[Toobuilder]

OK, I can see the light at the end of the tunnel on this panel remodel and I've hit a brick wall; I hope someone here can help! The airplane has MAC servos for both roll and pitch trim, and electric flaps. For indication it has the little multi-element LED indicators for all three functions. As these have proven to be unreliable in this airplane, and the GRT Horizon display has analog inputs for these functions, I'm planning on trashing the LED indicators in favor of the GRT display. That's the plan - and that's about as far as I can go. I don't understand the feedback mechanism (How does the indicator "know" what position the surface is in?) Does this little device have something to do with it?

Here's another , for the flaps:

There appears to be very little info about these things on the Web, and all searches keep turning back to the Ray Allen page. Are these the same products?

Part 2 of the question concerns the interface with the GRT displays. The manual explains that the analog inputs are available to support a 0-12 volt input signal, but that's about as much detail as it covers. Does information exist (like a schematic) that shows the wiring interface for the position indicators? Does the display function have to be "enabled" after the signal lines are hard wired?

Thanks much!

 

[h&jeuropa]

Here's a link to the wiring diagram on the GRT website

http://www.grtavionics.com/File/Wiring Diagrams/Horizon Trim Position Install.pdf

Then you have to calibrate it as described in the setup manual.

Hope this helps.

Jim Butcher

 

[Toobuilder]

So the first picture is a "Servo/Position Sensor"? And the "Aux IN" is actually one of the 8 analog inputs?

Is there any info on the MAC units pictured? I see the green, orange and blue wires, but there are also a few more on the MAC unit that I need to know what they do.

Thanks for the info!

 

[Toobuilder]

Partial mystery solved: The item in picture #2 is a linear potentiometer. The part that has me confused is the fact that there is no mechanical connection to the flap system (it is broken, link removed long ago). How this interfaces with the GRT makes sense to my pea brain (variable input voltage based upon flap position). But what about the units in the first picture: what is the sensing logic to them, and their output?

 

[mburch]

But what about the units in the first picture: what is the sensing logic to them, and their output?

Those look a lot like the old style of relay that Ray Allen used to sell:

(click for full size)

If it is, then it doesn't have any relationship to servo position - it just mixes two sets of switch inputs into one motor output. I'll make a guess that your airplane has a trim switch for both pilot and copilot...?

The MAC/RAC trim servos typically have a built-in potentiometer, so you should be able to grab onto the colored wires coming straight out of your servo.

good luck,
mcb

 

[Mike S]

I agree, they look like relay boxes.

The servo has the feedback pot in it already, only something like the flaps with a non RA servo drive needs a separate feedback pot.

Here is a set of photos of the actual unit------notice it has a movable part that is hooked to the flap arm. This is on my 10.

http://picasaweb.google.com/mikestarkey025/FlapPositionSensorMount?authkey=Gv1sRgCI3D47nVqdKRYw#

 

[h&jeuropa]

As others have said, I think your photos are of the relay boxes. You can find installation instructions for them at

http://www.rayallencompany.com/RACmedia/instructionsT2andT3.pdf

The actual trim servo will have five wires two white and 1 each orange, green & blue. The white are the power for running the motor. Power them one way for one direction, reverse the polarity for the other direction. The other three are attached to the potentiometer internal to the servo which provides the servo position information. Connect them as shown in the GRT diagram. Since you state you have the LED indicators, you should be able to just run the wires from them to your GRT. No other changes needed!

The relay decks "The REL-2 Relay Deck is designed to convert SPDT action switches into a DPDT action. The REL-2 will also drop both power
white power leads going to the servo motor to ground. This motor braking function enables very precise servo positioning". If your servos are working correctly, leave them as they are.

You may not need the relay decks. I just use a rocker switch without relay decks on the trim servos in my Europa.

Jim Butcher
Europa XS N241BW

 

[Toobuilder]

Matt -

The airplane does not have trim control for the back seater. Well, it didn't... I just added a pitch control switch for the rear seat just recently. As a "ground seeking" circut, I simply wired it in paralell to the existing circut.

Mike -

Yes, that's what my flap position transmitter used to look like, but I have no idea how it could have performed its job from where it was mounted. I'll bet that someone in the past broke the thing and simply stuck it somewhere out of the way.

 

[Toobuilder]

Jim - Thanks for the info and links. I have what I need to validate the basic installation.

So, with the potentiometer built in to the servo, (providing my variable voltage output) then all I have to do is route this into the analog port(s) on the GRT and configure the display. Correct?

Thanks so much for all the help everybody!