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Electric trim center?

JeremyL

Well Known Member
Hey everyone, I searched but I couldn’t find exactly how to easily find the center of travel for the ray allen trim Servo so that I can cut the rod to the proper length. So if you could impart your wisdom on how to do this?
 
Servo Part # gives a hint

Hi, the servo part number includes the range of travel for the servo, e.g. a T3-12A has 1.2" travel. Get a 9V battery and touch the two power wires until the servo is fully retracted, then reverse the wires and drive out till you're at half-stroke (which for the servo above would be 0.6" or 15mm. If you want to get really creative you can wire in the indicator light temporarily and just drive it until the middle light only is illuminated.
 
Hi, the servo part number includes the range of travel for the servo, e.g. a T3-12A has 1.2" travel. Get a 9V battery and touch the two power wires until the servo is fully retracted, then reverse the wires and drive out till you're at half-stroke (which for the servo above would be 0.6" or 15mm. If you want to get really creative you can wire in the indicator light temporarily and just drive it until the middle light only is illuminated.

Thank you a ton. I will give that a try, sounds easy enough the way you explained it.
 
Thank you a ton. I will give that a try, sounds easy enough the way you explained it.

You wont necessarily want the rod sized for neutral with the servo at its mid point since you want about twice as much nose up travel of the tab as you have for nose down travel.
 
You wont necessarily want the rod sized for neutral with the servo at its mid point since you want about twice as much nose up travel of the tab as you have for nose down travel.

I see, so how would I do it properly in order to take that in to account?
 
I see, so how would I do it properly in order to take that in to account?

One way would be to measure how much travel your particular servo has between fully retracted and fully extended (or use the model # of the servo... the 12 is 1.2 inches of travel).

Then adjust the servo so that it is retracted 1/3 of the total from what it is when fully extended.

Make a push/pull rod of proper length with the tab in its neutral position.

That should get you pretty close to meeting the minimum deflections specified in the manual and a properly made rod will have enough adjustment range to tweak it as needed.
 
One way would be to measure how much travel your particular servo has between fully retracted and fully extended (or use the model # of the servo... the 12 is 1.2 inches of travel).

Then adjust the servo so that it is retracted 1/3 of the total from what it is when fully extended.

Make a push/pull rod of proper length with the tab in its neutral position.

That should get you pretty close to meeting the minimum deflections specified in the manual and a properly made rod will have enough adjustment range to tweak it as needed.

Thank you Scott, I will give that a go. If my math is correct and I follow what you have said. Run it until it’s fully extended and then retract it until it has retraced .4” (1/3 of 1.2”) level the tab in trail and cut the rod to that length so that it still has enough “bite” into the rod ends. Does that sound about right?
 
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Does that sound about right?

1/3 of travel, not necessarily .4". And that is 1/3 of travel from the nose down side of the servo travel range. Remember that trim travel direction is opposite of elevator direction.
 
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