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Old Aug 26, 2008, 07:05 AM
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Re: predator outrigger ?

I am new to model boats and think you have made the same mistake I did on my
first model - the wrong motor.
I suspect you are using a brushed motor like this
(http://www3.towerhobbies.com/cgi-bin...&I=LXJ765&P=7). It operates
at 11,000 RPM and puts out 145 watts of power. The power and RPM are not
high enough to generate much speed. After a steep learning curve, I'm on my
second boat. I'll share what I've learned about motors with the hope that
others will correct me where I am wrong or add to the discussion so we can
both learn something.
There are two basic types of motors: Brushed and brushless. In general,
brushed motors are rated by the number of turns (poles in the armature) -
The fewer the turns, the higher ther RPM but the greater the current draw.
From memory, the motor cited above has 22 turns. Typically, boaters will
use a 7 to 12 turn brushed motor from a model car, such as
(http://www3.towerhobbies.com/cgi-bin...&I=LXRBE1&P=7), which
operates at a much higher RPM.
I have switched to using brushless motors. Brushless motors are given a Kv
rating, the number of RPMs per volt, and a wattage rating, of power produced
(745 watts equals 1 HP). Two types of brushless motors are available:
outrunner and inrunner. Since outrunner type motors need air for cooling,
they aren't usually used in boats. In-runner motors can be water cooled and
are the type typically used. My latest model is a 24" rigger with a Feigao
540L motor (http://www.offshoreelectrics.com/products.php?cat=42). At 7.2
volts it turns over 19,000 RPM. Riding on the outriggers and the prop, I
would estimate its speed in the 40 MPH range (double that of my first boat).
I have found the folks at Offshore Electrics to be very helpful, answering
several questions in the building of my second boat. Too, you may want to
see what the manufacturers are offering - here's an example:
http://www3.towerhobbies.com/cgi-bin...=LXMDJ4**&P=ML.
Here are a couple of interesting web sites I've found:
http://www.fastelectrics.com/default.asp
http://www.drcwebservices.com/ffe/Default.htm
http://www.twistedliquidracing.com/Home_Page.html
http://bbyracing.com/elecmonohulls.asp
http://www.minicatracingusa.com/Samu...is%20here.html
I hope all this helps and I'm looking forward to the responses from others.
Randy

"tobias" <tobias.3epve4@no-mx.forums.yourdomain.com.au> wrote in message
news:tobias.3epve4@no-mx.forums.yourdomain.com.au...
>
> I've build this predator outrigger, with a strait shaft.
> I've got a speed 600 motor an a 40 mm graupner prop.
> It doesn't go very fast
> Am I doing something wrong
>
> GR Tobias (NL)
>
>
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> tobias
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