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Author Topic: Which motors are best?  (Read 3233 times)

boatman126

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Which motors are best?
« on: November 15, 2012, 09:26:46 AM »

Hi all
I am about to build a 1/12th scale model of a 50 foot Princess ocean cruiser. She will be twin engine powered on a semi planning hull. The props will be to scale and be 4 bladed.  She will be quite a heavy boat as it will include the internal fitout.
It has been suggested to me that brushless motors would be best, I have never built with brushless motors before and wonder if this advice is correct.
Can anyone suggest the best set up ie motors, esc, battery size and type, props for this project.
Thank you in anticipation
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nick_75au

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Re: Which motors are best?
« Reply #1 on: November 16, 2012, 11:31:18 PM »

What size will the props be?, do you have a voltage in mind? these answered will help in finding a suitable motor :-)


While I'm a strong advocate for brush-less motors, brushed motors will give you what you want to achieve, Brush-less motors are generally available in a wider range of power and speed than brushed motors these days which makes it easier to select a motor matched to the requirements of the boat.


Cheers
Nick
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boatman126

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Re: Which motors are best?
« Reply #2 on: November 19, 2012, 10:00:17 AM »

Hi Nick
Thank you for your offer of help.
I think the props will be about 40mm four blade.
I have always worked on 6 volt in the past but will run with what you would think best for a boat of this size.  Also what would be best Gel or other.
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nick_75au

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Re: Which motors are best?
« Reply #3 on: November 19, 2012, 10:23:58 AM »

Hi,
 I would use a higher voltage and a different type of cell, Gel cells are not the best type for any sort of semi/planing hull (too heavy and poor mid to high current performance), Li-po is hands down the best type of battery but with the inherent slightly higher charge and discharge maintenance and "danger" factor involved. This is up to you to assess whether you want to go this route, Ni-MH is the next best option with less hassle but also somewhat lower performance.


I would recommend a nominal 12 volt system Ie 3 cell Li-po or 10-12 cell Ni-Mh with a motor of about 800 to 1000 Kv and 28 mm case size, I run a 1.2 meter Axebow semi displacement hull using DT700 brush-less motors on 3 cell Lipo 5 blade 40 mm props for excellent performance without being stupidly overpowered. This motor is a "bell type" high torque low RPM compared to the majority of brush-less offerings.


A brushed motor equivalent would be a speed 600 BB turbo 12V with a 2.5:1 reduction, a speed 500E with a 1.5:1 reduction or a speed 600 14.4V direct drive as a few examples.


Hope this gives you some where to start


Cheers
Nick
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boatman126

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Re: Which motors are best?
« Reply #4 on: November 23, 2012, 08:57:39 AM »

Hi
Thank you for your help Nick :-))
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bj

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Re: Which motors are best?
« Reply #5 on: November 25, 2012, 07:16:11 PM »

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red181

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Re: Which motors are best?
« Reply #6 on: November 25, 2012, 08:27:05 PM »

its a MASSIVE question to answer as there are some many variables, I would suggest you visit your local clubs and have a look what other people are using with similar boats, its such a personal preference brushed and brushless, personally I'm brushless and lipos, does not suit all though, it depends on what you ultimately want, long run times at moderate speed, ballistic speed short run times etc, I am currently rebuilding a 4 foot aerokits Fireboat (build log is in naval section) its twin screw, brushless, run time will be 20 mins, 25mph, suits me, but others may want 2 hrs run time and 10mph,
the only thing I can advise at this stage, you mention the props as though that decision has been made, to me that seems to be building the boat backwards, this is just my opinion, I would suggest sort out your motors/esc's/batteries, and get a suitable prop to that setup, buy some cheap props at a quid a go, when you have the set up you want, give someone like propshop your setup they will then make scale props to suit, might be the cheaper option to do it this way :-))
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boatman126

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Re: Which motors are best?
« Reply #7 on: November 26, 2012, 08:25:17 AM »

Hi
Thank you for your help
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nick_75au

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Re: Which motors are best?
« Reply #8 on: November 26, 2012, 08:56:47 AM »

I dunno Red, I reckon the prop on a scale boat is fairly well determined what size they will be %)
Quote
The props will be to scale and be 4 bladed
, that gets a ball park idea of what power is needed , agreed the first props may need tweaking so cheap props are a good start, but I've found that plastic props perform (sometimes very) differently to the metal ones.


Cheers
Nick


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boatman126

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Re: Which motors are best?
« Reply #9 on: November 26, 2012, 09:01:48 AM »

Yes this is true.  The props have to be the scale size to the boat being replicated and the same type.
As this model will be displayed in display case when not in use
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bj

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Re: Which motors are best?
« Reply #10 on: November 26, 2012, 04:59:15 PM »

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boatman126

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Re: Which motors are best?
« Reply #11 on: November 26, 2012, 05:07:44 PM »

Hi
Link still not working?
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Martin [Admin]

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red181

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Re: Which motors are best?
« Reply #13 on: November 27, 2012, 07:47:58 AM »

with you on that nick, later post says it will be displayed in a case, so I see importance of prop, I was thinking more of performance, get a feel for what is happening with the cheapo stuff, then pay the big bucks for good props, and retune the set up maybe?, hoping they dont fall off in the lake!
 
I'm about to do just that, got what I want with cheap ones, then gave all the readings to propshop who made be some nice scale cleavers, but they will be counter rotating to help dull down any torque roll, its the first time ive done this, I dont want to loctite the props on, so hope it wont fall off, too flippin expensive! :}     
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