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Thread: FW- Crash Course

  1. #31
    Ocracoke's Avatar
    Team Kaizen

    American Wire Guage works on the principle that smaller the number (generally), the thicker the wire. So 8AWG wire is thicker than 10AWG for example.

    You can go too thin. I've had a wiring loom from one of my beetleweights catch fire due to a short. It was using 26AWG wire (which is the same guage of wire as that used on the RC wires to the receiver) and normally is OK in the low powered application I use it for in the BW (Shu! for the record) but when it faulted, I distincitly remember the smoke and then the wire glowing before it melted like a fuse would do. Left a nice burn mark on my hand that did.

    Similarly with my Middleweight, when that developed a short during the middle of a battle with some Heavyweights, the RC wire melted. That would officially be the first time any of my robots have caught fire during a fight.

    You can also go too thick where it'd be impractical to use, heavier and introduce uncesserary resistance in the circuit, it depends on the load being applied through them. The 12 or 14AWG wiring recommendation is from components I've used in the past where they've been that guage before.
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  2. #32

  3. #33
    This is a useful table on wire sizes: https://en.wikipedia.org/wiki/Americ...AWG_wire_sizes

    Note that the "ampacity" for 14awg is only 15-25 A (depending on the temperature of the insulation), but that's for continuous use. Assuming the wire starts cold, it will bit of time long time to heat up and melt. The 10s fusing current is 166 A, which is a more useful number to think about - e.g., we use an 80 A fuse in our FW (with 14awg wire also for the most part), so that tells me that the fuse will blow way before the wire melts, which is all you really need to worry about (as long as you've picked a sensible fuse of course).

    As well as melting, the other issue with thin wire is that the resistance of the wire itself will suck some power when it's running a high current, so you can potentially impact performance or even cause a brown out* even if the wire doesn't melt - e.g., if you have a really short burst of high current the wire will not have time to heat up, but the drop in voltage could trip an ESC say (by making it think your battery is depleted).

    In summary, use 14awg for any power wiring as Lucy says and you'll be fine. Also it makes sense to use silicone insulated wire as it's more flexible than PVC or Teflon coated - even 14awg is quite hefty and ideally wants a bend radius around 20mm.


    *This is when something temporarily glitches due to a low voltage or other anomaly in the supply, like a partial blackout, it's not related to your reaction to seeing a big spinner facing your robot in the arena

  4. #34

  5. #35

  6. #36
    The general rule for what plug to use for your removable link is to go for the same type that is on your LiPo, that way you know it can handle the current.
    Powerhouse Robotics

  7. #37
    Ocracoke's Avatar
    Team Kaizen

    however i have run into some problems. i have miscalculated my lipo as its needs a 90amp fuse not a 60amp one, but i can find a 100amp fuse, does a higher rating ruse make a difference?
    The fuse needs to be rated below the burst current of your LiPo. Stick with the 60amp fuse, you'll probably be OK.

    also what plugs do people use for their safety links?
    In the FW and MW categories, I use XT90 plugs. I did use to use XT60s in my FWs but the wider cup of the 90 I find easier to solder. I may yet switch to EC8s for my MW and likely for me HW.
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

  8. #38

  9. #39

  10. #40
    Ocracoke's Avatar
    Team Kaizen

    am i right in guessing the wire is soldered to the fuse through the maxi holder or is it wrapped.
    It is soldered through if I am understanding you correctly, at each end.

    also would this go before or after the link?
    In the photo I posted on page 3, the fuse is before the link, which has always worked for me but I don't think it matters either way (though perhaps someone else can weigh in on that one).
    Last edited by Ocracoke; 23rd November 2020 at 19:46.
    Team Kaizen - Build Diary for all the robots

    AW: Amai, Ikari, Lafiel, Osu, Ramu
    BW: Shu!, The Honey Badger
    FW: Azriel
    MW: Jibril, Kaizen

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