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HomeAircraftHelicopterHelicopter Main Discussion › correct me if im wrong
02-25-2013 05:46 AM  5 years agoPost 1
bricktop

rrApprentice

gone

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1kv= 1700 rpm on the motor. you figure your main gear and pinion gear to get your head speed.

the amperage draw from your motor (depending on flying style) dictates the esc you can use in accordance with the c rating on the battery because of heat which can damage your battery. but also if your motor is trying to pull more amperage than your esc is rated for it will fry your esc? where does the bec come in? what is a bec? what does it do? this is what i need someone to explain to me. in a nutshell...how does all of this work together?

kv= motor rpm > determines amps being used > determines esc to be used > determines battery c rating > ???

Is this right?

I didn't say you did it...I said I was blaming you.

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02-25-2013 08:11 AM  5 years agoPost 2
misskimo

rrElite Veteran

Alaska 17 years, before mississippi for 31y

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Words from good ole KC
OK, now that I got your attention
This is how to tune an electric helicopter, the detailed version, in one spot, for people who really want to learn their s...stuff.
----
"S" is the number of lipo cells in series.
"V" is voltage, assume one lipo battery cell is 4 volts
"P" is the number of cells in parallel.
"C" is the manufacturer's RECOMMENDED rate for discharging a battery.
1000mA = 1A
"A" stands for amps
AMPS ARE WHAT YOU REALLY NEED TO KNOW
----

EXAMPLE 1
I am handing you a 10s 2500mA 25C battery...what can you assume about it?
You can assume the voltage, capacity, current, and POWER it MIGHT be capable of delivering.
10S x 4V = 40V
2500mA = 2.5A
40V x 2.5A x 25C = 2500 Watts
-----
1 HP = 768W "W" = Watts. 2500 / 768 = 3.25 HP
----
EXAMPLE 2
thanks for the battery pal, but you said C ratings were a 'recommendation'....so I probably CAN NOT get 2500 watts continuously right?
RIGHT.
I don't waste my time finding exactly how much power I can get. Years of experience has taught me to slash max PAPER power in half and do my math from there.
Then I go fly around until I KNOW something very useful....more on that in a minute.
In the first example, we can assume the battery is good for ATMOST 2500W
I ASSUME it is NOT CAPABLE of doing paper power continuously, so I divide paper power by 2, 2500 / 2 = 1250W
-----
EXAMPLE 3
Why are you interested in that number?
1) I time my flights. 2) I check how many mA the charger "puts back"
Unfortunately, if you don't have a charger that does this, you'll have to get geeky to figure it out...telemetry, etc.
Lets say I time my flights for 4 minutes. I do 5 flights of 4 minutes each, my charger says I put back roughly 2000mA after every flight.
2000mA / 4 minutes = 500mA per minute
500mA = 0.5A
I now KNOW something about my setup, I know I am using around 0.5A per minute or drawing an average of 30A
----
EXAMPLE 4
OK 30A great...what does that mean?
Amps are an hourly measurement...0.5 x 60 = 30A..thats where I got the 30.
We're still using your 10s 2500mA 25C battery
30A x 40V = 1200 Watts
This is my average power, it represents how much power I used over all my timed flights AND how much current I averaged.
1200W is so close to 1250W that I'm done wondering if my setup WORKS.
I can expect the PAPER power 2500W still...I just did things that prevent the helicopter from taking all 2500W constantly and frying something
The heli will use 2500W in short bursts...but the battery cannot do 2500W for the whole flight...thats why I divide by two.
Why two?...it has to do with choice of pinion, use the smallest first and work up....I have noticed anything that does not work with this math is overgeared, overweight, under-batteried, etc, etc.
The whole point here, is to find a balance between performance and what WORKS.
----
EXAMPLE 5
The math for this setup is good, what else can I assume now?
From my personal experience I can assume if my helicopter averages what using shy side estimates said it would do, then my amp 'spikes' under load will not affect the battery.
Lets assume we know the right pinion, we can assume spikes are within what we know about the setup after timing it and checking the mA
1) 25C x 2.5A = 62.5A (math says 60A...we're ok)
2) the sticker on my ESC says (circle) more / less than 62.5A
ALMOST DONE
-----
EXAMPLE 6
OK cool, but I don't need a 10s 2500mA 25C, I need 6s
it is very easy to change voltage in the SAME helicopter.
1) 40V x 2.5A x 25C = 24V x 25C x ______A
2) 40V x 2.5A x 25C = 24V x 5A x ______C
The math is not difficult,
1) 4.16A. Realistically, 4200mA
2) 20.8C. Realistically, 25C
-----
EXAMPLE 7
I am going to copy your setup because basic addition and multiplication is too difficult for me to understand and I need answers handed to me...even then I don't get what they mean and probably shouldn't be flying rc in the first place because I am a total idiot, BUT I changed the voltage to 6s after everyone on six different forums said that heli needs 10s, so what ESC do I need???
If our 10s example draws 30A, spikes 60A, you can ASSUME with some confidence that a 6s will draw 10/6 x 30 A = 50A
what does it spike on 6s?...100A
If your ESC says 100A, you should be ok in this example, if it does not, thats why any one of us who have been doing this forever, will recommend more volts before trying to figure out what else you got going on...THE WHOLE GAME IS TO LOWER THE STRESS ON COMPONENTS however necessary: by voltage, current, weight, gearing, whatever.
...then go stress the hell out of them again....it's a strange game.
----
I said before AMPS ARE WHAT YOU NEED TO KNOW. current is the big thing to pay attention to when picking components
1) can the battery stand the power you want?
2) does the ESC match the battery?
3) did you gear it right.
-----
when setting up a new electric heli, always use the smallest pinion you can get away with, this will result in the lowest current draw. Then you can gear up once you figure out the setup.
----
Thats all I got to say about learning your way around electrics, I did so after 15 years of playing with them NEVER using a tach, voltmeter, pitch guage to do set-up...had some time on glow before electrics that really helped me understand the theoretical side of tuning.
I think that side is more important than running around like a chicken with his head cut off asking which piece of equipment to buy, that stuff changes all the time, the science doesn't.
Anyways I know its long, but this is the stuff that WORKS, its not all 'mine' its a blend of things I have learned myself and from others, and it has all been applied.
It took me too long to write this and I need a break

Below is KC's post with the technical issues corrected. He said I could post it.
- John
-------------------------------------------------------------------
OK, now that I got your attention
This is how to tune an electric helicopter, the detailed version, in one spot, for people who really want to learn their s...stuff.
----
"S" or "s" is the number of lipo cells in series.
"V" is voltage, assume one lipo battery cell is 4 Volts
"P" is the number of cells in parallel.
"C" is the manufacturer's rating of the battery used to derive a RECOMMENDED MAXIMUM current for discharging a battery. It is applied as multiplier to the capacity (in mAh of Ah) of the pack to derive a current (mA or A).
1000 mA = 1 A
"A" stands for amps
AMPS ARE WHAT YOU REALLY NEED TO KNOW!
----
EXAMPLE 1
I am handing you a 10s 2500 mAh 25C battery... What can you assume about it?
You can assume the voltage, capacity, current, and POWER it MIGHT be capable of delivering.
10s x 4V = 40V
2500 mAh = 2.5 Ah
2.5 Ah x 25C = 62.5 A (Funny stuff with units, but that’s the way it works. Apparently, C has units of A/Ah)
40 V x 62.5 A = 2500 Watts
-----
1 HP = 768 W, "W" = Watts, 2500 / 768 = 3.25 HP
----
EXAMPLE 2
“Thanks for the battery pal, but you said C ratings were a 'recommendation'... So, I probably CAN NOT get 2500 Watts continuously right?”
“RIGHT.”
I don't waste my time finding exactly how much power I can get. Years of experience has taught me to slash max PAPER power in half and do my math from there.
Then I go fly around until I KNOW something very useful. More on that in a minute.
In the first example, we can assume the battery is good for AT MOST 2500 W.
I ASSUME it is NOT CAPABLE of doing paper power continuously, so I divide paper power by 2, 2500 / 2 = 1250 W
-----
EXAMPLE 3
Why are you interested in that number?
1) I time my flights.
2) I check how many mAh the charger "puts back."
Unfortunately, if you don't have a charger that does this, you'll have to get geeky to figure it out... telemetry, etc.
Let’s say I time my flights for 4 minutes. I do 5 flights of 4 minutes each and my charger says I put back roughly 2000 mAh after every flight.
2000 mAh / 4 minutes = 500 mAh per minute
500 mAh = 0.5 Ah
0.5 Ah/minute x 60 minutes/h = 30 A
I now KNOW something about my setup, I know I am using around 0.5 Ah per minute or drawing an average of 30 A.
----
EXAMPLE 4
OK, 30 A great... What does that mean?
We're still using your 10s 2500 mAh 25C battery.
30 A x 40 V = 1200 Watts
This is my average power, it represents how much power I used over all my timed flights AND my average current.
1200 W is so close to 1250 W that I'm done wondering if my setup WORKS.
I can expect the PAPER power 2500 W still. I just did things that prevent the helicopter from taking all 2500 W constantly and frying something.
The heli may use 2500 W in short bursts. But, the battery cannot do 2500 W for the whole flight. That’s why I divide by two.
Why two? It has to do with choice of pinion, use the smallest first and work up. I have noticed anything that does not work with this math is overgeared, overweight, under-batteried, etc, etc.
The whole point here is to find a balance between performance and what WORKS.
----
EXAMPLE 5
The math for this setup is good, what else can I assume now?
From my personal experience I can assume if my helicopter averages what using shy side estimates said it would do, then my amp 'spikes' under load will not affect the battery.
Let’s assume we know the right pinion, we can assume spikes are within what we know about the setup after timing it and checking the mAh
1) 25C x 2.5 Ah = 62.5 A (math says 60 A...we're ok)
2) The sticker on my ESC says (circle) more / less than 62.5 A
ALMOST DONE
-----
EXAMPLE 6
OK cool, but I don't need a 10s 2500 mAh 25C, I need 6s
it is very easy to change voltage in the SAME helicopter.
1) 40 V x 2.5 Ah x 25C = 24 V x 25C x ______Ah
2) 40 V x 2.5 Ah x 25C = 24V x 5 Ah x ______C
The math is not difficult,
1) 4.17 Ah. Realistically, 4200 mAh
2) 20.8C. Realistically, 25C
-----
EXAMPLE 7
I am going to copy your setup because basic addition and multiplication is too difficult for me to understand and I need answers handed to me. Even then I don't get what they mean and probably shouldn't be flying RC in the first place because I am a total idiot; BUT, I changed the voltage to 6s after everyone on six different forums said that heli needs 10s, so what ESC do I need???
If our 10s example draws 30 A, spikes 60 A, you can ASSUME with some confidence that a 6s will draw 10/6 x 30 A = 50 A
What does it spike on 6s?...100 A
If your ESC says 100 A, you should be ok in this example. If it does not, that’s why any one of us who have been doing this forever will recommend more volts before trying to figure out what else you got going on. THE WHOLE GAME IS TO LOWER THE STRESS ON COMPONENTS however necessary: by voltage, current, weight, gearing, whatever.
Then, go stress the hell out of them again... It's a strange game.
----
I said before AMPS ARE WHAT YOU NEED TO KNOW. Current is the big thing to pay attention to when picking components.
1) Can the battery stand the power you want?
2) Does the ESC match the battery and current requirements?
3) Did you gear it right?
-----
When setting up a new electric heli, always use the smallest pinion you can get away with; this will result in the lowest current draw. Then you can gear up once you figure out the setup.
----
That’s all I got to say about learning your way around electrics. I did so after 15 years of playing with them NEVER using a tach, voltmeter, or pitch gauge to do set-up. I had some time on glow before electrics that really helped me understand the theoretical side of tuning.
I think that side is more important than running around like a chicken with his head cut off asking which piece of equipment to buy; that stuff changes all the time, the science doesn't.
Anyways I know it’s long, but this is the stuff that WORKS, it’s not all 'mine', it’s a blend of things I have learned myself and from others, and it has all been applied.
It took me too long to write this

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02-25-2013 08:22 AM  5 years agoPost 3
misskimo

rrElite Veteran

Alaska 17 years, before mississippi for 31y

My Posts: All  Forum  Topic

In short

Voltage X Kv Divided by gear ratio X 85% for gov

Sounds like you have a 500 size heli by what you listed.
Bec. Its a regulator so you dont have to slap on a rx pack, Tone down weight,

T

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02-25-2013 09:09 AM  5 years agoPost 4
KC

rrElite Veteran

WA

My Posts: All  Forum  Topic

Tony knows his stuff 85% or 5/6th is on the money for Kontroniks at 70-75% governed.

To answer your questions quick: your motor will pull more amps when the pinion is too big. A BEC isn't recommended at all unless you buy a Kontronik, its the only BEC worth a crap...and now the long version if you want to NEVER fry a component ever again.

Start with a recommended setup, use the smallest pinion first, fly it a bunch, and measure how much you put back into your batteries

if you average under half of voltage times C rating times capacity, you're on the right track.

why divide by two? short answer: if a motor is 80% efficient, and a gear train is 80% efficient, then the product of those two systems is 63% efficient.

If an ESC is 95% efficent and the other stuff is 63% efficient....then you're looking at 59% efficency.

50% ("divide by two" ) accounts for other things going on, but to be honest I NEVER go that high.

I'm too paranoid! I usually aim for 25% as my average current draw because I can then slam on it and not draw over 50% for more than a few seconds.

Nothing on that heli is stressed.

What affects current draw the most? asking for ridiculous headspeeds wastes more juice and fries more ESCs than anything. You gain 2% in acceleration for every 1% weight decrease versus 1% power increase. Every doubling in power is at best a 40% increase in acceleration....In a nutshell, he who detunes, flies not fries.

The Kontroniks are the only ESC that can really get away with oversize pinions but even those benefit from using an appropriate pinion.

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02-25-2013 10:58 PM  5 years agoPost 5
Richardmid1

rrProfessor

Leeds, England

My Posts: All  Forum  Topic

Way to confuse the guy! He hasn't even mentioned a governor!

Bricktop, BEC stands for Battery Eliminator Circuit, basically it takes the input voltage from your flight pack and drops it down to 5-6v to power your receiver, servos, gyro etc. instead of using a separate 5-6v receiver battery. Some ESC's have built in BEC's and some don't.

KV means rpm per volt, so a 1000kv motor at 10 volts will do 10,000 rpm for example. Now you just work out motor KV and pinion needed to get to the headspeeds stated in the manuals.

Heres a really easy way to pick an ESC, check what capacity packs said heli uses and divide the Mah number by 100, this will roughly be the average current draw of the heli. Now obviously you want some spare so use an ESC 50% above that. E.g. a 425 blade heli using a 6s 3000mah pack, 3000/100 = 30, 30 + 50% = 45 amp ESC needed. Another example a 700 using 12s 5000mah pack, 5000/100 = 50, 50 + 50% = 75 amp ESC needed.

You may want to go above these ESC ratings for piece of mind or if you fly in very hot climates but 99% of the time this theory will work fine.

60% of the time, it works every time!

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02-26-2013 01:10 AM  5 years agoPost 6
McKrackin

rrProfessor

Lucasville,Ohio

My Posts: All  Forum  Topic

.....

I literally never use the word literally right.

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02-26-2013 01:31 AM  5 years agoPost 7
KC

rrElite Veteran

WA

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Bricktop, feel free to pm me if you have questions

Ernie, good job

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02-26-2013 05:11 AM  5 years agoPost 8
bricktop

rrApprentice

gone

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alright

I didn't say you did it...I said I was blaming you.

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02-27-2013 02:43 AM  5 years agoPost 9
Thrust Bearing

rrNovice

Cincinnati, Ohio - USA

My Posts: All  Forum  Topic

Here is a good site for basic information.
http://www.rcheliwiki.com/KV_rating
Good thread!

Easy on the stick...

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