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Thread: Trim with the Garmin G3x

  1. #11
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    Default Re: Trim with the Garmin G3x

    Pat,

    Think the booster is the only way. The trim motor wants too much current for the GSA to supply. I am in the process of doing some of my wiring and this is the schematic I came up with. NOTE that I have not tested this so can't tell you it's right with 100% confidence but think it's in the right Zip code. Also I am using a trim switch on the stick and not the center console so you won't see the switch wiring that Kitfox uses. I think the VPX will swap the power and ground when you command nose up or down.

    Hope this helps

    Gary

    Autopilot and Trim.jpg
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  2. #12
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    Default Re: Trim with the Garmin G3x

    Yes you need the safety trim from TWC. It provides power to the trim motor.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  3. #13

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    Default Re: Trim with the Garmin G3x

    One other factor to note is that the trim switch provided by KF can handle the current required to activate the trim actuator. If you
    plan on using trim buttons on the control stick, though, they typically don't have the capacity for higher current. If you are using trim
    buttons on the control stick you'll need to use the TCW Safety Trim Booster which can use low-current buttons to control the
    trim and can provide sufficient current to drive the trim actuator. The Booster is also connected to pitch servo so that it can be
    controlled by the AP (Garmin).

    You'll find mention of the Booster here: https://www.tcwtech.com/product/safe...vo-controller/

    The Booster also has a pitot input for controlling trim actuator sensitivity based on airspeed when you're using
    manual trim control.

    Victor
    Building SS7
    915iS
    Garmin G3x

  4. #14
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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by VictorV View Post
    One other factor to note is that the trim switch provided by KF can handle the current required to activate the trim actuator. ..........Victor
    In this case the OP is wanting to use trim that routes through the Garmin autopilot pitch servo and it is the limiting factor for current and not the switch itself. The servo won't carry the current that the trim motor is looking for.

    Gary
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  5. #15

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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by Geek View Post
    In this case the OP is wanting to use trim that routes through the Garmin autopilot pitch servo and it is the limiting factor for current and not the switch itself. The servo won't carry the current that the trim motor is looking for.

    Gary
    The current does not flow through the AP servo. Only the control signal goes through the servo. The actuator current comes directly from the TCW Booster.
    Building SS7
    915iS
    Garmin G3x

  6. #16
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    Default Re: Trim with the Garmin G3x

    With regard to the VPX and whether or not it swaps polarity on trim output pins (J1 pins 11 and 12). I emailed VPX the drawing and asked the question because if it didn't, I was going to have to replace the VPX in my trim system with two relays (not hard but just another component in the system). Really happy with the response time from VPX- great support. Turns out the VPX does swap the polarity on those two pins so it puts out both the 12VDC and ground needed to correctly send signals to the auto pilot that then passes the commands to the trim booster. You still need the trim booster to power the trim motor since both the Garmin auto pilot and the VPX are limited to provide a max of only 1Amp and I've heard that the trim motor requires something along the lines of 7 amps. Only thing on the drawing that VPX noted was that I show power on J2 and there is no power available on J2. That is there only as a reminder to me because I am still laying out my power distribution (adding an external alternator). Hope this helps

    Quote Originally Posted by Geek View Post
    Pat,

    Think the booster is the only way. The trim motor wants too much current for the GSA to supply. I am in the process of doing some of my wiring and this is the schematic I came up with. NOTE that I have not tested this so can't tell you it's right with 100% confidence but think it's in the right Zip code. Also I am using a trim switch on the stick and not the center console so you won't see the switch wiring that Kitfox uses. I think the VPX will swap the power and ground when you command nose up or down.

    Hope this helps

    Gary

    Autopilot and Trim.jpg
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  7. #17
    patrick.hvac's Avatar
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    Default Re: Trim with the Garmin G3x

    Hello

    Thanks for your input.
    I was struggling to decide why I would complicate things by bringing the VPX into the trim system.
    What I really want is EFIS indication and VPX says it can't be done without a RAC T2.
    From what I can see there is no difference in indicators between T2 internals and POS sensor pot feedback. (Both 0-5K)
    The RAC RP4/POS combo uses +5V instead of the VPX +2.5 for some reason but the premise is the same and should scale.

    I think I am going to wire the J2-18/19 switches into the VPX for trim. The POS to J1-8/9/10 and then run the J1-11/12 outputs to the GSA and onto the BSTR.
    This means the BSTR switch output is not being used on #2 therefore cut/cap.

    I have to admit. I didnt think my wiring diagram would be 12 pages but here we are.


    Independent Switch Trim.jpg
    VPX Trim.jpg
    🇨🇦CANADA
    Flying | SS7 | G3X | Edge 912

  8. #18
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    Default Re: Trim with the Garmin G3x

    English? Are you trying run trim power from the vpx?
    Last edited by Shadowrider; 04-17-2022 at 09:27 PM.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  9. #19
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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by Shadowrider View Post
    English? Are you trying run trim power from the vpx?
    I'm not. VPX won't do it on its own - not enough poop. In English and in my case, I am not using the switch on the console but rather a hat switch on the stick. That console switch swaps the 12V and ground between the two wires going directly to the trim motor to make it change direction. The stick switch is just gives a ground. So the solution is to either make the hat switch command two relays that will do the swap for you when commanded or use the hat switch to command the VPX. What I had confirmed with the VPX guys was verifying the output from the VPX was indeed that the 12V and ground were swapping depending on which way you commanded the trim. I didn't find anything in the manual that told me specifically that it did that. I saw a drawing that sort of said that but in my tiny mind I was still making an assumption.

    As for the trim indicator that Patrick is talking to - I'm not doing one but think he is talking about using the VPX to put the position up on the EFIS and the acronyms might be what the VPX is using. Since I'm not using one, I am staying away from that rabbit hole. First plane I ever flew in the Navy didn't have a trim position indicator in the cockpit. It was a black line painted on the fuselage that the horizontal lined up with - the KISS principle. It worked so that's my trim indicator.

    Geek
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  10. #20
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    Default Re: Trim with the Garmin G3x

    Ah makes sense now what your doing. As for trim indicator yeah it’s not really needed. With the 915 I will give you the gouge. All the way nose up for landing, and almost all the way nose down for takeoff. Its not like a turbine aircraft, if it’s trimmed wrong it’s not going to kill you.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

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