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Author Topic: Brushless recommendation for Twin screw Kort propís 85 - 92mm  (Read 307 times)

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Hi all,

Okay so i would like to turn a pair of Kort propís 85mm - 92mm 4blade
On either 6v 14ah x2 in parallel or x1 12v 22ah Sla
With a toothed belt reduction,
I would like to get to 3000rpm

Now Iím concerned that the amps drawn by the motors might knacker the batteries,
For instance the 12v 22ah is this enough to run say a pair of 5055 430kv
Could someone offer some advice or suggest a motor that could then be geared down to suit rpm requirement.

Many thanks
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canabus

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Re: Brushless recommendation for Twin screw Kort propís 85 - 92mm
« Reply #1 on: August 07, 2018, 09:02:28 AM »

Hi Batfish
You picked the right motors, but, the batteries will not handle the motors !!!
Lipo batteries with handle the power, also you will require TWO ESC's .
One for each motor .
Canabus
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16-21

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Re: Brushless recommendation for Twin screw Kort propís 85 - 92mm
« Reply #2 on: August 07, 2018, 09:27:33 AM »

Thanks for the response.
Sadly I can not use lipo only Sla
So I guess Iím limited to motor choice.
Itís a twin screw independent motors to two esc anyway.

If I used two 6v 14ah in parallel 6v 28ah surely that would be sufficient?
I donít want a dragster itís a tug boat.
I would have thought using geared reduction would lower the amps drawn.


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dreadnought72

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Re: Brushless recommendation for Twin screw Kort prop’s 85 - 92mm
« Reply #3 on: August 07, 2018, 10:05:03 AM »

Looking at the motor, they're 20-30 volt, 70A max, capable of 1750W output.


Two of those is 4.5hp!


 :o :o


My Wayfarer, loaded and crewed is maybe 400-450kg, and a 2.5hp outboard moves her easily 3kts.


How big's the model?!


Andy
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chas

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Re: Brushless recommendation for Twin screw Kort propís 85 - 92mm
« Reply #4 on: August 07, 2018, 10:09:40 AM »

I find this a fascinating question. I had a quick look at the spec, and the motor is rated at 30 volts max, 70 amps. To get around 3000 revs at the prop you'll be gearing it about 2 to 1., or no gearing on 6 volts. A quick and very amateur calculation gave me current drawn of around 5 amps, no problem for your SLA batteries.
  Either my half remembered calculation is miles out, which is very possible, or you will be ok. I hope someone like Malcolm who is a proffesional in this sort of thing can clarify matters, as this is a route that more model boaters will be going down in the future.
Chas
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16-21

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Re: Brushless recommendation for Twin screw Kort propís 85 - 92mm
« Reply #5 on: August 07, 2018, 10:10:18 AM »

Andy,

If your lucky they would produce around 300 Watts each.
The figures stated on them are 1750 Watts at 29.6V
And 70amps.

28Ē tug with Korts 85-92mm props undecided on prop size as yet.
Motors can not be direct drive.
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Charlie

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Re: Brushless recommendation for Twin screw Kort propís 85 - 92mm
« Reply #6 on: August 07, 2018, 10:10:29 AM »


I believe that is just the battery capacity. Powering some big brushless motors may try to draw more current than the batteries can handle.

If I used two 6v 14ah in parallel 6v 28ah surely that would be sufficient?
I donít want a dragster itís a tug boat.
I would have thought using geared reduction would lower the amps drawn.

16-21

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Re: Brushless recommendation for Twin screw Kort propís 85 - 92mm
« Reply #7 on: August 07, 2018, 10:14:10 AM »

Chas,

A 5045 660kv on 6v gives me 3960.
What reduction would i need to get 2800-3000rpm

Iím trying to get at least 1hr run time out of the model
Maybe 6v 28ah per motor will give me that
Or if 12v then i only have space for 1 12v 22ah battery.
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NickelBelter

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Re: Brushless recommendation for Twin screw Kort propís 85 - 92mm
« Reply #8 on: October 18, 2018, 11:50:35 AM »

The reduction is really the key here, since you have a specified final RPM of 3000.  You need to decide on a particular belt reduction if you want to be able to finalize your motor choice.  I'd recommend a 3:1 reduction making for 9000rpm on the drive pulley, which at 12v means a 750kv motor.  The lower RPM the motor, the more money it seems. 

Don't go with a 6v battery as that will double the amperage for the same wattage and everything will run hotter. 
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