Kora 15-12 on 5s

[demosa]

I finally tried the Kora 15-12 on 5s with 18t pinion.
Because my 5S batteries are new I only hovered in the back yard.

The facts:
The average voltage reported by eLogger is 18.78Volts.
The Kora 15-12 is 920 KV
The efficiency of the Kora motors is reported to be 83%.
The maximum rotation speed of the Kora 15-XX motors is reported to be 15000rpm.
The Kora 15-12 is a 14 pole motor.

Based on the above, I was expecting a main rotor rpm of :
920 * 18.78 * 0.83 * 18t / 94t = 2746rpm with wide open ESC.

Based on my eLogger measurements, I'm getting 2970rpm with 80% open ESC. This results in 2970 * 94/18 = 15509 motor rpm (over the limit !)

The motor, ESC, and batteries are not more than 104F with 78F ambient temp. at the end of a 6min hover. I'm putting back about 2000mAh into my 3300mAh batteries.

So either the KV of the Kora is higher, or it's a lot more efficient or I'm smoking dope... Can someone explain this to me ?

In any case, this setup looks great to me but I'm a little concerned about the motor rpm going over 15000.
On the other hand I think it's exactly that fact that makes this a very powerfull combination. I wish I could put in a 17t pinion but I would have to modify the magnesium frame to do that (elongate the motor mounting holes).

Maybe the Kora 15-14 would be better for a 5s setup ?
Any thoughts or comments ?
Thanks !

[rotodingo]

Yes, 15-14 is a better idea. I'm using the 15-12 because i used 4S at first. I have a 15-14 on a Super Voyager E.

Nicolas

[Jafa]

I'm running the Kora 15-12 on 5S
I did dremel the magnesium frame (18T I think)
It's working fine for me - good power and still cool

The RPM limit is not a hard limit - I'm not worried about it at all

[demosa]

I will also try the Kora 15-14 when I can find one to buy.

The 15-12 is great but I feel I'm not taking advantage of its full potential because my gov is at 70%. My point is that since the 15-12 spins so fast, I should be able to open the gov to say 90% and translate some of that excessive RPM (which I don't need) into torque by lowering the pinion size. But 18t is the smallest I can fit without modifying the magnesium frame and I'm not willing to do that.

Jafa, what is your gov setting and what RPM are you getting ?
Also, what do you mean "is not a hard limit" ? The 15-12 manual clearly says max allowable rpm 15,000 and it's got to be bad to run it higher than that, no ? Maybe excessive wear on the bearings or something...

I have to say though I'm impressed by the Kora. Even when I push it hard, it barely gets warm... I really like cool running motors !

[eltavito]

I have a kora 15-14 for sale, $100 shipped.
PM me if interested, I have pictures in my home desktop.

Thanks,

Occy

[Jafa]

I'm running a Jazz 55 at full power
Getting high 2850~2900 RPM

Yeah, the manual says the limit is 15,000 rpm
But what do you think will happen?
It's not like a car with valves and valve springs that will bounce over a certain RPM
And if you pulled an extra 1,000 rpm, that's only 6% over, it's not a big deal
I have not had any problems with my Kora running around and over 15,000 rpm

[demosa]

Jazz at full power and you are only getting 2900 with 18t pinion ?
I can't see how can this be !
I wonder if either your Kora 15-12 or my Kora 15-12 is mislabeled... Yours sounds more like a 15-14 to me.

If I open my Jazz to 100% the rpm will be well over 3100rpm with 18t pinion.

What gives ?

[Jafa]

I've just checked, it's actually 75 (sorry)
I think I had it wide open on my old 4S setup

[demosa]

Ah, ok this makes more sense... :)

I basically want to run the Jazz at something like 90% and still have a 2900rpm. It sounds like the 15-14 would be there ...