Kora 15-12 and 5S

[rotodingo]

Hello,

I was using 4S 3700 and now 5S 3300. The results below are with brand new TP extreme batts. So they will be lower after some time.

Jazz 55-6-18. 18T pinion

2690rpm with 70%.

2800 rpm at 75%.

fly great. Too much power for me in fact.

Nicolas

[John Heli]

Hi Nicolas,

would you buy the Kora 15-12 again or would you prefere a 15-14 or 15-10?

Thanks,
John

[rotodingo]

Well, it depends on how you want to fly. I can't fly the Lepton above 2800 rpm. He is far too fast for me. I have to calm him down by lowering head speed.

In my case a 15-14 would be better on 5S. Because i would be able to have a little higher % on the Jazz, a little biger pinion and still have 2600-2800 rpm.

For somebody ussualy flying with 3000-3200 rpm, the 15-12 is very good i think. But 15-14 will work too with biger pinion.

I think the 15-12 is more universal. 4 or 5S are usable with the same motor and good power/head speed. So if you start by 4S with the project to go 5S later, the 15-12 is the one. If 5S is the first choice, use kora 15-14.

Nicolas

[John Heli]

Thank you for your detailed information! I am currently flying a 3DX500 with the stock engine, but I am planing to switch to a Kora. I also use the Jazz 80 and fly on 4s. But I am flying a little longer blades (440mm) and I prefere lower head speed, so maybe the Kora 15-14 is a good option for me.

[larryfl]

when you went to 5s from the 4s was it major power difference? or just a little

[Jafa]

Fully agree with rotodingo/Nicolas

I started with 15/14 on 4S - it was ok but not great
I changed to 15/12 on 4S with 21T (22T would be better)
This gave me more power and 2600 rpm - flies great

The trick with the Kora is run them between 12,000 rpm and 15,000 rpm
They produce more power with more RPM

The 15/14 on 5S will be doing ~12,400 which is fine
(on 4S it's only doing ~11,300 is only so so)

The 15/12 will rev at 1,000 rpm over it's maximum on a freshly charged 5S pack
but only if you have a very high throttle curve
The manual warns you not to exceed 15,000 rpm

[rotodingo]

Originally Posted by larryfl

when you went to 5s from the 4s was it major power difference? or just a little

I have more power, no doubt. But i compare hold 4S batt with bew 5S... In fact i think i don't have a so much higher power than with 4S. But ESC and motor are cooler. Batt too i think but it's cold right now outside.

I may try a 15-14 soon. With 5S it should be better.

Nicolas

[husafreak]

Anyone tried the KORA 15-10 w/4s?

[Rush]

How do you compute the maximum rpm of a motor on a 4S Lipo?

For example, a Kora 15-12 on 4S 3700 FPs would be doing what rpms at 100%? Just wanna understand how it works so i can match electronics better.

Regards

[Jafa]

KV * volts * 0.85 = Motor RPM
(0.85 is the expected efficiency)

920 * 14.8 * 0.85 = 11,573

Motor RPM / (Main Gear Teeth / Pinion Teeth) = Headspeed

11,573 / (84 / 21) = 2893

[Rush]

Thanks Jafa.. much appreciated.

Isnt the Lepton Main Gear 94T? for the 3025-10, 815Kv on 14.8V and 24T, headspeed would be quite low then.

10,252.7 motor rpms,
2618 rpms only....

need to work out a higher KV motor then. I plan 2800-300 rpms on the setup

Regards

[Rush]

After days of research and indecision, I'll go with a

CC 60 ESC (high governor mode)
Kora 15-12
24T Pinion
Fp 25C 3700 / KP 25C 3200 / KP 5000 (if it fits)

I think this will be a more reliable esc/motor/lipo combination.

I found the Hyperion 3025-10 specs out... at 46A rating, there's a big chance i will burn this motor out with tictocs and the ever probable bailout... better to be safe than sorry with cost of parts these days.

Although considering the pricing for Lepton parts these days, i find that its not as unreasonable as it may have been a year or 2 ago.

Thanks guys! much appreciate the help that you have given.

Regards

[rotodingo]

24T will be a little too big. You should use 23T i think. But i have a Jazz, not a CC. It may give you a different HS.
The Hyperion is wrong labelled about the KV. It's higher than indicated.
Nicolas

[Rush]

i ordered the 23T revcon pinion as well just in case the HS goes beyond 3000... I need at least 2800 in governed mode so a fixed endpoint HS of 3000+ at 100% tcv should be ok for the CC60. at least thats what i found on the CC35.

I'm not comfotable with the 3025-10 amp pull of 46A only. i feel it is a little to small for this heli with the way i want to fly. I'm no Alan Szabo but i can drain a 1800 mahr in a 450 w/in 3mins if i bang it hard. So i'll play on the safe side.

[Jafa]

You wont be pulling anyware near 3000 with a Kora 15-12
With a freshly charged pack and a 21 or 22 pinion
you will at 2780 to 2840 (approx)
And it's all down hill from their during the flight

My Kora 15-12 was not even happy on 22T
It's performance was much better on 21T
I very much doubt that it will be viable on 23T or 24T

You could try the 3025-08
it has a similar KV to the Kora 15-12
an a 10 amp higher rating than the 3025-10
(I share your concerns on the amp ratings)

[Rush]

Jafa,

Thanks. I was computing the HS and motor rpms nased on the formula you gave me. But I used 94T for the main gear.

I get

Motor Rpm: 920Kv x 14.8V x 0.85 = 11573.60
Headspeed: 1157.60/(94/24) = 2950 rpms at 100% tcv.

The above is correct right? Does the15-12 bog on 24T? I plan on running 2600 normal, 2800 idle 1. Was the motor temp to high? or it was bogging?


I suppose i could get the 15-14 for a 4S setup?

[Jafa]

Your mathes are certainly correct
The problem is that the motor just will not give that performance
This is the problem and trick with electrics
Finding the efficient operating zone of a motor
Finding a battery/motor/pinion combination that just works

On the 22T pinion the Kora could not hold the head speed
It was washing off all the time and giving poor performance
Not to the point of bogging - but not as solid and enjoyable as 21T

On the 21T I get free flowing flight and no significant head speed decay
The motor comes in cool every time also

If you put a 24T pinion on this motor it will struggle

The Kora 15-14 is a 5S motor - it does not perform well enough on 4S

The best setup that I have tried (four motors and many pinions)
is the Kora 15-12 on 21T

The only variable that I have not investigated is the ESC
I run a Jazz at full output in governed mode
Many people are running the Align 75amp, not governed at 100% flat throttle

[rotodingo]

At first i was using the Kora 15-12 with 24T pinion on 4S. Jazz was at 60% with 2800 rpm. It was working fine. Really. You can see it fly here. http://rotodingo.over-blog.net/article-5664016.html
It was winter with cold ly-po. And the heli wasn't really tuned.

After that i used 22T and it was even better. Now i use 5S with 18T and 2700 RPM at 72% on the Jazz.

Nicolas

[Rush]

Jafa,

after doing more math, i just figure that there's no way 14.8V will be rocketship material. 14.8 spins the motors (A30-10Xl, 3025-10, 15-12) to only about mid range of its limits. The exception might be the 15-12 which gets closest to it efficient powerbacnd range of 12k-15k rpms. to get good performance out of these motors would need 5S.

Or a higher kv motor... like 1100kv types which, on 14.8 spins at higher rpms.

[Jafa]

I fully agree - the 15-12 works well on 14.8v
I've tried a number of 1100kv motors,
they generate heat and you get shorter flights
So the Evo Lite 4250 battery would be good

I like the 15-12 - luke warm - nice performance

I cannot believe a 15-12 works ok on 24T - I may have to test that