Spin her up!! Rev it up high! (maybe)

[FighterCat57]

I'm finding that running a higher RPM setup with smaller prop has been producing more top speed and lower peak amp draw with less heat measured post run.

I'm thinking it's because of the nature of electric motors and their tendency to "torque" up to speed and draw large amounts of surge amps while coming up to rpm.

By using a smaller prop and spinning it up, it allows the motor to come up to speed gradually without that hard amp hit from trying to spin up a larger prop. A longer torque curve if you will.

Now, my setups are sport, not racing, but I've nearly hit 60mph on 4s and am only drawing 53 amps peak, with a theoretical max of 40k rpm.

Mind you, I'm using ceramic bearings and wire drives that are made to handle high rpm, as well as a motor rated at 60k rpm.

The major drawback is seemingly slower initial acceleration and some initial cavitation like behavior.

What say the pros on this approach to a low heat, sweet sounding sport configuration? Clearly it is much more demanding on the rotating hardware, but could it be a viable solution for sport setups?
________
Futurama Forum

[tiqueman]

Hey Ben. I found this to be tru as well while building a 32" cat. Seemed a lot of folks were recommending the 642 for it. Turned out the 442 pushed it the best, allowing it to wind a bit more. BUT, you eventually will get down to a size that is not large enought to push whatever size boat you are running and then begin to lose speed with even more rpm. So basically what Im saying is, from my findings and understanding, its not that youve gone smaller to run faster, its that youve hit the right prop for efficiency on a specific hull/ motor.

Which of your builds is this?

[dana]

it is a proven theory. the guy who bought my elam brushless ran it on the x640 i sent it with..then he tried an x642 that he had laying around, and guess what? he got more top speed with the x640 and cooler temps. he also ran the x640 in is vacupickle and said it ran much better. so yes smaller props are better. so it cavitates more from a dead stop. who cares about that....

[FighterCat57]

Hey Ben. I found this to be tru as well while building a 32" cat. Seemed a lot of folks were recommending the 642 for it. Turned out the 442 pushed it the best, allowing it to wind a bit more. BUT, you eventually will get down to a size that is not large enought to push whatever size boat you are running and then begin to lose speed with even more rpm. So basically what Im saying is, from my findings and understanding, its not that youve gone smaller to run faster, its that youve hit the right prop for efficiency on a specific hull/ motor.

Which of your builds is this?

Both of the 32" cats, the EKOS and the Apparition.

I'm actually running the EKOS on the stock ESC's.

[ED66677]

on my 29" mono I use a 42mm CF prop, if I go down to 40.5mm she runs slower, not much but still a bit, if I go for a 43.5mm she goes faster, I never tried a bigger prop as the 43.5mm one already gives big amp, I cannot confirm what you guys have seen or experienced!
I bet I would have had the same result if I started with a 45mm prop and went down to 43.5mm one, I agree with you Tiqueman, he has gone for a smaller prop witch is the right one for his hull.

[FighterCat57]

on my 29" mono I use a 42mm CF prop, if I go down to 40.5mm she runs slower, not much but still a bit, if I go for a 43.5mm she goes faster, I never tried a bigger prop as the 43.5mm one already gives big amp, I cannot confirm what you guys have seen or experienced!
I bet I would have had the same result if I started with a 45mm prop and went down to 43.5mm one, I agree with you Tiqueman, he has gone for a smaller prop witch is the right one for his hull.

Yep, it's my point of reference!

[ED66677]

Yep, it's my point of reference!

are you talking about the kind of same hull?

[FighterCat57]

are you talking about the kind of same hull?

Yes, both hulls are the 32" cat, one is a single, one is a twin.

[ED66677]

can you tell what hull, motor?
mine is a 29" DF copy, Feigao 8XL, Swang 100A ESC, home made drive line (semi rigid!) 42mm CF prop.

[tiqueman]

Ben, I never thought to ask... Coming from owning the Skunk 2 and the HOTR/ App hull and finding they are both exactly the same hull w/ a slightly different deck... how the EKOS hull compare in design. Is it the same as well...

HOTR and Skunk side by side pic.. dont mean to get off topic, just curious.

[FighterCat57]

Ben, I never thought to ask... Coming from owning the Skunk 2 and the HOTR/ App hull and finding they are both exactly the same hull w/ a slightly different deck... how the EKOS hull compare in design. Is it the same as well...

HOTR and Skunk side by side pic.. dont mean to get off topic, just curious.

Identical.

[tiqueman]

I thought they may be. What about quality. I will say the Skunk is MUCH better, straighter, more solid and cleaner crisper lines than the HOTR. How the EKOS compare on that note?

[FighterCat57]

I thought they may be. What about quality. I will say the Skunk is MUCH better, straighter, more solid and cleaner crisper lines than the HOTR. How the EKOS compare on that note?

I'll do a line up of the HOTR, Apparition and EKOS sometime and get some detailed comparisons. So far the App & EKOS have been very close.

[Fluid]

High rpm alone is simply not always the best route. The motor/hull combo will determine the best prop and rpm to use. Sure there are times when a lower pitch prop will give higher speeds - if the original prop was placing too great a load on the motor and forcing it out of it efficiency range. There are just as many cases when a higher pitch prop will give higher speeds, sometimes with lower amp draw too.

The bottom line is you have to experiment with your setup to determine which prop works best. Then if you change the setup a bit - raise the prop, better cells, different motor - you'll have to start over again. This is one of the parts of the hobby that keeps me here for so many years....


.

[tiqueman]

I'll do a line up of the HOTR, Apparition and EKOS sometime and get some detailed comparisons. So far the App & EKOS have been very close.

That would be cool. Interesting how many knock offs there are of a boat and slight changes render it different. Oh well, I still think its a fantastic hull design.. whoever originally made it....