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Retractable wires for arm extensions

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  • Retractable wires for arm extensions

    We have re-designed our arm for more reach for the championship. One challenge with the extra reach is wire management. I have seen teams with a retractable wire mechanism as a solution. However, I am having trouble finding one. Also, the answered question regarding one mentions an "appropriate" wire gauge. I can't find the actual wire gauge stated for the servo extensions or the retractable wiring devices that I have found. Without documentation that the wire gauge matches, would we face an issue at inspection in Houston?

    I know some of you have used them. Would you please share with me where you purchased them and how you proved to the inspectors that the wire gauge was sufficient?

    Thanks in advance for any help on this matter.

  • #2
    Specs should be available for what you're buying, you could measure the diameter once you have it.
    Table of gauge and diameter -
    http://www.ohmslawcalculator.com/awg-wire-chart

    The game manual tells you what gauge wire is required to modify servo wires

    RE14 j
    iii. PWM (servo) wires are 20 AWG or 22 AWG.

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    • #3
      I did find specs on Servo City. Pitsco does not list the gauge, at least anywhere I could find. The standard servo wire from Servo City is 24 AWG. The heavy duty is 22 AWG.

      I have searched locally for these items. I finally found a store yesterday with two different types. Nowhere on the packaging does it show the gauge. A google search of both products also failed to show the gauge.

      I can measure them to make sure, but once they are connected, there will be no way for the judges to measure the diameter of the wires. I read on a reddit post that a team was required to produce proof of the gauge of wire used at inspection. I suppose purchasing one that specifically states the gauge of 20 or 22 would be the best thing to do. However, I have been unable to find one. The examples used in the answered question section are both for heavy duty extension cords, not a 4 foot or so extension of 20 gauge 3 wire cable.

      Are folks custom making these? Or is there a product I could readily order that fit the requirements for servo extensions? I am not taking the easy way out and just asking here. I have searched in person and online and have failed so far to find what we need. With time dwindling, I am seeking some direction from you fine folks that are more experienced in this area.

      Thanks again for any input.

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      • #4
        I would think that if you documented in your Engineering Notebook that you measured the diameter of the wires and had a table showing what gauge wire that was is acceptable documentation.

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        • #5
          Another, slightly different approach that our team used, with the goal of reducing total amount of wire going out the extension: Custom cable assembly that took multiple power ground connections from servo outputs and put them on just two wires for pos and neg power, these were 12 AWG (slightly overkill for 3-4 servos but not too much) and then the smallest insulated wire we had around for the servo control signals: some was 24 AWG, some was 26 AWG, All stranded. Team needed to plan for heavy load, and hence high current, on servos because of the way the mechanism worked.

          The #12 was from a speaker cable so it was low voltage with thin insulation.

          This all went through several lengths of cable-schlep (or no-name knockoff version) to get up the arm.

          Soldering the #12 wire was a tricky thing: it's big and took a bit to heat up and still wanted to work on melting the insulation.

          Maybe this isn't a good approach for Worlds, unless the mechanical part of this is important.

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          • #6
            Check this - http://www.coilcablespecialist.com/e...ables/shielded

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            • #7
              Thanks for the input! We ended up ordering some of these for servo extensions. It specifically says in the description that they are 3 wire 20 gauge cables. They extend about the right distance and retract to about where we need them to. Most importantly, they are verifiably legal. I even ordered a couple of extra of these to have on hand for the inspectors to verify the wire gauge, if needed.

              https://smile.amazon.com/Coiled-Cable-conductors-extends-5ft/dp/B012J4615M/ref=pd_sbs_0_4/132-6597230-6875403?_encoding=UTF8&pd_rd_i=B012J4615M&pd_rd_r=c7c234d8-5562-11e9-a5e6-893391744a24&pd_rd_w=QkHUw&pd_rd_wg=m10ML&pf_rd_p=588939de-d3f8-42f1-a3d8-d556eae5797d&pf_rd_r=YFFVEPQ0CJF5T4ESPTVQ&psc=1&refRID=YFFVEPQ0CJF5T4ESPTVQ

              I'm more nervous about the inspection at the World Championship than I am about the competition. I am the mentor and will not be able to be there on Wednesday for the inspection. At all of the past competitions, I have been there to help if something needed to be tweaked to pass inspection. (Walmart run for mailbox numbers because the ones used were too narrow, for example.)

              Also, the kids have heard a rumor somewhere that if the robot does not pass immediately, that is it. There is no time given to correct anything that may not fit the specs. I can't believe that teams would not be given a chance to correct anything, especially with the costs involved in going to the tournament and the hard work it has taken to get there. We have worked very hard to make sure we are compliant, but with so many rules there could easily be something we missed. We have gone over the robot self-inspection and are working on our own "pre-flight checklist" including orientation of sensors, wires tucked, intake device in proper location, etc.

              Thanks again for the input!

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