Somebody needs to make a spreadsheet..

[Andy W]

.. that allows you to enter in servo movement, desired control horn or servo arm length, surface chord, and desired range of motion, that would tell you how long the other parameter needs to be.
I've built models where I've gone with the better setup of small arm on servo, long arm on surface, and not had enough movement, or had too much and had to reduce. I'd like to get it closer first time..
..a

[Sparky Paul]

Dude!!!!
The number of variables is staggering!
The variation between OEM manufacturers servo arms and 2nd party horns alone
would require an extensive library of parts dimensions..
Then there's the chords to use to finger the angular deflections..
Building a spread sheet for just these two arms (Futaba) and large and 1/2A horns with all the possible locations for the pushrods ....
Who's got the time?
Experience, experience, experience..
Never use the closest hole on the surface horn. It creates an ideal situation for flutter, as there's little mechanical advantage to keep the surface in place..
go out on the servo arm to get more motion..
etc...

[Andy W]

Hmm.. According to one vendor, the shortest arm on the servo is what should be used for least flutter.

I wasn't looking for a library with data, I meant just a simple calculation when you provide the measurements.

I.e. (numbers guessed, it's not in front of me) on my Gambler DLG, the elevator is about 1 1/4" wide, provided horn has holes at about 5, 7 and 9 mm from the hinge point, and I need about 15 degrees motion in each direction. Servo (HS55) has about 90 degrees of movement. How long should the servo arm be using say the middle arm on the control horn so I can adjust later if needed..

..a

[Dennis L. Payne]

Try these links.

http://home.germany.net/100-173822/schwerp.htm

http://www.csd.net/~cgadd/eflight/calcs_servo.htm

or how about this one.. (attached zip file)

I am sure that one of these will meet your needs

[Antonsoarer]

Too many variables/parameters but some basic rules that seem to work: (sure there are many more)

Stay close to the Servo center (shorter output arms) for maximum holding & moving power.
Use long surface horns (longer than the servo arm) for the same reason as above
It’s always a trade-off between holding/moving power and movement range.
Use five Rx batteries for more power.
Use thicker wires and low internal resistance batteries for more power.
To maintain power use mechanical adjustments for surface movement reduction not the transmitter (end point or travel) adjustments.
If you can’t eliminate slop use horn/arm lengths to reduce slop relative to movement, if the servo end is sloppy use a longer servo arm.

[macr0t0r]

Let's REALLY simplify this:
(1) To minimize slop and flutter, start with the control rod on the outer-most of both the servo and the control=horn.
(2) Do one of the following:
(2.a) If you need more throw, then move inwards on the control-horn.
(2.b) If you need less throw, or the servo is not applying enough force, then move inwards on the servo head instead.
(3) If you can't get enough throw from the servo's torque, install a stronger servo (obviously).

That's it. Bringing a computer into this is only going to cause confusion and miscalculations (like computers always do). :p

[Sparky Paul]

The upper setup in the sketch has 12 combinations of connections, the next ahs 25, the bottom has 20.
With a 1:1 setup, servo arm hole to surface control horn horn, the servo angular motion will be the surface angular motion.
For the upper setup, it would be the outer hole on the servo arm, and the 2nd up from the bottom at the horn.
The 3rd up on the horn will have less surface travel than servo travel, and the 4th up even less.
The worst combination is outer servo arm hole, lowest control horn hole.
For a surface with a lot of chord, on a fast airplane, this is almost a guarantee of flutter.
In addition, there's dual rates, EXPO and ATV adjustments to tailor surface deflections.
Chords can be changed to affect responsiveness.
The possibilities are enormous when all of them are considered.

[SoarNeck]

http://members.cox.net/evdesign/pages/linkage_design.html

[Sparky Paul]

Adam, that looks like an extremely comprehensive program.. probably worth the $9.95.. the Plane Geometry thing at $19.95 (mentioned the prices as these aren't specified in the samples) is probably also a goodie to have.

[Dennis L. Payne]

Sparky Paul, I purchased both of these sheets a while ago and they are first class. The plane geometry is totally mind blowing and you get a real feel of the performance of your design. What is even better is the support that Envision provide, I had a problem with a Delta configuration model and they fixed that in 24 hours, really excellent.

[SoarNeck]

Yep, I second Dennis's thoughts. I only purchased the aero program, but it's now one of the first tools I use to evaluate a new design. The manual that comes with the sheet is basically the Cliff's notes version of a full course on aerodynamics, and would almost be worth the purchase price in-and-of itself.

[Lazy]

Adam, aero program work only with imperial system or metric too ?
Rgrd
Vladimir

[SoarNeck]

Imperial only. Canada is officially metric, but I can work with either after years in this hobby!

[Lazy]

inappropriate comment removed by moderator
I too, but it pretty complicate life :D

[Frank B]

I think you guys complicate things too much. What Andy is asking for are some simple triangular calculations. I will see if I can come up with something.

If I understand it correctly, you should have the following parameters:
- Servo movement in degrees
- Servo arm length (or more correctly: distance to the hole you want to use)
- Control horn length (same as above)
- Control surface cord
- Desired control surface movement

You then enter the known parameter values, and the program calculates the others, correct?

I could use a program like that myself. I have a model where my dual rate on the elevator is set to 15%. If I had known that when I build the model, I would have used longer control horns.

[Sparky Paul]

I think you guys complicate things too much. What Andy is asking for are some simple triangular calculations. I will see if I can come up with something.

If I understand it correctly, you should have the following parameters:
- Servo movement in degrees[/quote}
.
How many servos are there available? 50?
[quote]
- Servo arm length (or more correctly: distance to the hole you want to use)

There are 3 or more arms for each servo.
Now there's 150 choices for arms and servos.
There's 4 (at least) holes per arm.
Now there's 600 choices, for servos, arms and holes.

- Control horn length (same as above)

10 horns, 4 holes per horn.
24000 choices..

Who has the time to do this?
The more variables, the more the choices multiply.

- Control surface chord
- Desired control surface movement
You then enter the known parameter values, and the program calculates the others, correct?

I could use a program like that myself. I have a model where my dual rate on the elevator is set to 15%. If I had known that when I build the model, I would have used longer control horns.
.
Just getting the values for the servo arm holes is an impossible chore.
Experience is the simplest method.
.
Not that I'm not thinking of a way to do this... :)

[Andy W]

Frank has it right - I didn't indend to include servo makes. You don't need it.
Just input (as I stated at the start of this thread):

1) servo movement (degrees, measured by simply hooking up a servo and wiggling it!)
2) surface chord and desired range of motion in linear measurements
or
desired range of motion in degrees
3) desired control horn
or
servo arm length
Whichever of (3) you DIDN'T provide, it would calculate for you..
..a

[Andy W]

(and you could make it fancy by including more than one hole in the control horn and servo arm - say three each - but that would only give you 9 possible combinations, three would be identical)..
..a

[Andy W]

(.. and you could account for various control surface thicknesses, top/middle/bottom hinged, etc.)..

[Frank B]

Sparky, I think you misunderstand the task. You have one servo with known degree of deflection, and one control surface with a desired degree of deflection (acording to the instructions, that came with the plane). The task is to find the length of the two horns in order to get the control surface deflection needed at full servo deflection. You enter a value for the length of one horn, and the program tells you what length the other horn should be. It's that simple. If your servo horn has three holes, you just enter one value at a time and check the results, and then select the pair you want.

Andy, do you know what difference it makes if the surface is top or bottom hinged? Does it deflect more one way than the other? If it does, the thickness must determine how large this difference is.

I will do some calculations.

[Andy W]

The surface thickness and top/middle/bottom side (actually, "this", middle, and "other" side) hinges would alter the distance between the hole in the control horn and the pivot point..
..a

[Andy W]

.. and all of these calculations would have to assume the control horn is installed 'correctly' with the hole 90 degrees from the pivot point. Cases where this is not true (i.e. low profile, displaced horns for spoilerons on sailplanes, for example)would require further calculations.
..a

[Frank B]

I was just about to ask that. :)

[Sparky Paul]

With all those parameters known, what's to stop -you- from fingering it out? :)

[Frank B]

Nothing is stopping me.
I have started work on the spreadsheet. :)

[Frank B]

Here is my first shot at a spreadsheet.

You can use any units you like (mm, cm, inches), as long as you use the same units everywhere. Angles are in degrees.

This first version can only calculate the length of servo horns and control surface horns. Leave one of the two fields empty in the input column, and it will be calculated.

Only enter one value for the control surface deflection, either vertical movement or deflection in degrees. If you enter both values, the value for vertical movement will be used in the calculations.

Also featuring control surface thickness and hinge placement. :)

[Andy W]

With all those parameters known, what's to stop -you- from fingering it out? :)

I'm one of those guys that says "I'm sick of trying to do this the same way every time" and spends 5 hours building a tool to save 5 minutes next time! :D
..a

[Andy W]

Frank, you're my hero -
is Angle of control surface deflection around center (i.e. total is double value entered here?)
..a

[Frank B]

The angle is from neutral to full deflection in one direction, ie. half of total deflection (same for the servo).

[Sparky Paul]

Try this...
Filling in the spread sheet columns and rows is left to the user.... :D

[Frank B]

I just found a small bug (- instead of + in one of the formulas). I have replaced the zip file.

[Frank B]

New version uploaded.
I have added another calculated value. Nothing Andy requested, but I thought it was appropriate.

(Download from post #26)

[Andy W]

Excellent.
Thanks for doing this!
..a

[nuevo]

Has anyone looked at the servocalc.zip in post #4 of this thread? This spreadsheet already does what everyone is asking for and more. It even calculates how much torque is required from the servo to move the surface. Also accounts for servo horns being offset from the hinge line, if you like.

[Sparky Paul]

Here's a sketch and equations....

[Frank B]

That's the formulas I used. I hope they are accurate enough for our purpose.

Actually there is a little inaccuracy when the two horns are of different length, in which case the control rod will change angle and thereby decrease the distance between the horns a bit. The control horn will move a little further than the servo horn. This is so small a change, that I have desided to ignore it. :rolleyes:

[Sparky Paul]

Yes, there's ways to get way too detailed in any of this.
Just getting all the units in the proper format... why do spreadsheets demand radians?
No one uses those for anything? :)

[Frank B]

Radians seems to be standard for use in programming languages (it's the same in Visual Basic). Actually it is more convenient than degrees when used internally, but people are used to degrees, so you have to convert them in the interface.

[raptor22]

Yes, there's ways to get way too detailed in any of this.
Just getting all the units in the proper format... why do spreadsheets demand radians?
No one uses those for anything? :)

They are rally common if you take higher level math like calculus. Can really be quite convenient.

I'd liken their use to the US use of the metric system.

--Alex

[Sparky Paul]

About the only time I'm aware of that the difference in motion for horns matters is with seperate elevators, and two externally mounted servos.
Unless one of the servos is reversed, either with a Mix option or a reversing Y-harness, the elevator motion per side will be different.
Not a large amount, but enough to be bothersome to a precision aerobat, for instance..
In the sketch, note the servo with the arm pointing down.. the horn it pushes on rises with up elevator, as does the arm on the servo.
The other servo arm goes down as it pushes the elevator up. This slight amount of motion results in the surface on that side moving just a bit differently than the other side..