Push-pull cable actuation

[43st]

Greetings Eng-tips!

I'm looking for Push pull cable, similar to throttle cable, but for a larger application (perhaps 200lbs or so, max 11' distance, roughly 4" push/pull). But this is the easy part.. the more difficult part is that we need the parts to be crimped and fitted in our shop. Most off-the-shelf bits are pre-crimped on the ends.

Can anyone suggest a source for something like this?

 

[rb1957]

surely if a cable comes pre-crimped, you can cut the crimp off and re-crimp ... no ?

else just buy some wire and some reasonably rigid tube (to support the cable) ... no ??

 

[ornerynorsk]

McMaster Carr has a nice selection.

 

[43st]

I'm looking in McMaster, as well as Aircraft Spruce. They have some stuff.

We have a deflection in a frame, it was to be expected. We've tried a semi-rigid linkage (chain and tube) and the deflection makes it an issue. Thus the idea to use something flexible.

 

[MadMango]

I've used Sava before for custom push-pull assemblies:

http://www.savacable.com/pages/prod_04_00.html

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[btrueblood]

Cablecraft (div. of Tuthill) manufactures cable. However, I also know they don't like to have OEM's crimping the fittings, and prefer the cables be assembled by their suppliers. That said, we have had assemblies crimped by another local shop, after getting past the sales office at Tuthill to a technical type.

FWIW, there is a lot of "lost motion" in push-pull cables, and a tendency to have the friction force increase over time. If I was to do it again, I would go with all-tension cables (e.g. aircraft controls). Not that I would ever do it again - prefer hydraulics.

 

[43st]

I'm currently looking at to cut-to-length bowden cable.. with end collets. I'm aware of the lost motion, and I think that will be ok. The item we're moving will push back against a bumper in its closed position. We will trim the piece in it's open position.

Just need to be careful of it's load and travel distance, can't get too crazy.

 

[Clyde38]

We've tried a semi-rigid linkage (chain and tube) and the deflection makes it an issue.

Have you considered linear chain push-pull actuation devices?
ex:

http://www.rarodriguez.co.uk/framo-linear-chain.php

[link

http://www.linkedin.com/in/clydehancock

]

[/url]

 

[43st]

Thanks for the suggestion Clyde38.

We've used linear chain in the past, but it doesn't fit in this application I don't think. Ultimately this is a straight up linkage, the twist is that it needs to be designed to accommodate a large deflection in it's main frame and not jam up.

 

[btrueblood]

43,

Do at least look at the Tuthill designs. They use an overwrap on the center cable, both to provide more compressive strength, and to keep a smoother surface in contact with the outer guide sheath to minimize wear and friction.

The problem is that the overwrap needs to be very carefully removed before crimping fittings in place, and special crimp fittings made that cover the overwrap "tag end" to keep it from unravelling. Thus, they limit who can do the work.

 

[43st]

The low friction test piece came this morning from Mcmaster, it doesn't have a name on it but I wouldn't be surprised if it was the Bristow type by Tuthill.

We're going to bulkhead the connectors to get to the length we need. I think I can package this well. Still need to transfer motion from rotatory, but that shouldn't be difficult.