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Matt Dralle
Site Admin

Joined: 08 Nov 2005
Posts: 26321
Location: Livermore CA USA

Posted: Tue Dec 13, 2016 4:32 pm Post subject: Trim position indicator

Hi Don,



 I think you want one of these:



           https://www.aircraftspruce.com/catalog/elpages/racpos12sensor.php?clickkey=35250 



 

  



         



 At 03:48 PM 12/13/2016 Tuesday, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com>



 I'm looking for some idea on how to implement a trim position sensor. 



 Attached is a picture of the aileron trim mechanism. 



 DC motor on the right drives a cogged belt with an idler pulley on the left. There is no limiter on the motor. It can run continuously.  When it is unable to pull the bellcrank, the belt begins slipping. 



 The mechanism works fine.  I'm not looking for a new trim mechanism. 



 But I would like to know where the system is positioned.  I thought about a small magnet on the belt and then some type of sensor but I think that would be too coarse. 



 So I'm wondering if anyone has any ideas on how to implement a sensor.



 



 

 Read this topic online here:



  http://forums.matronics.com/viewtopic.php?p=463896#463896



 



 

 Attachments: 



  http://forums.matronics.com//files/fff_small_544.jpg



 	
 

 



 Matt G Dralle | Matronics | 581 Jeannie Way | Livermore | CA | 94550

 925-606-1001 V | 925-606-6281 F | dralle(at)matronics.com Email

  http://www.matronics.com/ WWW | Featuring Products For Aircraft

_________________
Matt Dralle
Matronics Email List Administrator

alec(at)alecmyers.com
Guest

Posted: Tue Dec 13, 2016 4:52 pm Post subject: Trim position indicator

how about a servo potentiometer geared to the idler pulley



On Dec 13, 2016, at 19:30, Matt Dralle <dralle(at)matronics.com (dralle(at)matronics.com)> wrote:

  



 Hi Don,



 I think you want one of these:



           https://www.aircraftspruce.com/catalog/elpages/racpos12sensor.php?clickkey=35250 



 

  



         



 At 03:48 PM 12/13/2016 Tuesday, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com (don(at)velocity-xl.com)>



 I'm looking for some idea on how to implement a trim position sensor. 



 Attached is a picture of the aileron trim mechanism. 



 DC motor on the right drives a cogged belt with an idler pulley on the left. There is no limiter on the motor. It can run continuously.  When it is unable to pull the bellcrank, the belt begins slipping. 



 The mechanism works fine.  I'm not looking for a new trim mechanism. 



 But I would like to know where the system is positioned.  I thought about a small magnet on the belt and then some type of sensor but I think that would be too coarse. 



 So I'm wondering if anyone has any ideas on how to implement a sensor.



 



 

 Read this topic online here:



  http://forums.matronics.com/viewtopic.php?p=463896#463896



 



 

 Attachments: 



  http://forums.matronics.com//files/fff_small_544.jpg



 	
 

 



 Matt G Dralle | Matronics | 581 Jeannie Way | Livermore | CA | 94550

 925-606-1001 V | 925-606-6281 F | dralle(at)matronics.com (dralle(at)matronics.com) Email

  http://www.matronics.com/ WWW | Featuring Products For Aircraft

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Tue Dec 13, 2016 5:43 pm Post subject: Re: Trim position indicator

Hey Matt,



I thought about that.  But since this isn't a linear mechanism, I couldn't figure out how to implement that sensor.

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Dec 13, 2016 6:34 pm Post subject: Trim position indicator

 	  Quote: 	
		  



 But I would like to know where the system is positioned.  I thought about a small magnet on the belt and then some type of sensor but I think that would be too coarse. 



 So I'm wondering if anyone has any ideas on how to implement a sensor. 	


 [img]cid:.0[/img]



 

   There's a family of ten-turn potentiometers. You

   might be able to couple one of these to your

   idler pulley.



   See  http://tinyurl.com/gunkre5



 

   Bob . . .

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ashleysc(at)broadstripe.n
Guest

Posted: Tue Dec 13, 2016 6:52 pm Post subject: Trim position indicator

Hi Don Johnston;

Ray Allen makes a trim position sender that you could actuate by anchoring one end and fastening the other to the crank arm. It will not send a "stop" signal to the trim motor, so you will have to provide some other method of limiting the stroke of the trim motor.

Cheers!   Stu.



---

donvansanten(at)gmail.com
Guest

Posted: Wed Dec 14, 2016 12:25 am Post subject: Trim position indicator

Your trim system is a "spring bias" system. The belt spring connection could be used to drive the device that Matt suggested. Thete are a few caveots.1 the sensor has only 1 inch of travel.

2 you would need to find the "neutral point by trial and error

3 if the belt spring connection travels more than 1 inch total you would need to usr a bell crank to cot the input to the sensor to one inch total.

4 spring tensions must be equal with neutral trim (only in the air unless your elevator is fully balanced)

Set up, double sided tape the sensor so that a rod connected to the belt spring connection and attached to the slide in the sensor pushes and pulls the sensor slide as the trim is moved up and down.

If the indicator register bsckwsrda, swap the power and return wires on the sensor. Fly and move trim. If tbe center point is too far off mlve the sensor in or out to correct .

Hope this helps. Btw this is similar to the aileron trim set up in an RV7 except it is driven by a servo with the motoon sensor built in.

On Dec 13, 2016 17:51, "donjohnston" <don(at)velocity-xl.com (don(at)velocity-xl.com)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com (don(at)velocity-xl.com)>

 

 Hey Matt,

 

 I thought about that.  But since this isn't a linear mechanism, I couldn't figure out how to implement that sensor.

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=463899#463899

 

 

 

 

 

 

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Dec 14, 2016 11:17 am Post subject: Re: Trim position indicator

Bob is right. The ten LED trim position indicator detects the reference 1.2V FULL SCALE. At the LSB it can only read 0.12 V which is below the noise level in the environment. This is not hard to fix. 12V full scale would eliminate the problem.



My approach to this was to make a trim wheel, which indicated the trim position with a little fiduciary line (like Cessna). I no longer make these but might do so in the future. The Trim Wheel is right at the top of my "I-had-this-part-in-my-old -airplane-and-need-another-for-my-new-airplane list." The "Trim Wheel" potentiometer also changed the voltage to my TSCMR, True Servo Controller for Mac and RAC. This can also be used separately with your own potentiometer, as well as a pushbutton-row assembly or what have you.

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

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Dec 15, 2016 9:50 am Post subject: Trim position indicator

At 06:51 PM 12/13/2016, you wrote:

  	  Quote: 	
		  how about a servo potentiometer geared to the idler pulley



 On Dec 13, 2016, at 19:30, Matt Dralle <dralle(at)matronics.com (dralle(at)matronics.com)> wrote:



 

 	


   I've been mulling this over the past few days.

   Had to spend a lot of time on the road . . . good

   opportunity for sifting the seeds of ideas.



   That idler pulley seems the opportune

   location for tapping into trim system position

   data. With a little creating work on a small

   lathe, you could remount that pulley on

   a shaft supported by a bushing extending

   through the mounting surface. Is there room

   behind that bulkhead to mount a potentiometer?

   

   It seems likely that full stroke travel of

   the trim system will not produce more than 10

   revolutions of the idler pulley. The pot

   would be rigged to produce 50% of full scale

   voltage with the trim system mechanically

   neutral.



   Simple electronics can offer electrical adjustment

   of the pot voltage should mechanical neutral be

   offset from aerodynamic neutral.



   If you had a voltage representing trim postion,

   where/how would you display it?



 

 

   Bob . . .

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Thu Dec 15, 2016 6:58 pm Post subject: Re: Trim position indicator

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 06:51 PM 12/13/2016, you wrote:

 

That idler pulley seems the opportune location for tapping into trim system position data. With a little creating work on a small lathe, you could remount that pulley on a shaft supported by a bushing extending  through the mounting surface. Is there room behind that bulkhead to mount a potentiometer?



   Bob . . . 	




Yes, that would be an elegant solution.  There's plenty of room on the forward side of the bulkhead. However, I don't have access to a machine shop. 



The position data would be sent to the VPX. It has inputs that can handle the Ray Allen position sensors which then displays it on the GRT HXr EFIS.

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 17, 2016 5:48 am Post subject: Trim position indicator

At 05:48 PM 12/13/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com>



 I'm looking for some idea on how to implement a trim position sensor. 	


   I'm going to Wichita today and may have

   a chance to meet with my counterpart in

   the mechanical side of our cooperative

   endeavors. I may have an idea for fabricating

   a potentiometer assembly on your idler shaft

   using ordinary hand tools . . . Gene will,

   no doubt, have some ideas to contribute . . .

   need to know if your idler pulley has

   a built in bearing to function as an idler

   or does it attach to a shaft that is carried

   through an external bearing.



 

 

   Bob . . .

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Sat Dec 17, 2016 2:45 pm Post subject: Re: Trim position indicator

Bob,



The idler has an integrated bearing and is held in place with an AN bolt.



Don

alec(at)alecmyers.com
Guest

Posted: Sat Dec 17, 2016 2:51 pm Post subject: Trim position indicator

put a gears wheel on the shaft of a servo pot and bolt it to the bulkhead so the toothed belt is tangent to and drives the gear.



On Dec 17, 2016, at 17:45, donjohnston <don(at)velocity-xl.com> wrote:






Bob,



The idler has an integrated bearing and is held in place with an AN bolt.



Don





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=464065#464065

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Dec 18, 2016 8:51 am Post subject: Trim position indicator

At 04:50 PM 12/17/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>



 put a gears wheel on the shaft of a servo pot and bolt it to the bulkhead so the toothed belt is tangent to and drives the gear. 	


   That seems the simplest approach . . . what are the

   pitch and width of the cog-belt?



 

 

   Bob . . .

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Sun Dec 18, 2016 2:21 pm Post subject: Re: Trim position indicator

 	  Quote: 	
		  put a gears wheel on the shaft of a servo pot and bolt it to the bulkhead so the toothed belt is tangent to and drives the gear. 	




I like it!   



I can pick up another cogged pulley that has an ID which will fit over the shaft of a pot.  



Now I just need to figure out what type of pot.  Since the VPX will accept an RAC trim position sensor, does anyone know what the spec's are for that?  I'm assuming that it's basically a linear pot. 



-Don

user9253

Joined: 28 Mar 2008
Posts: 1931
Location: Riley TWP Michigan

Posted: Sun Dec 18, 2016 4:58 pm Post subject: Re: Trim position indicator

Another builder informed me that the Ray Allen servo pot is 5K ohm.

Unverified.

_________________
Joe Gores

rlborger(at)mac.com
Guest

Posted: Sun Dec 18, 2016 7:46 pm Post subject: Trim position indicator

Gents,

FWIW, high quality gears, sprockets & chain drives are available from http://servolink.com

In addition, the web page has facilities for drive design.  Technical support is also available.



Blue skies & tailwinds,Bob BorgerEuropa XS Tri, Rotax 914, Airmaster C/S Prop (75 hrs).Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP3705 Lynchburg Dr.Corinth, TX  76208-5331Cel: 817-992-1117rlborger(at)mac.com (rlborger(at)mac.com)



On Dec 18, 2016, at 4:21 PM, donjohnston <don(at)velocity-xl.com (don(at)velocity-xl.com)> wrote:

--> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com (don(at)velocity-xl.com)> 	  Quote: 	
		  put a gears wheel on the shaft of a servo pot and bolt it to the bulkhead so the toothed belt is tangent to and drives the gear. 	
I like it!   I can pick up another cogged pulley that has an ID which will fit over the shaft of a pot.  Now I just need to figure out what type of pot.  Since the VPX will accept an RAC trim position sensor, does anyone know what the spec's are for that?  I'm assuming that it's basically a linear pot. -DonRead this topic online here:http://forums.matronics.com/viewtopic.php?p=464159#464159

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Dec 19, 2016 10:44 am Post subject: Trim position indicator

At 06:58 PM 12/18/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 Another builder informed me that the Ray Allen servo pot is 5K ohm.

 Unverified. 	


   The value of the pot is very non-critical . . . 1 to 10K would

   work . . . it's simply a voltage divider that is biased up

   with a 5v source from your EFIS system.



   You'll want a MULTI turn pot that will accept more

   rotation than what results from full-stroke motion

   of the cog-belt against the add-on pulley. Here's

   a likely candidate . . . 



  http://tinyurl.com/gn4rs23



 

   for a 10-turn device to which you can add the pulley

   and bracketry to make the installation.



 

 

   Bob . . .

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Thu Jan 05, 2017 4:08 pm Post subject: Re: Trim position indicator

I'm making some progress on this. 



The VPX guys say use a 10K linear pot. 



I've determined that with the appropriate timing gear that I'll be getting 3/4 of a revolution total. Which means I don't need a multi-turn pot. 



And I just happen to have a 10k pot in the drawer (Alpha 813 B10K).  And it's got a 1.75" shaft (which is very important since that bulkhead is rather thick).  But I can't tell if it's linear or audio taper. At 50% of travel, I'm getting about 6K ohms. 



IIRC, if it's an audio taper 10k pot, at 50% of travel, I would be seeing about 3k. 



Does anyone know if this particular pot is linear or audio taper?

alec(at)alecmyers.com
Guest

Posted: Thu Jan 05, 2017 4:33 pm Post subject: Trim position indicator

Most audio pots aren't really logarithmic, they're a two or three straight line approximation. The 25% and 75% travel resistances should enable a better determination, but the B in the code usually means linear taper.

I'd most definitely use a dedicated servo pot, cheap panel pots wear horribly and lose contact; not much of a deal if your old amp volume knob goes a bit crackly, but probably not helpful in your application.

On Jan 5, 2017, at 19:08, donjohnston <don(at)velocity-xl.com> wrote:






I'm making some progress on this. 



The VPX guys say use a 10K linear pot. 



I've determined that with the appropriate timing gear that I'll be getting 3/4 of a revolution total. Which means I don't need a multi-turn pot. 



And I just happen to have a 10k pot in the drawer (Alpha 813 B10K).  And it's got a 1.75" shaft (which is very important since that bulkhead is rather thick).  But I can't tell if it's linear or audio taper. At 50% of travel, I'm getting about 6K ohms. 



IIRC, if it's an audio taper 10k pot, at 50% of travel, I would be seeing about 3k. 



Does anyone know if this particular pot is linear or audio taper?





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=464739#464739

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Thu Jan 05, 2017 4:59 pm Post subject: Re: Trim position indicator

 	  alec(at)alecmyers.com wrote: 	
		  I'd most definitely use a dedicated servo pot 	




What's a "servo pot"?



This will provide a visual indication of the trim position.  Something that I haven't had before.  So if it stops indicating, it's absolutely not a problem. If it stops rotating, that would be annoying, but not insurmountable.



Edit: just did some googling on servo potentiometer... Holy crap!  $60!  



http://www.ebay.com/itm/Rotary-Potentiometer-Wirewound-3549S-Series-10-kohm-Linear-10-2-W-Servo-/401236171094?hash=item5d6b8a1956:g:7rMAAOSwcUBYQNgh



If that's what they cost, I'll keep tooling around without the trim indicator.

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