Number cells/Motor Kv/Prop Size/Hull Size

[Flying Scotsman]

Another person on this site with big boat building experience and set up is...Peter Zicha
His only problem is he likes to eat and not what his mamma told him to eat

Douggie

[mickvk]

--hull size /--------Cells---------/ ----Motor Kv----- / -------Prop Size------/---Type ESC---/-BEC-/ESC Amp Rating

17”- 24” / 2s LiPo or 6 cell NiMh / 5500 -3200Kv / 30mm - 40mm Diam. / Low Voltage / Avail. / 120 amp

20"-27" / 3s LiPo or 8 cell NiMh / 3500-2500kv / 35mm – 42mm Diam. / Low Voltage / Avail. / 120 amp

24”-29” / 4s LiPo or 12 cell NiMh /2650-1600Kv /37mm - 46mm Diam. / Low Voltage / Avail~Disc / 120-240 amp

26”-32" / 6s LiPo or 18 cell NiMh /1800-1100Kv /40mm - 52mm Diam. / Low or High / Disc. / 120-180-240 amp

30"- 36" / 8s LiPo or 24 cell NiMh / 1350-800Kv /45mm – 55mm Diam. / High Voltage / N/A / 180-240 amp

34" - 42" / 10s LiPo or 30 cell NiMh / 1100-600Kv /47mm + Diameter / High Voltage / N/A / 180-240 amp

38" - 46" / 12s LiPo or 36 cell NiMh / 900-550Kv / 50mm + Diameter / High Voltage / N/A / 240 amp

I'm trying to understand why the recommended RPM range is 20,000 to 40,000. Is there any explanation for what the downsides are? I expect that props that are small enough to turn at 50,000 rpms do a lot of cavitating.... Is that right? what about on the low end of the spectrum trying to drive a windmill sized prop at 10,000? Thanks.

[ryan_t888]

It's more difficult to get a large prop spinning at low RPM to go fast and handle well. My gasser turns 15000RPM. When I gun it during a straightaway it can literally jump to one side under prop torque. You can certainly run under 20 000RPM if desired.

The minimum size prop is 27mm. If you drive 50 000+ RPM, the size necessary will be too small in some cases to actually reliably make this setup work. Also the thrust will not be great enough to push the hull on plane. There must be a good balance between pitch speed and thrust to efficiently drive the boat ahead.

Ryan

[ED66677]

as Ryan wrote if you run below 20000rpm (I would even say 25000), the appropriate prop that will make your boat go fast will be so big that the prop torque will be a serious problem, if you run above 35-40000rpm the prop will be so small that it will gave a poor efficiency (prop slippage) can you imagine a 40" boat with a 37mm? chances are that the hull won't move at all!
That said, running efficiently above 40-50000rpm is possible, it requires oversized components and short run time (SAW).

[mickvk]

Got it. Thanks guys, that's very helpful.

[exotica]

...great thread.

[KillerDave]

What about a spreadsheet to help users decide on a build?


"Updated" with Lipo and esc amp ratings. There are too many variables for this to be exact for all of the different hull and motor loads. Many setups will fall outside of this general data spreadsheet. Just hope this gives you a better understanding of FE for designing successful setups.

--hull size /--------Cells---------/ ----Motor Kv----- / -------Prop Size------/---Type ESC---/-BEC-/ESC Amp Rating

17”- 24” / 2s LiPo or 6 cell NiMh / 5500 -3200Kv / 30mm - 40mm Diam. / Low Voltage / Avail. / 120 amp

20"-27" / 3s LiPo or 8 cell NiMh / 3500-2500kv / 35mm – 42mm Diam. / Low Voltage / Avail. / 120 amp

24”-29” / 4s LiPo or 12 cell NiMh /2650-1600Kv /37mm - 46mm Diam. / Low Voltage / Avail~Disc / 120-240 amp

26”-32" / 6s LiPo or 18 cell NiMh /1800-1100Kv /40mm - 52mm Diam. / Low or High / Disc. / 120-180-240 amp

30"- 36" / 8s LiPo or 24 cell NiMh / 1350-800Kv /45mm – 55mm Diam. / High Voltage / N/A / 180-240 amp

34" - 42" / 10s LiPo or 30 cell NiMh / 1100-600Kv /47mm + Diameter / High Voltage / N/A / 180-240 amp

38" - 46" / 12s LiPo or 36 cell NiMh / 900-550Kv / 50mm + Diameter / High Voltage / N/A / 240 amp

Always start testing with a small prop and work up to your desired amp readings!


HULL SIZE AND OSE MOTORS

This is a general guideline for the motors OSE sells. I know it is hard for this to cover all selections, since FE setups can be complex and extend over a wide range of extremes. Remember this is more for conservative setups to help new guys get started.

hull size…..... /…...... Neu….... /….. Feigao.540…../…..KB45...../...700SC../.SV27./.Proboat./..Ammo../.380.

<<"-20"....../.....1506........../.......Fiegao.S......./................./................./......../............../.............../.380 L

17”-24”…../….. 1506,1509./…..Feigao S-L…...../…............../................./......../............../................/........

20"-27"…../….. 1509,1512./…..Feigao L-XL...../….............../...700SC../.SV27./.Proboat./..Ammo../........

24”-29”…../…..1512,1515../…..Feigao XL…...../….............../...700SC../.SV27./.Proboat./..Ammo../.......

26”-32"…../.....1512,1515../…..Feigao XL….../…..KB45...../.,..700SC../.SV27./.ProBoat./............./........

30"-36"…../….. 1515,1521./…........…………..../….. KB45...../.............../........../.............../............./........

34"-42"…../….. 1521,1527. /…........………..…/….. KB45...../................/........./................/............./........

38"-46"…../…..1527,2215. /….. ......……..……/….............../................./........./................/............./........

MOTOR MAXIMUM WATT RATINGS.

Always look at the maximum WATTS the motor is rated to handle. The heat will kill the magnets and possibly the controller if you get it to HOT.

Continuous rating/ 30 second rating

Neu -
1506 - 700 watts/ 1500 watts
1509 - 1000 watts/ 2000 watts
1512 - 1200 watts/ 2500 watts
1515 - 1500 watts/ 2700 watts
1521 - 1700 watts/ 3000 watts
1527 - 2100 watts/ 3300 watts
2215 - 3000 watts/ 5000 watts
2230 - 6000 watts/ 10000 watts

KB45 - 1500 watts/ 2700 watts

Feigao
XL - 800 watts/ 1600 watts
L - 600 watts/ 1300 watts
S - 450 watts/ 1000 watts
380L - 450 watts/ 1000 watts

SV - BlackJack 800 watts/ 1600 watts

Ammo 2300 - 700 watts/ 1400 watts

700sc - 650 watts

Volts (X) Amps = Watts

Always calculate your setup Watts and prop it to run close to your motors Max Amp rating. (maximum effeciency rating)

FeCalc can get you in the ballpark for loaded 2-pole motor watts and amps. It is just an estimate, but can give you a good idea of which prop to start testing with.

Hi there,

I think you replied to my thread about my on board Li-Po fire???
As you might know, I am new to FE and there are a few things I don't understand...

In the motor KV ratings, The speeds go from high to low i.e. 1800 - 1100 Kv???
Also, Can you explain your comment about running the motor as close to its max amps???

Thanks....

[ED66677]

Link the KV to the hull size i.e for a 2S setup, 17"-24" and 5500KV-3200KV, you would use a 5500KV motor for a 17" hull and a 3200KV motor for a 24" hull, this can be explain by the fact that under 2S a 5500Kv motor will spin a smaller prop than a 3200KV motor, too small of a prop (too small compared to the hull size) would slip a lot, i.e a 29mm prop on a 40" hull will do nothing at all.
Motor manufacturers have datasheet, i.e Feigao tells that a 540-08XL is rated for 83A you then want to use it around this value, you need a recorder to do so, (EagleTree Micro Logger)

[KillerDave]

Link the KV to the hull size i.e for a 2S setup, 17"-24" and 5500KV-3200KV, you would use a 5500KV motor for a 17" hull and a 3200KV motor for a 24" hull, this can be explain by the fact that under 2S a 5500Kv motor will spin a smaller prop than a 3200KV motor, too small of a prop (too small compared to the hull size) would slip a lot, i.e a 29mm prop on a 40" hull will do nothing at all.
Motor manufacturers have datasheet, i.e Feigao tells that a 540-08XL is rated for 83A you then want to use it around this value, you need a recorder to do so, (EagleTree Micro Logger)

Got it! Thanks buddy! :-)

[bigwaveohs]

Let me correct previous spreadsheet , has one mistake in the chart view. This is the correct one.

What are "For Chart Purposes" numbers?

[agressive1]

Hey

Im after some help on what size Motor and what ESC i would need for my type of hull.

The hull iam using is a 37.5" Mono Hull which is 11" wide, Iam wanting it to be brushless and iam wanting to at least get about 10 minutes out of a battery. I do want this boat to be quick also and specially do want it to run for that 10 Minutes.

So what Brushless motor will i need, Feigao preferably?
What ESC will i need, dont want something to extreme and expensive?
What lipos, size, Volts etc, should i run 2x Lipos in parallel?
What size prop do i need?

[RayR]

Hey

Im after some help on what size Motor and what ESC i would need for my type of hull.

The hull iam using is a 37.5" Mono Hull which is 11" wide, Iam wanting it to be brushless and iam wanting to at least get about 10 minutes out of a battery. I do want this boat to be quick also and specially do want it to run for that 10 Minutes.

So what Brushless motor will i need, Feigao preferably?
What ESC will i need, dont want something to extreme and expensive?
What lipos, size, Volts etc, should i run 2x Lipos in parallel?
What size prop do i need?

A 580 12L, Turnigy 180 esc, 2 x 6S 5000Mah packs and a X450 should get you where you want to go, without breaking the bank (completely).

All the best,
Ray

[agressive1]

The 580 12L

Whats that equivalent to the Feigao?

[RayR]

That is a Feigao. You are not gonna push that boat with the 540XL series with damaging the motor.

[agressive1]

Ok now i see

How would this ESC go with it, Its the last one for $159.95

http://www.rcboatbitz.com.au/

Also what brand LIPOS should i go for and how many Volts should they be?