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Custom Build - What motor to use?

Old 05-08-2021, 04:51 PM
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asunkari
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Question Custom Build - What motor to use?

Hey everyone,

I'm new to the RC Boating world, but I have experience in drones and RC airplanes. I'm currently working on a project to build an RC boat for my physics class for a drag race (the boat just needs to go straight - it does not need to turn). Obviously, since this is a drag race, the boat needs to be as fast as possible.

Because of size restrictions in the competition, the hull I'm using is relatively small w/ a catamaran stepped planing design. A CAD model of the design is attached, but the general specs is that it is 8 cm wide by 28 cm in length. The hull will be 3D-printed.

I want to use a brushless motor setup for the boat. Which motor would y'all recommend? I need a motor that is small enough for the boat, and I am not sure what kV I should use. If someone could provide me some guidance as to what motor(s) to use, it would be greatly appreciated. Also, what LiPo cell should I use?

Thank you in advance!
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Old 05-09-2021, 08:34 AM
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Got RPM
 
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Give us a few more details. What kind of water - flat smooth, slight ripple? How long is the race - 10 meters, 25 meters? One issue may be finding an appropriate prop. Another will be prop depth and CG position. The wrong settings will cause the cat to flip over on it’s back at full throttle. Is a catamaran hull required? A hydroplane might be a better choice for a short drag race.
Old 05-09-2021, 08:49 AM
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asunkari
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Originally Posted by Got RPM View Post
Give us a few more details. What kind of water - flat smooth, slight ripple? How long is the race - 10 meters, 25 meters? One issue may be finding an appropriate prop. Another will be prop depth and CG position. The wrong settings will cause the cat to flip over on its back at full throttle. Is a catamaran hull required? A hydroplane might be a better choice for a short drag race.
Thank you for your response!
  • The water is flat smooth - it is going to be indoors in a long plastic channel, so I don't expect the water to have any ripples.
  • The race will be 10 meters long.
  • The catamaran hull is not required, it can be a hydroplane. The only restriction given on boat size is that the hull can't exceed 35 cm in length and 9 cm in width. Additionally, the depth of the channel is 6 cm, so I just need to be careful in terms of the draft of the boat.
Old 05-09-2021, 10:27 AM
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asunkari
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Also, I was looking into these designs on YouTube: "3D Printed RC TWIN JET Boat" and "3D Printed RC JET Boat 300"

Perhaps placing a jet drive (like it's shown in these videos) on a hydroplane could solve the prop issue?
Old 05-09-2021, 11:50 PM
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Jet drives don't work on hydroplanes and are not a good choice for cats either. Both styles of hulls are made to fly over the water while a jet drive requires a boat to be in the water.
Old 05-10-2021, 06:55 PM
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Jet drives also do not give the acceleration needed for a drag race - they are inefficient compared to a propeller. And just 9 cm probably won’t work for a hydro, too narrow. For the short distance required a flattish-bottomed mono is probably best. 35 cm would be an advantage for directional stability and the ability to hold a bit more weight - more power. And speed is not the prime consideration, acceleration is.

When is the race?
Old 08-18-2021, 09:57 AM
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Sounds like a project for a small out runner or brushless 380 series motor.
Old 08-18-2021, 10:43 AM
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Just curious, what ever happened with this project? Had some other thoughts on it as well

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