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Old Apr 12, 2012, 09:13 PM
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Western PA, USA
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Advice for 1/24 Motor Launch Build

I'm looking for some generic advice on a battery/drive/control set up for a 1/24 Fairmile B build. She'll be 56" x 9", twin screw, and I'm guesstimating will displace 20-25 lbs. So, your thoughts/opinions/expertise welcome:

I have experience with sealed lead-acid batteries in my Dumas Triple Cockpit Barrel-Back and Graupner Saphir, and with LiPos in my R/C planes; but unlike them I may be storing this model over winters in extended freezing temperatures with no ability to trickle charge, and would like to use a battery type that can stand up to long periods of sub-zero temps without recharging--would NiCads be better? Or...?

For motive power: I'm only looking for scale speeds (on the 1:1, cruise was about 7.5 kts, and top speed around 20 kts) so I don't need anything dramatic. I already have a NOS Graupner 700BB turbo motor and would consider getting a second or using geared drive to turn the screws. A second motor appeals to me (to provide more maneuverability); but is it worth the added cost of a second motor and ESC? In either case, what size and pitch of prop might be suitable?

For the driveshaft/log, I'd be looking at something like 18-22" from prop to drive coupler; any recommendations for either a set or components?

Again, I welcome replies from those with experience powering similar-sized scale warships, or those with appropriate expertise.

Thanks in advance!
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Old Apr 12, 2012, 09:48 PM
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Don't know about no cold batteries... you can't take them out and store them inside?
But... automotive lead acids are designed for -40... but they need to be recharged, like starting the car every day.

2nd motor worth it? You bet... especially given the amount of work in a model that size.

http://www.rcgroups.com/forums/attac...mentid=1557585
http://www.rcgroups.com/forums/attac...mentid=2074741
http://www.rcgroups.com/forums/attac...mentid=2079910
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Old Apr 13, 2012, 03:37 PM
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Grafton, Ohio
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Oh ya.......dog boats!
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Old Apr 13, 2012, 04:00 PM
GILL
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United States, NJ, Hopatcong
Joined Aug 2005
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Storing the model in the cold is not a problem. I have left models in my trailer over the winter. Temps. down to about -15.
The batteries should be removed an kept in a warmer place. They are charged every so often. I put a trickle charger on the gel cells every month for 24 hr. the nicads and lipos I check and charge as needed.
I would go with the twins. The 700's geared 1.5:1 would work great at 12 volts.
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Old Apr 13, 2012, 06:55 PM
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Originally Posted by patmat2350 View Post
Don't know about no cold batteries... you can't take them out and store them inside?
That's the thing -- they will be inside, but that won't help. This model is intended to be used/kept at an unheated summer cabin on a lake in Canada, where 9 months out of the year the power is off and three months of the year it'll be below freezing much of the time. So they have to stand both low temp and long periods without charging.

I mean, I could haul the batteries back home every time, but I'd like other family members to be able to sail her with or without me, as I can't get up that way every year.

Thanks for the vote on dual motors--I had a hunch.

P.S. Very nice Fairmile 'D' you have there--any vids?
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Old Apr 13, 2012, 06:58 PM
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Originally Posted by GILL RC View Post
I would go with the twins. The 700's geared 1.5:1 would work great at 12 volts.
I really appreciate the specifics on the gear ratio for a pair of 700s, thanks.

Any recommendations for a supplier for the gearing?
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Old Apr 13, 2012, 07:01 PM
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MACK:
http://www.mackproductsrc.com/Power%20p2.htm
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Old Apr 13, 2012, 07:11 PM
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Thanks for the suggestion!
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Old Apr 14, 2012, 12:31 AM
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For those who want to build a "Dog boat", get the Anatomy of the ship series, fairmile D. The plans and the detailed photos all in the one!
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Old Apr 14, 2012, 12:04 PM
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What if you look around for a solar powered battery charger to trickle the gel cell for the winter? Of course I'm assuming Canada does get a little sun in the winter.

Absolutely go with twin motors and ESC's if it is within budget. I had a Dumas USS Crockett (51") with twin controls. It would not have been as much fun a model to own without that setup. She would pirouette by reversing the inboard screw and throwing the rudder over.
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Old Apr 14, 2012, 12:52 PM
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Originally Posted by Prins Willem View Post
What if you look around for a solar powered battery charger to trickle the gel cell for the winter? Of course I'm assuming Canada does get a little sun in the winter. ...
I thought of that, but it also gets a lot of snow, so it'd have to be set up inside a window, and the south-facing windows which otherwise would get the most sun (of what sun there is) are sheltered by a long porch roof. So it would have to be set up outside at a steep enough angle to shed the snow... I'll give it a re-think.

Appreciate the (now fairly unanimous) recommendation for dual power. Given the high overall cost of the project, a second motor and ESC, while not cheap, will not break the bank.

This
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