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Thread: Pitch Trim Control

  1. #1

    Join Date
    Dec 2019
    Location
    Idaho
    Posts
    117

    Default Pitch Trim Control

    Bear with me while I attempt to explain what I'm trying to do

    My goal is to be able to use both the KF-supplied pitch trim switch and buttons on the control stick.

    I'm using the Ray Allen G405 stick grip. When a button is depressed, the output wire is connected to ground.

    My avionics are Garmin and I'm using the GSA-28 servo. The trim switch is connected to the pitch servo which
    passes the signal along to the TCW Safety Trim Booster which then controls the pitch trim actuator. The safety
    trim booster is needed since we need to drive the trim actuator with more current than the stick grip can
    handle.

    Here's where it gets complicated. The pitch servo expect 2 signals A and B. To move the trim in one direction
    you put 12v on A and Gnd on B. To move the trim in other direction you just reverse the polarity and A is Gnd
    and B is 12v. This is what the KF-provided switch along with their wiring diagram provides.

    The question is how do you connect the stick grip buttons and the KF-provided switch together to generate the polarity-reversing
    signals? I was thinking maybe an H-Bridge might work.

    Here's the wiring diagram provided by TCW:
    TCW Servo Boost Wiring.jpg

    Victor
    Building SS7
    915iS
    Garmin G3x

  2. #2
    Senior Member
    Join Date
    Feb 2020
    Location
    Steilacoom, WA
    Posts
    730

    Default Re: Pitch Trim Control

    I could fill volumes with everything I don't know about electrical wiring, but I have this diagram built into my schematic
    https://www.tcwtech.com/wp-content/u...t-Switches.pdf
    That covers the rocker plus stick grip switches. I don't have an auto pilot so it may get complicated to make that work.
    Kitfox 5 (under construction)
    Commercial SE/ME, CFII

  3. #3

    Join Date
    Dec 2019
    Location
    Idaho
    Posts
    117

    Default Re: Pitch Trim Control

    Thanks Alex. That's good info. I also found this: http://www.rayallencompany.com/produ...cessories.html which looks like it does the right thing.
    I wonder how this works along with the Garmin servo....

    V.
    Building SS7
    915iS
    Garmin G3x

  4. #4
    Senior Member
    Join Date
    Nov 2019
    Location
    Leavenworth WA
    Posts
    613

    Default Re: Pitch Trim Control

    Or you could just buy a couple good relays and wire this in. I'm using the VPX which does this for me but literally this is all it takes.

    GMC-507 and Trim Relays.jpg
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  5. #5

    Join Date
    May 2020
    Location
    Brisbane, Australia
    Posts
    3

    Default Re: Pitch Trim Control

    That's a lovely wiring diagram @Geek. I see it has references to other pages as well. What did you use to draft it?

  6. #6

    Default Re: Pitch Trim Control

    It's in the G3X Touch installation manual.
    Mike Davis
    Fairbanks, AK
    Kitfox Series 7 SS (received kit on 18 April 2023) N967MD reserved
    Rotax 916iS received, still waiting on MTV-6-R propeller
    Build log - https://n967md.dcsol.com
    Murphy Moose #195 (sold)
    1968 C150H still flying regularly
    Quicksilver MX built and registered as experimental (destroyed in wind storm)

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