Finding the right prop size

[dbonomi]

Hi guys,

Need your help on finding the right prop size for my 37" Intruder cat. I'm using a big 300esc on this boat with a t.p. power 4070cm motor, rated at 2200kv-4d.
This motor produces a tremendous amount of heat in a 6s in series set up. The esc runs cool but the motor is hot. What size prop do you suggest to keep the boat fast but not too hot so I burn up the motor. I would appreciate a reply from some of you experienced boaters.

Many thanks,
Don

[zooma]

Too high kv for 6S. About 48000 RPM. You would have to run a prop that is too small for the hull.

[dbonomi]

How about if I go 4s in series or 8s in parallel?

Don

[srislash]

What size prop have you been running?
A hull that size should run a 47-50 mm prop. Or that's where I'd be srarting. Maybe a little smaller with a bit more pitch.

And yes to the 4s2p. Maybe even 5s, but 6s is really needing a good tune and likely something will give.

[srislash]

I was going to add, how are your connections to motor? Size bullet and good solder joint? Just thinking motor heat here.

[dbonomi]

Hi,

I made a big mistake buying a 4070..cm....2200kv motor for this boat and trying to run it on 6s in series. The boat flies but the motor temperatures are out of control. I'm using a Octura x442 prop. I tried a smaller prop but it's not right for this boat. I want to be using a 447-450 prop size with this 4070 motor but that's presently impossible. What size 4070 kv motor would you recommend for this boat? If I get a new motor, I was thinking maybe 1650-1700kv or lower? I still want to run this boat on 6s in series. What are your suggestions?

Thanks,
Don

[Fluid]

How about if I go 4s in series or 8s in parallel?

Even on 4S that motor Kv is really too high for that boat. The correct Kv will depend on the packs you use (mAh capacity, C rating and parallel) and how you want to use the boat. Actually your current motor would have worked with an x450....if you limit your runs to two or three passes tops. If you expect much run time then try a long motor with a Kv between 1100 and 1300 on 6S, this is what many 6S oval racers use. This Kv will allow you to use an appropriate-sized prop with decent speed and run time. A Kv of around 1500 will be a bit faster, but prop size will be reduced and run time shortened.

Exactly what do you mean by "6S in series"? We normally use 6S to mean the total voltage to the ESC; we would say 3S in series for a total of 6S to the ESC. "6S in series" could mean 12S to the ESC...

You probably need a new motor anyway. If it got really hot - over 170-180* on the can - then the magnets have been weakened and it will be even more prone to over-heating. Plus it can take out the ESC. A TP 4070 is the right size, just pick the Kv to suit our needs.



.

[dbonomi]

I use a Flier 300esc with this boat and at 0 degrees timing and it stays cool. I only do short straight runs for this boat for max speed. My batteries are tpe 5000mah 52c. I use them in series with this motor. The boat came with X442 prop. Are you saying that for short straight runs of 2 ot 3 laps, I should use a x450 prop. for max speed in these short runs and then check temperatures? The builder of this boat told me that these TP CM motors can handle over 200 degrees.

Best,
Don

[dbonomi]

Hi Fluid,

I use 3s in series for a 6s total output with this boat. Check my response in my previous email.

[TRUCKPULL]

Your first main problem is the CM motor.
They are only designed to run for a MAX of 10 second at a time. Let completely cool before you run again.
These motors were designed for Drag cars, can be used in a boat for SAW runs.

This is way the motor is getting hot.

Larry

[dbonomi]

Thanks Larry. For this quick straight "10 second run", what prop size would you suggest? x442, x445, x447, x448, or x450? or perhaps a different pitch size prop? Please give me more feed back.

Thanks,
Don

[MarkF]

Don
That motor is a 4s motor and then you can run 447 to 450 prop. If you run 6s you need to buy a 1400kv motor to 1500 and still use a 447 to 450 prop. On a1200 to 1300 kv you can run up to 455 prop. Also I got you that 7s 6000 mah pack you ordered. Do you still want it? I would like to get paid for ordering it for you.

Mark

[dbonomi]

to the guys who know props,

Can someone please tell me what is the maximum size prop I could use on my 37" intruder cat running on 6s. I'm using a tp power 2200kv CM. I want to record a fast straight away time of no more than 15-20 seconds. What do you suggest?

thanks,
Don

[TheShaughnessy]

[Erroneous]

Just run this. http://offshoreelectrics.com/proddet...?prod=oct-m575 ... But no really, more like this http://offshoreelectrics.com/proddet...?prod=oct-m645.. With good prep this prop is a BEAST.