Matching Elevator Travels
 

I have a BME 30% Yak, 8611's, Dubro HD stuff, CF rods, ball links on servo end. I need some procedures/ideas on how to setup these so that all three rates are equal on each side.... When I set High rates, matching both ATV end points, then my lowest rate isn't exactly both down/up...If I tweak ATV to minimize differences on LOW rates, then the others have errors.

I have already done most of the usual things, just would like some procedures/ideas from others who have had to solve this in case I've overlooked something in my setup.

BTW - I am not troubled with RATE of deflection, that's fine between the two servos.

RE: Matching Elevator Travels
 

,

RE: Matching Elevator Travels
 

Have you tried beating your head against a wall yet? I find the reduction of blood from the brain during this process, helps finding the solution.

Check ATV's +/- a few and a half a turn in or out on the rod. It's in there.

RE: Matching Elevator Travels
 

Now THAT ( , ) is an interesting response.......... [&o]

YNOT - the head beating just softened the sheet rock. Didn't help the elevators, but thanks. I'm thinking maybe adjust the control takeoff on the "high" side to reduce mechanical travel? Or ???

If turning a rod half a turn, won't I then have to re-sub-trim, thereby throwing off ATV's for that channel??

(If I'm missing something fundamental - SOMEBODY tell me - please.... :( )

RE: Matching Elevator Travels
 

Bob,

Assuming yopu are using dual rates or even triple rates (flight mode on JR radios). Is it possible to set the end points for each rate on each surface. I know in my 10X that is possible so if I cannot get exact mataches using the standard mechanical means, then I'll configure it in my dual/triple settings. The only thing I cannot change is neutral, but normally that is not a problem.

OK now for the most common reason I have found that I can usually correct without changing the radio setting amongst the flight modes

Usually, the servo arms are not aligning exactly the same on each elevator half or when dual servos or more are on a single surface. This will then make one control rod longer/shorter than the other. Sometimes when I measure them it is only a few millimneters but it really makes a difference in extreme throws.

Another thing is are both servo arms actually traveling the same distance in both directions. I've learned to use a paper protractor taped to the wing with the center line of the protractor lined up with the servo output arm. I then get a servo arm the allows itself to be on the protractor centerline when installed. I then power up the servo and move the stick in one direction to full travel and look at the angle. I then move the stick to full in the opposite direction and look at the angle. They should be exactly equal. This takes a bit of work and if you are using hitec servos it is easily prgramed to get the exact same angle in both directions.

Once I have that set, I will then get a control rod and get the ends I am going to use installed and connect everything up. I'll adjust the control horn height and control rod until I get the same throw in both directions, all the while I am still making sure I am getting the exact same throw on the servo arm in both directions. If that changes, I am most likely getting some binding somewhere in the linkage. If I am working with a surface with 2 or more servos then I do the exact same with the other servo taking inot account that if I did the innermost servo, the next servo going outward may beed less arm throw due to the wing/aileron/elevator getting thinner but still maintaing the same through as measured at the surface.

Ince I get all of this matched up then I can bet that I will not need to change anything in the radio except to lower the total percentage for low/middle and high rates.

I know it's a lot of work, but it works well and you will be rewarded with a plane that does not eat servos, longer lasting batteries and in the case of the ailerons, great rolls and in the case of elevators, the exact same travel for both in all condition

Down on the Deck has a great video on this in the instructional video section, though Don leaves a bit of what I wrote, out of his explanantion

RE: Matching Elevator Travels
 

If turning a rod half a turn, won't I then have to re-sub-trim, thereby throwing off ATV's for that channel??

That's what YNOT is getting at. Sometimes a slight error in the other direction counters your initial problem.

I know you are an experienced pattern pilot and you know how to set up linkages. When I set up my 3M Extra using 4 elevator servos, I had 14 servos to choose from, luckily out of that, I found 2 lots of 4 that matched perfectly. I used the other 4 on the rudder tray. If you have some more 8611,s it is worth swapping them around until you find the best match between them.

On the odd occasion where I have been unable to get them dead right, I have set it up so they are perfect on the sequence flying rate as this is the most important. then the snap and 3D rates have been slightly off.

Hope this helps
Alan

RE: Matching Elevator Travels
 

Bill, Alan - Thanks to BOTH of you.... there's some good stuff coming out of this, and helping me understand things a little better.

I guess the FIRST dilemma/question is - How do I *KNOW* the servo arms at NEUTRAL are 90* to the chordline of the stabilizer/elevators? (I understand that having them 90 relative to the servo case is meaningless) ??

Assuming that finding that, mechanically, is pretty important, AND that it's done with the least amount of subtrim possible?

RE: Matching Elevator Travels
 

I am by no means an expert on any of this but could you not put matchbox's on them and solve the whole problem.

RE: Matching Elevator Travels
 

The idea is to basically eleminate any matchboxes or radio setting that changes the mechincal advantage. You would be surprised just ow much servo arms are "off" and simply changing it to the other side of the servo gets it to line up correctly or even placing it on another servo and in the case of elevators, just placing it on the other elevator servo.

This happens with good aluminum arms to the Hitec thick fiberglass arms to the standard plastic arms on JR servos.

I just had this on a AW Yak I just finished with JR8611's. I eneded up replacing one servo arm with a new one because no matter where I put it, in relation to the elevator halves, I could not get equal throw all the way through the surface movements on both halves, I went to the LHS, grabbed another arm and it lined up. I needed no matchbox no subtrim, no Dual rate setting changes for all 3 flight modes.

I used a very simple method to check elevator halves that someone here told me about something like 2 years ago

Get 2 spring type clothes pins, glue a very stright stick of balasa to each one, I use 20 inch pieces so that they fit almost all planes up to 40%. Clip them to the exact same spot on each elevator halve and line them up so they meet exactly behind the rudder, now slowly move the elevators with the radio, they key being slowly, and watch the sticks, they should remain exactly equal the whole way through the travel. If not, then start looking at mechanical setup. Sometimes you can have to exactly the same servos but one is faster than the other and no matchbox or any other radio setup will fix that.

That is what I think Alan was talking about when he said about matching servos

As Alan said, but is a pretty experienced pattern pilot, so truth be told, I was pretty shocked by this question. It must have him pretty flustered

RE: Matching Elevator Travels
 

"Flustered" doesn't QUITE get it, Bill..... this is driving me NUTS. You see, the pattern experience does not prepare one for 35* travels, and triple rates with 70% expos.... and trying to get all three rates to be perfect and identical travels on both elevator halves... well.... it's a new "Learning Experience"

I use 1/8" CF rods that are glued to spring clamps with rubber pads to prevent slippage on the trailing edge. They are 12" long, so quite sensitive to the most minute changes.

At this point, I'm concluding there is something mechanical amiss....my bet is that my servos arms are aligned to the CASES but not "square" to chordline, so I'll be trying to figure that out next.

Yes, I *do* know my way around linkages and geometry and radio setups.... thanks for the compliments, guys, but this is a WHOLE different ball-game. And clearly not as intuitive as one might think.

RE: Matching Elevator Travels
 

You guys are doing a nice job of hitting all of the important stuff here. The protractors and the long stick trick are key to getting it perfect.
Its really not that critical EXACTLY where the servo arms are as long as they are as close to center as you can get them and in the same place relative to one another. We typically shoot for as close to 90 to the servo case and it works out very well and keeps things simple.

The more important thing as Bill said is that both sides are in exactly the same place. Since the arms are essentially 180 degrees opposite of each other this can be tough since you are going to be 1 spline off all things being equal using normal servo arms. 1 thing I have found that helps is to use a double arm on one of the elevator halves and just flip it both ways and see which one is the closest. Once I find the best fit, I just grind off the other side of the arm to make it a single arm. Often one side will be a perfect opposite to the other srevo's arm.

Other things to check that wil drive you nuts are 1, the location of the control horns on the elevator. Stating the obvious, they need to be in exactly the same place on the elevator half, if they are even a little off it can be almost impossible to get them to match up just right. 2. Also measure and make sure that the servo "box" in the stabs were put in the exact same place. If they are off, go back to beating your head on the wall.

Just a comment
Now this is not advertisment just a fact I thought worthy of mentioning. The Hitec programmables make this a non issue. You simply put the servo arms as close as they will get, use the protractor and the programmer to put the centers at 90 degrees to the servo (or wherever you want them, point is they are EXACTLY the same). Then using the protactors as a reference to make both sides equal, you adjust the servo travel to get the desired endpoint and throw you want. You pretty much can set one servo up and get it right and then just go to the other side and program in the same servo travel on the other servo. Then there is nothing left to do but adjust the pushrod length to get the actual throws identical (takes about 2 minutes) and they will be PERFECT in every way. Then you simply go to your dual, triple rates and dial them down, everything is perfect.
It takes a couple of trys to figure it out, but once you do, any airplane you do wont take more than about 10-15 minutes to get setup on elevators. Ailerons are even easier because the servos are moving the same way. This is really the way to go now that they have worked the bugs out of the programmer. Just something for folks to consider in the future.

Here are a few videos on how it works if you guys want to check it out. This is good stuff for not only programming but just a good video how-to in general.
[link=http://www.downonthedeck.com/videos_instruction.htm]Servo Setup videos[/link]

RE: Matching Elevator Travels
 

Mike,

Really nice explanation...

I have learned so much in geometry using the instructional videos Joe and Don have done. I agree the hitecs using the programmer make this a none event but it is still nice to learn to do it using the mechanical stuff as much as possible.

I think Bob has been beating his head on the wall too much lately, he's gonna have to do some wall board repair soon [sm=lol.gif]

RE: Matching Elevator Travels
 

I agree on both counts;)

There is a tremendous value in learning to do it the "old fashioned" way for lack of a better term. The only thing that is un resolvable in a purely mechanical setup is dealing with servos that are not moving at the same speed. Its not the noticable at 10-15 degrees throw, but at 35-70 degrees, it is an impossible situation. Everything else can be corrected with patience and practice.

RE: Matching Elevator Travels
 

If ur using the dubro 866 type arms where the top pivot is threaded in and out , one can vary the height of the arm from the hingeline. being so a shorter arm from the hingeline will give more throw for X amount of servo travel also so usually for me playing around with varying the height of the arm in cunjunction with tweaking the atv's solves the prob (albeit not 100%) but close i wud say .

RE: Matching Elevator Travels
 

Sillyness posted this a while ago. It worked for me on 2 different planes. You only need to set your ATV and subtrims. Both elevator halves track evenly throughout their travel using the "stick method". When you are finished you will notice that your servo arms are angled back just a bit. I use JR 10x w/ 8611 and 8411 servos on elev.


"Set your ATVs to approx 130% up and down (130% is for JR... may need to use slightly less on Futaba or Multiplex) to allow room for subtrim. Then I roughly center the surface with subtrim. Measure up and down throw. If you have more up than down, then shorten the pushrod (and vise versa). Now, re-center the surface with subtrim, but do not touch the ATVs... leave them alone at 130ish%!!! Re-measure up and down throw and repeat the above proccess until the surface moves the same amount up and down. Your servo arms will likely be tipped slightly toward the rear when done, but it depends on your geometry. If you end up using excessive subtrim you may need to rotate the servo arm 1 spline one way or the other. Look at your servo monitor page to make sure you aren't over-driving a servo (i.e. a servo stops before the stick reaches full travel).

The result is a setup where both halves will travel at exactly the same speed and they'll track together perfectly throughout the range of motion.... very linear. Mixing out the differential in the radio CAN give you a setup where the surface might match at the ends, but they are off at in-between throws. Been there. "

RE: Matching Elevator Travels
 

That sounds like the way it works! I too set my ATV's at 140 before I ever start woring on the setup and it never moves again. Everything is done mechanically, except for the programming if( now I always use them) I am using Hitecs[8D]

RE: Matching Elevator Travels
 

jon595, bubbagates - this ATV thing seems to be the solution, and I just basically finished duplicating that "no sub trim, high ATV" that is on the downonthedeck website.... works VERY well.... BUT...

If you're measuring REALLY closely, the travels are NOT identical for two of the three rates. I can get BOTH up and down to be VERY exactly matched, but only on ONE of the rate settings. The others are close, but very slightly off at on or the other end points.

(Head and sheetrock softening now....no hair remaining.... torch at the ready.... )

RE: Matching Elevator Travels
 

A chainsaw is easier [sm=spinnyeyes.gif] and much more fun

RE: Matching Elevator Travels
 

BTW - not being argumentative, here - but SOMEBODY 'splain to this simple Okie how the LENGTH of a pushrod (clevis to servo arm distance) effects TRAVEL? I ain't seein' this one, boys, and I need help.....

RE: Matching Elevator Travels
 

Lets assume we are working on dual elevator servos and you have the same length arms on the servos and your control horn connection on each half is the same distance from the surface.

Now lets take a control rod with ball links on both ends and the total distance from the center of the hole to the center of the other hole in the ball links is 3 inches for both setups. With 1.5 inch servo arms you might be getting 45 degrees of throw

Now lets take the rod on the right elevator and turn one of the ball links 1/2 turn outward. You have now moved that surface maybe 1/16th of an inch up. So now you adjust the subtrim to conpensate and recenter the surface. Now remember your right rod is just a bit longer.

Ok so now you do the stick trick and notice that the right side is getting to full through faster because the rod is longer but you adjusted your ATV's to get the same throw which you do get but the plane now rolls slightly right in the air because the longer rod is moving the surface to full travel faster. The reverse is true when inverted or the rod is shortened

Hope this splains this for ya

RE: Matching Elevator Travels
 

Triple rates on the BME Yak...? What are you thinking! This is not a competitive IMAC plane. Crank your high rates up to as much as you can get, add 35-60% expo and you are good to go. You will need to trim your elevators to get a little more rudder throw. I don't think you will ever use your low or medium rates. I found the suggested low rates much too sedate for any real aerobatic stuff.

Low rates:

RE: Matching Elevator Travels
 

Bob. I used to have the exact same problem on my planes.
Now, they looked perfect with the naked eye, but with the long stick trick I could get the high rates to match exactly.... but when I set the AFR and dual rate (futaba 9Z) I could not get them to match perfectly. I could get them close, to within 1/8" on an 18" long stick but not exact. I measured and remeasured pushrod lengths and control horn settings with a vernier caliper and they were exact. But the darn throws would not match up. As you said, I could go back and adjust for low rates, but then the high rate would not match. More head banging[:@]. I never really figured that out. I just accepted that 1/8" at 18" om low rates was just EXTREMLY close to perfect and dealt with it. Since I started programming, that became a non issue..

I just dont know and never figured out exactly what the problem was. Was it a servo resolution thing? Was it something to do with using subtrim? The ATV's were the same,,,, I just dont know? IF you figure it out tell me. That is what drove me to programmable servos. I have gotten pretty doggone good at setting up matched deflections mechanically, and what I considered imperfect some may have considered spot on, I dunno.

That slight difference seemed to make no difference on low rates for precision flying, but it made a big difference if I left the offset on the high rate. It would cause lots of problems like dropping a wing in a wall, hard to manage waterfalls, wingrock in harriers. Stuff like that so I always perfected the high rate.

RE: Matching Elevator Travels
 

bubbagates and Mike East and jon595 - ya'll have put "School in Session", and very patiently explained to me how to fix what I was SEEING, but not UNDERSTANDING. I have just "fixed" my BME Yak, and it is now WAY close enough on ALL three rates (yep, I fly using all three)....

I'll translate, so ya'll can tell me if I "got it".

Because of minor mechanical issues - hinge line to servo center, differences in parellel "height" of servo shaft to control takeoff, and differences in the control takeoff itself (even getting them the same distance away from, and OVER, the Hinge Line), the system introduces what I will label "radially-induced-rotational-differential".... Because the attach point is pivoting in an arc, and the control point takeoff is moving in an arc, we got troubles in the RELATIVE RATE OF MOVEMENT Have I got it so far?

So.... the long stick (or cf rods) to align the mechanical "neutrals", then tweaking the sub trim to change the REQUIRED LENGTH OF THE PUSHROD TO KEEP THE MECHANICAL CENTER, causes the need for "sub trim".

The sub trim changes, in combination with changing the length of the pushrod, maintains neutral "zero" mechanically, and corrects for the radially-induced-differential from the servo arm movement.

That's the ball game, right????? Game, set, MATCH. THANKS TO ALL OF YOU!!!!!!!!!!!!!

RE: Matching Elevator Travels
 

So if I read that correctly, you found the control horn connection not on the hinge line...Ya know, I forgot about that part

In any case, it sounds like you got it and learned a few things along the way. Even drilling for a 8/32 rod into the surface and not drilling perpendicular to the hiinge line, meaning straight up and down can really make things hard.

RE: Matching Elevator Travels
 

Yep, that stuff has to be perfect. Wherever the control horns takeoff aligns relative to the hinge line for each elevator has to be EXACTLY the same. Having a little differential (control horn takeoff not directly over the hinge line) is not too big of a deal as long as both elevator's cntrol horns are identically offset. That differential can merely lead to getting more up than down or vice versa, which is not good but a manageable situation. If the two control horns are not sitting in the exact same spot relative to the hinge line you are in for a losing battle trying to get the throws to be uniform. Like Bubba said and I agree. It can be really difficult to drill the holes in the hardpoints for Rocket City type control horns. If one is a little tilted and out of line, well things get interesting. I really like the Chip Hyde type control horns because they make it easy to get good alignment over the hingeline, but they are pricey and on the big planes I am a little nervous about the screws pulling out. I would say they are ideal for 30% plane or smaller. Only bad thing is, you are locked in on the distance from the bottom of the control surface to the pivot point. That being said, I think its worth the trouble to measure 10 times and make sure that the drill is lined up right and use the Rocket City or Hangar 9 type control horns. Epoxied into a hard point they are in there forever and totally adjustable.

Im rambling. Bob I am pleased that you got your surfaces all lined up. Its a great feeling to get that mess straightened out.

I know you are a thinker when it comes to this stuff. Just curious, there is another facet to this. Are you already aware of the advantages of using the shortest servo arm and longest control horn you can get away with and still get the max throw you need so you can leave your endpoints maxed out and gain maximum resolution? This is another biggie when it comes to 3D setups, maybe even moreso than pattern. And it is REALLY important on the throttle. Speaking Futaba, you should have you endpoints on the throttle at no less than 120/120 so that you take full advantage of servo resolution. If you are dialed down to 100 or less (of a potential 140 Futaba ATV/Endpoint) your thottle will work, but the transition will be much "jerkier" (is that a word?) and its a lot more sensitive especially in a hover. What it gives you is a setup where one click of throttle up or down does not cause you to rise or sink. It is very smooth and gives you some room to work the throttle. If you get it right you can make very sutble moves on the throttle to really zero in on a spot where the plane will settle into a hover. This is something I did not know until recently, and when I got it right I went from hovering 10-20' off the ground to being comfortable bring it right down to all but a tail touch. It makes a big difference.

For my BME 110 throttle arm, I took a big hitec servo wheel and shaped it to the right length and position so that it was plently long enough to get the resolution I needed and where it would give me linear response. I know lots of guys are making their own arm out of composite materials and carbon fiber sheeting as well.