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Old Oct 18, 2012, 09:59 PM
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United States, FL, Fort McCoy
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Aligning dual elevator servos GRRRR.

ok does anyone here know how to get two servos on the elevator to align??

There on a y cable and when there in the center position there perfect. when i move them up or down there no longer aligned. right one is always above left one. Ive aligned them at the up position and then there not aligned in the center position.
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Old Oct 19, 2012, 04:32 AM
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Unfortunately, unless each servo is on its own channel, there's no easy way. The way a servo works is by comparing the signal it receives with one generated internally reading the value of the feedback potentiometer, and moving the motor to zero out the discrepancy. Unless the servos are perfectly matched each will follow its own definition of where the target position is. Though to be honest I don't know if there are trimmers you can adjust in the servo circuitry to get them to match, or if modern "digital" servos can be calibrated electronically.
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Old Oct 19, 2012, 05:45 AM
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ive had this plane before and it worked perfectly with a y cable.
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Old Oct 19, 2012, 07:15 AM
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ive had this plane before and it worked perfectly with a y cable.
Not enough info
A the servos -- could be different (not matched )
B the geometry -- servo pivot to connecting point on each elevator AND hinge line not identical.
a non amplified Y harness or an amplified Y harness may be required (epends on the type/ age radio system)
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Old Oct 19, 2012, 07:15 AM
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Is there a reason you can't connect the servos to separate channels and use the 'servo calibration' or whatever it is called on your transmitter? Can you adjust pushrod distance from servo shaft center or/and elevator hingeline?
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Old Oct 19, 2012, 07:45 AM
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Always get the geometry as exact as possible then look for servo travel issues
a few tries with marking relative elev to pushrod throws on the fuselage ( a marking pen) will tell you where the error lies.
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Old Oct 19, 2012, 08:01 AM
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perhaps there's y servo splitters that allow adjusting the calibration for each servo as well. Personally I'd give each servo its own channel and go wild with transmitter mixing,. Also, if you had this same plane working fine before using just a y harness probably the servos are just mismatched. Better replace both of them rather than just one. If one has failed, the other might not be that far from failure either.
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Old Oct 19, 2012, 08:06 AM
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Originally Posted by Brandano View Post
perhaps there's y servo splitters that allow adjusting the calibration for each servo as well. Personally I'd give each servo its own channel and go wild with transmitter mixing,. Also, if you had this same plane working fine before using just a y harness probably the servos are just mismatched. Better replace both of them rather than just one. If one has failed, the other might not be that far from failure either.
There are "splitters" available -lots ofem -
One of the better ones is the JR Matchmaker-
Non 2.4 systems send info sequencially so elevator and it's selected AUX channel may have some real differences
The new 2.4 systems send this information "paired " so the rx sees same info in same time frame..
That makes pairing elev halves a snap - IF the servos and geometry are correctly matched.
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Old Oct 19, 2012, 10:45 AM
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Originally Posted by Atarie View Post
ive had this plane before and it worked perfectly with a y cable.
If you got matched movement it was simply good luck that you found two servos that were the same rotation.

Or as the others are saying you've got some non symetry in the system that is generating a little bit of differential motion.

To operate the same side to side the mechanical arrangement from output arm positions to how the pushrods connect at identical angles to the arms and all the way back to the control horns has to be identical. You want the arms to pushrods and pushrods to control horns to all meet at exactly 90 degrees when at neutral. Also the arms need to be matched for length and the pushrods need to go to the same holes on the horns.

The other thing is that if one elevator is out a little at full throw it's not the end of the world. The model won't even notice it in flight.
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Old Oct 19, 2012, 11:10 AM
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When we were setting up big IMAC/TOC models -this could be a real headache.
The elevators had 45 degrees each way (minimum) and sometimes the servos did not like over 125% throws - so it was a exercize in maxing out servo rotation - linkages and then making certain that the expo settings did not screw up the works
When we finally got the new 2.4 systems , this all became much,much easier .
I love these new systems !
My son and I I use the DX8 and 18 and a couple of my flying friends use the Futaba 18 ch stuff - With these setups , we can tweak out any errors found in tracking etc..
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Old Oct 19, 2012, 11:44 AM
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If you're using a simple "Y" harness, you would probably need to reverse one of the servos. There are a couple of brands of servo reversers available, and there are some "Y" harnesses with a built in reverser. If you go this route you'll have to work at the mechanical adjustments to get the two elevators to match up....and try to make the linkages identical on both sides. After that, watch the control throws to see if they travel the same angle on both sides. Depending on what kind of airplane you have, this can work. On a high performance model, you will notice it if one elevator travels farther (more angular travel) than the other. If it's a big trainer you might not notice

Both my son and I have had reversers fail. The airplane ends up wanting to roll severely when you pull back on the stick. Loops with a built in roll are impressive, but the airplane will be short-lived!! We have long since upgraded to 2.4 systems and use seperate channels.
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Old Oct 25, 2012, 01:38 PM
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i set the elevator servos on two different channels. Elevator and gear. When the elevator started in sync in the neutral position they were both perfect... they go out of what towards the highest and lowest movement... So i adjust the travel on the elevator on the gear channel so its perfect when high and perfect when low. Now when the elevator is in the central position its out of whack when it was perfect before.. Model is a phenoix models extra 330s. servos are hitec 645mg on both side brand new out the box..
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Old Oct 25, 2012, 10:03 PM
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We still don't know which radio you are using, so can't give specific answers. Can you adjust gear channel center point (servo calibration, sub trim, something else)? If so, adjust it to bring that half back to center, then adjust it some more to deflect the elevator to the other side of center. Now your end points will be wrong, re-adjust travel as you describe in your previous post. The neutral point will have moved closer to zero, but might still be a little off. Re-adjust center, overcompensating a little less than last time. Re-adjust travel. Repeat as necessary, each time making smaller and smaller corrections.
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Old Oct 26, 2012, 08:25 AM
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You may never get things the same -
Depending on total travel setting for each - the picture can. change -
Instruction manuals lead one to think that using offset, travel , subtrim etc.. the pairs can match- Mostly it is wistful thinking as info from the transmitter must be identical on each channel to get same movement.
No free lunch.
But-
leave each channel at 100%- then alternately plug each channel into each servo - look at TOTAL throws- are they the same?
was there enough free movement in each pair ( hinge and pushrod freedom are very important) to permit unimpeded travel?

Once you have one channel reversed - that center will change somewhat.
so - using some bits of tape and board stock- again check desired servo arm travel against elevator travels - radio off -get this pairing as exact as possible
then turn radio on and see what differences exist- maybe your radio will allow minor correction but it may be that center or relative positions will change as the servos move-
common on some older systems.
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