Plastic tubing for control snakes - RC Groups
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Nov 02, 2017, 03:32 AM
Registered User
Question

Plastic tubing for control snakes


Could anyone tell me which material it is that is normally used for the outer sheath of plastic control snakes?

I need some fine plastic tubing to guide pull pull cables through the back of a fuselage on a small model. Most of the hobby shop varieties are a bit on the large/heavy side for this purpose so I want to see if I can find something smaller/finer to suit.

The dubro micro pushrod kit ( https://www.dubro.com/products/micro-push-rod-system) seems to be around the right kind of size but I'm sure you must be able to buy just the tubing on its own from another source, probably cheaper too for quantity.
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Nov 02, 2017, 05:48 AM
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DACH's Avatar
Albert,
What about this?
https://www.hyperflight.co.uk/produc...bcat=PTFE+Tube
Dave.
Nov 02, 2017, 07:02 AM
An itch?. Scratch build.
eflightray's Avatar
If I need some short lengths of small bore plastic tube, I generally open a cheap ball point pen and cut off a piece, (the bit without the ink in ).

Hopefully you don't have that much tension on the push-pull cable to saw through anything. A little 'ackerman' helps reduce tension --





Ray.
Nov 02, 2017, 08:18 AM
Registered User
As post #3 shows, positive Ackerman is the better solution. Also, do not over tighten the lines, use just enough tension to not have any slack at neutral position
Nov 02, 2017, 12:18 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by DACH
Just what I was going to suggest too. And in case you don't realize it you don't want to use the tubing except for short lengths where it needs to bend around something. Teflon is slippery stuff but it can still drag needlessly on the lines if you use long runs of the stuff.

Another option if you just want to go around a single "kink" would be glass beads for making necklaces. Feed the line through the hole and running on glass should give you a low friction "pulley" to go around a kink in the path.
Nov 02, 2017, 03:09 PM
Registered User
Thanks that looks like just the thing I need. I only need it to run a short length just through the back of the fuselage incase I ever have to replace the lines which would be difficult if I thread them through the balsa formers without stripping off the covering.

I'll have to check my Ackerman because I think I've got my holes just a shade in front of the hinge line, shouldn't be too hard to make some new holes.

Thanks again.
Nov 02, 2017, 04:53 PM
Formerly ReelDoc
Jim Johns's Avatar
OK, for those of us who don't have a clue --- what the heck is Ackerman?
Nov 02, 2017, 06:01 PM
Registered User
There are probably better explanations out there but as I understand it Ackerman's principle here relates to the difference in linear movement in one direction derived from linkage being coupled to something that is moving in a circular motion. When I did my apprentship as a mechanic we were taught that on a car travelling around a corner the wheel on the inside of the corner prescribed a smaller radius than the wheel that was at the outer of the bend. Therefore to avoid tyre rub the wheels would have to be at different angles or 'Ackerman geometry' also known to us as toe out on turns.
Nov 02, 2017, 06:52 PM
-insert witty saying here-
Hemikiller's Avatar
Quote:
Originally Posted by Jim Johns
OK, for those of us who don't have a clue --- what the heck is Ackerman?
https://en.wikipedia.org/wiki/Ackerm...ering_geometry
Latest blog entry: ECSF 2017 SWap Meet - 4/2/17...
Nov 02, 2017, 10:23 PM
B for Bruce
BMatthews's Avatar
The car steering doesn't mean much in this situation. Although that is the key meaning of the term.

What it refers to here is setting the geometry of the servo arm, lines and horns such that if anything the slack line gets more slack as the surface moves away from neutral. If this isn't done and the last of the three examples ends up being the situation the lines will become tighter when the surface moves from neutral. And that just puts needless strain on anything.

I'd say the middle situation is ideal. But if one has to err at all it's safer to err on the side of doing the first option.
Nov 10, 2017, 05:26 PM
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Peteohms's Avatar
I use round cocktail stir sticks for small tubes.
Nov 10, 2017, 05:35 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by Peteohms
I use round cocktail stir sticks for small tubes.
That's a slick idea! And you can even match your liquor of choice to the personality of the model ! ! ! ! er.. I'm obviously assuming you'd just pluck it from the benchside libation and use it in this "secondary" manner....
Nov 10, 2017, 06:00 PM
Registered User
burlesontom's Avatar
My HS sells plastic tubing that they used to label as "Antenna Tube". I use it for running 30" steel pushrods through so it is just over a sixteenth of an inch inside diameter. Its about the same stuff Great Planes uses in their ARFs. And its cheap. You could use short sections or whole length in case you need to run new lines someday.

I was reading an article in the AMA mag last night and it made the point that plastic tubing just needs to be anchored at one end so it could stretch and shrink with temp changes. That makes sense to me even through I have always glued it at every bulkhead. In the future I will make tight holes in the bulkheads but will make it so it can expand and contract.
Nov 10, 2017, 08:34 PM
Registered User
Peteohms's Avatar
Quote:
Originally Posted by BMatthews
That's a slick idea! And you can even match your liquor of choice to the personality of the model ! ! ! ! er.. I'm obviously assuming you'd just pluck it from the benchside libation and use it in this "secondary" manner....

Damn, you caught me! That's what I use here.
Nov 11, 2017, 09:38 AM
Registered User
Another way to keep pull-pull controls tensioned is to cross them between the servo and control horns. Geometry is less important and the tension remains constant.


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