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Thread: Datum ski issue

  1. #1
    courierguy's Avatar
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    Datum ski issue

    I re-installed them a few days ago, my 11 th or 12 th. season, 400 plus hrs., on the RANS S-7S, all mountain flying, but when I went to make my first transition one ski kept blowing the 7 amp breaker. I double, then triple checked everything, to make sure nothing was binding up, but not only did the breaker keep tripping, it started to do it almost instantly, then it WAS instant, earlier it took a few seconds.

    Turns out the fix was simple. The 2 conductor cabling, protected by a wire loom, is spliced about a foot above the ski, as the linear actuator comes with a 2' or so length of protected cabling, which is enough to exit the ski but not nearly enough to reach up thru the boot cowl and to the panel, so a splice is a given. Good heavy heatshrink over the splice, but right where the wire loom exited the heat shrink, it had, near as I can tell, work hardened. You have a length of loomed cable, flexy as can be, but then a stiffer section because of the heavy duty heat shrink used by Datum. Some movement of the cable is to be expected as the ski moves, (why there is plenty of extra length also) and now that I think about that right side ski gave me warning as I thought it sounded "wimpier" then the other side, explained by the fact it was working with many broken strands, not to mention eventually shorting out as the two wires made contact. That explained the breaker behaviour. An easy fix, and nothing that would be a deal breaker in the boonies. Forewarned is forearmed, next time, if there is one, I'll go right to the wiring V. suspecting a mechanical binding or a bad actuator.

  2. #2
    wireweinie's Avatar
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    How were the wires spliced? Any pics?

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  3. #3
    courierguy's Avatar
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    They were soldered....., and I know that may be part of the issue. They failed a couple inches away from the solder joint. I buggered it up worse by the time I got the heat shrink off, so I didn't bother to take a picture. The heat shrink seemed to be like the type I've used in setting well pumps, some kind of goop or glue inside. I have not re-spliced it yet, and am open to suggestions. Crimp, or solder? I don't have a ratchet type good crimper, just a cheapie, this would be a good excuse to get a proper one, otherwise I'll solder I guess.

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    wireweinie's Avatar
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    Any time you get strands breaking at a connection, it's an indication of bad technique. In this case soldering a connection where there is to much flex in the wires. Soldering makes the connection to stiff and wrong flux and heat from the torch or iron further weakens the strands. A crimp type connection, when properly done, will outlast a solder joint every time.

    Is this a permanent connection? What gauge wire are you working with?

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  5. #5
    courierguy's Avatar
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    18 gauge is my eyeball guess. Permanent, yes. The thing is, the break happened 2 or 3" from the soldered joint, at the end of the heatshrink. The stiff heatshrink acted like a stiff soldered joint in effect, concentrating the inevitable flexing of the wire in one spot, that's what I found interesting. I'm splicing it back tommorow, and will use my crimper and probably just electrical tape. The wire loom is loosely zip tied to the bungee in such a way to allow movement but to still constrain it a bit, a compromise. The heavy duty heatshrink ended up being "too good", too stiff, and after 12 years of use the flexing added up. All a minor and easily correctable issue, and now I will keep a closer eye out for a re occurance, I'm just happy to have the mystery of the binding ski solved, before the wires shorted, I was trying to push 7 amps thru what amounted to 30 g or less wire, just one or two frayed strands. I did a quick test last night, now the actuator sounds like it should, like the other side, real torquey again, The gradual degradation of the bad side, as more and more strands broke, snuck up on me, I could hear it gradually getting weaker thinking back, but just blew it off. First ski flight of the season tomorrow morning!
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  6. #6
    courierguy's Avatar
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    forgot the pic
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  7. #7
    wireweinie's Avatar
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    Quote Originally Posted by courierguy View Post
    18 gauge is my eyeball guess. Permanent, yes. The thing is, the break happened 2 or 3" from the soldered joint, at the end of the heatshrink. The stiff heatshrink acted like a stiff soldered joint in effect, concentrating the inevitable flexing of the wire in one spot, that's what I found interesting. I'm splicing it back tommorow, and will use my crimper and probably just electrical tape. The wire loom is loosely zip tied to the bungee in such a way to allow movement but to still constrain it a bit, a compromise. The heavy duty heatshrink ended up being "too good", too stiff, and after 12 years of use the flexing added up. All a minor and easily correctable issue, and now I will keep a closer eye out for a re occurance, I'm just happy to have the mystery of the binding ski solved, before the wires shorted, I was trying to push 7 amps thru what amounted to 30 g or less wire, just one or two frayed strands. I did a quick test last night, now the actuator sounds like it should, like the other side, real torquey again, The gradual degradation of the bad side, as more and more strands broke, snuck up on me, I could hear it gradually getting weaker thinking back, but just blew it off. First ski flight of the season tomorrow morning!
    I agree that making the joint stiffer accelerated the fraying. But don't forget that the flux used crept way past the immediate area and no way to stop that. Flux works by chemically removing corrosion from the surface of the copper. Most fluxes are acidic so if not removed, the acid keeps right on eating away. Heat applied to the joint causes the flux to work faster and also causes it to travel up the strands of the wire. That means that the flux was there from moment one, up under the insulation, where it couldn't be cleaned off.

    In answer to your next question; use a flux called 'Nokorode'.

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    wireweinie's Avatar
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    I don't like to use butt splices but when I do . . . .

    Here is a pic that shows an example splice and the crimper for it. These are the best butt splices that I've found outside of some specialty stuff. Make sure you only use them on newer, clean wire or it defeats the waterproof advantage.
    Strip the ends of the wires to be joined and slide the blue 'plastic' sleeve over a wire. slide each stripped end into the metal sleeve, being careful to match the yellow stripe to the stripe on the plastic sleeve. Crimp the wires with the color matched slot in the crimper jaws. When both wires are crimped in place, slide the sleeve down and center it over the metal crimp sleeve.Heat the plastic sleeve with a heat gun until it shrinks down tightly over the ENTIRE splice area. When properly shrunk down it will produce a gas tight and water tight splice.

    Remember, butt splices only if you HAVE to. I.e., if it is in an area where the wires will need to be disconnected then use a connector!!!

    Crimp splices are better than solder joints in areas of vibration and flex.

    The end of both sleeves with the color band is slightly larger in diameter than the other end. Use this feature when joining wires of two different diameters.

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    Life's tough . . . wear a cup.
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  9. #9
    BC12D-4-85's Avatar
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    ^^^^And that school was worth my annual support fee

    Gary
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    jrussl's Avatar
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    Quote Originally Posted by wireweinie View Post
    I don't like to use butt splices but when I do . . . .

    Here is a pic that shows an example splice and the crimper for it. These are the best butt splices that I've found outside of some specialty stuff. Make sure you only use them on newer, clean wire or it defeats the waterproof advantage.
    Strip the ends of the wires to be joined and slide the blue 'plastic' sleeve over a wire. slide each stripped end into the metal sleeve, being careful to match the yellow stripe to the stripe on the plastic sleeve. Crimp the wires with the color matched slot in the crimper jaws. When both wires are crimped in place, slide the sleeve down and center it over the metal crimp sleeve.Heat the plastic sleeve with a heat gun until it shrinks down tightly over the ENTIRE splice area. When properly shrunk down it will produce a gas tight and water tight splice.

    Remember, butt splices only if you HAVE to. I.e., if it is in an area where the wires will need to be disconnected then use a connector!!!

    Crimp splices are better than solder joints in areas of vibration and flex.

    The end of both sleeves with the color band is slightly larger in diameter than the other end. Use this feature when joining wires of two different diameters.

    Web
    Very helpful, Web! Thanks for sharing these with us. Any links available to sites where they can be purchased.

    Jeff


    Sent from my iPad using SuperCub.Org mobile app

  11. #11
    wireweinie's Avatar
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    DMC seems to always be the gold standard even if expensive. If you don't want to pay their prices, I'm sure there are equivalent models out there. Mil-spec part numbers for some of the splices are in this same spec sheet.

    https://www.dmctools.com/oscar/catalogue/gmt232_2077/

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  12. #12
    frequent_flyer's Avatar
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    Quote Originally Posted by wireweinie View Post
    DMC seems to always be the gold standard even if expensive. If you don't want to pay their prices, I'm sure there are equivalent models out there.
    I find the Ideal crimper with interchangeable dies to be adequate for ring terminals, butt splices, and coax termination.

    One is shown here but it does not have the die set needed for those uninsulated butt splices:

    https://www.amazon.com/Ideal-Industr.../dp/B0000WU4JK

    For my infrequent use maintaining my amateur radio station and other misc jobs it's ok to spend a few minutes finding the right die set and fitting it.

    For avionics pin crimping JR Ready makes a cripper and positioners that seem to be quite good quality.

  13. #13
    courierguy's Avatar
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    I bought this last night: https://www.ebay.com/itm/323389917794, probably good enough for my rare use.

    My long time crimper has been my aircraft swedger, after I discovered a 3/32" copper nico was just right for 10 gauge stranded wire, the most common size for a lot of the solar work I've done in the past and still do a bit of for my own needs. Not UL approved I guess but pull tests showed it to be mechanically strong, and some 2 or 3 decades later they work long term also.

    I now feel the need to brag on the Datums a bit, after 11 seasons of this kind of use (pictured, not to mention my up taxi onto my ramp at home) the wire break was a pretty minor thing. Hard to see my tracks, but I landed up the draw on the shadow line, then while keeping a bit of speed up hugged the brush line and made my turnaround and then let the slope re-launch me. I love these sloped sites with multiple fall lines, they make me think harder then any other type of off airport flying I do. This was a couple days ago while "working", flying 30 miles to eyeball a upcoming crane job. When I provide these pre job inspections for my customers, I don't charge any extra, ha ha ha. It is actually a valuable thing, as I can spot issues and let them know before I roll up, "you have to move that trailer/pile of lumber, etc."
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