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Old Apr 15, 2010, 04:38 AM
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Lisbon, Portugal
Joined Jan 2010
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32-36" Catamaran Build

Hi,

I allways wanted to have a Catamaran with a twin setup.

I will be building next months one!

It will have a 3s setup. I want you guys to see if the setup i'm planning is Ok for a Cat of 32-36" (80-90cm):

Bat: 2x ZIPPY Flightmax 5000mAh 3S1P 30C
ESC: 2x Turnigy Marine 120A Brushless ESC
Motor: 2x KD36-60-06L 4000kv Brushless Inrunner

I'm planning to build the hull myself. I don't have any experience building boats. It will be built in Balsa wood and reinforced in FG in the inside and outside.

Thanks.
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Old Apr 15, 2010, 07:03 AM
I feel the need for speed!
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Southern U.S.
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If you are set on using a KD36-60 i would recommend 9L........maybe 8L

http://www.hobbycity.com/hobbyking/s...hless_Inrunner

http://www.hobbycity.com/hobbyking/s...hless_Inrunner
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Old Apr 15, 2010, 11:09 AM
nick 30
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i would suggest building the boat around foam, this will give you plenty of flotation, just use epoxy to attach the balsa to the foam
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Old Apr 15, 2010, 02:49 PM
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Quote:
Originally Posted by scorpion1 View Post
If you are set on using a KD36-60 i would recommend 9L........maybe 8L

http://www.hobbycity.com/hobbyking/s...hless_Inrunner

http://www.hobbycity.com/hobbyking/s...hless_Inrunner
Why? because of the kv?

Quote:
Originally Posted by nick30head View Post
i would suggest building the boat around foam, this will give you plenty of flotation, just use epoxy to attach the balsa to the foam
In foam with balsa?! Never saw that. Like the outside? :s
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Old Apr 15, 2010, 03:09 PM
nick 30
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build the boat out of foam first with an area cut out for batts, motors, esc's etc glue the foam sponsons and tub together and then sheet with 3mm balsa, tha balsa will add more strength when all pieces are pretty much one sheet, once all balsa is on either coat with epoxy or as i do with fibre glass resin
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Old Apr 15, 2010, 03:21 PM
I feel the need for speed!
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The kv on the motor you listed is too high in my opinion, the 9L or maybe even the 8L would be better for the 3s setup you mentioned.
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Old Apr 15, 2010, 03:56 PM
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Originally Posted by scorpion1 View Post
The kv on the motor you listed is too high in my opinion, the 9L or maybe even the 8L would be better for the 3s setup you mentioned.
Considering that these motors are not that efficient, with a 4000kv motor, I should get something like: 4000 * 11.1 * 85% = 37700 RPM.

Is it to much? I want it fast.
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Old Apr 15, 2010, 04:34 PM
I feel the need for speed!
scorpion1's Avatar
Southern U.S.
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Originally Posted by HibridOPT View Post
Considering that these motors are not that efficient, with a 4000kv motor, I should get something like: 4000 * 11.1 * 85% = 37700 RPM.

Is it to much? I want it fast.
A more accurate calculation would be 12.6v x 4000 = 50,400 x .85 = 42,840........thats SAW racing territory. You are certainly free to do what you like......................
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Old Apr 15, 2010, 06:04 PM
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Originally Posted by scorpion1 View Post
A more accurate calculation would be 12.6v x 4000 = 50,400 x .85 = 42,840........thats SAW racing territory. You are certainly free to do what you like......................
12.6V is the voltage of the battery without load. 11.1 is the voltage that will hold under load I think.
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Old Apr 16, 2010, 02:33 AM
nick 30
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most people i know that have given me advice on this forum for my 32" boats have said run them on 4s, i use 2x feigao 8XL motors and there good
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Old Apr 16, 2010, 04:06 AM
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Originally Posted by nick30head View Post
most people i know that have given me advice on this forum for my 32" boats have said run them on 4s, i use 2x feigao 8XL motors and there good
Ok so that would be also around 35k RPM.

Can you explain me the difference what will be between 3s with 6L and 4s with 8L which in the end the setup will have the same RPM. Will it have more torque/power?
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Old Apr 16, 2010, 04:17 AM
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Usually lower kv means more torque. I have an 11S (3440) and a 14S (2775). On 3S Lipo, the 14 is faster than the 11 and it will take a bigger prop.
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Old Apr 16, 2010, 06:20 PM
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32-36" Cat Build

Quote:
Originally Posted by HibridOPT View Post
Why? because of the kv?



In foam with balsa?! Never saw that. Like the outside? :s
Hi, It is not necessary to build out of foam over balsa. Attached photos of
the cat I scratch built with balsa and Plywood sheeting. Foam was only used
in the forward part of the hull and sponsons. It is powered by a UL-1 BL motor
and Esc, 4s Lipos and Octura 640 prop. Boat handles perfect. Speed is 46.2 miles per hour on GPS and it has won many races in Limited Spec Offshore.
If you brace the fame correctly and cover with fiberglass resin and silkspan it
will be as strong as FRP. If I were you I would go with a single drive. Twin drives
are nice but a real pain in the Axx!. Enjoy and good luck wiwth your build.
Norman22
PS. Nothing gets hot, nothing burns, just keeps on running with no malfunctions race heat after heat.
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Old Apr 16, 2010, 09:32 PM
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Your motors must be around 35000 RPM unloded You will have the best efficiency and a large choise for props.
3S --> 3000 kV
4S --> 2200 kV
If you use a motor with too much RPM, the current will be higher that means more heat, less autonomy, less torque...
If it' s possible use 540L or 540XL motors
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Old Apr 16, 2010, 11:38 PM
I feel the need for speed!
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Southern U.S.
Joined Jun 2008
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Quote:
Originally Posted by Alfa Twin Spar View Post
Your motors must be around 35000 RPM unloded You will have the best efficiency and a large choise for props.
3S --> 3000 kV
4S --> 2200 kV
If you use a motor with too much RPM, the current will be higher that means more heat, less autonomy, less torque...
If it' s possible use 540L or 540XL motors

Thats what i had suggested..................8L or 9L on the 3s setup
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