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Theoretical question: I was told by an auto mechanic friend that replacing a clockspring in the steering wheel of a car with concentric conductive rings (separate ring for each component powered such as horn, airbag, etc.) on the steering column-side and contacts on the wheel assembly-side (thus replicating what the CS does now) would not be feasible. He mentioned this is because of the resistance the copper (or whatever material used) would pose too large of an impedance to DC current for it to be used.

Is this true, and if so, why? I understand current flow, impedance, and so forth, but I'm having a hard time conceptualizing why it would be insufficient.

For those that are wondering, I'm not asking because I plan to do this, but rather I was trying to envision a simpler solution to a complex clockspring that could be used in this application.

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    \$\begingroup\$ If I understood you correctly, you plan to have copper rings one around another and have them turn independently? If so, how are you going to lubricate them, to insure good contact with lubrication, to stop corrosion happening, so make system cheap etc. The resistance of the rings themselves would probably be low enough, but the added resistance of the contact between rings could be a problem. \$\endgroup\$
    – AndrejaKo
    Jan 30, 2012 at 18:55
  • \$\begingroup\$ The rings I would imagine would be fixed, whereas the contact points on the wheel assembly itself would rotate around the fixed rings as the wheel is rotated. The assembly is inside the car so corrosion should be minimal (I would guess), though I suppose depending on the materials used a groove could be worn in the ring over time which could prevent contact. But let's assume those issues can be solved. \$\endgroup\$
    – Garrett
    Jan 30, 2012 at 19:08
  • \$\begingroup\$ It's not clear what you are asking. What "clockspring"? Steering wheel contacts I have seen have been planar sliprings. "Clockspring" sounds more like a permanent contact. Basically a coiled conductor that winds and unwinds as the steering wheel is turned. It works because a steering wheel has limited travel. \$\endgroup\$ Jan 30, 2012 at 19:17
  • \$\begingroup\$ I don't know about every car, but the ones we were working on were late model Hondas, which use a clockspring for the electronics which are stored in the steering wheel. I understand this is the standard on almost all modern cars. \$\endgroup\$
    – Garrett
    Jan 30, 2012 at 19:20
  • \$\begingroup\$ There's a third possibility, using cables with U-turns: kostal.com/english/2-01-01-02.html \$\endgroup\$
    – starblue
    Jan 31, 2012 at 7:19

3 Answers 3

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In the context of this question, the term Clock Spring refers to a loop of wire which connects electronics in the steering wheel to the rest of the car. Clock Spring is viable, because steering wheel has a limited range of rotation. The loop might look like a spiral spring found in clocks, ergo the name. It's not a mechanical spring used for exerting force.

Clock Spring vs. Slip Ring. Slip rings can be found in places where range of rotation is not limited (e.g. helicopter rotor). Slip rings are subject to condensation, contamination, corrosion, vibration. A Slip Ring can be less reliable than a loop of wire. (Air bag is connected through Clock Spring.) A Slip Ring would be more costly too.

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  • \$\begingroup\$ Thanks, that's the info I was looking for initially. So I understand now that while what I am describing (slip ring) is a viable solution, it is not the most ideal in this context when compared to a clock spring. \$\endgroup\$
    – Garrett
    Jan 30, 2012 at 22:45
  • \$\begingroup\$ A slip ring would work, but can fail more easily. I live on a dirt road. There is no part of any of my vehicles that doesn't have a thin (or thick!) film of red, iron-rich, silt. It gets everywhere! \$\endgroup\$
    – lyndon
    Jan 30, 2012 at 23:58
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Not having been familiar with the concept, it appears that what I am referring to is a slip ring and could be used in automotive applications so far as I can tell (anecdotal note from @Olin Lathrop).

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I really think the automaker suppliers could do a better job with a slip ring than the old style clock spring. I am familiar with slip rings from the size of a dime to 5 feet in length and the condensation, overall wear problems and impedance which does not really apply to DC, are non-issues for something of this size and working environment. Most slip rings are used in applications like helicopter rotors and the like, but that is where they excel and for a very long time at a relatively high rotational speed. Government projects require testing for projects that the cycle count is higher than most automakers can count, so reliability is there. it must be a cost issue, but with the airbag in the steering wheel controlled by the CS, it should be a higher priority because failure should not be an option.

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