How much power is enough power?

[Crash]

When choosing Motors if we look at the wattage ratings how much is enough and how much is too much?
Myself I'm running a motor That's rated at 6200 Watts often Peaks out at 10000 Watts or 13 hp
and has broke four Flex shafts in a season wondering I can get the job done with less wattage or horsepower saving the driving line.?
Is there a formula to choose the rite wattage motor for a given set up.?
Thanks guys
Dan

[Fluid]

Motor maximum watt ratings are deceptive. They may be max for ten seconds, for extended running - or they may be marketing hooey. In many cases it is the ESC which limits power, not the motor. 10,000 watts on 8S is well over 400 amps, good luck finding an ESC which can handle that for very long.

Are you racing? Are you winning? If you are breaking flex cables then either the cables are too small, too weak, or are improperly installed/supported. Too, how you drive can effect cable life - lots of full throttle hits from a stop or from low speeds puts a very large instantaneous stress on the cable.


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[Crash]

My data log showed 430amps with my big prop on it at over 10000 watts recorded as well.
At that rate its over 13 horse power, I am not surprised stuff brakes.
My question is to , how much is enough.
I can run a 3600 watt motor on 8s at 2070kv and go faster then my 1650 kv 6200 watt motor on 8s.

[Fluid]

Part of the problem may be the motor Kv. That is on the high side even for a 6S racer. Depending on the hull size, a motor Kv of 1000 rpm may be more appropriate. That gives a wider safe rpm range and with the appropriate prop can give competitive speeds. But we don’t have enough information - we are not mind readers.

Again I ask, are you racing? If so is your boat speed competitive? And exactly what hull are you running? Too, exactly what motor and prop are you running?


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[rol243]

must be running a 3/16 inch shaft. if you have that much h.p. etc try a 1/4 inch shaft.

[Crash]

Well, I was trying to get a answer that applys to choosing the rite motor wattage and what's necessary amount of power and what's too much..more of general question not exclusively about my set up but, ok.
Mine is a 36 inch mono
8s
Today it has a 646 prop on it, I also run a 452
I do not race it.
Runs in the upper 70's mph
At 78% throttle.
Motor is a tp
4060 1650kv

[Crash]

must be running a 3/16 inch shaft. if you have that much h.p. etc try a 1/4 inch shaft.

I looked into the 1/4 inch drive, there are no props under 60mm at 1/4 inch shaft

[rol243]

yes there are 1/4 inch flex shafts which come with a 3/16 step down so you can run 3/16 bore props.

[NativePaul]

500 watts per kilogram is generally enough power for me. It is what my racegoers run at so I set my fun running boats for the same, it gives me enough speed and enough run time for my tastes and scales well to any size boat I have built.

It is not for everyone though, I know fun runners that want more runtime at the expense of speed, that want more speed at the expense of runtime, that want more runtime at the expense of expense, and plenty that want the imposible. Fun running driving styles vary lot, and fun runners all want something different from the boats, so there is no simple answer.

Breaking 4 shafts in a season sounds like too much power for your shafts, or too small a shaft for your power, but it could be something misaligned in your driveline (I broke 3 wires in one boat this season and it turned out to be a slightly eccentric bore in the stub shaft, not enough to notice spinning it by hand, but enough to rapidly fatigue the wire right next to it in use).

What is your driveline and are they all breaking in the same place?


If you go up from 1650kv to 2070kv without propping down a lot you will be pulling a LOT more power than you are now, whatever the motor is rated at. Even if you do prop down it is a very high Rpm and as fluid says, at those RPM a small difference in prop size makes a big difference to amp draw, you might get away with it for a few seconds on a SAW run, but I wouldn't recommend it. It sounds like you could use propping down on the setup you have.

[Prodrvr]

There is no such thing as too much power

[Crash]

500 watts per kilogram is generally enough power for me. It is what my racegoers run at so I set my fun running boats for the same, it gives me enough speed and enough run time for my tastes and scales well to any size boat I have built.

It is not for everyone though, I know fun runners that want more runtime at the expense of speed, that want more speed at the expense of runtime, that want more runtime at the expense of expense, and plenty that want the imposible. Fun running driving styles vary lot, and fun runners all want something different from the boats, so there is no simple answer.

Breaking 4 shafts in a season sounds like too much power for your shafts, or too small a shaft for your power, but it could be something misaligned in your driveline (I broke 3 wires in one boat this season and it turned out to be a slightly eccentric bore in the stub shaft, not enough to notice spinning it by hand, but enough to rapidly fatigue the wire right next to it in use).

What is your driveline and are they all breaking in the same place?


If you go up from 1650kv to 2070kv without propping down a lot you will be pulling a LOT more power than you are now, whatever the motor is rated at. Even if you do prop down it is a very high Rpm and as fluid says, at those RPM a small difference in prop size makes a big difference to amp draw, you might get away with it for a few seconds on a SAW run, but I wouldn't recommend it. It sounds like you could use propping down on the setup you have.

Thanks.
My shafts keep breaking at the weak spots, at the drive dog knotch, at the prop shaft meets flex cable. It once twisted the solid steel section shaft.
I have checked and rechecked drive line and now I just think its too much torque for the 3/16 shafts.
If a guy runs a motor rated at. 3600 watts 1650kv and a guy runs a 6200 watt 1650kv does one draw more amps ? Does it make more power aka torque in same set up boat and prop and lipos same?

[Crash]

There is no such thing as too much power

lol, you been saying that but there may be a thing as too much power in this case, #gofundme for rc parts has been started'

[larryrose11]

If a guy runs a motor rated at. 3600 watts 1650kv and a guy runs a 6200 watt 1650kv does one draw more amps ? Does it make more power aka torque in same set up boat and prop and lipos same?

Power = Volts * Amps.
Voltage*Motor KV*efficency = Loaded RPM.
The prop is what determines the amp draw for a given setup.
For a given hull and prop, If the motors have the same KV and efficiency, then the amp draw will be the same. The motor power rating is what the motor is capable of producing.

[Prodrvr]

lol, you been saying that but there may be a thing as too much power in this case, #gofundme for rc parts has been started'

I need a Gofundme account lol

[Prodrvr]

Where are you getting your flex shafts from?