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Flaps are driving me bonkers


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GuyB

Hi

Hoping  someone here can solve an issue. Setting up a recently purchased F5J model. All fine apart from the flaps. 
 

They are on separate channels assigned to throttle stick. They are moving at different speeds. They align either fully down or fully up (flush with ailerons) but during travel one moves further than the other, then the other “catches up”. So at say 20% down, one is further down than the other. Not by much but enough to annoy / create roll. Hard to describe so attached a short video 

I am using a Hitec Aurora 9  and have spent a couple of hours on all the functions I can think of including servo speed but can’t solve it 

any thoughts?

thanks as always 

Guy 

 

https://youtube.com/watch?v=0OFAS5MG5YA&feature=share

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mikef

Could it be that the servo curves are out of kilter?  I find I need to tweak the curves to match the travel at all points but you may have a lump on the left flaps' curve I think.

The pictures below are flapperon servo curves on an F3K wing - you can see that the 5-point curves are not the same, or straight lines.  If I made a large change to one of the intermediate points, the effect would be as your video.

B1018B88-BB1F-4B05-8E73-417E744FCC1B.jpeg

C3C4F728-4824-40A0-A1E7-A211C927D022.jpeg

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GuyB

Hi Mike

Thanks for the reply. Makes sense. I can see these curve diagrams on certain screens on the Aurora 9, just not sure how I access these curves directly  to set them the same. Getting brain ache so will have another look one evening this week 

GUY 

 

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mikef

Setting them the same should be a starting point.  You will then need to tweak slightly to get matched travel.

Does the left flap curve look odd compared to the right flap curve?

My Royal Evo let’s me set both servos to the same adjustment point (P1 to P5) - then I can turn a knob to get the match before moving on to the next point.  Maybe yours does this too?

 

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satinet

Probably the flap horns or LDS system aren't exactly the same on both sides. I.e they are hinging on a different fulcrum. If the height and/or horizontal position of the horns is slightly different the flaps will move differently even with exactly the same servos/servo horns/servo position/tx settings etc. 

Sometimes you can correct it with the end points but often you need to use a mixer type curve on one or both flap channels which I don't think the A9 had from memory (although I think some of the free mixes did).

 

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PeteMitchell

I have found when I have used servo end points to correct surface neutral position, rather than adjusting the mechanical linkage, that this can cause the surface with the most end point correction, to move at a slower rate than the other one.

No idea why this should happen, but usually an endpoint adjustment of upto around 10% or so causes no problem.

Another thing worth checking, hope it helps🙂

 

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MikeE

If it's badly out, I would consider rebuilding one of the linkages. 

There is no substitute to an accurate build. 

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mikef

Watching the video, I don't think a linkage problem could produce that effect.  I'm thinking faulty servo/jamming linkage or a Tx programming problem.  I agree that it's important to aim for identical geometry on the two sides of a paired control but you're getting a distinct interruption to the smooth movement on one side - it would take wilful asymmetric design to cause that.

I have no experience of the Aurora 9 but I found a manual here:-

https://hitecrcd.com/files/Aurora_9X_Manual_EN_V1.2.pdf

Page 86 speaks of an 'offset curve' but it's not clear what it does or whether it applies to individual servos or to controls (that may move more than one servo).

Page 88 shows the monitor function - what do the servo movements look like on this display when you move the flaps - are they even?  If yes, it's one of the flap servos that's bad.

7 point curves are mentioned in the manual, but only mixer outputs.

 

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MikeDaBike

I had a very similar issue with a glider purchased second hand. One linkage was completely different from the other. One had a significant bend in and the other didn't.  They were also different lengths. The behaviour was quite similar to your video. I would extract both linkages and make sure they are identical / use a servo tester to check they are set up correctly in terms of mimicking each other's movement

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oipigface

I had a similar problem recently with a Pitbull 2. The plane has had a chequered history, and its current wings were not fitted at the same time, but the servos are the same type. After spending ages tearing the installation apart to check the servos and finding nothing, I tracked the problem down to a programming error. Since mine is a Futaba system, it’s probably not of much interest to try to remember exactly what it was, but I had somehow managed (in landing mode) to have one flap moving 198% of the aileron movement, while the other moved 98%. 
Sorry to be vague, but it didn’t take anything but a careful check of ALL the pages of the programming to find something obviously weird, which when corrected proved to solve the issue, so I didn’t have to think much about it. 
My suggestion is that you do the same. 

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MikeE

You could just make a new program just controlling the two flap servos and nothing else.

Easier then to ensure you have a clean feed.

Alternatively if your transmitter gives you servo outputs as a number, compare them. Watch that they are increasing smoothly and identically.

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EssexBOF

It is imprtant before installing the flap servo's to ensure that they are both set to be in an identical position re the arms, with the Tx, set with centering set to zero and all off sets & weights set to zero as well. The arms need to be in an identical position when viewed from the side. If they are not you will get a variation, as to there relative position, when you put your imputs in. On Open Tx it is usefull to be able to adjust the speed as well. If we still had linear servos, ,problem would be less, but the end travel could well be different, but adjustable. Another tip, is to use the X arms, rather than the single arm, as you will find that by repostioning the arm, at each 90 degree postion there is a difference re the splines on the output shaft, so it is possible to get them to where they match on the servos, without resorting to other methods.

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MikeE

The two examples above are both ideal for aileron servos but not optimum for Flaps.

Flaps travel mostly in one direction, and only require small amounts of 'up' .

You need to try to ensure that you use all of the available servo rotation.

This will ensure that you have strong linkages that don't break gears or horns if you catch a flap on landing, and also will give you fine control.

Servo horns need to point directly down the line of the control rod when the flaps are fully down.

Servo arms need to be as far forward facing as possible (linkages normally restrict hem a little) when the flap surface is up to the amount needed. (don't be greedy here, large am punts of up flap add nothing worthwhile.)

 

Setting the servo you need to do as mikef says and make sure that each servo has the same input value.  But this should not be zero. It will also be an opposite value in the one servo. i.e. +30 , -30. 

Once each servo is rotated to the chosen value add the horns as mirror image sof each other.

Make both control rods as identical parts, solder any clevises in place, you do not want them adjustable, and ensure surface horns are jigged onto the flap surfaces. 

Connect all the rods up at both horn and servo, and glue the servos into place while they are powered to their appropriate value (=30 - 30 in example) and tape surfaces level while it all dries.

 

 

 

 

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GuyB

Big thank you to all that have replied and spent time on this. Lots of things to try and hopefully I will find a solution. 

Guy

 

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satinet

Don't worry we've already spent many hours trying to get flaps to move evenly. 

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