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Trim tab indicator

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mdnanwelch7(at)hotmail.co
Guest

Posted: Wed Oct 13, 2010 10:54 am Post subject: Trim tab indicator

Guys, 

  

   I have a Ray Allen Company trim tab servo and I would like some help.

  

   The servo has three wires that go to a one-piece tiny LED position indicator

 (which they call their RP3 INDICATOR).   I called the factory and the guy said 

 these 3 wires are from a 5K ohm potentiometer inside the servo.  By way of a 

 pot, the RP3 INDICATOR shows the linear position of the trim tab.

  

   (the orange wire and the blue wire are from each end of the pot.  The green

 wire is the wiper)

  

  

   Here's my problem;  my eyesight isn't very good up close, where is where I need

 to mount that RP3 indicator (I have an overhead panel and the indicator would be

 about 12" away from my eyes.  (Too close!)  Plus, I'd rather not be limited to a 

 1/2" x 3/4" LED display.  I would prefer to have separate LEDs, maybe around 

 8-10 of them, placed in a better view on my instrument console in front of me.

  

   Is anyone familiar with any circuitry that could light up a row of LEDs (one at a time)

 that is resistance driven.  According to the tech support guy, the green wire is

 the "slider" of the pot.  I assume only one LED would light up, at any given resistance,

 etc, etc.   

   If a guy had 10 LEDs, then it could work like 0-500 ohms lights #1 LED.

 500+ to 1000 ohms would light up #2 LED, 1000+ to 1500 ohms would light #3, etc, etc.  

  

   I have included the Company installation guide, refer to "Figure 4" for the indicator.

 (see attachment for their RP3 indicator)

  

   I guess if I could go with the Ray Allen indicator, which is better than nothing, but I'd rather

 use my own LEDs if anyone knows of a separate circuit.

  

 Thanks a bunch!!

  

 Mike Welch

instructionsT2andT3.pdf

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larry(at)macsmachine.com
Guest

Posted: Wed Oct 13, 2010 12:03 pm Post subject: Trim tab indicator

Hi Mike,

You’ve got a good system and I have the same and yes, the indicators are hard to read in any daylight.  I’ve become accustomed to looking at the 

trim tab on my left wing to see what’s going on.  The elevator is more easily felt than seen and it has such authority that you can adjust it by feel much easier.

The stick sometimes needs to be bumped for the aileron to be responsive, but it generally is for a changing fuel load.

I’d think not going further with indicators would be a best option.

Best regards

Larry McFarland 601HDS at www.macsmachine.com

 

 

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Mike Welch

Sent: Wednesday, October 13, 2010 1:50 PM

To: aeroelectric-list(at)matronics.com

Subject: Trim tab indicator

 

Guys, 

 

  I have a Ray Allen Company trim tab servo and I would like some help.

 

  The servo has three wires that go to a one-piece tiny LED position indicator

(which they call their RP3 INDICATOR).   I called the factory and the guy said 

these 3 wires are from a 5K ohm potentiometer inside the servo.  By way of a 

pot, the RP3 INDICATOR shows the linear position of the trim tab.

 

  (the orange wire and the blue wire are from each end of the pot.  The green

wire is the wiper)

 

 

  Here's my problem;  my eyesight isn't very good up close, where is where I need

to mount that RP3 indicator (I have an overhead panel and the indicator would be

about 12" away from my eyes.  (Too close!)  Plus, I'd rather not be limited to a 

1/2" x 3/4" LED display.  I would prefer to have separate LEDs, maybe around 

8-10 of them, placed in a better view on my instrument console in front of me.

 

  Is anyone familiar with any circuitry that could light up a row of LEDs (one at a time)

that is resistance driven.  According to the tech support guy, the green wire is

the "slider" of the pot.  I assume only one LED would light up, at any given resistance,

etc, etc.   

  If a guy had 10 LEDs, then it could work like 0-500 ohms lights #1 LED.

500+ to 1000 ohms would light up #2 LED, 1000+ to 1500 ohms would light #3, etc, etc.  

 

  I have included the Company installation guide, refer to "Figure 4" for the indicator.

(see attachment for their RP3 indicator)

 

  I guess if I could go with the Ray Allen indicator, which is better than nothing, but I'd rather

use my own LEDs if anyone knows of a separate circuit.

 

Thanks a bunch!!

 

Mike Welch

 

 

 

   [quote][b]

mdnanwelch7(at)hotmail.co
Guest

Posted: Wed Oct 13, 2010 12:43 pm Post subject: Trim tab indicator

Hi Larry,

  

   Thanks for the reply.  I suppose I could have been more specific.  I have the trim tab

 on the elevator, not an aileron.  Impossible to see the tab's position in flight.

  

   I would like some sort of lighted indication to show it's position, and preferably something I 

 can focus on.  Something the size of a quarter 12 " away from my eyes isn't too good, neither is 

 the quarter sized LEDs on  my instrument panel 36" away, although it's better.

  

   If I had my druthers, I'd have a vertical line of (10)  3mm LEDs, half an inch apart.  This I could 

 see REALLY well.

  

  

 Mike

 

   From: larry(at)macsmachine.com

To: aeroelectric-list(at)matronics.com

Subject: RE: Trim tab indicator

Date: Wed, 13 Oct 2010 14:58:42 -0500



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Hi Mike, 

You’ve got a good system and I have the same and yes, the indicators are hard to read in any daylight.  I’ve become accustomed to looking at the  

trim tab on my left wing to see what’s going on.  The elevator is more easily felt than seen and it has such authority that you can adjust it by feel much easier. 

The stick sometimes needs to be bumped for the aileron to be responsive, but it generally is for a changing fuel load. 

I’d think not going further with indicators would be a best option. 

Best regards 

Larry McFarland 601HDS at www.macsmachine.com 

  

    

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Mike Welch

Sent: Wednesday, October 13, 2010 1:50 PM

To: aeroelectric-list(at)matronics.com

Subject: AeroElectric-List: Trim tab indicator



 

  

Guys, 

 

  I have a Ray Allen Company trim tab servo and I would like some help.

 

  The servo has three wires that go to a one-piece tiny LED position indicator

(which they call their RP3 INDICATOR).   I called the factory and the guy said 

these 3 wires are from a 5K ohm potentiometer inside the servo.  By way of a 

pot, the RP3 INDICATOR shows the linear position of the trim tab.

 

  (the orange wire and the blue wire are from each end of the pot.  The green

wire is the wiper)

 

 

  Here's my problem;  my eyesight isn't very good up close, where is where I need

to mount that RP3 indicator (I have an overhead panel and the indicator would be

about 12" away from my eyes.  (Too close!)  Plus, I'd rather not be limited to a 

1/2" x 3/4" LED display.  I would prefer to have separate LEDs, maybe around 

8-10 of them, placed in a better view on my instrument console in front of me.

 

  Is anyone familiar with any circuitry that could light up a row of LEDs (one at a time)

that is resistance driven.  According to the tech support guy, the green wire is

the "slider" of the pot.  I assume only one LED would light up, at any given resistance,

etc, etc.   

  If a guy had 10 LEDs, then it could work like 0-500 ohms lights #1 LED.

500+ to 1000 ohms would light up #2 LED, 1000+ to 1500 ohms would light #3, etc, etc.  

 

  I have included the Company installation guide, refer to "Figure 4" for the indicator.

(see attachment for their RP3 indicator)

 

  I guess if I could go with the Ray Allen indicator, which is better than nothing, but I'd rather

use my own LEDs if anyone knows of a separate circuit.

 

Thanks a bunch!!

 

Mike Welch

 

 

 

[quote]



-List" target=_blank>http://www.matronics.com/Navigator?AeroElectric-List

ttp://forums.matronics.com

=_blank>http://www.matronics.com/contribution



[b]

etienne.phillips(at)gmail
Guest

Posted: Wed Oct 13, 2010 1:00 pm Post subject: Trim tab indicator

Hi Mike



It should be easy enough to dismantle the RA indicator, and replace the display with individual LEDs. I'm not familiar with this particular indicator, but from the picture, the display looks identical to one that I'm using in my own design, which is simply 10 electrically discrete LEDs in a single housing. De-soldering the 20 pins, yanking out the display and running short wires to individual LEDs (remembering that polarity on LEDs is important) shouldn't be out of any aircraft builder's depth. Obviously though, I would expect a voided warrantee from this sort of behaviour...

To design and build a replacement circuit is a non-trivial exercise involving an IC and a circuit board at least - if you're committed to using LEDs. However, it would be easy enough to replace the entire contraption with a 12V voltmeter (similar to this 10V variety http://tinyurl.com/2f3akj4 ). Connecting either side of the pot to GND and 12V would result in the green slider connection varying from 0-12V through the travel. A simple 12V needle gauge would be able to display that comfortably, with no electronics. It is usually possible to replace the markings on the gauge with your own meaningful ones.

Hope that helps or provides an alternative stimulus...

Thanks

Etienne



On 13 Oct 2010, at 8:49 PM, Mike Welch wrote:

[quote]Guys, 

 

  I have a Ray Allen Company trim tab servo and I would like some help.

 

  The servo has three wires that go to a one-piece tiny LED position indicator

(which they call their RP3 INDICATOR).   I called the factory and the guy said 

these 3 wires are from a 5K ohm potentiometer inside the servo.  By way of a 

pot, the RP3 INDICATOR shows the linear position of the trim tab.

 

  (the orange wire and the blue wire are from each end of the pot.  The green

wire is the wiper)

 

 

  Here's my problem;  my eyesight isn't very good up close, where is where I need

to mount that RP3 indicator (I have an overhead panel and the indicator would be

about 12" away from my eyes.  (Too close!)  Plus, I'd rather not be limited to a 

1/2" x 3/4" LED display.  I would prefer to have separate LEDs, maybe around 

8-10 of them, placed in a better view on my instrument console in front of me.

 

  Is anyone familiar with any circuitry that could light up a row of LEDs (one at a time)

that is resistance driven.  According to the tech support guy, the green wire is

the "slider" of the pot.  I assume only one LED would light up, at any given resistance,

etc, etc.   

  If a guy had 10 LEDs, then it could work like 0-500 ohms lights #1 LED.

500+ to 1000 ohms would light up #2 LED, 1000+ to 1500 ohms would light #3, etc, etc.  

 

  I have included the Company installation guide, refer to "Figure 4" for the indicator.

(see attachment for their RP3 indicator)

 

  I guess if I could go with the Ray Allen indicator, which is better than nothing, but I'd rather

use my own LEDs if anyone knows of a separate circuit.

 

Thanks a bunch!!

 

Mike Welch

 

 

 

<instructionsT2andT3.pdf>

[b]

bbradburry(at)bellsouth.n
Guest

Posted: Wed Oct 13, 2010 1:06 pm Post subject: Trim tab indicator

Mike,  

You can get bifocals (trifocals?) with the close lens on the top and on the bottom and the distance vision in the middle.  This might help with your problem if you need to mount stuff on the ceiling of your cockpit.  Personally, I would not do that since I have close vision problems as well.  I wear progressive lenses which allow me to compensate for things at different distances but still close.  I just move my head around and can bring things into focus anywhere in the cockpit.  

When I am working in the plane and have to see close, but must look thru the top of my glasses, I just use reading glasses so every thing close is in focus.  Works fine unless I try to walk across the hangar… :>)  

Oh the trials and tribulations of getting old!  Beats the hell out of the alternative, though.  :>)  

   

Bill B   

         

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Mike Welch

 Sent: Wednesday, October 13, 2010 4:39 PM

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: Trim tab indicator  

  

   

Hi Larry,

  

   Thanks for the reply.  I suppose I could have been more specific.  I have the trim tab

 on the elevator, not an aileron.  Impossible to see the tab's position in flight.

  

   I would like some sort of lighted indication to show it's position, and preferably something I 

 can focus on.  Something the size of a quarter 12 " away from my eyes isn't too good, neither is 

 the quarter sized LEDs on  my instrument panel 36" away, although it's better.

  

   If I had my druthers, I'd have a vertical line of (10)  3mm LEDs, half an inch apart.  This I could 

 see REALLY well.

  

  

 Mike

        

  

From: larry(at)macsmachine.com

 To: aeroelectric-list(at)matronics.com

 Subject: RE: Trim tab indicator

 Date: Wed, 13 Oct 2010 14:58:42 -0500    

Hi Mike,  

You’ve got a good system and I have the same and yes, the indicators are hard to read in any daylight.  I’ve become accustomed to looking at the   

trim tab on my left wing to see what’s going on.  The elevator is more easily felt than seen and it has such authority that you can adjust it by feel much easier.  

The stick sometimes needs to be bumped for the aileron to be responsive, but it generally is for a changing fuel load.  

I’d think not going further with indicators would be a best option.  

Best regards  

Larry McFarland 601HDS at www.macsmachine.com  

   

       

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Mike Welch

 Sent: Wednesday, October 13, 2010 1:50 PM

 To: aeroelectric-list(at)matronics.com

 Subject: Trim tab indicator  

  

  

   

Guys, 

  

   I have a Ray Allen Company trim tab servo and I would like some help.

  

   The servo has three wires that go to a one-piece tiny LED position indicator

 (which they call their RP3 INDICATOR).   I called the factory and the guy said 

 these 3 wires are from a 5K ohm potentiometer inside the servo.  By way of a 

 pot, the RP3 INDICATOR shows the linear position of the trim tab.

  

   (the orange wire and the blue wire are from each end of the pot.  The green

 wire is the wiper)

  

  

   Here's my problem;  my eyesight isn't very good up close, where is where I need

 to mount that RP3 indicator (I have an overhead panel and the indicator would be

 about 12" away from my eyes.  (Too close!)  Plus, I'd rather not be limited to a 

 1/2" x 3/4" LED display.  I would prefer to have separate LEDs, maybe around 

 8-10 of them, placed in a better view on my instrument console in front of me.

  

   Is anyone familiar with any circuitry that could light up a row of LEDs (one at a time)

 that is resistance driven.  According to the tech support guy, the green wire is

 the "slider" of the pot.  I assume only one LED would light up, at any given resistance,

 etc, etc.   

   If a guy had 10 LEDs, then it could work like 0-500 ohms lights #1 LED.

 500+ to 1000 ohms would light up #2 LED, 1000+ to 1500 ohms would light #3, etc, etc.  

  

   I have included the Company installation guide, refer to "Figure 4" for the indicator.

 (see attachment for their RP3 indicator)

  

   I guess if I could go with the Ray Allen indicator, which is better than nothing, but I'd rather

 use my own LEDs if anyone knows of a separate circuit.

  

 Thanks a bunch!!

  

 Mike Welch

  

  

    

   	  Quote: 	
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mdnanwelch7(at)hotmail.co
Guest

Posted: Wed Oct 13, 2010 2:55 pm Post subject: Trim tab indicator

To Etienne and Bill,

 

  The problem with tearing apart the factory indicator and trying to afix my own

LEDs (and it be successful) is it's a $100 gamble.  I could more easily live with it

 in one piece,

 

  Yeah, I know if someone has come up with a solid state design it would be 

an expensive proposition.

 

  I thought about the meter idea.  Still thinking about it.  Probably not likely to go that

route, tho.  



   How about this idea??  

  Has anyone seen or are aware of a "linear switch type of thing.  My thinking is

I could attach something to the trim tab pushrod, and have it make contact along a linear

set of contacts.  

  

  My eyes probably aren't as bad as I make it sound.  I just need glasses for reading, a lot like

most other guys in their 50's and 60's.  I'm not like I'm "Mr Magoo blind", or anything.

 

  The truth is, if I had to, I could live with that little sucker on my overhead panel.  I'd rather

do that,  than cut it up and try to make it into what I'm after., and risk throwing away $100.

   I could even live with it on my front panel, too.  

 

  I was just curious of anyone knew of an "already existing" design floating around somewhere.

 

  Thanks for your input.                  Mike Welch

 



 		 	   		    [quote][b]

Allen Fulmer

Joined: 10 Jan 2006
Posts: 79
Location: Alexander City, AL

Posted: Wed Oct 13, 2010 3:58 pm Post subject: Trim tab indicator

Mike – Do you have an EFIS?  I know my GRT Horizon will display the trim servo position using the 3 wires you mention.  I suspect the other EFIS players will do likewise.  

   

By the way, I have two of the MAC led indicators that I will not be using and you would be welcome to one.  I don’t know what they are worth but for $5.00 I will mail one to you.  

   

Like others have said, they are not very readable in sunlight.  I have one in my RV4 that is useless.  But I also do not need to see the trim tab position as I adjust by feel in flight and a certain “guesstimate” for takeoff position.  

   

Allen Fulmer  

2458 Oakwoods Ln.  

Alexander City, AL 35010  

   

       

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Mike Welch

 Sent: Wednesday, October 13, 2010 5:52 PM

 To: aeroelectric-list(at)matronics.com

 Subject: RE: AeroElectric-List: Trim tab indicator  

  

  

   

To Etienne and Bill,

  

   The problem with tearing apart the factory indicator and trying to afix my own

 LEDs (and it be successful) is it's a $100 gamble.  I could more easily live with it

 in one piece,

  

   Yeah, I know if someone has come up with a solid state design it would be 

 an expensive proposition.

  

   I thought about the meter idea.  Still thinking about it.  Probably not likely to go that

 route, tho.  

 

   How about this idea??  

   Has anyone seen or are aware of a "linear switch type of thing.  My thinking is

 I could attach something to the trim tab pushrod, and have it make contact along a linear

 set of contacts.  

   

   My eyes probably aren't as bad as I make it sound.  I just need glasses for reading, a lot like

 most other guys in their 50's and 60's.  I'm not like I'm "Mr Magoo blind", or anything.

  

   The truth is, if I had to, I could live with that little sucker on my overhead panel.  I'd rather

 do that,  than cut it up and try to make it into what I'm after., and risk throwing away $100.

   I could even live with it on my front panel, too.  

  

   I was just curious of anyone knew of an "already existing" design floating around somewhere.

  

   Thanks for your input.                  Mike Welch

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_________________
RV7 QB Fuselage
Eggenfellner H6 on orde
N808AF reserved
Alexander City, AL

mikerv6a(at)ao-cs.com
Guest

Posted: Wed Oct 13, 2010 5:32 pm Post subject: Trim tab indicator

Mike



If you decide to construct an indicator, it's certainly

possible to use various single-chip microcontrollers

to do this job. For a simpler solution, check out

National Semiconductor's LM3914 bar graph display driver:



http://www.national.com/ds/LM/LM3914.pdf



It's fairly likely that this is the basis of the Allen

trim display.



Available from several distributors.



Mike Linse

Corvallis, OR



 	  Quote: 	
		     I was just curious of anyone knew of an "already existing" design

 floating

 around somewhere.



   Thanks for your input.                  Mike Welch

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Oct 14, 2010 5:34 am Post subject: Trim tab indicator

At 08:29 PM 10/13/2010, you wrote:

 	  Quote: 	
		  



Mike



If you decide to construct an indicator, it's certainly

possible to use various single-chip microcontrollers

to do this job. For a simpler solution, check out

National Semiconductor's LM3914 bar graph display driver:


	


    There's another option. We have a quantity of

    Tripplet 120 minature meter movements. This

    is the same core we use for the 9007 loadmeter.

    These could be offered as trim indicators also

    by fitting with scale plates not unlike those

    shown here:



http://www.aeroelectric.com/Pictures/Instruments/Trim/Trim_Indicators.pdf



   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Thu Oct 14, 2010 5:57 am Post subject: Re: Trim tab indicator

Allen Fulmer's idea of connecting the trim servo pot to an EFIS is the easiest.

If no EFIS, then the schematic on page 2 of the data sheet referenced by Mike Linse will work.  http://www.national.com/ds/LM/LM3914.pdf

For the 0V to 5V signal source, make a 5 volt regulator like this: http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html

Connect aircraft power to the input of the 5 volt regulator.

Connect ground and the output of the 5 volt regulator to the trim servo pot orange and blue wires.

Connect the green wire from the servo pot to pin 5 of the LM3914N.

Joe

_________________
Joe Gores

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Fri Oct 15, 2010 6:29 am Post subject: Re: Trim tab indicator

I've posted lots on this subject, and offer a TSCMR (True Servo Controller for MAC-RAC), which allows you to use a linear or rotary potentiometer or stepped resistor switch to control the trim box. Even if you don't want one, the details should interest you:



periheliondesign.com/moreproductsfiles/ServoController%20macrac.pdf



I decided to re-engineer the TSCMR with many additional features but don't currently sell it. It got complicated. Details on request.



Regarding position indicators, the advantage of using a pot, trim wheel or any non-pushbutton means of control is knowing where the trim is set. The Ray Allen trim indicator expects 1.28V MAX voltage. Minimum voltage is raised off zero a tiny bit, but not enough to prevent transmitter, intercom, etc. noise from getting into the display.



There are a zillion ways to build higher output LED bar graphs, any you'll probably have to roll your own with brighter LEDs. The LM3914 is current limited. Perhaps the easiest approach is drive optoisolators such as 10 of the TLP222G which then drive whatever LED you want up to 85 mA or so.



Google "Bargraph kit" for many available roll your own kits.

RAC Trim and Trim Indicator Schematics.pdf

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

mdnanwelch7(at)hotmail.co
Guest

Posted: Fri Oct 15, 2010 7:37 am Post subject: Trim tab indicator

> I've posted lots on this subject, and offer a TSCMR (True Servo Controller for MAC-RAC> --------

 	  Quote: 	
		   Eric M. Jones

 www.PerihelionDesign.com


	


 Eric,

  

   That is a very nice article and design you've got.  Probably more than I need at this point, tho.

  

   From the contributions so far, I have an little bar graph indicator coming from Allen Fulmer, which I 

 will check out.  Next, and what seems to hold the most promise, is that circuit Joe Gore supplied using 

 the LM3914.  I suspect that that will be the one I use.  It appears to be easy enough (for me) to build, 

 and provides exactly what I was after in the first place...a line of 3mm LEDs, with one lit up to show the 

 tabs position.

   I like the meter Bob offered, too, but the LED design is my preferred goal.

  

   Thanks to everyone for their generous input.  This list is truly an asset to the homebuilt enthusiast!!

  

 Mike Welch

 		 	   		    [quote][b]

klburris

Joined: 19 Dec 2009
Posts: 18

Posted: Fri Oct 15, 2010 12:27 pm Post subject: Trim Tab Indicator

[img]cid:image001.jpg(at)01CB6C74.3B3D9990[/img]       <![endif]-->    

Bob:  

A couple of questions on your miniature meter movements;  

How does one change the scale? Is it difficult to get the face plate off? Would just a piece of paper with the scale you want printed on it be sufficient for the scale or would you have to use a special paper? I presume the meter is a 0 to full scale operation. Is there any ‘easy’ way to make it a center zero meter such that you could use it for a –30 0 30 ammeter? Also, I was unable to find the product listing for the price of the miniature meter on your webpage. How much is the meter?  

Thanks in advance.  

<![if !supportEmptyParas]> <![endif]>  

-- Keith  

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Bob Nuckolls wrote;   	  Quote: 	
		  There's another option. We have a quantity ofTripplet 120 miniature meter movements. Thisis the same core we use for the 9007 loadmeter.These could be offered as trim indicators alsoby fitting with scale plates not unlike thoseshown here:http://www.aeroelectric.com/Pictures/Instruments/Trim/Trim_Indicators.pdf<![if !supportEmptyParas]> <![endif]>

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nuckolls.bob(at)aeroelect
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Posted: Sat Oct 16, 2010 6:41 am Post subject: Trim Tab Indicator

At 03:21 PM 10/15/2010, you wrote:



Bob:



A couple of questions on your miniature meter movements;



How does one change the scale?



      I lay out a new scale plate in AutoCAD.

      For b/w plates, I print the new scale on

      full-sheet Avery label material (sticky

      back w/peel-off cover) and a laser printer.

      For color I use matt photo paper and color

      printer. New scales are attached to the back

      side of the existing scale plate.



  Is it difficult to get the face plate off?



      I don't take off the old one, just put the

      new one over the old one or on the back side

      of the existing plate.



Would just a piece of paper with the scale you 

want printed on it be sufficient for the scale or 

would you have to use a special paper? I presume 

the meter is a 0 to full scale operation. Is 

there any ‘easy’ way to make it a center zero 

meter such that you could use it for a –30 0 30 ammeter?



     It depends on the pointer's zero-springs.

     SOMETIMES . . . the rear spring has enough

     adjustment travel to allow moving the zero-

     current pointer position to the center of

     the movement's travel. I've not tried it

     with these devices that I can recall.



Also, I was unable to find the product listing 

for the price of the miniature meter on your webpage. How much is the meter?



     The instruments I hypothesized in the posting

     do not exist. I would have to do some 'real'

     scale stickers and modify some new instruments.

     I have a load-meter that is already in stock.



https://matronics.com/aeroelectric/Catalog/AEC/9007/9007.html



     The instrument with a shunt is $70. To do a

     one-of-a-kind would be a bit more.



   Bob . . .

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