Elevator Mis-match

[borealnw]

off the subject a little what in your opinion is the best Throttle servo for IMAC and 3D?

1bwana1 thanks so much for the links and the advise. I do have a buddy who has a programmer and we both are following this thread. He is one of the best builder and pilots I know and together with everyones helpfull advise we hope to fix the problem. Thanks again.

[bgold]

If it's good enough for your flight surfaces it's good enough for the throttle. Use the servo you are using on the rest of the plane, your throttle is kind of important also.

[infinitemass]

I know this has probably been covered but have you taken a look at this?
http://www.rcaerobats.net/Spektrum/d...l_ailerons.htm
Especially step 5 on elevator set up.

[JoeAirPort]

	Quote: Originally Posted by 3D-Seth
	No. You will end up with un-equal elevator travel this way. See attached picture that I drew. Because the servo is below the stab, when the servo turns towards the elevator, the linkage goes straight much quicker. When the servo turns away from the elevator, it has the reverse effect; pulls the linkage away much quicker. This is why it needs to be mounted with the servo arm towards the front of the airplane. **Note: this is only for fuse mounted elevator servos, not stab mounted elevator servos. Seth

This is a really good example of what Joe Hunt called the "to be determined center" (from his old DOD site's instructional video). It's "to be determined" by your air frame's servo pocket postions, control horn type..etc. In this case it ended up a few degrees away from the hinge line. If you had the servo pocket higher and the push rod going under the servo, then your "to be determined center" would be in a different place. Possibly towards the hinge line this time. I had an Edge that was like that. People thinking they can do all this in a servo programmer, match box, equalizer, radio etc. had better study up. Because the brothers in this hobby that have figured it out know better (Joe Hunt and others that taught us this...credit to them).

[JoeAirPort]

Here's some interesting pic's that show linkages that have perfectly symmetrical throws on the servos and surfaces. This is the Edge I mentioned in my previous post. The elevators end up opposite of what Seth posted on page 2 because the servo is up higher, the push rods are under the servo, and also these are Nelson horns...they are not pivoting on the hinge line. That's adds to the offset from 90 degrees. The ailerons have some offset too but not as much. I probably could have drilled that elevator horn bolt more straight but that can all be dialed out with the push rod length adjustment. I think I would have prefered that servo pocket a little higher.

The 2nd elevator is the Ultra RC 87" Yak (Extreme Flight with different covering). That really shouldn't have any offset but I probably glued the horn in not on the pivot...or the horn slots were not cut quite close enough. Again all dialed out in the push rod length.

The last is my Extreme Flight Extra aileron servo. This was the first I ever had that the servo arm tilted away from the hing line at center. It's all in where the servo pocket is located with respect to the horn.

[borealnw]

Thanks for the info Infinite. I see from the list (from the link) that I have them reversed. I have elev in Aux 1 (flap). Will reverse them to see if there is any difference.

Thanks Joe I think I see your point on the geometry issue. On my plane the servo is on the fuss and the elev horns are 1 1/8" down off the surface. The servo arm goes in a down position at 1 1/2" This offsets the linkage just off of level. So if I am reading your info right then my servo arm should tilt slightly to the rear of the servo (plane) toward the elev horn. Question? Both linkage arms need to be the same size to aquire the same speed of travel (correct???).

Looked at the links for programming the servo's and the write up on mismatched servo's. When my servo's come back from hitech I will go over them again in setting them up.

What are the cons of using a y harness. My first thought is power overloading or underpowering the servo's. Is this also the case with using a matchbox or a smart fly EQ.

Thanks so much all for your help.

[1bwana1]

[quote=borealnw;924900

What are the cons of using a y harness. My first thought is power overloading or underpowering the servo's. Is this also the case with using a matchbox or a smart fly EQ.

Thanks so much all for your help.[/quote]

The big problem with a "Y" harness is that the standard servo connectors are not designed to carry the current that two high powered servos can generate. This can cause a loss of performance in the servos, and rarely a failure in the connector. The matchbox can solve it, as can the Smart-Fly EQ. The mini-Deans Connectors I provided a link to can solve these power issues, but will not help with matching the servos like the PowerBox or EQ. Since you have programmable servos you should be able to just use the better connector and save some money.

[jonathanmanopla]

does anyone have a protractor for hitec 7955

[JoeAirPort]

	Quote: Originally Posted by borealnw
	On my plane the servo is on the fuss and the elev horns are 1 1/8" down off the surface. The servo arm goes in a down position at 1 1/2" This offsets the linkage just off of level. Q1) So if I am reading your info right then my servo arm should tilt slightly to the rear of the servo (plane) toward the elev horn? Q2) Both linkage arms need to be the same size to aquire the same speed of travel (correct???).

Q1) That's my guess but go through the procedure I outlined earlier and it will end up where it ends up...likely you're right though.

Q2) Both horns and servo arms should be the same size. After you go through the process you may end up with push rods that are very close but still a fraction of an inch different. No two sides of a plane are identical. I match my linkage on each side separately instead of just doing one then making the other side equal. But I like tinkering with this stuff and don't mind doing both. You could probably get away with it.

[PSF]

hitec makes their own protractor that the servos fit in.

[TManiaci]

I know I'm a little late in the game here, but I thought I would throw in and try to help. To illustrate the importance of mechanical geometry balance, this first image shows how an offset from the linkage connection point on the Surface Horn is offset from the hinge centerline can cause a differential throw. In this example, a 1/2" offset from the centerline is shown. For an equal stroke/displacement of a 90º servo push-pull stroke, you can see that the offset throws are significant.

Differential Throw.JPG

In this example, a 5/8" rod travel fore and aft shows an 8º throw differential. Geometry MUST be as perfectly balanced as you can possibly attain. A 1/16" erros is no small matter, it can result in a substantial travel error. Bad geometry can not be "programmed away" 100%.

I don't like using protractors or angle toys, they still leave you with errors. The resolution of those tools do not provide enough accuracy unless you magnify the size considerably. An alternate method is to magnify the throws by extending the surfaces with long straight bars, like these 1/2 hardwood sticks. Attaching them to both elevator halves in the same place on either side, and extending way out beyond the Rudder, you can eyeball the parallel lines of the sticks very easily.

IMG_7886.jpg IMG_7888.jpg

You would be amazed at how much more balance precision you can attain with this method. With this approach, you can actually see a huge change with just one click of the subtrim when you stand so your line of sight is 90º from the side. Using your radio with rates, you can check solid stable points at any mid-throw point to verify the travel is balanced throughout the throw.

You can also see the speed of the throws much easier too. Magnifying the motion really enhances your visual capacity to make all aspects of the system perfectly matched. Using slow stick action, you can watch the parallel effect really well.

My contribution....

[blackbeer]

That is pretty much the way I do it Tman except I use cf rod and angle the two ends at each other just behind the rudder. It is the method I used to see that even though my neutral was dead on and my full up and down was dead on the movement of both sides was not the same speed or degree of movement. It also showed me that when I switched from high to low rates it changed again, as well as when I changed expo and changed the travel settings. It's why I dove into the manuel for my 8U and found that there was a difference in resalution between channels 1-4 and 5-8. By messing with the expo settings, the travel settings, and the rates I have been able to get them close but then if I hit my mix switch for knife edge it gets cranky again. I think it's time to make the jump to 2.4. Anyway, great thread, lots of good info.

Tom