Hi,
I seem to run into this problem over and over and over. For some reason people are just not setting up their planes correctly mechanically before they start doing electronic adjustment.

First, you should make sure all your transmitter servo trims are at zero. Then, check all your servo arms and make sure they are as perpendicular to the servo as possible. Sometimes rotating the arm 180 degrees offsets you by a 1/2 spline so you are closer to perpendicular. Then you should program the throw in your radio on all your flight surfaces (ailerons, elevators, rudders, flaps if you got them and what ever else moves the air) so that the high-rate throw in the transmitter is the maximum minus a little bit. So if your radio will allow you to set your travel to 150 then you should back that off to 140 but program that into all your flight surfaces. The 10 points is to allow some room for the electronic adjustment outside the radio. You should do this if you are using any external adjustment device, Equalizer, MatchBox, MSA-10 or anything else that does what these do.

Next you want to make sure your radio is set for your high rates. You can use your radio subtrim (offset) to get your servo arm perpendicular to the servo pushrod. This is very important. If you have ganged servos then you want to make sure the primary servo has this done. The others can be done using the electronic subtrim adjustment of the external adjustment device. You want to keep your plus and minus throws equal in the transmitter. Then MECHANICALLY you want to get all your surfaces VERY CLOSE to where you want the final throw to be for high rates. This is for all surfaces. If you mechanics are not setup well you are going to run into problems down the road. At neutral you want all ganged servos to have their pushrods perpendicular to the servo arm.

Last you you want to go in and use the external device to do fine adjustments to get the surfaces final positions. Set up the primary servo first, get the endpoints where you want them. Move to the next servo. Get the servo arm perpendicular to the pushrod at neutral. If you have to adjust the length of the pushrod at this point so that it does not fight the primary servo at neutral. Then move to the endpoints and adjust them so they do not bind. Then move on to any other ganged servos.

Doing things this way will make everything perform better.

Great information , I'm gonna print it out and hang it in the shop , I try to do all those things but seems like I always have to start over because I forgot to do one little thing that will effect the whole set up .. Thanks for taking the time to write this

Can I add one thing?

Make sure to reset or start with a fresh model memory.

Good stuff.

Your assuming the servos are 90degrees to your hinge line. I think it is better said to make sure your servo arm is parallel to the hinge line instead of perp to the servo.

If i may add---Make sure your linkage attach points on the control horn are the same vertical distance from the hinge center line and that the attach point is directly over the hinge center line with the surface at neutral. Also make sure when you start your linkage / rods are the same length.

Thanks for all the additions. I appreciate the extra input.

Hi,
Yes, these are all very good corrections to my initial post. I was kind of thinking of one specific example and this makes it much more general. Thank you,

Originally Posted by parpar1

Good stuff.

Your assuming the servos are 90degrees to your hinge line. I think it is better said to make sure your servo arm is parallel to the hinge line instead of perp to the servo.

If i may add---Make sure your linkage attach points on the control horn are the same vertical distance from the hinge center line and that the attach point is directly over the hinge center line with the surface at neutral. Also make sure when you start your linkage / rods are the same length.

Amen Ritchy. Great Job. I'd like to emphasize the importance of getting the servo arm at 90 degrees to the centerline of the servo. I happen to believe it is so important that I have developed a process to get them perfect.
I use the AirWild servo arms which are comprized of a hub to which the arms ar attached with #2 SHCS.
I made a fixture to hold the servo in a milling machine. With the hub mounted on the servo spline and the servo powered up in the neutral position (with zero sub trim), I drill four new screw holes in the hub square to the "X" and "Y" axis. The "arms" are now mounted in a perfect 90 degree position.
I realize some may think this is extreme but but that's how much importance I associate with getting this part as close to perfect as posible.

DONT FORGET!!!!!!!!! Set your Matchbox back to "ZERO" after you make your adjustments!!!! LOL

I have a slightly different method that was taught to me by pro builder extrodinaire Cam McCausey. He calls it squaring the plane. It insures that mechanically everything is in alignment and that the servos are at the same point in their circular rotation at anypoint in the travel of the surface. This is the only way to prevent binding throughout the travel of the control surface. By doing this I can hold my ailerons at anypoint in the travel without binding.

Below is copied from a couple of posts on the IMAC website so some of it is repeated.


What started all this is I never check whether the arms are exactly 90 to the case or not. Who says the servo boxes themselves are in perfectly square, what is important is the arms are at the same point in the circular rotation, which using the method above ensures.

First the height of the control horns from the hinge line to the pivot point on the horn needs to be the same for very close. This usually results in the outboard horn on the aileron being longer than the inboard horn because the wing is thinner.

Then with the plane turned off and the surface centered, I adjust the linkage so that a straight edge can be laid across the two servos so that it runs through the servo arm screw down the center of the arm through the second servo arm screw and down the center of its servo arm. Doing this ensures that mechanically the two servos will travel through the same degrees of rotation at the same time. This is critical so they match at all points in the travel. For example when the surface is deflected both arms will be pointing at 2 o'clock rather than one at 2 and 1 at 1:45.

At this point you have to disconnect the linkage from one of the servos, and power up the plane. Odds are there will be some subtrim required to center the surface back up, but you do not want to adjust the linkages at this point because you know mechanically they are in perfect alignment, so it must be done on the radio. From there I set the endpoints on the servo so that I get the amount of throw I want up and down. They may be off (i.e. 97 up and 101 down)

Once this is done I use the subtrim and endpoints to match the second servo so that its linkage can be connected without any binding. If this procedure is done you get virtually no servo humming or binding at anypoint throughout the travel.

If you do not match the linkages mechanically and just use the radio to set the subtrim and endpoints you are guaranteed to have binding at some points during the travel, just not at the center and end points. Or if you adjust the linkage length so that you do not have any subtrim you will get the same binding at somepoint just not at the centers and endpoints.

The only way I have found to eliminate the subtrim is to use a servo horn like the Airwild Unihub (when using a non programmable servo). Because this can be attached to servo in 4 different positions, you can try all 4 until you find the ones that allow you to lay the straight edge between the two servos without using any subtrim. I was able to do this on my Carden and I have no subtrim and no binding at anywhere in the travel, you could run the wing on a Y-Harness.

This method of squaring the plane can be done with the stabs. Just take them off the plane put the stab tube in the the stabs. Center the surfaces, then lay a straight edge between the the servos and adjust the linkage so the straight edge runs through the servo arm screws and down the center of each servo arm. If the height of the horns from the hingeline to the pivot point is the same then you have everything mechanically correct. At this point you will need to use subtrim and endpoints to match them at the center and endpoints, but when you do, they will match throughout the entire travel. Again using a Unihub is the only way to do this without subtrim or programming a servo.


Using SWB or any other arm will require adjustments in subtrim and endpoints because you rarely can find any servos that match perfectly or allow you to "square" the wing. But I have done many planes with SWB arms using the method above and it always works out because mechanically it is correct.

BTW this method works with any servo without needing to program it.

Once I started using this method my average battery usage per flight when from about 375mah per battery per flight to about 150-180 mah per battery per flight in my Carden (2 flight batteries)

My main point is that using the straight edge and getting your control horns the same height to ensure you have the correct mechanical setup solves 95% of the problem. When doing this with SWB arms you will be required to use some subtrim and endpoint adjustments to get them to match because you don't change the mechanical setup. However even solving the issue with the radio with SWB will give you a setup that does not bind throughout the range. Kenny's plane you can hold the aileron in any location without binding. If perfect the spread between the upper and lower end points is the same even though they may be shifted a little bit because of the subtrim.

With the 2 planes I have done using unihubs we were able to square the plane with no trim and very small variance in end points. The change in endpoints is because of a millimeter in difference in control horn heights.

The mismatch at different rates is due to incorrect mechanical setup.

Thanks for posting. This set-up is just one of many challenging things for me during assembly. The other being firewall installs on Pilot frames, but that's another story I suppose..

One more thing I drew up some servo protractors a couple of years ago when I was setting up the plane the way Bob describes. I have attached them below.

NICE!

need a hitec protractor now.

I just got a PM asking for something to visualize what I am talking about. I have attached 2 pictures showing wing and stabs.

The important thing to remember is that all of this is done without power to the servos. Hold the surface neutral and adjust the linkage length till the arms line up. Once this is done you do not adjust the linkage lengths again, everything is done electronically. As long as the horns are the same height from the hinge line and you set the center and endpoints on the radio so they match, then the surface should have no binding throughout the range, because the servos will always be at the same point in the rotation at the same time.

The reason this is so important is because linear motion is not proportional to angular rotation, so if they are not mechanically aligned like this then at half travel one servo may generate 1" of linear deflection and the other 1.1" of linear deflection which would cause binding. They would then match again at the endpoint because of the radio. The radio can always make two servos match at the centers and endpoints, but not throughout the range.

Originally Posted by audi murf

NICE!

need a hitec protractor now.

They are all pretty similar one of those may work.

Originally Posted by The_Wreck

I just got a PM asking for something to visualize what I am talking about. I have attached 2 pictures showing wing and stabs.

The important thing to remember is that all of this is done without power to the servos. Hold the surface neutral and adjust the linkage length till the arms line up. Once this is done you do not adjust the linkage lengths again, everything is done electronically. As long as the horns are the same height from the hinge line and you set the center and endpoints on the radio so they match, then the surface should have no binding throughout the range, because the servos will always be at the same point in the rotation at the same time.

The reason this is so important is because linear motion is not proportional to angular rotation, so if they are not mechanically aligned like this then at half travel one servo may generate 1" of linear deflection and the other 1.1" of linear deflection which would cause binding. They would then match again at the endpoint because of the radio. The radio can always make two servos match at the centers and endpoints, but not throughout the range.

Thank you John..