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Trim Tab Servo

StressedOut

Well Known Member
I've installed my trim tab server in the LH elevator, but when I hook it up to the push rod it's deflected about 20 degrees down. I'd like to neutralize its position, but gently trying to turn the actuator screw poking out the back doesn't work and I don't want to force it.

I read about using a 9 volt battery to power up the servo and move the tab, but I have no idea which wires I should connect to in order to do this.

My choices are green, orange, blue and two white wires. I have no idea what functions these wires have so I don't want to randomly connect them to the battery in a process of elimination for fear of damaging the servo.

Can anybody enlighten me as to the functions of each of these wires? I'm a total novice when it comes to electrical work.

Thanks.

UPDATE: I found the instructions that came with the servo. It looks like the green, orange and blue wires go to an indicator, so the white wires should actuate the servo. I assume swapping the white wires on the + and - terminal of the 9 volt battery would run the motor in opposite directions. Can someone confirm?
 
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Pretty sure it's the two white. Sure enough that if it was mine I'd go for it. If it moves the wrong way reverse the connections on the battery. The other wires are for sensing the position for your position indicator. If you don't have the instructions that came with servo then just google it and I'm sure it will come up under Ray Allen.
 
It’s exactly as you said. Do yourself a favor and once you hook up the battery and watch, label the correct white wire ‘+ moves tab up, nose down’. You’ll be thankful when you do the final wiring. One DAR here has said that he finds nearly 50% of them running backwards.
 
one more tidbit: once you wire the servo to the rest of your avionics, if you happen to have the two white wires reversed, you can change this easily in the software configuration in your EFIS. Same for autopilot servos (but, strangely, not for the flap motor in the G3X Touch).

_Alex
 
Your wiring hunch is correct.

I'm not sure what you mean by neutralize the trim tab, but if you mean adjust for an equal amount of up and down travel from neutral - don't do that.

On the 14, the tab will deflect down far more than it will deflect up. This is because when you deploy the flaps you want a lot of nose up trim at full flaps.
 
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Your wiring hunch is correct.

I'm not sure what you mean by neutralize the trim tab, but if you mean adjust for an equal amount if up and down travel from neutral - don't do that.

On the 14, the tab will deflect down far more than it will deflect up. This is because when you deploy the flaps you want a lot of nose up trim at full flaps.

+1. In addition, if it’s like the -10, the two tabs will not move together. Adjust them so they both hit ‘in trail’ at the same time.
 
I'm not sure what you mean by neutralize the trim tab...

I'm pretty sure that he just wants the trim tab in trail with the elevator trailing edge so it looks nice and neat while stored for the duration of the project.

As others have said, it's the two white wires which need to be held on either pole of a 9v battery. One wire/pole orientation will run the motor either up or down - simply reverse the wires for the other direction. Also, you can do this with your fingers; you're not going to zap yourself. :)
 
Thanks everybody for your suggestions. I currently have no way to connect to the wires since I installed the mini-Molex connector on the servo. I ordered some additional plug and socket connectors and a bunch of pins and #22 wire just in case. I'll make a test harness out of it.
 
I used two paper clips and a 9 volt battery to center mine.

BTW, now is the time to remove that micro molex connector and use something else. After several intermittent problems I cut it out and replaced with sub-d pins covered in heat shrink.

Mine failed first flight. Replaced it with a better quality connector, the method you mention is also excellent.
 
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