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Old Nov 12, 2009, 08:14 PM
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boredom.is.me's Avatar
United States, GA, Buford
Joined Nov 2007
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Question
Is anything over 32,000 rpm (lets say 76,000) deadly?

Why does prop rpm matter? From what I understand, a small prop spinning at a faster rpm can equal a larger prop spinning at a lower rpm. Is it imperative to keep rpm around 32k? I was wondering because I wanted to put 76k rpm (at 7.4v) to a 15mm prop on a 9 inch boat.

Basically just a mini-z cat with a 1220 (inrunner) with 10300kv.

Kev
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Last edited by boredom.is.me; Nov 13, 2009 at 08:43 PM. Reason: grammatical error in title
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Old Nov 12, 2009, 09:33 PM
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Raydee's Avatar
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THe motor will probably self destruct at that RPM.
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Old Nov 12, 2009, 09:38 PM
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Joined May 2006
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Deadly!!!LOL...

No But with high RPM'S comes heat.An with the heat comes expansion.For one It's got to stay cool.Two you better have the strength In your strut an hardware.Three a very, very small tolerance.If one part of that drive system Is out of balance.It goes poof really fast destroying things!!!I have spent a good deal of money.On making two Es-1 Aquacraft outboards spin over 36grand In Rpm's.So far so good here good luck with It.
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Old Nov 13, 2009, 12:18 AM
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United States, CA, Santa Barbara
Joined Jun 2009
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As far as deadly... I would say as long as your face is farther than 5 feet from any moving part and the projectiles don't hit a major artery... then no not "Deadly". But still very dangerous. Maybe something you would ask JckSS to do...

Put a gear reduction in it and run a bigger prop.
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Old Nov 13, 2009, 02:48 AM
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Cavitation is the problem you wont be able to maintain grip on the water with anything past (guess) 50k. SAW boats spin up in that direction. What motor are you thinking that 10.5k kv inrunner at hobbie king?
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Old Nov 13, 2009, 07:14 AM
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AA Is absolutely correct!!

What Amp Abuser said Is so right.On my ES-1 Outboards Ive gone threw 3 different props Size.Also material makes an still fighting cav probs...I know I can get It to bite!!!Just need to find the right set-up.Im going to try a three blade Octura M series prop next.
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Old Nov 13, 2009, 01:37 PM
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I was talking about a 12mm dia. 10300 kv motor that has been used for micro ducted fans. The reason I ask is because the highest I have seen is the 5800kv (can't remember exact kv) feigao, excuse spelling.

This is it: http://www.hobbyking.com/hobbycity/s...idProduct=9068
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Old Nov 13, 2009, 05:29 PM
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Seattle
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I can think of a couple factors working against high rpm motors in boats.

For 10300kv in a micro ducted fan you have low resistance turning in air and water is 80x more dense and would require a very very small prop - and there are practical limits to prop size.

Another factor with a small prop is slippage since slippage will increase dramatically at some point if the prop is too small for the boat.

Acceleration will also suffer with smaller props.

For a given amount of power it is easier to run something with 6s with 100 amps rather than 2s and 300 amps, which generally means a lower kv motor on higher voltage.
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