×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Cable Rotation

Cable Rotation

Cable Rotation

(OP)
Hello,
I am designing an electronics package for a camera that pans back and forth 180˚ but never completes a revolution. Currently I have the power cable going down along the pan axis and out through an IP-68 cable gland in the bottom of the enclosure. This works for weather protection but I have concerns about the cable fatiguing over time due to twisting back and forth. Although the camera does not spin around and around, it does pan back and forth a few hundred times a day. The cable is secured and strain relieved at the top, then runs about 12" unsupported until reaching the cable gland. Thus there would be about 15˚ of "twist" per inch. Does this raise any concerns with you all? Can you think of any immediate issues? Or are there resources for cable fatigue in these types of applications? Most of what I've found online is for high-speed motion or CNC, which this is neither.

See attached for quick sketch

Best,
-Shea

RE: Cable Rotation

For cable wear/breakage cases like this I am unaware of a way to calculate reliability. We have always had to create life testing rigs and perform testing.

Not sure if you have room in your budget but you could always add a slip ring in there to eliminate any cable twisting. Good suppliers will be able to tell you the life expectations based on their own testing.

I am not endorsing this supplier, this link is just provided as a reference for what a slip ring is: https://www.moflon.com/slip-ring/?gclid=EAIaIQobChMI46nP28-O7AIVyEXVCh029QtZEAAYASAAEgIMIfD_BwE

RE: Cable Rotation

I'd put a loop or two of cable in the box, to reduce the relative twist/bend per inch. Use the thinnest cable possible, with the slickest (e.g. teflon) wire insulation, and a slick, durable cable jacket.

RE: Cable Rotation

I'd use the highest strand count you can find and double the loop length. It will last a longggggg time.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Cable Rotation

Work hardening is a definite possibility, so the less stress the better; of course, our system was doing a scan every 1.5 seconds, but we ran into issues with our flex cable, which had copper deposited on Kapton. Oxygen-free copper was our solution

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Cable Rotation

(OP)
Thank you all for the responses!

@hendersdc The slip ring definitely makes sense, especially for power. However, the cable we're using is power over ethernet, so would the slip rings have any issues with passage of data? Is there a lot of noise?

@btrueblood and @itsmoked That makes sense, do either of you suggest securing the extra loop of wire or should it be sort of free-floating?

@IRstuff Does the oxygen-free copper just have more resistance to work-hardening? I was hoping to strain-relieve the cable enough so that the twisting was the result of motion alone and not the weight of the cable or other potential forces on it.

RE: Cable Rotation

sheafromme,

Read up on the deflection of beams. A beam subject to a bending moment will curl up into a radius. If we set that radius to ρ...

1/ρ = M/EI

That should help you work out the stresses from bending your cable.

--
JHG

RE: Cable Rotation

Sheafromme,

You can find slip rings that are rated for very high frequency signals (10's of GHz), there are also some that are already set up specifically for ethernet like this one: https://www.moflon.com/me1221.html

RE: Cable Rotation

You would want the loop to be free. This allows the cable to distribute the bending forces. It will naturally distribute them in a manner that minimizes stress in the cable.

I have to disagree with btrue on the Teflon. Teflon jacket is about the stiffest jacket you will ever come across. That stiffness results in the cable not wanting to bend at all which in-turn causes the cable to bend mostly at the ends where it enters the strain reliefs. With all the bending at just those two points you can see where that will quickly lead. Teflon would be OK in a clean environment dragging (not bending) over a mostly smooth surface and it's da'bomb for chemical resistance.

Keith Cress
kcress - http://www.flaminsystems.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close