Small flex shaft design and supplier

[sbrats]

I am looking to see if this is possible and that someone may be of some assistance.

I am currently working on a robotic concept that utilizes a hollow flex shaft drive - the flex shaft would be required to transmit a rotational motion (slow motion and only 360 degrees in total) plus a pull load while bent at 90 degrees. In my previous concept I utilized a thin aircraft cable to this - however there is a desire to now have this item as an 'hollow' object so that another feature can be passed down the middle.
Ideally the hollow shaft is around 2mm ID and external diameter of no more than 3.5/4.0 mm. I have utilized a disassembled bike brake cable and used the spiral wound 'flat metal' sheath - this works except the flexibility in bending (to go around a articulated joint) is to stiff. This in turn appears the same as the outer metal casing on a Speedo cable.

Can anyone suggest a supplier with capability to make something like this in prototype quantities, but in a thinner flat material (to increase the flexibility) The current material thickness is about .025" (.635mm) or suggest another type of construction to achieve the same type of result.

Regards..

Stephen

 

[patprimmer]

Have you tried an appropriately sized coil spring

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[sbrats]

Yes I have, unfortunately in tension the spring will elongate, which is undesirable.

Thanks

 

[Tmoose]

"in tension the spring will elongate"

Isn't that the definition of low bending stiffness, unless the stiff element is at the neutral axis ?

 

[sbrats]

Tmoose..

"Isn't that the definition of low bending stiffness, unless the stiff element is at the neutral axis ?"

Yes..
Previously I utilized an small dia aircraft cable at the neutral axis (fixed at both ends)- this allowed the desired rotational and pull. By using a spring (so now I have a hollow feature as desired) this will also allow rotation but under pull - because of the spring wire size - I will get elongation and not the desired amount of control. I was looking at the sheath and seeing that it will bend and allow pull without the same amount of elongation as the spring - while still being a hollow feature - allowing me to pass another control cable down the center.
I think that i will need to look at a different configuration.

Thanks

 

[MiketheEngineer]

How about a small sewer snake or throttle cable off a lawn mower or a "grabber" - a device they sell in hardware stores about 18'' long used to retrieve small parts from small areas.

Just some thoughts

 

[benta]

Don't know where you are in the world, but Suhner in Germany is expert on flexible shafts.

http://www.suhner-transmission-expert.com/site/index.cfm/id_art/14496/vsprache/EN

Benta.