Anyone using plastic servo arms sucessfully in jets? I know the $10 aluminum ones are better, but are they necessary? The HD black servo arms included with the premium Hitec digitals are extremely robust. I'm not even remotely concerned about the strength of the actual arm or any flexing of the arm....my concern is the arm "slipping" on the output shaft....not sure how much force this would take? Anyone with actual input on this?

As a comparison, Nelson sells an aluminum arm that bolts to the stock plastic servo arm for the 3D guys and many have used them without issues....I did have one of these "slip" a tooth on a 36% 3D plane, but was doing knife edge loops and aggressive blenders...no fault of the servo wheel I would think that a 36% 3D plane with 45* of throw on huge control surfaces would be far more stress than the jets with very little throw at higher speeds.....

Thanks

I use the plastic arm shown on this servo exclusively.

http://www.horizonhobby.com/Products...rodId=JRPS8711

Me too!! Well, maybe not exclusively, but a whole lot.

Raf

I have good luck with the red ones from Hitec. Is black the new color?

The newer Hitec digitals have a better assortment of HD arms included....the standard red X is still included, but there are some new super HD black arms included...one of them is approx 1/8" thick.....you'd need a hammer to break it....

I use the JR heavy duty (#JRPA215) and Hitec heavy duty plastic arms, with clevises. If using an offset linkage (such as a ball joint), I always use a metal arm due to the significant twisting/torque load applied to the arm.


Barry

Barry boy!we meet again[8D]

you are so corect in what you sed. well done /bravo!

These are good.
They have a metal ring round the spline boss to help stop it bursting and slipping on the servo output shaft under extreme load.
I'll try and find out who sells them, lost the bag they came in !

i use the stock arms that come with JR servos, BVM uses the same and that's well proved their durability IMO.

One of the JR 215 heavy duty nylon arms stripped the splines on my KingCat flap a couple of times.........they were supplied with the 8611 servos, just the same as the 8711's than Sean showed in his post.

I bought some of the same part number arms once, only to find that they were the standard duty arms that had been mislabeled. Every bag in the model shop was the same.......
I have switched to the metal arms from Jetpower and Hangar 9 wherever practical.

SWB clamping arms are too thick to use with a clevis, and the threaded holes are too large for a 4-40 clevis pin, which would make them sloppy even if you machined the thickness down to accept a clevis. I haven't seen any arms from SWB that are thin enough with 4-40 clevis pin sized holes.
Do they make such a thing?

Until they do, I'll stay with Hangar 9 and Jetpower machined aluminum arms.

Harley Condra
BVM REP
JetCat REP

Harley, you have touched on an interesting subject to me.

I personally have never had what you indicate happen, however, I have not only seen it happen to others, I have heard of many reports of this.

What ends up happening is you throw them away, when in fact, John Redman has been asking for at least a couple of years to have examples of this sent to Horizon to his attention so that Horizon can address it.

I flew a Euro at Desert Jet that had this happen. I was able to get it down in one piece, but when the problem was identified, I put new ones on, and the owner threw the old away, and when I was talking to Redman about it later, the trash had already been emptied in the dumpster (DOH!)

Please anyone who comes across this, send to Redman at Horizon. They have heard reports of this, but never seen it.

Hi,

What do you guys think of the gray HD arms from DuBro? Harley, have you used these?

Sean and Harley, some clarification please.....

The HD servo arm splines stripped or the standard ones that happened to be mislabled/packaged stripped?

Shaun,
I have used the gray colored Du-Bro heavy duty plastic arms, and have seen them fail...both failed on the FA-18F elevator servos when I belly landed it in an alfalfa field after a flameout.
The airframe was undamaged except for a few broken landing gear door hinges and the elevator servo arms. A testament to the strength of the design, but since the arms failed, I replaced them with $6.00 Airpower machined and anodized aluminum servo arms.
No more Du-Bro arms for me. An inflight failure could have cost me the entire jet as opposed to the price of a set of hinges from Tam.
Why spend thousands on a jet and go cheap on the servo arms?
Quothe the raven "Nevermore".

Harley Condra
BVM REP
JetCat REP

The Hanger 9 servo arms that Dreamworks sent me for JR servos don't fit. I noticed that they are so tight that they seam to be "re-cutting" the servo arm teeth. Is this normal?

No, I don't think that is normal.
The splines should fit snugly, but not so tight that they re-cut the servo output splines.
The Jetpower part number that I use with JR servos is 416125, "Servo arm half long". They are available for other brands as well, in more lengths. The half long arm features two metric threaded holes, which are just the right size for a 4-40 clevis pin to fit correctly.

In my earlier post on this thread, I mistakenly stated the brand "Airpower".
Correction: The brand I meant to say was "JETPOWER". Just a little middle aged confusion on my part.....
I will go back to that post and correct it.

Find them at [link=http://www.jetpower-usa.com]jetpower.at[/link]

Harley Condra
BVM REP
JetCat REP

That's the problem, the hanger 9 metal arms are not uniform across the board. Some fit perfect, some don't fit perfect. You are not losing your mind!

Some were loose and produced slop. I quite using them when I had to buy 4 to get 2 to fit right. Can't speak for any other metal ones although the SWB ones seem to be good, but I don't like them for the same reason Harley doesn't, you can't use a clevis.

By the way Harley, next time you won't strip the spline, you will break the gears in the Servo!

I've said before, I felt vindicated when they started shipping the HD plastic with the 8711 which is essentially JR saying this arm will hold up to 400 oz torque. Some people thought I was nuts when I was putting them on an 8611. Thought I would break it. I've done my own load tests, it's strong!

I have used the dubro h/d arms on my fiberclassics Kangaroo and they have been great.
Maden flight was in 2000 with a JPX, updated to a Jetcat P-80 in 2002, using JR8411 servos and lost count on how many flight's it has
done but its still as good as gold, 5 cell 2400mah battery has been replaced a couple of times just to be safe.
so the dubro horns have served well over time

cheers Pete

Could one of you guys clarify this? Did the HD arm spline strip or an improper labled standard arm?

Thnaks...

The ones I saw were standard arms, not the ones I recommend, however, that being said, the most recent ones I saw failed were the "circular" arms included with an 8611 on the elecon of a Euro tied in with Comp arf's composite arm that attaches to the circular horn.

As a point of clarification, the stripped splines on one of my my KingCats occured on the JR215 heavy duty arms, NOT the mislabled standard duty arms.

My KingCats have 8611's, and I'm not really concerned with flight loads stripping the gears . I think that improper ground handling strips more gears than anything else.

That is a good reason to stay with your jets during the noon time line up, as small children and even some adults will sometimes acccidentally bump a flight control surface and ruin a gear train.

Harley Condra
BVM REP
JetCat REP

After looking through my servo stock, the arms that "Spartan Missile" has shown in his post look like the arms supplied with the old Hitec HS-700, HS-705MG and HS-800, HS-805MG ball bearing Mega servos. I still have a couple of 705's and 805's hanging around doin' nothing.
They have some pretty husky arms on them, and I like the ring to strengthen the spline boss.

Harley Condra
BVM REP
JetCat REP

I bought some High strength servo output arms from Horizon, stock No's; DUB 674 & DUB 673, at about $9 for a tree of 8 arms, not a bad price. But by the time i had paid P&P, & the UK Customers & Excercisers (robbery without violence), had got their sticky little mits on them & not only charged VAT, but import duty as well, & then had to pay the Post Office in UK £8 for the service of paying the vat on my behalf, they have worked out at about $5 per arm.
I dare not use them now. Cheers. Ray

FYI the arms in photo post #8 were available on their own (didnt come with a servo) and fit both hitec & jr servo metal output shafts very snugly.

Did some tests today....not sure what they prove, but here is the info.....I took a final gear output shaft from a Hitec MG servo and clamped it in my vise, put on various servo arma (Dubro HD and the black HD plastic arms supplied with the Hitec HD digital servos)...did a pull test on my digital scale and here's what I got...

the HD Dubro stripped the splines in the servo arm at 51 pounds....1" from the center of the arm

the HD hitec arms stripped between 45 and 52 lbs, also 1" from the center of the arm

the HD Hitec arms stripped at 64 pounds when the scale was attached .75" from the center of the arm, allowing more force on the scale due to the decreased leverage on the output shaft with the shorter moment arm (leverage)....

Finally, the aluminum output shaft of the servo gear sheared off (as the picture shows) after about 4-5 tests on it.....

Somebody that's a lot smarter that me feel free to chime in here regarding the validity of the tests....

The bottom line is, the splines are much stronger than I thought them to be.....how much force is the little nylon gear in the servos gonna take.....how much force will the hatch/mounting cover theat the servo is mounted to gonna take....how much will a clevis take, etc, etc, etc????

Couldnt test JR, as I dont have any......

If you're running a 180 oz servo, 180/16oz in a pound is 11.25 lbs of force (if the equation works that way....any engineers reading)?
the arm would never strip before the servo stalls out and the control surface "blows down" in the relative wind during flight.....