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Author Topic: What motor for a 31 inch whateback hull  (Read 411 times)

Mu17

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What motor for a 31 inch whateback hull
« on: February 28, 2019, 08:59:19 PM »


Hi,
     recommendation needed for powering a 31 inch fibreglass whaleback hull weighing 1kg bare moulding,
I want to use a single motor and prop and 3s lipo , scale detail will obviously add some weight


A Leopard LC 2838 1038KV was suggested and a Ground 18A-SL Ver 2.0 esc
However I am struggling to find the motor at the moment - only a 2835


Now then - these are all just numbers to me - what I am looking for is  decent durable motor /esc that will get the boat up on the plane at scale speed - with the ability for an occasional silly blast !


Any help - in plain English ! most appreciated  :-)
Paul



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coch y bonddu

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Re: What motor for a 31 inch whateback hull
« Reply #1 on: February 28, 2019, 09:18:57 PM »

I think the numbers you have been given could possibly be wrong ....this is the same KVA as what you need the only difference is yours is Lc 2838 and the one in component shop is lc 2826


https://www.facebook.com/1418849218428380/photos/a.1846200502359914/2146750672304894/?type=3&theater

Check out this site

https://www.componentshop.co.uk/

Give them a ring they will sort you out with a Motor and Esc

Dave
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canabus

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Re: What motor for a 31 inch whateback hull
« Reply #2 on: March 01, 2019, 02:54:35 AM »

Hi Mu17
Depends on the prop size you are planning to run.
A couple ideas of Hobbyking setups I have used.

Three blade 32mm prop, Prop Drive 2836-1400kv(15,560 rpm on 3S) or the Prop Drive 2836-1800kv(438Watts)(19,980 rpm on 3S), 60 Amp ESC and a Turnigy 2650mah 3S 30C Lipo(T2650.3S.30) 250grams.

Three blade 37mm prop, 3639-1100kv(800Watts)(12,210 rpm on 3S) same ESC and Battery.

If you require longer run time a Zippy Compact 3700mah 3S 60C(9067000041-0)(338 grams).

I am using the last setup in a 1920 Gentleman's Runabout which is only two and a half inches longer, but with a good scale speed.

Canabus
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Mu17

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Re: What motor for a 31 inch whateback hull
« Reply #3 on: March 02, 2019, 01:10:49 PM »


Apologies for the slow reply


I am probably looking at a 35mm two or three bladed prop - no larger.
Not familiar with the Gentlemans Runabout but its sounds more sedate than an MTB ?
I'm looking for a respectable turn of planning speed with a bit of 'race power' for very occasional use.
Paul
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canabus

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Re: What motor for a 31 inch whateback hull
« Reply #4 on: March 02, 2019, 10:43:57 PM »

Hi Mu17
I did do a write up on this forum of the boat.

Canabus
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Mu17

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Re: What motor for a 31 inch whateback hull
« Reply #5 on: March 03, 2019, 02:09:18 PM »


Hi,  eventually found your very nice build - what a shame to hide all that double diagonal planking !

Your runabout is a few inches longer than my MASB but obviously length is a very crude indicator of power required. My bare hull and deck - no gear, weigh approximately 1kg - can I ask how much your boat weighs in comparison.

I was aiming to run a 30 to 35mm prop.
Tech isn't my strong suit but I am trying to better understand the power requirements, given that one of your suggested options is a 2836 - 1400kv or 1800kv.
Dave has suggested  2826 - 1038.
So what is the plain English value of the higher kv  and does this disappear if I go for  35mm prop or a 3 blader ?

Also, what is the value of going to a larger 3639 1100kv

Can you explain the real world performance difference - on the water - between the 2836 low and high KV set ups  and also the 3639 ?

As the MASB is a typical MTB type scale model, I'm looking for impressive/scale performance and a bit of extra blast is nice to have in reserve but it doesn't need to be an out and out race boat.

My club sails 30 minutes alternating slots of power and sail, so a 30 minute run time is fine. If I can get several runs out a 3s 3000 lipo (?) that's even better.


Thanks for your patience
Paul   
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canabus

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Re: What motor for a 31 inch whateback hull
« Reply #6 on: March 04, 2019, 04:24:00 AM »

Hi Mu17

The kv is the revs per volt, so on 3S (11.1 volts) the 3639- 1100kv(800Watts) is 12210 rpm(unloaded).
One horse power is about 750Watts.
The larger diameter motor has more power than the 28mm motor and would not get hot.
The 2836-1800kv is 438 Watts on 4s, so it be less on 3S.

My main problem is a lot of the hobby shops and websites do not tell you the power output of the motors.

Looking at the Hobbyking site for example is a hit and miss.

I have one motor which is 35mm and purple, no numbers or markings !!!
It's under the 1100kv by it's performance in a boat.

A 3000mah would be OK for your run time, but depends on the person on the throttle.
The runabout has a 3700mah and easily gets 1/2 hour!!!!

The runabout ready to go is 5 pound 12and 1/2ozs with the battery weight of 10 and 1/2.

As for ESC's our club mainly use the Hobbyking car one's (HK 45 to 100Amp) same program card only change the settings for 2 to 4S batteries.

No water cooling !!!

Canabus
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gra2

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Re: What motor for a 31 inch whateback hull
« Reply #7 on: March 04, 2019, 08:42:46 AM »

Hi I run a 1/24 scale 77ft Elco PT and a 1/24 scale Higgins PT using the 3639-1100kv motor and 36mm three blade brass props.
Battery used is a 3s Lipo.
Both boats perform very well with power in reserve.
Boats approx. 38" length, hope this helps.
My Higgins build is on this site.

Gra2
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Mu17

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Re: What motor for a 31 inch whateback hull
« Reply #8 on: March 07, 2019, 06:43:57 PM »


It may well be that I am missing something fundamental but the runnabout is probably 20-30% heavier than the MASB will be and a few inches longer. the Elco will be 7 1/2 inches longer and has power to spare.

Surely a 2836 will be fine but I am still failing to get my head around the need for such high kv with that motor ?
Paul
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