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Thread: Advice please: sourcing motors for 54" twin cat

  1. #1
    Join Date
    Apr 2019
    Location
    WV
    Posts
    20

    Default Advice please: sourcing motors for 54" twin cat

    I'm running a 12S power supply.

    I'm down to the sss5694/1000 kv or 1200 KV. both 12000 watt max. The 1000KV draws 240amps max with a max voltage of 50.

    The 1200kv draws 292amps max and has a max voltage of 41. I've done the math a million ways and 3.5*12 keeps coming up at 42. Will I damage these motors at 42 volts? I'd really like the extra RPM.

    Another option for me is the 56104/790 its rated with a max draw of 180Amps, 58V, and max watts of 11000.

    What is the best solution? What motor should I be considering that I am not currently?

    The hull is fiberglass with a full CF inlay.

    for all intents and purposes I'm completely new to the hobby. I don't know what I don't know and what I do know is probably wrong. Any help would be appreciated.

    I'd like to order motors today or tomorrow.

    Thanks,
    Dan

  2. #2
    Join Date
    Jun 2010
    Location
    Mi
    Posts
    629

    Default

    you should use the motor RPM calc on the OSE web site.
    https://www.offshoreelectrics.com/conversion.php

    12*3.7*0.8(efficiency)*1200 = 42624 RPM. Too hot.
    Riggers may be able to do SAW runs at that RPM, but probably not a cat. Target 38000 RPM or less.
    Further, I would not run the SS motors so close their max voltage. It will work, but it won't be a robust setup. Do you want to run the risk of burning down the boat?

    As far as other motors, Have you considered Neu?
    For the same size and KV motor, they have higher voltage limits. They generally have higher efficiency.
    TP would be another proven option.
    Last edited by larryrose11; 04-29-2019 at 11:04 AM.
    Cheetah, Super Rio, (Mod) Starship (Mod and sold),

  3. #3
    Join Date
    Apr 2007
    Location
    AZ
    Posts
    7,664

    Cool

    We really need to know what you expect from the big cat. I know you are new, but you will have to decide your priorities. If you can answer a few questions that will help us to give you what you want.

    What is the size of your pond?
    What run time are you expecting?
    What speeds are you expecting?
    Why did you choose such a large boat as your first FE?

    But - if you really are a beginner, this is not a good first project at all. I have seen too many beginners try a big complex boat as their first build - it seldom ends well. You will likely fail, damaging expensive equipment and becoming discouraged. I very strongly recommend that you set the big cat aside for a few months and start with a more basic FE boat. The Proboat Veles or Aquacraft Motley Crew cats would be a good place to start. After a few months of experience - and mistakes - you can consider the big cat build. This is not meant to discourage you, it is instead a reality check.


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  4. #4
    Join Date
    Apr 2019
    Location
    WV
    Posts
    20

    Default

    Hi Larry,

    Thanks for the response.

    I did consider neu. They got out of my price point pretty quickly.

    the sss56104/1000 kv at OSE should be 50v, 280 amp, 14000w Right?

    12*3.5*8*1000 is 33.6k rpm. Still too much?

  5. #5
    Join Date
    Apr 2019
    Location
    WV
    Posts
    20

    Default

    Fluid,
    I live on a river. I can easily see 300 yards in each direction from my dock. Mornings are generally glass calm.

    20 minutes or so.

    70MPH? Maybe more.

    It was on ebay and priced where I felt comfortable. I haven't built a FE ever. The last boat I built I was 12. Dumas hotshot 2 with a 3.5KB outboard. 30 years ago. I build scale rock crawlers. I liked the idea of a hull large enough to be roughly be 1/10 scale. Offshore race cats run 42 to 52 feet. 54 inches is right in there at 1/10 scale.

    As far as my tech abilities I'm pretty confident. I build guitars for a living, I build guitar amps as a hobby, I have designed and built whitewater kayaks and surfboards. I'm not an unhandy fellow.

    I have considered sidelining this but I'm kind of pot committed.

    Plus. It's cool.

  6. #6
    Join Date
    Jun 2010
    Location
    Mi
    Posts
    629

    Default

    DanInWV,
    The numbers in your calculation are not correct.
    12 Series cells
    3.7 Nominal voltage. Probably a good estimate for fully charged, but under load.
    0.8 motor efficiency
    1000 Motor KV unloaded
    12*3.7*0.8*1000 = 35520 RPM. This is a decent RPM range.

    As for run time, something like 3-5 min is more like what you should expect.
    As an example, just for fun. lets roughly caculate the energy to run 20 min.
    lets just say you are drawing 6Kw average per side.
    6000*20 min/60 (min per hour) = 2000 wh-hrs of energy
    2000 w-hrs / 44.4v = 45 Ah per side. The would be a 12S / 9P arrangement, or 36 6S-5000 mha battery packs in total. The boat would be so heavy, I'm not sure it would float.

    BTW, I do agree with Fluid. He is an seasoned expert.
    Such a large and powerfull undertaking for your first FE is quite daunting, and will likely be expensive too.
    Cheetah, Super Rio, (Mod) Starship (Mod and sold),

  7. #7
    Join Date
    Apr 2015
    Location
    TX
    Posts
    199

    Default

    Yep in fast electric world 3-5 minutes typically is the norm. My hot setups come in after 3 minutes.

    I would start with an almost ready to run boat and experiment with voltage and kv until you get some experience under your belt. You'll end up doing a better job on your big cat no doubt and have a lot of fun on the way. Believe it or not smaller boats are very fun too

  8. #8
    Join Date
    Apr 2019
    Location
    WV
    Posts
    20

    Default

    I calculated the cell voltage at 3.5 as opposed to 3.7v.

    I'm still in this one folks.

    I'm ok with daunting.

  9. #9
    Join Date
    May 2018
    Location
    TX
    Posts
    208

    Default

    I’m giving these a try in my 54” build.
    Attached Images Attached Images

  10. #10
    Join Date
    Sep 2011
    Location
    ca
    Posts
    164

    Default

    If 20 min. runtime is your first priorety, you would look for something like 500 kv/12s/5-6000 mah each side and 55 - 57-1,4/-2-blades props...And 50-55 mph

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