Bob Mitchell

This is my first RC plane and it's just about ready to go. A couple of the control throws are off center, for lack of a better term. For exmple the elevator has more up travel than down. I know I can adjust the throws by moving the clevis on the control horn or at the servo arm, but how do I get them centered so the throws are equal in both directions.

Thanks,
Bob

Nathan King

The goal is to set your servo arm perpendicular to the control rod when your gimbals are centered.

piper_chuck

My Feedback: (12)

Here are a few things to check:

Make sure the transmitter trim is centered for the channel.

Check that the servo arm is centered relative to the pushrod.

Jetdesign

My Feedback: (8)

Yep, make sure the servos are centered (trim) and then that the control horns are perpendicular to the push rods. The control horns are designed with off set angles built in; if the horn is not perpendicular to the push rod, and doesn't seem to want to be that way, you can turn it 90 degrees and try, then another 90 degrees and try again, until you get really close. Adjusting the clevises will not help in your case. That allows you to center the throw to whatever surface (say the elevator to the stabilizer).

Bob Mitchell

Nathan (and the others who have replied)

Thanks for the suggestions.

3 of the four channels set up just fine. On the 4th, the servo arm is splined such that it's just off perp one way or the other. I gather that if I try rotating to the other 3 servo arms that I may get it to line up just right. Correct?

Nathan King

Each multi-piece servo arm has little numbers stamped on each arm piece; this is the number of degrees off from perfect center. Find the one that sits on your servo perfectly and cut the others off. I hope this is making sense.

Missileman

One other thing is how the control horn is mounted on the flight surface.
It should be mounted with the holes directly above the hinge line, if it is not it will cause the same problem.
I have seen people mount them anywhere even all the way to the outside edge of the control surface.

flyX

it's a bit tough to get it exactly center (90/90)because of the gears or the way the servo's arm fits onto the servo.
It's a good thing you notice stuff like that.

If you have a computerized TX, you can adjust the center.

Or you can mount the servo slightly off

craigss11

When you turn the Tx and Rx on the servo will centralise, then place the servo arm at 90 degrees to the servo
Next attach the arm to the outer hole on the servo arm,this will give you a starting point.
Adjust the clevis until you've got the control surfaces level to the wing,vertical and horizontal stabilisers.
Then check each control for throw deflection in both directions.
Check the required throw measurements,if you require more or less travel adjust them using the travel adjustments on your TX,this is if you've got a computerised Tx
Cheers[8D]

CGRetired

My Feedback: (1)

Center the servo by turning it on with controls on your TX all zero'ed out... no trim.

Remove the servo arm from the splined shaft and rotate it 90 degrees and put it back on. Do this until it is perpendicular. At one point, one of the arms will be perpendicular to the servo body. When you find the one that is, then just tighten it down and then set your elevator throws.

CGr.

da Rock

Keep in mind that the servo arm and the pushrod are where the 90degree angle has to be. The angle the servo arm makes to the servo body is of absolutely no consequence.

overbored77

My Feedback: (11)

Found this on the Central Hobbies site.

CGRetired

My Feedback: (1)

Alright. You are correct.. but I was assuming the obvious.. that the builder would make the servo square in the servo mount and that the servo mount is square with the fuselage centerline. At least, that's how I build mine. Then the servo arm being 90 degrees to the body of the servo as shown in Overbored's picture.. would make sense.

flyX

it only solves half the challenge anyway...or on the servo side.

You must also consider the control surface side. Sometimes a z bend is nice.
Also consider, if you run a single rod (not push and pull).....it will be stronger when the servo pull.

So...do you actually want the control surface to travel equal distance on both side ?
I don't think so...that's why it's nice to have a computerize TX. This way you can adjust the expos indiviually
on either side of the servo. (after you get the 90/90 as close as you can)


That's why it's nice to have a flight instructor. He'll give little hints...such as, add slight down elevator trim
when trying to make a landing or landing approches.

Montague

Lots of good stuff.

Note that on some planes, you want more throw in one direction than the other. This is most common on elevator. Most sport planes will tend to be more responsive to elevator in one direction or the other. Using non-equal throws is a way to make the plane respond closer to the same in both directions. On the flip side, if you find that the plane feels touchier in one direction than the other in the air (and you don't have a computer radio), you can use slight offsets of the servo arm at center to make the plane respond more evenly.

When I'm setting up the elevator on my new planes, I really don't sweat the throw being exactly the same in either direction. I'm going to fly the plane and see how it feels, and tweak from there until I get the up and down response that I want.

Equal throw on rudder and ailerons matters more, but even there, roll rate and response feel to rudder input is more important than actual surface throw.

opjose

An interesting article in FlyRC recently goes into setting up differential mechanically by NOT doing this...

dr_wogz

My Feedback: (3)

Well, here's another thought to pionder (As I'm now pondering it..)

From where do you measure the amount of throw? Tip? Root? midpoint?

I ask, because some planes have tapered control surfaces such as my 4 Star. The tip of either the elevator, rudder or aileron is much smaller than the root / base. So, if I want 3/4" of throw, do I measure that 3/4" of travel at the root? the tip? the midpoint / average?

landeck

My Feedback: (1)

You measure throw at the widest point of the control surface.

Bruce

JeffinTD

I built a flex flight Yak, and if I recall correctly the directions have you set the arms differently. It gives a mechanical aileron differential.

rhutson172

The first thing I would check before making any other adjustment is that the end point adjustments on the servo throw are the same in both directions.