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Garmin G3X Autopliot Auto Trim with Big Trim Motor

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tfarrell839

Joined: 10 Nov 2012
Posts: 27
Location: Watsonville, CA

Posted: Fri Nov 22, 2013 6:31 pm Post subject: Garmin G3X Autopliot Auto Trim with Big Trim Motor

So here is our current conundrum:



We are installing a new G3X panel in a Glasair II RG.  It has the Garmin autopilot.  The Garmin autopilot has auto trim included.  Garmin drives the trim motors directly with the pitch or roll servo.  In this case, we're only interested in the pitch servo.  The servo wants to see a 12V signal coming in from a DPDT trim switch: one polarity for up, reversed for down.  It then outputs to the trim motor.  The output is rated to only 1A.  The Glasair uses a rather large trim motor, a linear actuator with a 500 lb rating that draws 3.6A under load.  It has this because it has to pull on a pretty hefty cable and spring system.  The Garmin also has variable trim speed control, the faster you go, the slower it will drive the trim.  Garmin accomplishes this by outputting a pulse width modulated (PWM) signal to vary the speed of the trim motor.  Our problem is that we need relays to operate our motor, so it seems we can't get variable speed control and we aren't even sure if we will get any auto control of the trim at all.  



So finally, my question: Can we use FETs, an H Bridge (which i don't fully understand) or something else to amplify the current proportionally to the PWM signal? 



I should add, we have two sticks, each with trim control.  The legacy system that is in there has Bosch type relays that control the trim.  



I am including a schematic for a possible recommendation from Garmin.  The caveat to this installation is that it seems we would have to run the trim at full speed all the time.  



I appreciate any thoughts,



 Best,



Tim

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Tim Farrell
Aircrafters
831-722-9141

jluckey(at)pacbell.net
Guest

Posted: Fri Nov 22, 2013 9:30 pm Post subject: Garmin G3X Autopliot Auto Trim with Big Trim Motor

Tim,

Does the Garmin PWM output change polarity or is there a separate channel for trim direction?



FYI, No attachments came w/ your email.





        From: tfarrell839 <tim(at)AirCraftersLLC.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Friday, November 22, 2013 6:31 PM

 Subject: Garmin G3X Autopliot Auto Trim with Big Trim Motor

  

 

 --> AeroElectric-List message posted by: "tfarrell839" <tim(at)aircraftersllc.com (tim(at)aircraftersllc.com)>



So here is our current conundrum:



We are installing a new G3X panel in a Glasair II RG.  It has the Garmin autopilot.  The Garmin autopilot has auto trim included.  Garmin drives the trim motors directly with the pitch or roll servo.  In this case, we're only interested in the pitch servo.  The servo wants to see a 12V signal coming in from a DPDT trim switch: one polarity for up, reversed for down.  It then outputs to the trim motor.  The output is rated to only 1A.  The Glasair uses a rather large trim motor, a linear actuator with a 500 lb rating that draws 3.6A under load.  It has this because it has to pull on a pretty hefty cable and spring system.  The Garmin also has variable trim speed control, the faster you go,  the slower it will drive the trim.  Garmin accomplishes this by outputting a pulse width modulated (PWM) signal to vary the speed of the trim motor.  Our problem is that we need relays to operate our motor, so it seems we can't get variable speed control and we aren't even sure if we will g!

 et any auto control of the trim at all.  



So finally, my question: Can we use FETs, an H Bridge (which i don't fully understand) or something else to amplify the current proportionally to the PWM signal? 



I should add, we have two sticks, each with trim control.  The legacy system that is in there has Bosch type relays that control the trim.  



I am including a schematic for a possible recommendation from Garmin.  The caveat to this installation is that it seems we would have to run the trim at full speed all the time.  



I appreciate any thoughts,



 Best,



Tim



--------

Tim  Farrell

Aircrafters

831-722-9141





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=413837#413837





Attachments: 



http://forums.matronics.com//froElectric www.aget="_blank" nbsp;    * HomebuiltHELP www.mypilosp;                 -Matt Dralle, Lilities -=   --> http://www.matronics.com/Navigator?AeroElectric-List

=======================

 

 

  

 [quote][b]

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tfarrell839

Joined: 10 Nov 2012
Posts: 27
Location: Watsonville, CA

Posted: Fri Nov 22, 2013 10:16 pm Post subject: Re: Garmin G3X Autopliot Auto Trim with Big Trim Motor

As I understand it, yes it changes the polarity in the sense that if it gets positive on pin 11 and negative on 12 then it will output positive on 13 an negative on 14 and vice versa. 



I don't know why the attachment didn't come through. I see it here when I m on the list serve. I'll post a link tomorrow. 



Thanks, 



Tim

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Tim Farrell
Aircrafters
831-722-9141

jluckey(at)pacbell.net
Guest

Posted: Sat Nov 23, 2013 7:51 am Post subject: Garmin G3X Autopliot Auto Trim with Big Trim Motor

Tim,



That's not quite the answer I was looking for.  But rather than try to figure out what's happening via text in emails, let's start w/ whatever diagrams you have.  Then we can drill deeper as necessary.



Standing by until you post the link ...





        From: tfarrell839 <tim(at)AirCraftersLLC.com>

 To: aeroelectric-list(at)matronics.com 

 Sent: Friday, November 22, 2013 10:16 PM

 Subject: Re: Garmin G3X Autopliot Auto Trim with Big Trim Motor

  

 

 --> AeroElectric-List message posted by: "tfarrell839" <tim(at)aircraftersllc.com (tim(at)aircraftersllc.com)>



As I understand it, yes it changes the polarity in the sense that if it gets positive on pin 11 and negative on 12 then it will output positive on 13 an negative on 14 and vice versa. 



I don't know why the attachment didn't come through. I see it here when I m on the list serve. I'll post a link tomorrow. 



Thanks, 



Tim



--------

Tim Farrell

Aircrafters

831-722-9141





Read this topic online here:



http://forums.matronicsThe Builder's Bookstore www.homebuilthelnbsp;  * Race Consulting

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tfarrell839

Joined: 10 Nov 2012
Posts: 27
Location: Watsonville, CA

Posted: Sat Nov 23, 2013 12:47 pm Post subject: Re: Garmin G3X Autopliot Auto Trim with Big Trim Motor

let's try this.  HEre's a link:



http://www.aircraftersllc.com/docs/Garmin%20Suggestion.png



Tim

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Tim Farrell
Aircrafters
831-722-9141

tfarrell839

Joined: 10 Nov 2012
Posts: 27
Location: Watsonville, CA

Posted: Tue Nov 26, 2013 8:44 pm Post subject: Re: Garmin G3X Autopliot Auto Trim with Big Trim Motor

Any thoughts on using transistors in this setup instead of relays?



Thanks,



Tim

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Tim Farrell
Aircrafters
831-722-9141

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