Servo arm question?
 

Hey Guys
Bought 5945's for my extra. They came with a nice aluminum arm but it is tapped for 2-56 not 4-40. Is it safe to drill and tap the last hole on that arm for a 4-40 ball link? OR It also came with some real thick heavy duty plastic servo arms. Alot thicker than the norm. Could a guy safely use these with a ball link set-up?

Thanks in advance

Charlie

RE: Servo arm question?
 

You can safely use the plastic arms with a good HD clevis such as the HD sullivan units that we sell with our HW kit. Never use ball links on a plastic arm in a high stress environment, the ball links will twis the plastic arm and can fail themselves or allow flutter.

Tom Fawcett
Wild Hare R/C

RE: Servo arm question?
 

Tom, do you also hold that opinion for the new phenolic extra HD servos Hitec is includingm with their big digis. I believe they are designed just for ball links as they are to thick for any current clevis I have been able to try on them.

The attached photo is of the Dubro HD servo arm and the new Hitec XHD servo arm.

RE: Servo arm question?
 

I don't know where this idea that the Hitec arms are too thick came from. The HD Sullivan clevises work perfectly with the new Hitec servo arms. And yes, I still discourage use of ball links even with those arms.

Why test fate? I know something which works, I am not going to encourage people to use something that I believ is unsound engineering.

TF

RE: Servo arm question?
 

Tom, I'm not trying to start an arguement here, I'm trying to get educated.

I have tried the 4-40 Sullivan gold-n-clevis, Great Planes, Dubro & Hayes clevis; to include the new HD plastic
Dubros. None of these clevis fit the new Hitec XHD plastic servo arms. The arm is to thick. I have been on the Sullivan website and see no new HD clevis. We have no hobby shop here so have to order everything.

Do you have a part number for the clevis you believe fits these horns. I had great hopes for them over using the $8 aluminum arms I was considering.

RE: Servo arm question?
 

I must correct my earlier statement.

I just opened some new Hitec servos. I found that the arm that comes on the servo does in fact work with the Sullivan clevises, however the longer single arm in the package is too thick.

There are two different thicknesses of arms and the thin one works but the thick one does not.

Silly me. Sorry for any confusion.

TF

RE: Servo arm question?
 

If a guy wanted to get metal arms and use ball links, how long do they need to be.
I want to get the full 3D throw for the 28% Extra.
I'm thinking 1" for the ailerons and 1 1/4" on the elevators using 5945's?
The 3/4" aluminum arm that comes with the 5945 fits all Hitecs, looks cool on the 225's I'm using on the throttle and choke.

RE: Servo arm question?
 

31, it depends on how short the arm on the control surface is, but I have found that the 1 & 1/4 arms on elevator and aileron will give you the maximum throws you want. 1" may be to short. But I have 5945's on mine and it is performing flawlessly. If you don't want to go with the new thick Hitec arms, give SWB's site a look. they have some nice aluminum arms tapped for 4-40 ball links. PS: I have tapped the XHD Hitec arms for 4-40 ball links and they are working great, look cool also. They are only coming in the newest releses, so you may not have gotten them.

RE: Servo arm question?
 

I have the new arms and had planed to use ball links untill I read what Tom said about ball links and plastic arms, backed me right off that idea.
I was looking at AirWild's MLP arms, they come in 1" and 1 1/4" but with only one hole for the ball link, so you got to pick the right one or drill a new hole if you guess to long.
I ordered the hardware kit with the Extra and plan on using the surface control horns in the kit.
Maybe I should wait untill I have the plane and test fit with the Hitec arms, then order the right ones.
Here's a link to AirWild. What do you guys think of these arms?

http://www.airwildhobbies.com/MoreIn...&level=2&id=21

RE: Servo arm question?
 

Go back and read Toms last post. He made a mistake; he did not know that Hitec had a new xtra HD arm. several are using them with no problem whatsoever. They are two thick and sturdy to twist. I use them with the new Dubro 899 HD balllink and H9 titanium pro-link shafts connecting to a Nelson Hobby Rocket city clevis on the control serface. a little pricey but an awesome setup.

RE: Servo arm question?
 

The airwild arms in my opinion are the strongest on the market and with only the one hole will not flex a all. They also have absolutly no slop on the gear train, however because they are desinged to fit so tight, my experience is that once they are on the metal gear, they DO NOT COME OFF. Has anyone else had this experience.

RE: Servo arm question?
 

I haven't tried Airwild. but if you want to go high-end, SWB makes some great aluminum servo arms tapped for 4-40 that are really cool and $8 a piece.

RE: Servo arm question?
 

This is not correct. I know all about the new arms. What I was not aware of was the fact that they are not all the same.

The shorter half arm and at least 1 of the full arms are thin enough to use the Sullivan clevises.

But the longer half arm is indeed too thick. That does not mean I endorse them for ball links, I do not ever think ball links have a place with plastic arms.

TF

RE: Servo arm question?
 

FWIW-- the twist load on the typical ball link is NOT desireable on a plastic arm-- and is worse if the spline engagement is not very tight and well supported.
For this reason - I resist use of ball links unless there is no other way to do it .
I would shave the new arm and use a HD clevis with some lock or retainer on most applications.
I have a ton of various ball links so the availability is not the problem I am fighting.
It is the the offset of applied loads.
Wehave seen that a good direct linkage can be very light and even 1/16" dia rods are capable of handling all the loads --as long as there is no offset.
a simple bent rod end with a snapped over retainer is also very effective.
As for metal arms - they are in some cases a necessary evil--I also have a bunch of em

RE: Servo arm question?
 

I apologize Tom and stand corrected on mis-interpreting your comments.

So it appears that the discussion bowls down to whether or not you should use ball links at all, and especially not on plastic arms. Lately, nearly everything that is discussed on RCU's forums, whether its this, or DA50 engines or any number of subjects seems to garner "expert" opinions on both sides of the issue. When you get two completely resonable responses on both sides of an issue it makes things kind of hard.

I have no vested interest in any system other than it is slop free , works properly, looks good and does not fail.

Dick, your and Tom's comments seem completely plausible. but my question would be why there is so much development of quality HD ball links and so little work on clevis'. If the entire idea of using a ball link at all, is bad; you would think there would not be so many options out there. I tend to think what you are saying is correct. But I have done a lot of experimenting trying to get the most optimum connection between the servo and horn that I can.

Dick, If I understand and accept your argument - it is that any ball link puts to much force on the servo/arm due to the offset.

[a side note - I called Hitec while I was working on this to ask them about these new arms and ball links. Jeeesssh! They got a long way to go at that company! A direct quote from the guy at Hitec "we don't know anything about any of that stuff, they were developed overseas,etc, etc, can't tell you anything". So much for going to the manufacturer]


So here are a couple of questions to help me out:

(1) If you use aluminum arms do you feel the stresses from offset are still to high on the servo and a ball link should be the last choice?

I generally find that most of the clevis' I have tried have slop in them. The pins just do not fit the holes in the servo arms all that well and even if they do fit they soon wiggle out the holes to a loose fit. Question (2) do you not worry about this and just use your basic metal clevis? or whose clevis' and arms are you using?

After reading all this I am probably going to get rid of my neat balllink connectors and go the the new HD plastic clevis from Dubro or Hayes and try Hitecs new "standard" HD black servo arm.

RE: Servo arm question?
 

Boy did I open up a can of worms or what?:D[X(] All good info though. I'm with splais. I'm curious to the answers to his questions. Seems like alot of people are using ball links.

Charlie

RE: Servo arm question?
 

Ball links may be OK on aluminum servo arms, but I personally see no reason to tempt fate.

When I get something that works I stick with it.

TF

RE: Servo arm question?
 

The new Hitec short arm, the thin one Tom says fits the Sullivan clevises, is 7/8" hole to hole.
Is that going to get the 3D throw using the horns that come in the hardware kit or do we need longer aftermarket arms?
Tom sells the Airwild MLP 3” full arm for the rudder, seems MLP's all-around would be good. If so how long, 1" or 1/4"?

RE: Servo arm question?
 

To get your 3D "throws" you need 1-1/8 inch from center of shaft to clevis pin hole. The SWB and AirWild 1-1/4" metal arms both do the job very well. Set your servo travel to have reached full servo travel with the flight surface in the 3D position at high rate. Try to keep the distance from the center of the flight surface hinge line to the clevis hole on the flight surface arm be the same as the distance from the servo shaft center to clevis pin hole distance on the servo arm.

I probably didn't explain that as well as I should have, but you likely get the picture.

RE: Servo arm question?
 

OK - If you have a servo which has a well designed output shaft --which fully engages the servo arm to prevent rocking , then the offset ball setup is fine .
but look at some servo arm/servo setups - the arms can actually tilt under load --from movement at the splined joint.
The DuBros seem to be the worst at this -tho with a clevis they are not as bad.
I really don't understand whay no one has offered a clevis with a 3/32" metal pin.
a polished pin in good nylon - can be an interference fit with NO slop. And still operate smoothly.
The ball links are metal balls in nylon retainers - and they are zero fit.
Ball links sell for more money and so they are a desireable sales item -
I recently did a CHyde Cap - and the clevis holes in the brass bushed horns were of undetermined dia.
I tinned and soldered the holes, then drilled to .0625.
HD nylon clevis then fit snugly and it works with perfect control -no slop anywhere.
This business of adding high buck linkages to low load applications - makes little sense to me .
Worse yet -I see some that are actually not as effective as simple clevis setups.
My favorite "what for" setup is the ball link -then threaded piece then Carbon fiber tube -then the other end -same way .
Look at the parts count - possible failure points
This setup is supposed to save weight (like lightweight tail wheel collars)
What the heck is going on?

RE: Servo arm question?
 

Thanks dick, for the info.

You know the best all around sure-fire simplest way I have found to attach a control rod on .40 size planes using 2-56 rods is the "circle bend end" through a plastic control horn. It is slop free, light weight, and provides 2-axis movement. I have not had much luck trying that method with larger 4-40 rods, primarily due to the size.

The servo arm geometry on the Edge elevator servo and control arm is such that a straight clevis attachment to the servo works fine. I have found the DUBRO Safety Lock Kwik Link (PN 817) or the Hayes HD 4-40 plastic clevis to be strong, good looking and slop free. The only thing I have found is that a metal clevis pin in an aluminum arm rarely fits well. I have no idea if the slight amount of slop is a problem or not; it's just one of those personal little bug-a-boo things.

The aileron servo to control horn linkage is a different matter. It is not a straight line from the plane of the servo arm to the control horn. As the aileron moves up and down there is a certain amount of up and down movement of the control rod at the servo arm regardless of which attachment method you use. That is the primary reason I have felt this installation called for a ball link. Currently I am using the new XHD plastic Hitec arm with the new Dubro 899 HD ball link and H9 titanium pro-link connecting rod. The setup is rigid and slop free.

The SWB servo arm is tapped for a 4-40 ball link and would work also. I'm not sure what the hole in the Airwild aluminum arm is. But I guess I will take another look at the geometry involved with the idea of a clevis vice ball link. My only other thought is that most of my full deflection aileron movement is at very slow speeds that I would think do not put that much stress on the control linkage.

RE: Servo arm question?
 

The Air Wild arms are tapped 4-40. I typically use the Air Wild 1.25" arms on ailerons and elevator halves, with ball links at the servo side of the control rod and the black plastic Dubro Safety Lock Kwik Links at the control surface end. Make a clean, slop free set-up. By the way, the Air Wild arms are a nice design, and strong as hell.

RE: Servo arm question?
 

Hey Everybody, I need to clarify something that I've been saying. Apparently I have midunderstood a lot of people.

When people talk about ball links, I was thinking they were talking about the ball-socket connectors that Dubro and Great planes sell. They have a metal stud that threads into the servo arm with a nut on the back, and at the top of that stud is a ball. Then there is a plastic socket that screws onto a pushrod and then snaps over the ball on the stud.

These work OK on lighweight stuff like throttle linkages but will twist the end off a plastic servo arm in a heavily loaded situation.

But some people referring to ball links are talking about the little brown rod-ends that Nelson products sells as the RCL87, variously called ball links, swivels, rod ends, etc.

This is a good product, suitable for all large scale linkages. While I retain my bias against side loading a servo arm, this type of part does not apply anywhere near the twisting force that the little GP unit does and should be much less likely to twis the end off your arm.

These are very reliable used on an aluminum arm such as the 3" Airwild arm that we sell.

Sorry for being confused.

Tom Fawcett

RE: Servo arm question?
 

I believe the rod end Splais shows in the picture above is one of Dubro's, and I think they call it a Swivel Ball Link. Those are what I was refering to and what I often use, along with Hangar 9's version. It would be nice if all these manufacturers used the same naming convention!

RE: Servo arm question?
 

Me too. That one shown in the photo is yet another design, sort of in between.

The farther the center of the ball is from the servo arm the more twisting force is applied to the arm. This one is in between the really bad ones and the pretty good ones.

TF