The Murphy Builders Site

I have a problem with my elevator trim the problem has come up 4 or 5 times
in the last 10 hours.. I have two trim switches with relays to the servo all
Mac products, all has worked flawless for 500 hours.
When I click the trim switch it does not move the trim. If I reverse the
trim switch for a quick bump then reverse again the trim works it that
direction. I have not been able to replicate the problem on the ground it
only happens when I'm flying and I have only noticed it on takeoff. Has
anyone had this kind of problem? Does anyone have an idea on trouble
shooting?
Al
Moose, N526AP





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Possibly the trim motor has a dead spot for starting. You may not be
able to replicate on the ground because duplicating the position of the
dead spot might be tricky. It should be near where the in-flight failure
occurs. Might require numerous attempts to replicate on the ground if
this is the case. but it should be possible to find the spot. Just a
guess but is an idea.

On Fri, 2005-08-07 at 16:01 -0700, Al Paxhia wrote:

I have a problem with my elevator trim the problem has come up 4 or 5 times
in the last 10 hours.. I have two trim switches with relays to the servo all
Mac products, all has worked flawless for 500 hours.
When I click the trim switch it does not move the trim. If I reverse the
trim switch for a quick bump then reverse again the trim works it that
direction. I have not been able to replicate the problem on the ground it
only happens when I'm flying and I have only noticed it on takeoff. Has
anyone had this kind of problem? Does anyone have an idea on trouble
shooting?
Al
Moose, N526AP





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Hi Al,
No problem here so far. We only have elevator trim. I'll take a look at
the circuitry and see if I come up with any suggestions.
Did you attend Arlington? We were going to have the Moose there but the
weather forecasts caused us to abandon our plans.
Dick Shotwell
Moose 096
N235DS
Twin Falls, ID


----- Original Message -----
From: "Al Paxhia" <paxhia2@comcast.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 08, 2005 17:01 PM
Subject: Electric Trim Problem

I have a problem with my elevator trim the problem has come up 4 or 5

times

in the last 10 hours.. I have two trim switches with relays to the servo

all

Mac products, all has worked flawless for 500 hours.
When I click the trim switch it does not move the trim. If I reverse the
trim switch for a quick bump then reverse again the trim works it that
direction. I have not been able to replicate the problem on the ground it
only happens when I'm flying and I have only noticed it on takeoff. Has
anyone had this kind of problem? Does anyone have an idea on trouble
shooting?
Al
Moose, N526AP





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A dead spot, that is what it seems like. Is there a way to test a servo
motor without taking it apart. As I recall the Mac servo's are a sealed
unit. Another thought is moisture, the servo is located in a moist
environment, could moisture cause this type of problem?
Al
----- Original Message -----
From: "wrightdg" <wrightdg@davincibb.net>
To: "rebel builders" <rebel-builders@dcsol.com>
Sent: Friday, July 08, 2005 5:50 PM
Subject: Re: Electric Trim Problem

Possibly the trim motor has a dead spot for starting. You may not be
able to replicate on the ground because duplicating the position of the
dead spot might be tricky. It should be near where the in-flight failure
occurs. Might require numerous attempts to replicate on the ground if
this is the case. but it should be possible to find the spot. Just a
guess but is an idea.

On Fri, 2005-08-07 at 16:01 -0700, Al Paxhia wrote:

I have a problem with my elevator trim the problem has come up 4 or 5
times
in the last 10 hours.. I have two trim switches with relays to the servo
all
Mac products, all has worked flawless for 500 hours.
When I click the trim switch it does not move the trim. If I reverse the
trim switch for a quick bump then reverse again the trim works it that
direction. I have not been able to replicate the problem on the ground it
only happens when I'm flying and I have only noticed it on takeoff. Has
anyone had this kind of problem? Does anyone have an idea on trouble
shooting?
Al
Moose, N526AP





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Al,

I'm not knowledgeable in servo technology. I'm not even sure that they
commutators that can cause dead spots. I think they do because they
operate on direct current. Accordingly the only test I can think of is
to leave it on the dead spot when found in flight and land without
changing the trim if possible. This would then give the postion of the
dead spot when on the ground. That allows you to ensure that proper
voltages are arriving at the servo and that its not working at that
point. Once you know that, it is sensible to try swapping out the servo.
Good luck.

Garry

On Fri, 2005-08-07 at 21:34 -0700, Al Paxhia wrote:

A dead spot, that is what it seems like. Is there a way to test a servo
motor without taking it apart. As I recall the Mac servo's are a sealed
unit. Another thought is moisture, the servo is located in a moist
environment, could moisture cause this type of problem?
Al
----- Original Message -----
From: "wrightdg" <wrightdg@davincibb.net>
To: "rebel builders" <rebel-builders@dcsol.com>
Sent: Friday, July 08, 2005 5:50 PM
Subject: Re: Electric Trim Problem

Possibly the trim motor has a dead spot for starting. You may not be
able to replicate on the ground because duplicating the position of the
dead spot might be tricky. It should be near where the in-flight failure
occurs. Might require numerous attempts to replicate on the ground if
this is the case. but it should be possible to find the spot. Just a
guess but is an idea.

On Fri, 2005-08-07 at 16:01 -0700, Al Paxhia wrote:

I have a problem with my elevator trim the problem has come up 4 or 5
times
in the last 10 hours.. I have two trim switches with relays to the servo
all
Mac products, all has worked flawless for 500 hours.
When I click the trim switch it does not move the trim. If I reverse the
trim switch for a quick bump then reverse again the trim works it that
direction. I have not been able to replicate the problem on the ground it
only happens when I'm flying and I have only noticed it on takeoff. Has
anyone had this kind of problem? Does anyone have an idea on trouble
shooting?
Al
Moose, N526AP





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If that is proving difficult then one could just temporarilly connect a
voltmeter to the two power wires that go from the control to the servo
and go flying. If there is no voltage there while in the dead spot then
it is a control problem. I would deem this unlikely (but certainly
possible) considering it works fine on the ground.

If there is voltage then it is a servo or wiring issue to the servo in
which case one could further run two temporary wires from the servo to
the voltmeter to prove whether it is an intermittant wire or a servo
issue. However at this point I'd just open the servo and clean/tinker or
just replace the servo unless I suspected an intermittant wiring break
which is also certainly possible at 500 hours.
Might be as simple as a chunk of debris in the gears. Mine comes apart
easily. It occasionally helps to also ask the manufacturer for suggestions.

Profound statement warning:
The unexpected occurs more often than I expect ;)
For example when I finally investigated replacing the battery in my
Braun electric toothbrush that had been running slower and shorter
between charging - turns out the stainless output shaft was just seizing
up in the brass bushing... If playing with the thing on the ground you
might try applying some pressure to the trim tab while someone plays
with the switch if you haven't already...

Ken

wrightdg wrote:

Al,

I'm not knowledgeable in servo technology. I'm not even sure that they
commutators that can cause dead spots. I think they do because they
operate on direct current. Accordingly the only test I can think of is
to leave it on the dead spot when found in flight and land without
changing the trim if possible. This would then give the postion of the
dead spot when on the ground. That allows you to ensure that proper
voltages are arriving at the servo and that its not working at that
point. Once you know that, it is sensible to try swapping out the servo.
Good luck.

Garry

On Fri, 2005-08-07 at 21:34 -0700, Al Paxhia wrote:

A dead spot, that is what it seems like. Is there a way to test a servo
motor without taking it apart. As I recall the Mac servo's are a sealed
unit. Another thought is moisture, the servo is located in a moist
environment, could moisture cause this type of problem?
Al
----- Original Message -----
From: "wrightdg" <wrightdg@davincibb.net>
To: "rebel builders" <rebel-builders@dcsol.com>
Sent: Friday, July 08, 2005 5:50 PM
Subject: Re: Electric Trim Problem

Possibly the trim motor has a dead spot for starting. You may not be
able to replicate on the ground because duplicating the position of the
dead spot might be tricky. It should be near where the in-flight failure
occurs. Might require numerous attempts to replicate on the ground if
this is the case. but it should be possible to find the spot. Just a
guess but is an idea.

On Fri, 2005-08-07 at 16:01 -0700, Al Paxhia wrote:

servo

reverse the

ground it

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Two thoughts came to mind. It may be responding differently under load in flight than on the ground. Have you contacted MAC and asked them. I would love to hear what they say.

Rick Muller
SR70

-------------- Original message --------------

I have a problem with my elevator trim the problem has come up 4 or 5 times
in the last 10 hours.. I have two trim switches with relays to the servo all
Mac products, all has worked flawless for 500 hours.
When I click the trim switch it does not move the trim. If I reverse the
trim switch for a quick bump then reverse again the trim works it that
direction. I have not been able to replicate the problem on the ground it
only happens when I'm flying and I have only noticed it on takeoff. Has
anyone had this kind of problem? Does anyone have an idea on trouble
shooting?
Al
Moose, N526AP





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I did talk to the Ray Allen factory today and they want to see the servo.
The problem may be in
the servo or the servo relay is weak. The servo is the old MAC-8 and is the
largest servo they make. This servo is close to its max limit on the Moose
trim tab. He suggested making the arm on the trim tab larger to reduce the
forces.
Thanks for input, I'll keep you posted on what we find out.
Al
----- Original Message -----
From: <rickhm@comcast.net>
To: <rebel-builders@dcsol.com>
Sent: Monday, July 11, 2005 8:01 AM
Subject: Re: Electric Trim Problem

Two thoughts came to mind. It may be responding differently under load in
flight than on the ground. Have you contacted MAC and asked them. I
would love to hear what they say.

Rick Muller
SR70

-------------- Original message --------------

I have a problem with my elevator trim the problem has come up 4 or 5
times
in the last 10 hours.. I have two trim switches with relays to the servo
all
Mac products, all has worked flawless for 500 hours.
When I click the trim switch it does not move the trim. If I reverse the
trim switch for a quick bump then reverse again the trim works it that
direction. I have not been able to replicate the problem on the ground it
only happens when I'm flying and I have only noticed it on takeoff. Has
anyone had this kind of problem? Does anyone have an idea on trouble
shooting?
Al
Moose, N526AP





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An update on my elevator trim problem.
I replaced the servo and the problem was still there. It turned out to be a
sticky relay. I could hear the relay click but the servo would not operate
until I tapped the relay then the servo would go.
Replaced the relay and the system is back to normal.
Al
Moose, N526AP





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