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Old Dec 11, 2012, 10:06 PM
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Yep, RPM and thrust (pretty well hand in hand) are the only true 'output'
The inputs have many various reasons for being different, or 'hmm, doesn't SEEM to add up'.
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Old Dec 12, 2012, 03:25 AM
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so how long before people start quoting "shaft power" instead of input power?
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Old Dec 12, 2012, 05:32 AM
EDF rules... :)
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Originally Posted by WhalleyB0Y View Post
Excellent explanation! I would even go as far as to say the watts seen in a wattmeter could mean nothing if the the energy is being wasted in the form of heat or other electrical losses. The true measurement in this case would be the thrust.
The watts shown on the watt meter is a good indication of efficiency when the thrust/rpm is comparable. Where as watts/thrust conversion is dependant on how close the kv is matched to the work that the rotor is expected to perform.

Eric B.
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Old Dec 12, 2012, 05:36 AM
EDF rules... :)
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Originally Posted by anlucas View Post
If we had the ideal motor with super strong magnets/magnetic field, rpm/thrust would be directly proportional to amps/watts.

But, this is not the case with some of these outrunners. At some point they reach a point where the surplass energy just becomes heat rather than rotational energy. The thrust differences can be below 100gr.
+1, this is usually the case where the winding of the motor is not correct to produce a strong enough magnetic field to efficiently turn the rotor to the rpm the kv is asking for.

Eric B.
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Old Dec 12, 2012, 05:37 AM
EDF rules... :)
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Originally Posted by Odysis View Post
so how long before people start quoting "shaft power" instead of input power?
When Peter learns how to calculate it?

Eric B.

Maybe i should have used an emoticon such as .
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Old Dec 12, 2012, 05:41 AM
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(V - I * Rm) * (I - Io)...
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Old Dec 12, 2012, 05:26 PM
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We don't really care about 'shaft input power' at all....

What matters is how much you put in.... and what true power, which as to be the measurement of thrust/RPM, comes out.
Efficiency is irrelevant as you are stuck with what you have anyway. And all you really need to care about is what output you got in that system, versus any other comparison of what other systems got (via posts, or your own tests etc), for what input power... so if you got a better output, or lower input, your setup was more efficient. There are tons of references to compare against, so that you have reasonable guides as to what to aim for (what to buy or try etc).
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Old Dec 12, 2012, 06:41 PM
Big gov never Works
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Quote:
Originally Posted by anlucas View Post
If we had the ideal motor with super strong magnets/magnetic field, rpm/thrust would be directly proportional to amps/watts.

But, this is not the case with some of these outrunners. At some point they reach a point where the surplass energy just becomes heat rather than rotational energy. The thrust differences can be below 100gr.
So, what you are saying is, you were just wasting input power initially with excess heat. And by reducing the timing, you were just reducing the heat and gaining efficiency? Thats understandable. esp, since I don't use outrunners for EDF applications. I can see where their(out-runner) natural in-efficiencies over an in-runner, may show increased differences in timing, over the in-runner.

But like Isaid, I was not trying to be critical of your statement. I'm just not used to the use of out-runners in EDF. Thanx.

Fuzz
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Old Dec 13, 2012, 02:04 AM
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You're not stuck with it. Change motors... If motor A is 70% efficient, and motor B is 85% efficient, motor A will need to weigh twice as much to do the same job.

Well, not actually weigh, but have twice the surface area. Close enough approximation though.

Point is, trying to lump motor and fan together and ignoring the differences between motors is just as bad as ignoring differences between fans.
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Old Dec 13, 2012, 02:21 AM
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Point is, trying to lump motor and fan together and ignoring the differences between motors is just as bad as ignoring differences between fans.
+1. A really great motor for one fan could be a poor choice for another fan and vice versa.
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Old Dec 13, 2012, 06:32 AM
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It is not worth buying yet another motor just to get a few % better efficiency - if you can even work that out in advance before buying another one that is hardly better, or not at all..
Any setup you put together should at least be in the ballpark, unless you don't even know what you are doing and should never have tried yourself anyway.
The CS10 & 12 are so close to identical that the same motors will work totally fine in both.
All we are trying to do is compare the fans, not motors. It would be different if it was CS10 versus Wemo etc... but it isn't.
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Old Dec 13, 2012, 03:47 PM
Extreme CNC Alloy EDF
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Just got a new order of rotors in and I got some 12 blade to test out, but if they are presenting a similar load to each other I will just pull the 10 blade off the test fan and stick a 12 on to start the test runs off!
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Old Dec 13, 2012, 04:23 PM
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Just got a new order of rotors in and I got some 12 blade to test out, but if they are presenting a similar load to each other I will just pull the 10 blade off the test fan and stick a 12 on to start the test runs off!
i already did that with your alloy unit the numbers are almost the same.

Change sun 70mm 12 blade fan on 4s Het 2W25 2720KV (1 min 9 sec)
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Old Dec 13, 2012, 05:37 PM
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I suspect Mark will test on much higher power setups. 6S.... 1200W and higher...
So the fan MIGHT have a different curve that then shows a separation in their results at higher powers.

It is interesting that the 12 blade fits the ERC housing, and then that smaller gap should make it a higher thrust.... but then should also draw a bit more power (Amps) too.
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Old Dec 13, 2012, 06:45 PM
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It may also cause issues with stretch at higher power, likely I will have to machine down the rotors a little if I build fans with the 12b, we will see!
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