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Carbon fibre pushrods - help please.

#1
I'm building the hobby King Fidget http://www.hobbyking.com/hobbyking/store/__36753__HobbyKing_Fidget_Funfly_Aerobatic_EPP_Airplane_w_Motor_840mm_ARF_.html.

The pushrods are carbon fibre. Two pre-z-bent servo connectors with a straight carbon rod between them, then 2 pieces of heatshrink tubing are slid over the joints and shrunk over each end (before the z-bend). Like this:
IMG_20140203_220220.jpg


The problem I'm having is it's just not working at all. The carbon rods are slipping up and down inside the shrinktube.

I've tried a little tape inside before the shrinktube but they still slip. These are about 1mm dia. rods.

Obviously a little epoxy or maybe even CA would work, but I was wondering If anybody had used this method before and had any tips?
 

Freaky_1

old headcase
#2
What little experience I have with cf and heat shrink involved dripping CA into the end of the heat shrink on the cf end.
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#4
I've done it both ways before, and I prefer the "tied rod ends" using a fly-tying rig . . . but the shrink tube is faster and pretty reliable after it's glued.

Just make sure you pull out the thin CA *after* you've pulled the control rod off the horn ;)
 

xuzme720

Dedicated foam bender
Mentor
#5
I've had heat-shrunk ends come apart, even after gluing. Not a good thing and can be hard to pinpoint if it's only slipping and not pulled all the way out. It's faster to heatshrink/glue rather than wrap/glue/heatshrink, but it's still much faster to wrap them than it it to rebuild. If you don't think the plane is going to last more than a flight or two anyway, just heatshrink/glue them. You'll be fine for that long at least...
 

pgerts

Old age member
Mentor
#6
You need more heat if i can see the picture right.
Use aluminum foil to protect the foam and to reflect the hot air from the gun to shrink even on all sides.
 

quorneng

Active member
#8
Bedrock
Not directly related to the shrink wrap problem but you would do better to mount the carbon rod on the other side of the z bend.
As you have it the z bend in the servo arm is well offset to the rod causing it to bend when under load.
It would be 'stiffer' if it were mounted like this:
Zbend.jpg
You do have to make sure the servo arm is clear to move to the limit of travel.
Of course the best of all is a clevis which puts any load exactly down the centre of the rod with no bending at all.
 
#9
Note that carbon fiber comes coated with a mold release from the mfg. process. Absolutely *nothing* will stick to CF unless you sand it down and clean it up with acetone.
 
#10
Bedrock
Not directly related to the shrink wrap problem but you would do better to mount the carbon rod on the other side of the z bend.
As you have it the z bend in the servo arm is well offset to the rod causing it to bend when under load.
It would be 'stiffer' if it were mounted like this:
View attachment 17942
You do have to make sure the servo arm is clear to move to the limit of travel.
Of course the best of all is a clevis which puts any load exactly down the centre of the rod with no bending at all.
Can you elaborate on this as I'm not getting what you mean? Is the image in your post the one you meant to post?
 

xuzme720

Dedicated foam bender
Mentor
#11
He Photoshopped the carbon rod to be more in line with the level of the servo horn instead of on the outside. I hope that makes sense...