Servo & Linkage Blues - Insufficient Control Surface Movement - Why Does This Happen?

[Steve Rosenbach]

I've created a little video of my problem the you can view here: https://www.dropbox.com/s/q4gpap18ekg61ye/Servo Linkage Problems.mov?dl=0

This has happened to me a some of my FT builds, and I don't understand what is happening to limit the servo travel in one direction (in this case, downward, which is what pushes the aileron upward.)

This happens to be on my latest build, and FT Tutor. The build was excellent up to this point.

I'd appreciate any help, many thanks!

 

[Indy durtdigger]

Try a z bend on that servo arm instead of that rigid metal mount. With it locked in solid it's just bending the push rod. I personally don't like those linkage anchors as they have come loose on me in flight and typically those are installed on the control surface rather than the servo. Also what is that push rod as it may not be rigid enough exacerbating the issue. Might also try a longer servo arm so you can tinker with the angles.

 

[Monte.C]

Try a z bend on that servo arm instead of that rigid metal mount. With it locked in solid it's just bending the push rod. I personally don't like those linkage anchors as they have come loose on me in flight and typically those are installed on the control surface rather than the servo. Also what is that push rod as it may not be rigid enough exacerbating the issue. Might also try a longer servo arm so you can tinker with the angles.

Yeah wow, 100%. You're really working that servo pretty hard, to force the pushrod into such a bend. I thought all those kinds of linkage anchors were on a full swivel.

 

[Monte.C]

yeah, this camera is good for photography.

You won't get yourself very far here. Save yourself the effort and go fishing somewhere else.

 

[Taildragger]

I've created a little video of my problem the you can view here: https://www.dropbox.com/s/q4gpap18ekg61ye/Servo Linkage Problems.mov?dl=0

This has happened to me a some of my FT builds, and I don't understand what is happening to limit the servo travel in one direction (in this case, downward, which is what pushes the aileron upward.)

This happens to be on my latest build, and FT Tutor. The build was excellent up to this point.

I'd appreciate any help, many thanks!

i would say in your case the linkage stopper isn't able to swivel freely on the servo horn

 

[AIRFORGE]

yeah, this camera is good for photography.

No Nolan. Just no.

 

[Steve Rosenbach]

i would say in your case the linkage stopper isn't able to swivel freely on the servo horn

Thanks for that idea ! It helped me solve the problem.

I had the linkage stopper secured tightly to the servo arm - I've always done it this way, and sometimes it works fine and sometimes not.

So un-tightened the connection (to the washer and nut under the servo arm) enough to allow the linkage stopper to swivel freely - and that did the trick!

I will put a drop of hot glue under the nut so as to keep it from getting further loosened, but now my Tutor will be good to go... and I'll go back and fix this on my other planes.

Thanks again, Taildragger, and thanks to all who answered.

 

[Bricks]

Glad your major problem got solved.

If the video is showing correctly it looks also like your servo arm is not centered correctly as it travels farther in one direction versus the other. There is always one way the servo arm will install at 90 degrees, and this is how you want to position the servo when installing..

 

[Monte.C]

There is always one way the servo arm will install at 90 degrees, and this is how you want to position the servo when installing..

@Bricks thanks for that subtle but powerful insight. I remember Josh on an earlier vid building planes with one of his crew, he was centering the servo, mounting the servo arm, and he chuckled "haha it never aligns exactly perpendicular, does it" and they shared a little laugh. But I figured that one out some time ago. It's an odd number of teeth between the servo arm and the servo itself. It aligns at 90 degrees on one side and exactly 1/2 tooth off on the other side. When I need a servo I check one or more until I've got the alignment in the direction I want. I'm glad I'm not the only one who knows this. Thank you.

Did I make it complicated enough? The whole world needs to know!

 

[SSgt Duramax]

Glad you got it fixed. When I was having this problem my servo wire was too thin and buckled under compression but under tension it was fine. So it would move farther under tension than under compression.

I have since learned from my mistake.

 

[Quinnyperks]

yeah, this camera is good for photography.

totally unnecessary

 

[Taildragger]

Glad your major problem got solved.

If the video is showing correctly it looks also like your servo arm is not centered correctly as it travels farther in one direction versus the other. There is always one way the servo arm will install at 90 degrees, and this is how you want to position the servo when installing..

the ft tutor has this on purpose to act as mechanical differential aileron

 

[Bricks]

the ft tutor has this on purpose to act as mechanical differential aileron

IF your radio is capable I would rather do the differential in my transmitter, this way I can vary the amount of differential needed.

 

[TheFlyingBrit]

@Bricks thanks for that subtle but powerful insight. I remember Josh on an earlier vid building planes with one of his crew, he was centering the servo, mounting the servo arm, and he chuckled "haha it never aligns exactly perpendicular, does it" and they shared a little laugh. But I figured that one out some time ago. It's an odd number of teeth between the servo arm and the servo itself. It aligns at 90 degrees on one side and exactly 1/2 tooth off on the other side. When I need a servo I check one or more until I've got the alignment in the direction I want. I'm glad I'm not the only one who knows this. Thank you.

Did I make it complicated enough? The whole world needs to know!

That caught me out a couple of times, until I figured it out and turned the servo around. Now I just compensate with an off set on the transmitter saves time and looks neater.