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Old Oct 21, 2012, 01:04 PM
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A plot of EDF Wemotec 68mm and another Changesun 70mm 10 blades.


Consider that for the same power and thrust in the EDF Changesun requires a lot less Kv motor.

Manuel V.
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Old Oct 21, 2012, 01:14 PM
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Quote:
Originally Posted by manuel v View Post
A plot of EDF Wemotec 68mm and another Changesun 70mm 10 blades.


Consider that for the same power and thrust in the EDF Changesun requires a lot less Kv motor.

Manuel V.
Yeap, more blades & less RPM = less rotor whine but turbine like balanced wemo can be just as quite at high RPMs
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Old Oct 21, 2012, 01:27 PM
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Quote:
Originally Posted by GryphonRCU View Post
Hi Manuel V.,

I was looking for %KV. You have it in there.

Nice job.


Thank you,

Gryphon
Yes.
%Kv is same to %NLS

To calculate your fan rpm’s:

This is wrong.
Take the voltaje of the battery and multiply the Kv of the motor = fan RPM.
11.1V x 3600= 39,960.

A reality more about:

3 cell lipo, have a voltage of approximately 12.6Volts.
The new batteries 30 and 20 C 40C sustain discharge voltage 11V average. (Use the voltage rating is very rough and correct)

A very important factor that is missing from this equation is the NLS% (percentage of No Load Speed.)
In EDF is very important that the engine is not charged too much for this factor does not drop below 80%. Possibly in some applications where the motor is much torture can be used up to 75%. But it is highly not recommended.

Also consider the actual motor Kv can vary the die post for the manufacturer.


Take the voltaje of the battery and multiply the Kv of the motor and multiply for %NLS factor = fan RPM.
11.1V x 3600 x 80%= 31,968 RPM.


To Calculate what Kv motor you need:
Take the desired fan RPM, divide it by the battery voltaje = Need ed motor Kv.

45,000 / 14.8 = 3,040 kv.

As in the example above to factor% NLS,

45,000/14.8=3040*100/80= 3800 Kv.

Manuel V.
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Old Oct 21, 2012, 02:05 PM
EDF rules... :)
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Manuel,

Your calling motor efficiency %kv?

Eric B.
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Old Oct 21, 2012, 02:27 PM
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upper limit on motor efficiency at certain load

%kV, %NLS - I understand that to mean that under load the motor is revving at
lower RPM than at idle (no load).

Now there is a connection with motor efficieny, just don't know where I read that,
I think in a post by Juergen Heilig:
An electric motor can never have a higher efficiency (eta, in %) than exactly that
ratio, no load speed vs. speed under load (at the very same voltage, that is
important, and I think that is what Manuel V just pointed out).

While that is only putting an upper bound (cap) on the otherwise unknown motor
efficiency, it is still useful because by measuring RPM we can avoid a typical
mistake, i.e., overloading the motor (resulting in bad efficiency, lots of heat etc.)
That is happening very often because of the much higher load of high-blade fans
compared to the old-style 5- or 6-bladers. But this is known to readers of this
thread :-)

So the 80% rule is not bad in practice: Choose a setup so that your motor is
still having 80% of no load RPM under load.
However that requires that you measure no load RPM and record voltage
with precision (published kV figures cannot be trusted) and do the same under
load, then linearly approximate no load speed for the actual voltage under load.

OR use common sense: A cheap 100g outrunner with kV lower than 3000 will
be pretty efficient up to 40A, at 50A not so much anymore, and everything above
that will turn it into a good heating device...

Did my best and wrote a lot about simple facts, but I hope that it is at least
clear enough...
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Old Oct 21, 2012, 05:57 PM
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Manual,

Any chance of rearranging the graphs to be grams v watts, with both fans plotted against each other?

Ideally, with a line of best fit to smooth out the noise?
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Old Oct 21, 2012, 06:34 PM
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Quote:
Originally Posted by AirX View Post
Manuel,

Your calling motor efficiency %kv?

Eric B.

No.
Efficiency is the percentage obtained from the input power vs. power converted into work.

% NLS, Kv is the percentage of an motor resulting loading vs unloaded Kv.
I will always be greater than% efficiency.

In an EDF is very difficult to measure efficiency.
But you can easily measure the% NLS.
If a motor of 1000 Kv, is feed with 10volts, instead turn rotates to 10,000 rpm, rotate a 7,000 rpm, then the% NLS is 70%.

Manuel V.
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Last edited by manuel v; Oct 21, 2012 at 06:46 PM.
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Old Oct 21, 2012, 06:51 PM
Formerly "Heli Copter"
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United States, CA, Watsonville
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Quote:
Originally Posted by erh7771 View Post
lol...did that a 10 go vertical after 20 feet?

nice...

any watts\thrust numbers on the set up?

was it the 3300kv eflite motor?

regards
Motors are E-flite BL32, 2150kv both running on one 6S nanotech 5000mah 65-130C. Each motor is running peak 75 amps and 1600 watts. I haven't measured thrust, but the Jet weighs 7lbs. 11oz. and the thrust is better than 1:1. Most flying is done around half throttle, but full throttle verticals are excillerating.
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Old Oct 21, 2012, 09:51 PM
chuck
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the 75 to 85% of no load rule is exactly what i use on all prop driven planes also. seems to work well from a heating / efficiency standpoint. in the prop driven world, i find lots of people who love to over prop and then brag how their 100 gram motor is drawing 850 watts, funny

chuck.
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Old Oct 22, 2012, 05:41 AM
EDF rules... :)
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Quote:
Originally Posted by mopetista View Post
snip>So the 80% rule is not bad in practice: Choose a setup so that your motor is
still having 80% of no load RPM under load.
However that requires that you measure no load RPM and record voltage
with precision (published kV figures cannot be trusted) and do the same under
load, then linearly approximate no load speed for the actual voltage under load.

OR use common sense: A cheap 100g outrunner with kV lower than 3000 will
be pretty efficient up to 40A, at 50A not so much anymore, and everything above
that will turn it into a good heating device...<snip
And here I thought that the wire size/quality had everything to do with how much internal resistance cuased a percentage of power to be consumed into waste heat.
Which I was of the understanding was the cause for less rpm as load rises. The rotor load demands stronger magnetic feild which causes the amperage rise which causes the wire to heat up, while amperage rises voltage drops to hold power, voltage drops and rpms with it. Where is the mystical aspect coming from?

Eric B.
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Old Oct 22, 2012, 11:39 PM
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Quote:
Originally Posted by Odysis View Post
Manual,

Any chance of rearranging the graphs to be grams v watts, with both fans plotted against each other?

Ideally, with a line of best fit to smooth out the noise?

Thrust is calculated at 3% unless Wemo a certain power.
according to the opinion of erh7771.
The data were adjusted slightly to seat Watts RPM and linearity performance curve. (This would be like if all engines tested were of the same brand, efficiency and capacity.)

EDF Wemotec data are taken from the website:
http://www.extremerc.com.au/estore/i...ex&cPath=14_62

Manuel V.
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Last edited by manuel v; Oct 22, 2012 at 11:56 PM.
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Old Oct 23, 2012, 12:10 AM
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Wouldn't you also want to plot Power versus Thrust?
That would be a handy curve too.
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Old Oct 23, 2012, 12:37 AM
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If you select a blue dot, find power and RPM.
If upright extensions that point to find the thrust that power in magenta points.

Manuel V.
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Old Oct 23, 2012, 03:58 AM
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No, but you don't see a curve then. You only get single point values. And have to do it manually too.
The curve is to compare one fan to another in terms of power needs for thrust.
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Old Oct 23, 2012, 04:27 AM
It's watts for dinner
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Quote:
Originally Posted by Heli Copter View Post
Motors are E-flite BL32, 2150kv both running on one 6S nanotech 5000mah 65-130C. Each motor is running peak 75 amps and 1600 watts. I haven't measured thrust, but the Jet weighs 7lbs. 11oz. and the thrust is better than 1:1. Most flying is done around half throttle, but full throttle verticals are excillerating.
Which A-10 is that? I haven't been tempted up to this point but your vid made me want one...
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