Jump to content

carbon fibre push rods


Recommended Posts

The carbon fibre tubing is no problem. It's readily available. What is hard to find is neat end fittings with 2mm threads for medium sized models. The sets that are sold by most UK outlets are only 250mm long which is far too short for even a smallish model like (say) a Wot 4 if the servos are mounted well forward for CoG reasons.

I'm just embarking on the build of a Ryan ST 53" ws and I anticipate needing push rods at least 400mm long.

Geoff

Link to comment
Share on other sites

Posted by Ron Gray on 01/11/2018 07:12:28:

I use these **LINK**

How do you fix these to carbon rods??

For some time I have been using carbon tubes - approx 1/8" dia - the inside dia is just over the standard quicklink

threaded rods dia..

I roughen and then bend the rod slightly to give a friction fit inside tube and then run cyano down inside once I have length right.

I fly vintage and load on rods not great so strength of joint more than adequate

Link to comment
Share on other sites

John, wrapping the thread in cotton before inserting it and CAing gives even more grip. I've used the adaptors that Ron linked to by sizing the rod to fit over the large dia. or even using two or three short pieces of suitably sized carbon tubes to build it up to use a larger dia pushrod. I like to bind the outside of the rod in epoxy impregnated thread or wrap it with a couple of layers of glass cloth to prevent splitting on larger models. I tend to use epoxy for attaching the threaded adaptors rather than CA, can't bring myself to trust these new-fangled glues in high risk areaswink

Link to comment
Share on other sites

Here's a pic showing both ends of one I made earlier. As they used to say on BP wink 2

pushrod ends.jpg

Rod is 67cm x 5mm carbon tube, ends are bike spoke + 2mm clevises. The binding is Kevlar bought at a local fishing tackle shop cyanoed in place. Overall length 75cm, wt 18g, I've been considering remaking it using 4mm carbon tube which I calculate would bring the overall wt down to 10.3g but the saving in nose wt would only be about 5g, so not worth the bother.

For anyone considering the neater option of inserting the metal end into sleeved or unsleeved carbon tube it's probably worth cyanoing some binding strong thread or kevlar around the end of the tube as the carbon can split with relatively little side pressure.

Link to comment
Share on other sites

It’s possible to make a neat, strong pushrod fitting with small dia c/f tube, by whipping the end with Kevlar thread as mentioned above to stop the carbon from splitting. Fishermen use Kevlar thread for fly tying. Then, cover the Kevlar with heatshrink to keep it in situ. Tap the inside of the tube, screw in clevises/ quicklink/ studding etc, cyano and connect up.

Technically of course you can’t tap a thread in carbon fibre. Nevertheless, this works. I imagine the tap is roughening up the inside, but it will actually provide enough thread for the fitting to screw itself into the tube.

I did this with a Maxford Mentor tail end which needed bracing. They act in compression as well as tension so only the top side is braced, they’re strong and it’s an elegant solution. Also light and cheap. I shall probably use this method for pushrodsin future as they’re slim too.

BTC

Link to comment
Share on other sites

Another option with a tubular pushrod is to find or trim a piece of hardwood dowel to glue into the end of the tube. Then simply drill the dowel and epoxy in place a piece of studding or a threaded pushrod for your chosen clevis size, or just plain wire if you want to form a Z bend. You can still bind the tube if you're concerned about it splitting.

Trevor

Link to comment
Share on other sites

Those Irvine carbon push rods look very good but they're so short at 250mm they're only suitable for rear mounted servos or wing-mounted separate aileron servos. Even smallish models need pushrods around 400mm.

I bought some ends that fit on 5mm carbon tubing with 3mm fittings last year. I used them on my 1/4 scale Mew Gull and, despite being long (450mm ish) and unsupported the are absolutely brilliant with virtually no play. Not sure if that's the reason but the model is very solid in the air.

Geoff

Link to comment
Share on other sites

To roughen the inside of the tube holding the carbon rod I use a needle file or small drill bit in a pin vice. If the carbon is also roughened as above and epoxied in with decent resin it’s very strong indeed! I have bought fittings kits from RC World but also by the bits separately if i’m making long rods. I sometimes use the same solid rod That works for tail boom repairs on mini electric helicopters...let nothing go to waste 😉

Edited By Tim Flyer on 02/11/2018 12:45:55

Edited By Tim Flyer on 02/11/2018 12:46:54

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...