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Old May 12, 2013, 06:33 AM
NORTHLAND NEW ZEALAND
D design's Avatar
New Zealand, Northland, Totara North
Joined Feb 2012
592 Posts
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Need help chosing motor

Hi all.

I am designing a 700mm long powerboat for rescuing sailboats and for photography. Its single chined and is 200 mm wide. I have no need to go more than 10 knots. I need more tourque than speed. What kv rating brushless motor do you recomend. Thanks vey much
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Old May 12, 2013, 07:01 AM
NeverAgainVolunteerYourse lf
nick_75au's Avatar
Australia, QLD, Regents Park
Joined Mar 2007
3,726 Posts
Its realy going to depend on the prop, battery voltage and 10 knots is fairly fast. So its a planing hull. I reckon something around a 36-series motor 800-1000 kv on 12 volts and a 40-45 mm prop would be a resonable educated guess going on the basic info of your boat
Cheers
Nick
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Old May 12, 2013, 10:33 AM
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Tollytime's Avatar
United States, MI, Macomb
Joined Nov 2006
1,311 Posts
Hmmm. Do you want to go brushless or brushed.

Brushed?

I would recommend something along the lines of a Graupner 700BB motor for towing. You would need a small 12volt volt sealed lead acid battery like the one used to backup a home alarm system. I would try a 40-45mm prop. You will have to do a few test runs with different pitch sizes to see what works for you. You will need a ESC for brushed motors as well. I have looked into the same setup for a 700mm boat of mine years ago. I was sad to find brushed motor setups are outdated and anybody who still sells this stuff is way overpriced.

At least this guys prices are reasonable, sadly there is no water cooling.

http://www.kershawdesigns.com/Motors-ESCs-Brushed.htm

If you want to go brushless with lipo batteries, your world has opened up to a fiesta of options and fun. (for the same money or less)

You can start by paying around a hundred dollars for a good lipo charger that will give you years of good service and meet all your battery needs.

http://hyperion-world.com/products/p.../HP-EOS0606iAD

You can research plenty of motors, but this is what I've been using as a 550-700 motor replacement. Kinda big, but short enough to fit in the same areas as a 550-700 brushed motor.

http://www.hobbyking.com/hobbyking/s...nner_21T_.html

Water jacket

http://www.offshoreelectrics.com/pro...?prod=gnd-4196

Speed Control with reverse

http://www.hobbyking.com/hobbyking/s...ooled_ESC.html

Lipo 2s 7.4volt You got room for two!!

http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html
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Old May 12, 2013, 10:55 AM
BUILD SOMETHING!
CaptDH's Avatar
United States, CA, Avalon
Joined Oct 2002
752 Posts
55 turn integy lathe motor. $27 ebay and very low amp draw. Brushed Mtroniks speed control. It wont do 10 knots but will swing a 2 inch prop quite well with no water cooling. Pulls this 55# tug around. I have also used a $70 Pittman in this model and the results were the same.


D
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Old May 12, 2013, 04:56 PM
NORTHLAND NEW ZEALAND
D design's Avatar
New Zealand, Northland, Totara North
Joined Feb 2012
592 Posts
Thanks for the replies!
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