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  1. #1

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    jet drive surfboard

    I have an unusual project and need some advise. I'm running a 40mm Graupner jet drive with a KB45XL 11 motor-1000kv with a HiModel 200amp ESC. I have run on 6s and 5s packs. This setup only runs for 6sec. using a timer on a surfboard! On the 6s only the motor got warm and all the wiring,esc and battery were cool. After a few runs with 3-4mins. in between, the motor would get hot (100deg.?), expected. On the 5s pack the motor, connectors, and esc would get hot right away. Only 4mm connectors. I would have expected this from the get go with the 6s.
    Anyway this thing sucks up 144 AMPS while doing this. Output was 2200 watts. In testing and using this, probably 9o+ runs, I have gone thru 3 esc's, 1st one went about 60 runs then quit, the 2nd one ran 20 times got wet and torched,not pretty), this last one running on the 5s went 20+ runs in testing and finally de-soldered the caps. I tried to fix but no joy.
    I know that"s a lot of amps but shouldn't the esc be able to handle that especially for only 6secs at a time with cool off period in between?
    I don't know the rpms of the impeller but it seems to be close to the no load rpm.
    Of course this thing is only going 5mph instead of whatever, too much load? Any ideas what might be needed to make this work reliably? I'm looking for low speed thrust.

    Thanks

  2. #2
    Hoostas's Avatar
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    RE: jet drive surfboard

    I'm afraid I don't have any advice for you, but I'de love to see it. You got any pics?
    B4, TC4, E-MAXX, 1987 Kyosho Ultima, Team Losi Micro T, OFNA JL10e Drift, way too many slot cars and rockets

  3. #3

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    RE: jet drive surfboard

    To be clear about it, your motor OR your ESC is heating up first?
    if its your motor (and it sounds like it is) that generally is a sign of overload on the motor, in your case prop to agressive/large or you could add a gearbox,
    if the ESC was heating up first, that would be a sign of the prop/gearing combo not being agressive enough,
    Myself being a surfer, i allready know surfboards are realy considered high drag to the world of RC because of the scaling effect, they paddle fine with us on it, but we are just paddling.
    you could reduce the volts, lipo setup, that may breath some life into this but for the most part i think you need to gear down or realy downsize your prop. or even change to a lower KV motor.
    you are heating up quite quick, probbably not a minor change is needed.
    quote the maker for this info, but i think brushless motors should run around 170F ? been a while and its better to get the quote from the maker, generally that rule of thumb applies to running say in a car or boat for the entire battery duration, if its above a certin temp you need to gear/prop down, if its below that temp you CAN prop/gear up.
    ESC has its own prime temp for the end of a battery, usually around 140F, not sure exactly and it varies mfg to mfg so defintly get the correct quotes.
    boat websites/mags have alot of gear reduction systems if i rember, look into the RC tugboat world if you cant find them elsewhere because speedboats typically dont use any gear reduction, tugboats allmost allways and your surfboard even if its a shortboard resembles the tug alot more than the highspeed V
    by the way reading your post again, your motor heating up that quickly is a bad sign, you are being extremly hard on it, defintly gearbox or prop down right away, motors can fry to. 6 sec is extremly short for a motor to heat up.
    Very cool project, need pictures!
    short board or long board?
    Function over fashion, I dont do shelf queens!


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