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help with brushless motors

Old 01-31-2015, 06:40 PM
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malcham33
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Default help with brushless motors

I'm rebuilding an old boat and need motor and esc but have no idea what makes them tick. If someone could point me in the direction of info in what motors are are good for different applications that would be awsome. I have been looking at some because of the price but I don't know anything about them but that low kv is better for boats. If that's true I don't know. Just trying to find out what makes them tick.
Old 02-03-2015, 09:35 AM
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It all depend on what kind and size of boat you are re-building! A scale boat would requires reverse, a speed boat don't.
Old 02-03-2015, 11:35 AM
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It's an old fighter 550 from ABC hobby craft. I'm fiber Glassing a Broken spot of the hull back together and using the original prop shaft and rudder. Otherwise I'm going to use all new equipment. The hull is 21.5 inches long with a 7.25 inch beam. It's a flat bottom racer with a small keel down the middle for tracking.

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Old 02-05-2015, 06:44 AM
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A 200<300 Watts inrunner would replace that Mabuchi-550 really well, many choices from HK:
http://www.hobbyking.com/hobbyking/s...ess_Motor.html
http://www.hobbyking.com/hobbyking/s...C_4A_SBEC.html
You will also need a 5mm shaft coupler(The 550 has 1/8" shaft)and probably a different size prop for best performances.
Old 02-05-2015, 02:21 PM
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malcham33
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That motor looks pretty good but with it pulling a max of 100 amp it would no doubt fry that esc. i was looking at the trunigy 3660SL 3180kv Brushless Inrunner (WaterCooled) with Hobbyking YEP 120A speed controller or Turnigy AquaStar 160A Water Cooled ESC
Old 02-05-2015, 05:19 PM
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The Amp rating of motors is the maximum current before damage, the actual Amp depend on load(prop size)and voltage used. A 21.5" hull like your runs well with 400 Watts max(the 550 was barely 150 W). Off course it doesn't hurt to use a larger ESC for boats as they can draw a lot during acceleration, if you over power a small boat like this it will become very unstable being a submerged drive!
Old 02-05-2015, 06:02 PM
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malcham33
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so you are saying it will just be plain too fast and flip on turning? would 400watt be the absolute max on motor size? and by submerged drive you mean prop in the water?
Also i have herd that a low kv motor should be used in a marine applications. my understanding is that if i went a higher kv, i would have less torque therefore taking longer getting on a plane. but if then keeping the high top speed.

Last edited by malcham33; 02-05-2015 at 06:19 PM.
Old 02-05-2015, 07:36 PM
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A speed boat can't be too fastbut handling can be a problem if grossly over powered(even going straight). The ABC hobby craft hulls were designed more for look than performance like most RTR,boats with their prop under the hull instead of surface drive have a big change of trim depending on the shaft angle and prop size. A mono hull on plane can be very bouncy even on calm water. If you use Lipo instead of the original NiCad the center of gravity will change a lot because of the weight difference and that has to be taken into account too. A brushless set-up is a big step from the ubiquitous Mabuchi-550!
Old 02-17-2015, 01:55 AM
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I am running a shallow deep vee 24 inch boat with a stock Hobbyking F1 outboard on a 3S (11.1volt) 2650mah battery,60A car ESC with reverse. Servo is 9.45KG .
I have the boat balance point 200mm from the stern and the outboard trimmed in about 3 degrees.
The boat in a straight line sits level and rids on the prop with the boat about 20 mm out of the water.
Backing from the gas for the turns it handles very well.
Yes it insanely fast but at half throttle it's very mild.

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