JR Servo Matching

[Jaketab]

Help Please,

Attempting to gang 2 - JR 8711 servos in a phenolic plate. The servos are ganged at 1-1/4" (half arms) with titainium rods and 440 Dubro Ball links . Using JR Matchboxes, I am able to precisely match the neutral and max end points. However, binding occurs at other points throughout the range of travel. The servos do not travel in harmony together.

The servos came with a 3M Comp Arf Extra I purchased 2nd hand. The servo's are well worn with about 150 flights on them. The questions is - am I fighting a losing battle trying to match old servos that work well individually or - do new 8711's present the same problem when attemping to match throughout the range of travel??????

Thanks - Jaketab

[planestiffi]

jaketab have you set the servos as close as you can mech. first on both center and end point do each servo one at a time then hook them up and set them mech. as best you can then do your fine tune with the match box this seems to work vey well for me.

[ljaganna]

I have many many ganged servos in my 4 gas planes...all JR and no issues. You want to start from scratch on the matching attempt.
Get the mechanicals as close as possible. Reset your matchbox and match the center first. What I do next is match the endpoints on low rates(set to about 50% to 60% of my high rates)..I do some 3D so my throws on high rates are higher. Then I check the current draw at the high rates...haven't seen any unusual numbers.

The critical thing in my opinion is to use an inline current meter, to check actual currents. If you try using the "buzzing" noise as a may to decide what is binding or not....you will be off....JR servos will buzz just holding up one elevator half up against gravity...but they won't be drawing much current though..so the noise is misleding.
You really need the H9 inline current meter($50?) to get this matching correct.

I just matched some servos on my new 40% yak...With 2 8611s on the elevator I get currents of ~40-60ma when the servos are not holding up the surface against gravity...I keep the stab vertical to minimize the current values so I can match as closely as possible. I am about the same 40-60ma at the endpoints on low rates....when I switch to high rates...I get a bit more current about 100ma or so....but I thinking is to get the currents low at & around center....that's where the surface will be spending most of it's time anyway. Even in a hover...I flick to full deflection only for a fraction of second anyway.

Hope this helps...

[MODE 1]

Dont have the link but sure some one will post it. Theres a DOD video of how to setup multi servos and I believe its very informative you could try doing a search for DOD whilst your waiting.

[Jaketab]

Gentlemen thanks for responding.

The linkage and geometry is within a very close tolerance. I have switched out using 4 different (old) JR 8711 servos with same result. I have repeated the above proceedure many times. I can now program the Matchboxes in my sleep.

Neutral and (max) end points match precisely. I have triple rates on the ailerons. When matching high rates, medium and low rates do not match - and then vice verse.

I have not used an in-line current meter yet, but can tell from the distortion of the servo plate when the servos bind. Hope to get a meter soon.

When the servos were on the airplane, I borrowed a meter and found the binding at certain points in the travel as much as .5 amp. The geometry was off and may have stressed the servos over time.

Before I reinstall the servos in the aircraft, I hope to match on the phenoic servo plates with no load attached. The servos will be mounted and ganged on the inboard side of the aileron only where as before they were at inboard and outboard horns.

Just trying to determine if the problem is from the well used old servos or would new 8711's match any better???

Thanks - Jaketab

[ljaganna]

I don't think well used servos should have more of a problem.....a well used servo may have a little bit of gear slop, which would make it easier to match ganged servos.
So, if it were me, I'd stick with the existing servos & work on the linkages.....I don't how close your "close tolerance" is.....but I have in the past been surprised by this myself. As I had mentioned earlier, I was setting up new servos in my 40% yak last week....and on the wing which has 3 servos(JR 8611s), I aligned the center points mechanically, to what I felt was very good mechanical matching....but when I powered up all 3 servso....they were drawing ~0.3Amp....
I think tweaking the linkages & using the current meter will solve your problem...

[Hammbone]

You have found the drawback to using a matchbox. This is why I don't use matchboxes. They match the center points and end points, but can not match points in between.
There is only one way I have found to match JR servos with good results. The JR 12X tx has a "balance" function on it which will match the servos all along their range of travel.

I have limited experience with a Smart Fly EQ-10. It will match servos, but I wasn't very happy with the results when using it either.

Your only other option is to use Hitec programmable servos with the Hitec programmer.

Jim

[bodywerks]

Hitec programmers still only match center and end points. The only reason hitec servos might work better is because they are less precise.
I would make sure both arms on the servo are at exactly the same angle when neutral(assuming both servo cases are exactly in-line, or parallel, with each other). If one is at, say 90 degrees to the servo case while the other is at, say 87 degrees they will not swing across the same arc and you will have the binding you speak of. Beyond that, try Smart-fly equalizers - they seem to have finer matching steps than the JR matchboxes and are like half the price.

[Jaketab]

Thanks all,

Just to confirm, I'm matching the servos on a plate outside the airplane. Angles are precise. At 90 degrees - center to center distance of the servo gears = the center to center distance of the ball link connections. This is measured to +/- .005" with a digital caliper.

I own an older Hitec programmer and find it to be a very cumbersome process.

Short of buying a JR 12X, I'll try new servos and then set up to minimize the amp draw with a meter.

Jaketab