F3F Pushrod / Linkage Advice

[infopimp]

How beefy of a thread should I use for pushrods on an F3F racer that might go up to MoM weights?

4-40? 2-56? Does it matter?

Is there a particular brand/style of clevis that you prefer?

Thanks guys!

-steve

[P-51flyer]

I use dubro 2-56 on all my F3F planes.

Aaron

[jofo1]

pimp, solder all the clevis' or eliminate them altogether for slop free surfaces. I buy the threaded ones and solder them (obvious benefit over solder clevis' is the length can be adjusted and held in place while you solder, use acid flux). Clevis on the control horn, z-bend ground so it slips in without damaging the hole in the servo horn. I find that once the servo is mounted I never need to change the length of the linkage.

[djklein21]

I use all 4-40 rod and Sullivan clevises. I CA the threads once my plane is built. I don't solder them because sometimes you need to make small adjustments if you remount the servo. I am very particular about my mechanical setup. I make sure the wings are identical left to right. This is more important for a plane that is winch launched, because your launch camber setup uses more through and the sides need to be identical both statically and under load.

I use the Sullivan clevises because the drill bit I use to drill m control horns fits it perfectly.

2-56 is to small for a top driven bottom hinged set up. It tends to bend under the compression loads when the flaps are hit on landing. I always use 4-40.

[infopimp]

OK. I'll probably go 4-40 all around, fewest clevis as possible and solder em. I'm experimenting and ordered a few types of clevises just to see what is out there... thanks for the tips.

Back to my build... :)

[jgs99v]

What's the take on ball links?
Any feedback in the F3F or F3B scene?
Seems like this would present the least amount of slop and positive control - only limitation I've seen is the vertical stackup.

[P-51flyer]

What's the take on ball links?
Any feedback in the F3F or F3B scene?
Seems like this would present the least amount of slop and positive control - only limitation I've seen is the vertical stackup.

Too much slop in my opinion as well as they get bulky trying to keep things as low as possible.

On wings I normally solder one end and thread the other then hit the thread with CA.

Aaron

[timmig]

KISS method is best--and Like Dave is saying---440 for flaps especially. I do use 256 on ailerons many times--- but threaded clevis's and I also CA--incase an adjustment needs to be made when changing out a bad servo etc.
FWIW
Tim

[F3X]

Z bend at the servo for short arms under covers and max movement and NO SLOP and a threaded plastic clevis with metal pin on the control horn.
Straight linkages, no bends!
2mm or 2-56 wire, I usually cut the threaded portion in 1/2 though.
I never had a wire bend during F3J, F3F and the small amount of F3B.

Use Z bend pliers and drill the servo arm with a short length of the same wire you used as the pushrod.

[infopimp]

Tom: Is the idea of a plastic clevis that the failure might happen there on a rough landing... like a servo saver?

[glderguy]

Too much slop on ball links?????? If you fly helis you know just how important it is to have NO slop, and I truly mean NO SLOP lest your heli wander all over the place and you wear your thumbs out chasing it all over the sky! All my helis use ball links. Maybe I should switch to clevis'.....NOT!
Walter

[F3X]

Tom: Is the idea of a plastic clevis that the failure might happen there on a rough landing... like a servo saver?

Not really, The plastic Clevis I use hold tight on the threads, tighter than a metal one that you have to solder on or CA in place. Also metal to metal can generate a little RF noise its not so bad with the new Radios but the old timers will remember.
Don't confuse them with DuBro or Sig plastic clevis. Not the same animal. You've seen them on my How To builds and they come is some of the kits I sell.

Funny, I keep pointing to my How To pages for build info I guess they are not popular searches :( I think there is a lot of helpful info there.

[jofo1]

i like the plastic/brass pin clevis' too, they just don't have them at my LHS. the only issue with them is the pin is small and easily lost at the field, but they are clean. i dont like ball links because the are harder to get under the cover and they apply a torsional load to the horn, i think you ideally want the force on the horn only around the axis of rotation. fwiw, i would rather have the servo pop off the skin than break a plastic clevis; those clevis' are strong, that much force and the servo gears are going to be marginal.

[PDX Slope Pilot]

I liike the plastic/brass pin clevis too. Where can you order them online?

PDX

[Jurgen]

I got mine from:
http://www.topmodel.fr/top-model-en?sid=1f34004ebcb05f9acda6016d5cc52d5e
and search on the word CLEVIS
Expect a big post cost so maybe order a lot for many guys :)

[bobthenuke]

I've looked for these (MP Jet clevis) for a long time having received them in kits but never been able to source them individually and certainly not locally. Finally found a catalog with them listed... unfortunately, and as usual, this distributer is not located in the USA.

http://www.macgregor.aero/MPJ/MPJ%20Cat.pdf

[infopimp]

BTW, I found some adjustable titanium pushrods. Surely they will shave milliseconds off my time and intimidate my peers. I'll start a build thread here soon.

[F3X]

I carry the MPJ hardware, its not on my site (yet) but I have lots of the special small parts for the models in stock.

[F3X]

BTW, I found some adjustable titanium pushrods. Surely they will shave milliseconds off my time and intimidate my peers. I'll start a build thread here soon.


These will require a threaded connector on both ends and at the servo you will then need a longer arm so the clevis will clear the output shaft and then maybe now you need to cut through the servo cover because of the extra arm length and now you will need to lower your end point so the servo doesn't move the surface too much resulting in a much lower servo resolution per degree of travel resulting in a twitchy response and a model that is hard to fly very smoothly without expo around center and the resulting loss of torque from the expensive servos you just bought and the earth will stop rotating and we will all slide off the planet!

Go easy, go proven: A Zbend and a clevis! Save the planet!

[tewatson]

The only problem with z-bends is when the servo arm must protrude past the wing skin and move within a small blister on the servo cover...a la Pike Superior. A clevis keeps everything at the width of the clevis itself. Rods with z-bends add double the width of the rod (and then some) to the horn.

Tom

[F3X]

The only problem with z-bends is when the servo arm must protrude past the wing skin and move within a small blister on the servo cover...a la Pike Superior. A clevis keeps everything at the width of the clevis itself. Rods with z-bends add double the width of the rod (and then some) to the horn.

Tom

Never had a problem, many builds all made with Z bends. Pikes-all types!, Furios, Vikings, Zeniths, Acacia, ARIS. 2-meters and 60" ships etc. A properly done Z bend is narrow and also allows a shorter servo arm for more resolution, more servo torque applied to the surface, no slop, no wear. The Furio tapered bubble is probably the smallest servo cover bubble I have ran across and no problem!

[Terminator]

Well, if you use clevis pins at the servo arm it is a sure bet you will need to have the arms longer making the blister covers a must...with zee bends you don't need no stinking bubble covers...aka Aris, Skorpion to name a couple which employ top drive flaps and FLAT covers...where a clevis pin at the servo are will certianly make the arm to long to slide unde a flat cover...Zeebends or 90 bends on the pushods make this feat a piece of Cake...
Steve, leave the Ti turnbuckles to the car boys,..been there tried that...I employ Toms ideas and they worlk well...except for the Hayes clevis in the heat at Vincent...not so good.

Alan

[jgs99v]

Tom - Seems like all Z bend tools are not equal. When I built the Nemesis I had to purchase the Great Plains as this provided a narrower bend which did not make contact with the bubble sides. In the past we did use 90 degree bends and CA'd a washer to capture to open side against the horn. This is really clean!!! Forgot about that.

[jofo1]

i agree with Tom; a well done z-bend is plenty narrow. i use my bench grinder to grind the first bend "elbow" to a sharp edge at the end of the wire. it slips into the hole easily without damaging the horn, still a bit of a press fit which is absolutely slop free.

[F3X]

Tom - Seems like all Z bend tools are not equal. When I built the Nemesis I had to purchase the Great Plains as this provided a narrower bend which did not make contact with the bubble sides. In the past we did use 90 degree bends and CA'd a washer to capture to open side against the horn. This is really clean!!! Forgot about that.

Those are nice, Horizon USED to carry those and that is the pair I have plus the normal JAWS type (that I sell) both work equally well, with the long handle HH version being a bit tighter, sometimes too tight and they rub both sides of the servo arm just a little. For 2-56 and 4-40 the JAWS works better for 2mm the long handle works best.

Plus as Joe said you can grind a flat on the tang if you need narrow clearance. Grind before you put ot on the arm or you will melt the hole!

One tip I said but went unnoticed is to pre drill the servo wheel with a short piece of the same pushrod you are using. Slop free!

I just built my Altus. 2mm, Z bends and MPJ clevis all round. Oops I did use a Z bend at the Elevator servo and a L bend at the back...no clevis :eek:

[bobthenuke]

I carry the MPJ hardware, its not on my site (yet) but I have lots of the special small parts for the models in stock.


When will you list these for sale as separate components?

[target]

I called to Hobby Lobby, and asked them to order me some; I have a deal pending, they are a MPJet distributor (or at least they sell some of the other products).

I like the "L bend" over the "Z bend" where I can use it...
I used a threaded L bend on the v-tail servos for my Aris.

On the ailerons and flaps, I used a metal solder clevis at the servo arm, and the MPJet clevis on the flap/aileron horns... I had to relieve the metal clevis a bit in an arc to get the clearance (not as much a problem with a proper Z or L bend), and was still able to drill a hole closer to the output shaft center.

I have a clevis that has just the arm with the pin, the other arm is cut off. I force this into the servo arm hole with pliers, then heat the clevis pin with my soldering iron; presto! A perfect sized hole, no slop, no binding! Not my idea, read it somewhere from the Brits.

Save the world, but save your sanity first!

T

PS. Did you ever get some of that 3M tape, Tom? If so, what do you think???

[davidleitch]

An alternative to the Z bend is an L bend, with a small piece of shrink ca'd onto the L and then shrunk with a heat gun. An L bend is much easier to construct and the shrink wrap can elimate more slop because it goes right up against the servo arm. Never had one come off accidentally but easy enough to remove if you have to.

I also like the plastic clevis with metal pin but be aware that technically they are metric thread and the control rods will mostly not be. As others have said the MPJet ones are unfortunately hard to get.

[PDX Slope Pilot]

Do you put a little CA under the shrink wrap?

[target]

An alternative to the Z bend is an L bend, with a small piece of shrink ca'd onto the L and then shrunk with a heat gun. An L bend is much easier to construct and the shrink wrap can elimate more slop because it goes right up against the servo arm. Never had one come off accidentally but easy enough to remove if you have to.

I also like the plastic clevis with metal pin but be aware that technically they are metric thread and the control rods will mostly not be. As others have said the MPJet ones are unfortunately hard to get.

Here was one way to go.

T

[davidleitch]

Do you put a little CA under the shrink wrap?
Yes I do. My installations are not as neat as Target's and bitter experience has taught me that everything that can go wrong does.

[target]

Yes I do. My installations are not as neat as Target's and bitter experience has taught me that everything that can go wrong does.


My builds have come a long way, and I try to be neat, but the main focus for me is one of reliability. I would rather crash a moldie due to my own pilot error, than have an equipment failure that causes the same result...

Thanks, David.

Target

[infopimp]

Target: What is keeping that pushrod from coming out... i understand from your description you heat it up... but doesn't the slight back and forth eventually loosen that connection? Trying to understand the "pros" of that vs. other options described above. Please do tell... all ears.

[target]

Target: What is keeping that pushrod from coming out... i understand from your description you heat it up... but doesn't the slight back and forth eventually loosen that connection? Trying to understand the "pros" of that vs. other options described above. Please do tell... all ears.


The things I decribed in this thread are two different techniques, Steve. The picture uses what I call a "theaded L bend", the threads themselve keep the linkage in place. I started with a straight peice of MW with the threaded end, then bent it, right at the beginning of the threads. I took a 2-56 tap, and tapped out my 94761z servo arm on a 6mm radius new hole I'd drilled into it.
Then I glued it into the CF pushrod tube, and placed the servo in it's mount. After drying, I de-mounted it all, and wrapped some carbon tow around the joint (insurance and splitting prevention) and added some West systems to the tow...


The other heating deal, is used just with a regular clevis, to get the hole in the arm sized just right for the clevis's pin...


Here is yet another L bend option: