G3x/TCW Servo Boost Trim Speed Control

[VictorV]

I wanted to share some interesting info that others might find helpful when designing their electrical system.

I have a G3x and 2-axis autopilot using GSA-28 servos. I'm using a Ray-Allen stick grip and have trim up/down tied
to two of the buttons. Since the Ray-Allen switches connect to ground when depressed, I had to add a Ray-Allen
Relay module to generate the correct trim signals. The output of the relay module then goes into the GSA-28 pitch
servo. The output of the pitch servo then connects to a TCW servo booster which drives the Ray-Allen pitch
trim actuator provided by Kitfox. The connection diagram is shown below.

32991

I also connected a TCW "speed switch" to the Servo Booster which I thought would modulate the trim speed based
on airspeed.

I am not using the special trim up/down switch provided by Kitfox.

John M., after seeing this, said I don't need the speed switch since the G3x provides trim speed control.

After getting details from both Garmin and TCW I learned the following:


The G3x provides configurable trim speed based on airspeed
The GSA-28 converts the up/down switch signals to a PWM (Pulse Width Modulation) signal which goes to the TCW servo booster and controls the up/down speed of the trim actuator.
In order for this to work, the GSA-28 must have power applied.
Without power, the GSA-28 is just a passthrough for the trim up/down signals so full speed up/down is issued.
The TCW "Speed Switch" can't be connected to the TCW "Servo Booster". It can only be connected to the TCW "Servo Controller".


I am using a VP-X power controller and have the GSA-28 servo and external autopilot controller power controlled by the autopilot switch. Based on this info
if the autopilot power switch is off, the trim speed control is not active. My plan was to have autopilot power off most of the time unless I'm
using it but if I do that then I won't always have trim speed control. I assumed that I needed an autopilot power switch in case something goes haywire.
Fortunately trim still works even if the GSA-28 servo is powered off. I just need to decide if I want GSA-28 power on always or not.

The devil's in the details!

Here are links to the components mentioned:

TCS Servo Booster - https://www.aircraftspruce.com/catalog/elpages/tcwsafetytrim_boost.php
Ray Allen Stick Grip - https://www.aircraftspruce.com/catalog/elpages/g405.php?clickkey=41355
Ray Allen Relay Deck - https://www.aircraftspruce.com/catalog/elpages/servoRelayDeck.php?clickkey=852685
Garmin Pitch Servo - https://www.aircraftspruce.com/catalog/avpages/garminG3X-touch_11-11450.php?clickkey=649829
TCW Speed Switch - https://www.aircraftspruce.com/catalog/elpages/tcwairspeedswitch.php?clickkey=239880

Victor

[patrick.hvac]

33018
Here is how I wired mine. Very similar.
The pitch trim manual switch goes to VPX on J2. Output to the motor comes from VPX-J1 into the Pitch-GSA on 11-12.
I also put a RayAllen POS-12 into the VPX for position display on G3X through the VPX.
You can also disable the trim speed function in G3X if you want to keep it manual.

[Geek]

I did the same thing as Patrick using the VPX to do the polarity swap on the trim up/down commands. Replaces your Ray Allen relay deck.

Gary