Servorahmen IDS servo mounts etc - step by step install?

[purview]

balsa is used with in the layups and the wings are not as stiff as from other factorys made at this time. I have a wing from build ~2015 and had this top wing surface issue only on one position of the servo. the material choice of balsa is a good suspect here. a carbon cloth is on the cutout of the servos and on the position of the wing spar. the inside has a complete glass cover and the outside is with one carbon, I hope ;-)

the balsa used on such constructions is not up to date any more. only on planes for average use and not with some "tank issues".

sorry to hear and see your wing. this is frustrating and part of the mistakes modelling has within

cheers chris

 

[Konrad]

Thanks Chris.

I was warned that if buying RCRCM to only get the carbon lay ups. I didn't think that the glass would result in an assembly issue.

I will from now on, add my own carbon stiffener patch to all my composite builds.

Another note about these fine servo frames. I like to mount the cross bar so that the raised feature of the cross bar acts like a spreader bar keeping the legs of the mount parallel. A nice engineering feature of these servo mounts is that cross bar mounting pads allow the bar to be mounted in ether position. The cross bar pads are the same thickness as the servo mounting flange, so the servo is held in the same position if the cross bar is flipped . This should have no effect after the frame is glued into the wing. Mounting as shown in the photo below might make it easier to remove the servo if space through the servo opening is limited.

All the best,
Konrad

 

[Konrad]

I’m using the “mono” version of these. Is it the nature of the set up that the pin is held captive by the the wipers? Operationally this shouldn't be a problem, but should one want to change the rod it would be ugly!

I used the servo and tray to align all the pivots and just made sure that I kept the 0.35mm spec. (see drawing earlier). I’m now thinking that maybe just have the rod pinned and focused on keeping the pin parallel to the hinge, at stated distance. (I think I'm actually parallel to the top wing skin, servo tray mount when aileron is fully down).

Everything seems to function smoothly, it just isn’t perfect.

 

[Konrad]

As the Mono IDS is now the standard IDS I thought I'd redraw the installation drawing shown earlier. I hope this makes it clear as to what we are trying to do with that leg (support).

The 0.35mm offset is to allow for clearance of the backside of the push rod. The 1.25mm offset is to allow the push rod to ride above the lower wing skin when the flap is fully deployed near 90°. Please be aware that this introduces some differential movement to the control surface that you may want to address with the positioning of the servo arm or in the radio programming.

All the best,
Konrad

 

[Doc James Hammond]

Good stuff Konrad!

Doc.

 

[Konrad]

Thanks Doc.

I'm finding that I seem to like to offset the spoons a bit more than indicated in the drawings. It appears that the leverage is a bit better for the flaps. Now this results in the need for an adjustment in the surface differential. In my radio setups this means a bit less programed differential.

All the best,
Konrad

 

[purview]

how about to go behind the hingeline for AIL Dif?
what is the purpose of the support to the hingeline? Is this a weak spot?

 

[Konrad]

Not a weak spot. It is there to help drive the lower skin (Hinge). Otherwise the force only goes along the top shin to the TE and back to the hinge. This may or may not give a soft control response. If the aileron has a drag spar and the spoon is glued to the drag spar, these legs aren't needed.

Putting the pin behind the hinge line exposes more of the spoon to the airflow. The main purpose for the IDS is a cleaner installation. So it might be thought as counter productive. If one wants more down than up in the aileron it might be best to accomplish this in the radio's programing, or with the servo arm, not mechanically at the aileron.

I like a bit more offset than the 1.25mm for my flaps, this is a leverage issue when the flaps are fully deployed (90°).

All the best,
Konrad

 

[purview]

not even thought about that that the top shin and the lower wing skin can be deformed. The argument of a soft response is now clear.

If you can show the needed servo horn on the flap and the mechanical dif on the servo control? what is the left "up" movement with your configuration?

 

[Konrad]

The IDS responds just like normal servo push rods and horns to mechanical differential. Here are some drawings showing this at an exstreme 70/30 ratio. Please be aware that the direction of the differential will change depending on which side of the axis (hinge or servo output) the arm or horn is placed.

All the best,
Konrad

 

[purview]

on IDS servo horns it is only possible to offset mechanical with the teeths of the spline. the correct alignment of let's say 45° is only possible if the tooth can locked within the alignment of the servo horn. The tidy solution is then within the TXs's solution. This mechanical setup is mainly dependent on the servo brand and the numbers of teeth (the resolution of mechanics) and sometimes is not the same as on a left or right wing servo position and configuration. The place of the spoon is in the deflection mode (down) and in front of the hinge more outside of the upper airfoilline, but it is still a better solution (aerodrag perspective) than conventional

[I Need about 3/4 the same throw up on the flap as on AIL, yet I didN't tried the same up as on AIL due to mechanical limtis]

Do you see a solution to try different lengths and angles before gluing the damn thing together?

 

[Konrad]

Correct. This is the same for conventional horns and rods. I'm trying to show that this mechanical differential can come from both the servo arm or the control horn. What is nice, is understanding that both can be used to make up for mechanical limitations (Often poor builds).

The mechanical offsets is a primary (initial) setting, limited by the resolution one gets with the servo output shaft splines. It is expected that for the finer (final) setting, that the radio program will be used to balance (match) both servo arm positions in neutral.

True this neutral offset will often take some potential throw away from the max throw end of the controls movement. I try to select the spoon to servo arm length ratio so that each servo is using 90% to 100% of the available rotation for at least one of the endpoints. Note both curves will not look the same in the program if using programed neutrals other than zero.

What is nice about most higher end radios is that the response of the control surface can be custom tuned to match each other. This is often done with the use of 5 or 7 point curves. But you are correct one needs to have the potential movement available from the servo and control surface to be able to match the end point of the surface movement.

So your flaps can't come up the 3/4 point because why? The hinge doesn't allow it? Or that you are now binding the spoon with some wing structure? If the issue is push rod motion, change the spoon to servo arm ratio to get the needed motion. This might mean needing to allow the servo arm to extend past the wing surface. Servo covers are used to address this source of drag.

Yes, I try to get the mechanics close before glueing in the servo. This is why it often takes me 2 days to get a set of servos installed in a wing. This is true wether I'm using the IDS or classic horns and push rods.

All the best,
Konrad

P.S.
I'm now thinking that your upward flap limit might be due to the alignment of the hinge, horn and arm pivots all being in a straight line. This is known as locked geometry.

 

[purview]

in the already build one it is due to a small servo horn and an opposite demandment of needed throw for the down flaps. and yes deflection with a straight line geometry and some space problems, of course paired with too small offset. I also glued the control horns exactly above the hinge.

the IDS solution looks like it can bring the pushrod nearer to the servo output shaft spline

 

[Konrad]

Sorry I don't understand what this means "opposite demandment of needed throw for the down flaps"?

With flaps (heck any surface) I calculate the total motion needed, both up and down. I then work out the ratio for the horn (spoon) and servo arm needed to get this using 90% to 100% of the servo's rotation. Once I have this I then think of where the servo and push rod will be placed. I then make adjustments based on any constraints I may see in the installation (Like spars or the need to lock linkage for example). Once I have the geometry for the full range to surface and servo movement I then check to see if the servo arms are closely matched in the center (neutral position). If possible I then make adjustments (often this will be in the programing).

(FYI: Often my flap servo arm is close to twice the length of my aileron servo arm. I often need about 1.75 time more motion in my flaps than I do in my ailerons).

Yes, the IDS does allow for smaller servo arms (bringing the pushrod closer to the axis of the servo's output). This is nice if you can now only use 50% of the servo's rotation. Effectively using a shorter servo arm allows for more efficient use of the servo's resolution and power. But remember it is the ratio of the spoon's lever (pivot point to hinge) and the servo arm length that gets you the needed throw. Now the smaller the levers the more critical the servo backlash and other points of linkage slop.

Now if need be, don't be afraid to grind out the current installation and start over.

All the best,
Konrad

mini Mach (Sanda Models)

One of the benefits (or curses) of having Aloft Hobbies as my local hobby shop is that I get to go through customer returns. I went in to Aloft Hobbies looking for a 60” racer other than a Sunbird and walked out with a customer returned Sanda Mini Mach. I’m still in need of a good value 60”...

forum.alofthobbies.com

 

[purview]

yes I thought about this the last year. after one year I had to replace four to five servos and might be thinking that a proper installation can help to minimize the servo demand. but not quiet sure if servos have not been overloaded in the past or wetted in morning flights.

That is some reason why I'm looking for another solution. On a new plane and not on my well flown and known one...

"..." it means the effective deflection of a surface where the motion is split into two not equal halves where the zero point is set by the aerofoils chord line. I was saying that I have the limit in upper movement because with this geometry and the needed down deflection the travel is limited.

it is a good point to start with the 100% servo rotation and fit the geometry according to the calculation. On the IDS solution there are prefitted pushrod lengths and servo control horns. So the deflections are only adjustable with the offset position of control horn and spoons @ hinge line

what is the up deflection of #43 second picture. #46 is with the indicated 3mm correction and means that the spoon is on the right position. the length can only corrected with control horn offset or the next longer or smaller pushrod or to replace the servo frame?

 

[Konrad]

No, In post 43 I had selected too short a push rod. I did this knowing that too long a push rod would mean I'd have to cut into the main spar to mount the servo! But I could have selected a 3mm longer push rod to place the servo in the servo pocket a bit better. This is only an esthetic issue (true any mass behind the spar can add to flutter issues but as this isn't a DS ship it isn't an issue). I could not change out the push rod after the epoxy cured without messing up those nice epoxy wipers. I was me just being a bit too cautious and using too short a push rod.

The only issue I had with the IDS spoons on that Mach II is that the pins are not "exactly parallel" to the hinge when taking into a count all three axis. Close enough, but when taking into account the wing's thickness taper there is an error if mounting the servo to the top wing skin (top skin and hinge are not parallel).

All the best,
Konrad

P.S.
I don't see the offset having too much effect on the deflection. I see it more as a means, to insure that there is clearance between the wing skins (2mm to 4mm thick skins) and the push rod. On the flap if using less than 1.25mm the push rod is likely to drag on the bottom skin as the flap reaches 90°.

But yes ,I too at times, use the clocking of the servo arm to adjust the push rod motion.

 

[Konrad]

Originally the Servorahmen IDS spoon had an offset to help address the top skin thickness. I saw this same offset in the IDS for the KST X0-8 mono. But with the mono IDS for the larger KST wing servos offset appears to be in the wrong direction. This hasn't been too much of an issue untill now. With thin wings, Ok thin trailing edges like we see in the Aeroic double cusp airfoils, this can limit the amount of up (pull) motion as the spoon binds with the inside of the bottom skin.

I found that flipping the spoon gained the much needed space to allow for the much needed surface motion. This isn't too bad, but I did have to remove the support legs. (See attached drawings)

All the best
Konrad

 

[Hank GB Z]

Konrad,


When you flip it over and remove the support do you replace the support with someting else (piece of hard wood?). To me it looks like a possible failure due to tension down the road.

Hank

 

[Konrad]

Good question. One of the few issue with the original spoon was that it was too smooth. This could lead to the spoon coming free of the control surface. The later mono IDS has these teeth on the side to help hold the spoon in place. To your question I fill all the space with an epoxy/cabosil mixture. I honestly don't know why the support legs are provided as it just makes the install more difficult. (One need to make sure they bond to the control surface. Not the main wing.

 

[Wayne]

Interesting, I had not noticed that until now.