trpastor

Hey Guys

I have a 50cc extreme flight yak. In one of the ailerons I'm getting 33 degress of throw up and down (with about 140 travel adjustment) and in the other about 42 up and down.

They are both on the same hole in the servo arm. They are both in the same hole in the control horn.

I'm wondering if there's a slight change in either of these 2 posistions (see photos) how steep of an angle there is from the arm to the horn (how far from paralell) or how much of an angle there is from the top to bottom (far from paralell)

If you look at hte photos, can you tell me if I'd gain a mechanical advantage if I altered either of these? I.e., if I moved towards the red or the green line

Thanks!
Tim

mintie

I would have to say that the first pic shows the arm at a very off set angle..Not sure if this is helping much,
Those ball joints are working to the max here..better to have a longer arm and less angle on the balls.
You can achieve this by putting the servo further from the aileron and making the push rod longer ...Not sure if this is possible on your plane.
To get the same throws on both sides some times I have to use different holes on the servos.
I certainly would not use the red line as the ball joint would be at extreme angle,and might even jam. balls are not meant to work in the position.
A little bit of experimenting is needed here.

The Bluehead

Hey Tim, First thing I see in the first pic is the bad angle of the servo arm and the aileron. If you can rig it, move the aileron horn out so the linkage will run at 90 degree angles. To about where the green line is in the pic #1. That will ensure that all available servo deflection will move cause direct control surface deflection. Also, if you move the connection on the aileron to the inner hole, you will increase the throw of the aileron.

As for the difference in the 2 sides, are they 1. both sides exactly the same linkage set-up wise, angles and lengths? and 2. do the servo arms actually deflect the same amount?

If you start with both servos actually deflecting the same amount, (same types of servos are kinda important here too. Strength, deflection, and speed), build straight slop-free linkage, the deflections are not too hard to rig. Bit hard to diagnose from the pics, but this will be a good start.

Good luck, Will

ro347

My Feedback: (13)

where did you get those servo arms?

Phlip

My questions are: 1. are you a) running both servos on the same channel with a Y connector, or b) are you slaving one channel to the aileron channel? 2. If the answer to the first question is "b," can you adjust the travel of both servos independently on your transmitter? If you're runnig with a Y, and both servos are the same model, they should deflect the same amount, in which case you need to set up both sides linkages the same and the ailerons willalso deflect the same.

To answer your question, yes, those things willmake a difference, among other things. They reallyshould be set up as mirror images of each other.

Good luck,

Phil

da Rock

Pushrods should always make a right angle with the servo arm at neutral.
Your first picture shows that pushrod/servoarm angle is nowhere close to a right angle. When the angle isn't 90degrees the surface will deflect more one way than the other.

Pushrods should always make a right angle to the hinge line. Draw a line down the pushrod to the point it connects to the horn. At that point draw a line from the connect point to the hinge line. If the line along the pushrod doesn't make a 90degree angle with that last line, the surface will deflect more one way than the other.

In your 1st picture you don't have anywhere close to a right angle. The green line comes closest to 90degrees. If you're going to put in a better positioned aileron horn, put it at 90.

Your 2nd picture shows a horn that's adequately long to have good leverage. But it doesn't show the angle from the pushrod to the connect point down to the hingeline. Position your new horn so that angle is 90degrees.

The ratio of horn length to servo arm length looks good enough from what can be seen in the photos. The ratio is certainly within what an average servo appropriate to the airplane should be able to handle. If you've got strong enough servos for that size plane, the horn/servoarm ratio certainly shouldn't be a problem.

da Rock

If one side deflects differently than the other you've either got a bad servo, two different servos, or you've rigged the two sides differently.... as others have mentioned. If an aileron deflects more one way than the other, you don't have right angles at the servo arm and/or the horn.

Jetdesign

My Feedback: (8)

I know people say pushrods should be 90 degrees to servo arms at neutral, and that makes a lot of sense. However, in situations like this one, the manufacturer or designer of the plane uses that angle to create some differential, or even like mechanical expo in one direction.

My yak is setup the same way. I actually had a similar issue to you, but my problem was due to unequal servo movement. Not all servos have the exact same range of movement. Mine are programmable so I was able to change it. You may have to adjust it in your radio if the servos are not programmable.

As to your questions about mechanical advantage: well yes, and no.
The first pic, the green arrow would give an increase in mechanical advantage near the neutral point. As the servo deflects the aileron up and is exposed to force from the wind, the servo will be at a 90 degree angle to the rod then, and will be giving you the strongest mechanical advantage when the aileron is under load. Makes perfect sense actually.

The second pic, the angle that the rod is at in relation to the servo is creating the least amount of torsional strain on the servo itself. If you were to have the rod along the red line, any force applied to the servo horn by the aileron would not be planar. You want all forces to act in the plane (parallel to) of the servo horn. The servo gear is meant to spin, not to twist. I feel like this isn't the best explanation, but I'm hoping you still get my point.

Both setups look correct. If they are perfectly symmetrical on both the right and left wings, then your problem lies in the servos or the radio.

Jetdesign

My Feedback: (8)

For some reason I feel the need to expand.

In general, we say to keep control rods perpendicular to (i.e. 90 degrees) the servo horn at the neutral position. What this does is ensure the control surface will move at the same rate of speed in either direction (the servo moves at a constant rate, the control surface generally speaking moves at the sine of this rate). The servo will exert the greatest amount of force on the control surface when the control rod is 90 degrees to the servo horn.

This can and will be changed if people want to optimize the control surface for a particular function. In the case above (first pic) the designer decided that he wanted the control surface to be the most responsive when the aileron is deflected up. As the servo rotates clockwise, it will approach a point where the control rod is 90 degrees to the servo horn. At this point, the control surface will be moving at it's highest rate of speed and the servo will be in it's strongest position.

Above I called this 'mechanical differential' - it is not differential in the sense that we normally think about it, since the control rod is not perpendicular to the control surface. Since the servo horn is parallel to the control surface, the distance between the two will remain equal at all times, and thus the control surface will move in equal directions up and down. As such, both ailerons, right and left, should move the same amount. If the operator were to adjust the servo to be 90 degrees to the control rod 'as is', he would be creating aileron differential and get different amounts of travel, up and down.

I know this is beyond the question asked, but it's kind of cool what people (like the designer of this plane) are doing to optimize mechanical systems on airplanes (and in general). Nothing wrong with a little ingenuity

Last, the second picture as I stated above is correct. Servo horns are not designed to twist, and servo motors are designed to apply forces in the direction of shaft rotation. It is best to have control rods operating in the plane of the servo horn wherever possible.

da Rock

If the servo arms are the same length, and the aileron horns are the same, and the rods are in the same holes, the differences in throw come from the servos moving different degrees of rotation. The difference comes from either the servos or your TX.

With the setup you show in the left picture, your deflections should show differential, more movement one way than the other. You say the deflections are the same "up and down". If that is true, either something in the TX is causing an abnormal result or the ailerons are getting blocked by something.

If that rigging and those components were designed by someone for 3D flight, you really should be getting way more than 33 degrees and most of them give better than 42.

Phlip

Mechanical Advantage–noun Mechanics.

the ratio of output force to the input force applied to a mechanism.

While I like most of what I can follow of gaRCfield's explanation, I have always thought that the greater the mechanical advantage, or higher ratio of output force to input force, the lower the output speed will be. What I have quoted, above, is backwards. So Ithink there's some confusion here about the term mechanical advantage. The mechanical advantage can't be at it's highest when the pushrod is 90 degrees to the servo arm, as that is the spot where the output speed will be maximized. As the servo arm rotates and the pushrod angle moves away from 90, the speed will decrease and the mechanical advantage will increase. So the servo is at it's weakest position when the pushrod is at 90 degrees to the output arm.

Phil

Lnewqban

Hey Tim,

Check these scale drawings I made for your set up.

Don’t pay attention to the dimensions, they are just relative values to show you how much horn deflection equal rotation of the servo arm will cause.

Note that the green set up will produce a more symmetrical deflection than the red one.

The smaller the space the horn deflects respect to the servo arm deflection, the bigger the mechanical advantage of the servo over the control surface.

Regards!

trpastor

Hey Guys

thanks for all your help.


I am running dual aileron. They are the same type of servos. I'm thinking the programming is off in one over the other. It seems to me they should be closer than they are otherwise. I don't know how I can check that though... maybe add a stick 12" long to the arm and see how much range they get?

I don't have a programmer for hitecs. These are programmable, but what do I use to change it? I've never done this.

When I said I'm getting 33 up and down, 42 up and down, those were based on having some SLIGHT adjusment in radio. so if I was getting 44 and 42 on one side I set the travel adjustment to 42. So there is SOME differential I guess, but not much? Does that sound about as much as you'd expect?

Thank you all for the info! It's been really informative.

cappaj1

My Feedback: (1)

This is listed on Tower's site:

http://www3.towerhobbies.com/cgi-bin...4&I=LXWCE8&P=K

Jetdesign

My Feedback: (8)

I guess that's what happens when I start rambling at 2am. You're right, the servo has to work harder when the control rod is at 90*, but at this point the control rod is moving the fastest relative to the servo speed.

loser

My Feedback: (37)

I partially agree..... To get equal deflection of the surface, I think the push rod should attach the onto the control surface at a location 90 degrees from the MIDPOINT between where the pushrod attaches to the servo arm and the servo output shaft (rotation point). This also assumes that the servo arm is parallel to the hingeline at neutral. In the pics above the current set-up is closest to that "set up". Any other geometry will cause a slight amount of differential. That is the way i try to set-up all my aerobatic types.... Use exponential to soften around center stick.... just my $.02

Steve

loser

My Feedback: (37)

ACTUALLY....was just pondering this and it hit me that to minimize the offset of the surface horn location and still get equal throw, you could do this. I wish I could include a drawing but here goes. If you drew lines from the servo arm hole you are using to the hingeline (90 degree) when the servo is at neutral and at full deflection you would have two parrallel lines about an inch or two apart. These lines show where the servo arm mount hole is at 90 degrees from the hingeline when servo is at neutral and max throw. I would think the ideal place to have the surface attachment point is exactly in the middle of these two lines.....perfect symmetry between pushing and pulling of the servo as it swings through its arc of movement??? Well....makes sense to me.....Darn....should have paid more attn in geometry class....lol.

Steve

Lnewqban

Is this what you described?

cappaj1

My Feedback: (1)

I noticed you're using what looks like carbon fiber servo arms. Where do you get those and also who makes the rods arms and ball ends? I have a Aeroworks Yak to build and am new at this, so would like to use the best components. I may even have that type hardware in my ARF kit which I haven't checked yet.

trpastor

Hey Guys

Thanks for all the help! The servos I think were limited a little through programming. I used the HPP 21 to RESET defaults (center and end points) and it was getting WAY more throw then. SO I guess whoever had it before me limited those for some reason (probably ignorance mostly).

I'm getting what I need now I think.

Thank you again!

The carbon fiber arms came with the extreme flight plane originally. But you can get good aluminum arms from mpi hanger 9 etc
http://www.horizonhobby.com/Products...ProdID=HAN9151

EXTREME FLIGHT

trpastor, I was just made aware of this thread. Looks like you have it figured out. My first suggestion was going to be to re-program the servos. Using the stock set-up and horn locations should provide you with equal throws on both ailerons.
This type of set-up and pushrod offset is very typical on planes designed for 3D flying with maximum control surface deflection. When the surface is deflected 35-45 degrees the pushrod will be very close to parallel to the servo case and will allow the best mechanical set-up to keep the surface deflected. If you are not interested in 3D style flying and only wish to sport fly the aircraft simply move the ball link in on the servo arm toward the output shaft.

trpastor

Thanks Mr. ? Extreme flight I called you guys and was going to ask about this but I got the message.

I did have another question for you that I haven't gotten a solid answer to though. the tail is off kilter a bit. My friend made me aware that this was a common problem in the first run. The person at your company who emailed me back wasn't aware of it, but my buddy pointed me to the site that the owner there (maybe you?) had posted replies addressing the problem. I was just looking for the fix. He said at one time there was an instructional video. I don't want any compenstation or to have you guys fix it, I just want to take care of it myself. but would like to see the correct info on it

thanks for any help on that.

EXTREME FLIGHT

Unfortunately all of that information was lost several years ago when my hard drive crashed. My suggestion is to fly the aircraft first and see if you have to trim it more than a couple of clicks. Most of the planes that we had issues with were out by less than a degree and were able to be fixed by twisting the tail and reshrinking the covering with a heat gun. A few were out by slightly more and for these the recommended fix was to use a fine tipped Dremel router bit and route around the fiberglass stab tube sleeve in the fuselage on one side of the fuselage and re-glue it.
But before doing anything I would suggest flying the aircraft first.

trpastor

yeah, that's also what my buddy said. Mine seems to be right about 1 degree, as you mentioned. could be a little more a little less.

I didn't think it woudl do much. Maybe If I start flying pattern, butI don't know that I would with this plane anyway
thanks for your help
Tim