Carbon Fiber Push Rod

[Motorman]

What OD and ID carbon fiber tube do I need on a Brodak Tanager or a Sig Banshee? Hole to hole is about 14".

I want to make music wire connectors, wrap them with thin copper wire and solder, then glue them into the carbon tubing with JB weld. How much grip length do they need?

I've seen 6mm x 4mm tubing on eBay from China and japan is this acceptable quality?

Thanks,
MM

[Crist Rigotti]

Get the CF push rods from Tom Morris right here on Stunt Hanagr Hobby.  He has threaded and M.W. ends too.

http://stunthanger.com/hobby/index.php

[Motorman]

I saw those but there's not allot of explanation on them. I see a 3/32 wire push rod with CF tube over it with 90 bends at both ends. How long is it, how do you set neutral? There's 3/16 CF tubing but no ID listed, is it strong enough for a 600 sq in plane without the wire going through it? Is it rolled or extruded? Why do some have the full wire and some just wire ends?

I did a search on here but didn't come up with much. Are there any good threads for a Carbon push rod newb?

MM

[Crist Rigotti]

Use the threaded ends and ball links.  The only way to go IMHO.

See reply #34
http://stunthanger.com/smf/index.php/topic,37716.0.html

[Randy Cuberly]

Use the threaded ends and ball links.  The only way to go IMHO.

See reply #34
http://stunthanger.com/smf/index.php/topic,37716.0.html

I agree completely with Christ!  This is the best technology available and will last longer than any airplane.

The only caution is to make sure that the ball links are very free.  If they are not then they can be made so by simply applying force with a pair of pliers on the outside of the round part of the link to force a little more clearance into the bearing.

Also make access available to them, especially at the elevator control horn, and use an adjustable elevator horn.

Randy Cuberly

[Howard Rush]

http://www.centralhobbies.com/control_linkage/pushrod2.htm

I use 5/32" pushrods with 4-40 ends. The balls screw onto the ends, providing adjustment. 

[Motorman]

Ok, so 6mm OD is total overkill?

[FLOYD CARTER]

Refer to the original question.

He wants to use CF tube and wrap his own ends.

So I would recommend 3/16" dia. or even 1/4" dia. tubing.  For ends, use 4-40 threaded rods, just long enough for the ball ends + about 1 1/2".  Drill small hole 1" from end of tubing (for the wire). Bend the wire end with about 1/8" "L" at the end.  Use epoxy and heavy thread.  Don't use copper wire.  Heavy thread works with the epoxy.

Floyd

[Steve Helmick]

You can get suitable CF tubing at any kite shop. If you want to simply stiffen a music wire pushrod, there's a size that's a little loose on 3/32" wire, and you could fill the remaining void with something like expanding foam insulation, possibly urethane glue, epoxy with micro-balloon filling, etc.

One of the problems with CF tubing is that all the fiber runs lengthwise, so the tube can split at the ends fairly easily. Binding with various threads and epoxy is ok, but a short length of aluminum tubing looks way cooler when Polished.  Steve

[Randy Cuberly]

Refer to the original question.

He wants to use CF tube and wrap his own ends.

So I would recommend 3/16" dia. or even 1/4" dia. tubing.  For ends, use 4-40 threaded rods, just long enough for the ball ends + about 1 1/2".  Drill small hole 1" from end of tubing (for the wire). Bend the wire end with about 1/8" "L" at the end.  Use epoxy and heavy thread.  Don't use copper wire.  Heavy thread works with the epoxy.

Floyd

Hi Floyd,
Yeah, I think everyone understood that but offered a better solution with the ball ends.  I noticed I did not mention that it would be best to use the titanium rod ends offered by Tom (I think) or by Central hobbies.
The wrapping of the carbon rod should definitely be done in any case since it's longitudenally constructed and can split if not reinforced at the ends.  I use carpet thread (very strong) and overlay it with CA, for about 1/2 inch at each end.  Easy and quick and fool proof.

5/32 carbon rod is plenty strong enough to pull a truck with...no need to use any larger...very stiff also.

Randy Cuberly

[Howard Rush]

I think there is an issue here about how people come up with the materials specifications for their airplanes.  If your spec is merely that the pushrod be round and black, 1/4" may be inadequate, particularly if the tubing is bowed.  Similarly, if you are going to stick some hobby-shop generic threaded rod into the end, 6-32 may be inadequate.  I have successfully used a grade-8 4-40 bolt with the head cut off as a rod end, but the titanium ends are lighter and more compatible with carbon.  

If you use good stuff, .156" OD tube is more than adequate for hundreds of flights on a 70-oz. stunt plane.  Just bind the ends as Steve and Randy suggest, use ends that can stand up to plenty of cycles, and give whatever you use a hefty pull and push test to ascertain that it's strong and stiff enough.

[Randy Cuberly]

I think there is an issue here about how people come up with the materials specifications for their airplanes.  If your spec is merely that the pushrod be round and black, 1/4" may be inadequate, particularly if the tubing is bowed.  Similarly, if you are going to stick some hobby-shop generic threaded rod into the end, 6-32 may be inadequate.  I have successfully used a grade-8 4-40 bolt with the head cut off as a rod end, but the titanium ends are lighter and more compatible with carbon.  

If you use good stuff, .156" OD tube is more than adequate for hundreds of flights on a 70-oz. stunt plane.  Just bind the ends as Steve and Randy suggest, use ends that can stand up to plenty of cycles, and give whatever you use a hefty pull and push test to ascertain that it's strong and stiff enough.

Thanks for clarifying that Howard.  I just happen to have a picture of a flap pushrod prepared as I said on a large stunt wing.

Randy Cuberly

PS:  Everything shown in the photo can be purchased from Tom or Central Hobbies...uhhh except the flap horn that is strictly from Mr Morris!

[Brian Hampton]

I use 5.5mm CF arrow shafts but the type with an alloy core. For the ball joint fittings I machine up alloy plugs about 1/2-3/4" long tapped 4-40 and held with Locktite (an alloy to alloy joint). One end has a 4-40 turnbuckle for adjustment where the LH thread cuts its own thread in the plastic of the ball joint. I shorten the turnbuckle so there's only about 1/8" of thread showing either side of the hex to eliminate any possible bending of the turnbuckle under compression loads. I use a 4-40 Nylock nut at one (or both) of the balljoints butting up against the alloy plugs so the shaft can't turn on the threads.

[Motorman]

If you use good stuff, .156" OD tube is more than adequate for hundreds of flights on a 70-oz. stunt plane.  

What is the good stuff and where do you get it?

I got some carbon push rod from stunthangerhobby and it appears to be pultruded tubing. The Ti ends didn't fit so I had to drill the tubing out. I was only taking a few thou out and drilling slowly by hand with a pin vise and the tubing split in two places. I cut an inch and a half off the end with my jewelers saw and the smell was of polyester resin. Not really impressed with this stuff.

Anyway, I also have some tubing I got from Tower hobby marked made in China. I took a saw cut on it and no polyester smell. It's a little bit bigger and heavier wall and the Tom Morris Ti ends fit right in. Testing continues but China tube is looking good.

MM 

[Robert Zambelli]

This is what I do - works very well.

Since the “in” pushrod material is carbon fiber, we can examine a way of fabricating them for long life and safety. The process is a bit tedious but yields a great result.
Here’s what you’ll need: Carbon fiber tube, 3/32 ID (arrow shaft works well), JB Weld, 3/32 music wire, dental floss/tape and a small assortment of shrink tube, a Dremel with a cutoff wheel, matches, and Exacto #11 and a heat gun.
Cut the hollow carbon tube to proper length - usually about 3 inches shorter than the required overall length. Make your ends from 3/32 inch music wire in whatever shape you require.  Insure that you have at least 1 inch of music wire inside the tube. Wipe the wire and the inside of the tube with lacquer thinner. Make a little scratching tool from 1/32 music wire as shown.

Use the scratching tool to rough up the inside of the tube ends. With a cutoff wheel, make some grooves in the wire, around 3/4 inch from the end that will be in the tube as shown. The grooves shown in the picture are cut a bit deep for clarity. They really need to be very shallow - .010 or so.

Mix up some JB Weld, apply a bit into the end of the tube and liberally coat the wire, forcing it into the grooves.
 
While slowly turning it, slip the wire into the tube for at least 1 inch. Wipe off the excess JB, making a smooth fillet. Set it aside to cure.
After cure, wrap the end with dental floss as shown.

Start about 3/4 inch up and wrap very tightly all the way to the metal. Secure it with a drop of CyA. Now, mix up another batch of JB Weld and smear it onto the wrapping as shown, really working it in.
 
Cut a piece of shrink tube about 1” long, slip it over the wrapping and shrink it with the heat gun (It may be easier to put the shrink tube onto the carbon tube before installing the ends). Is that slick or what? Now, all you have to is repeat the process on the other end with proper distancing and you’re good to go.

Why go through all the trouble? For me, it’s just the satisfaction of doing things neatly even if nobody sees them. On the other hand, suppose you splatter your plane and all that’s left in one piece is the control system. You can show it to everyone and they’ll be super-impressed at what a great builder you are!!!!!

[Mike Griffin]

Two years ago, during the Baton Rouge contest, Tom Morris and I set up shop right next to each other and we're talking about how we were finishing out the ends of our 3/16 carbon fiber push rods.  We were also talking about the cost of using the Titanium inserts.  I showed him how I was cutting off the head of a 4-40 bolt and securing it to the inside of the tube with JB Weld. I then wrapped the tube end it with Kevlar thread .  I talked with Tom a couple of weeks ago and he said this was what he was doing.  It works well and is less expensive than the threaded titanium ends.  When I do use the Titanium ends, I use the type that go over the tube and not inside it.  Any of the methods discussed here will work well if secured well.

Mike

[Garf]

Try this link:

https://www.centralhobbies.com/cat2.php?cat=27

[Motorman]

All I'm saying is pultruded tubing will split if you look at it. They make tubing with cross weave but, I'm still trying to find it in the size we use.

The other thing is I got 4 ball links and they were all right hand thread. Do they make ball links with left hand thread or do you just jam it in there and cross thread it?

I guess if you are using a long 4-40 bolt (how long?) you would use 2 right hand ball links but have to unbolt the elevator horn to make length adjustments right? 

MM  

[Robert Zambelli]

Correct!
The carbon fiber will definitely split when the fibers are on the longitudinal axis.
That's why I wrap them with dental floss and then coat with JB Weld.
I've never had a failure.

[Motorman]

Now I've found 5 possibilities for threaded ends on the CF rods.

Purpose made Ti ends. Light strong rust proof

4-40 Stainless steel all thread from Brodak. rust proof, not as strong as alloy

4-40 mild steel all thread also from Brodak. Don't know if it's cad plated, not that strong

3 inch long grade 8 alloy steel all thread bolt 4-40 from Micro fastener. 90 cents each

2 inch long 4-40 grade 8 bolt with 1 inch shank. Good cheap option but worried about rust.

MM