects to a chain which drives the rudder. This gear assembly is part of a magnetic clutch. It appeared to be one solid piece of metal when first removed from the servo drive. It's engaged by an electromagnet, which moves two locking pins into place. Pins are driven out of engagement by small springs whenever the magnet is turned off. Magnet, pins, and other parts of the servo were working fine.

Problem was the two metals welded themselves together, so the auto pilot was always engaged.

Solution was to soak overnight in WD-40 and then hammer lightly on the gear teeth while holding the lower section with a pair of vice-grip pliers. A few mm of movement became full rotation, then I was able to grease it and get full, smooth rotation out of it. Re-assembled and everything works better than before!

Long-term solution would be to replace this part with something made of metals that won't get stuck together. Not sure when I might get around to that...
__________________

__________________
-american
http://sv-synchronicity.com/
american is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Aries wind vane ... should I buy a spare "servo rudder" ? Scare_Rab Auxiliary Equipment & Dinghy 3 20-07-2014 19:58
Aries wind vane ... should I buy a spare "servo rudder" ? Scare_Rab Deck hardware: Rigging, Sails & Hoisting 1 18-07-2014 03:34
Just hooked up my tiller pilot / auto pilot boatsail Marine Electronics 4 27-06-2012 23:59
Servo pilot brand windvane steering Philsmith Auxiliary Equipment & Dinghy 0 27-04-2012 21:17
Dual Rudder Servo Pendulum Windvane self steering charliehows Auxiliary Equipment & Dinghy 18 16-04-2012 10:55



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 15:46.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.