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Old Sep 25, 2012, 06:13 PM
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Hi guys,

I bought the Suppo 2217K/6T and ran it with the watt meter attached. I got 27Amps draw with 317Watts of a 3S 11.1V LiPo. (8x4 prop)

I was looking at Dr.Kiwi's test results (link below) and he got max 19.3Amps and 206 Watts with his 8x4 prop. I'm not sure why there is such a large discrepancy??

http://www.flybrushless.com/motor/view/194
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Old Sep 25, 2012, 06:52 PM
Jack
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Read Dr Kiwi's description of his test procedures in post #1, I think that will explain the difference. He updated the description there a little last month, no major changes but knowing how he tests makes it a lot easier for others to compare their results to his.

I think of his data as being typical of sensible limits and safe for continuous operation. I'm guessing but I think yours are more like peak readings and you would probably not be able to continue at that power level with over heating.

Some people do fly by fire walling the throttle and going into a trance. I think it is particularly true of newbies to flying. If they use Dr Kiwi's data for choosing props and setting their performance expectations, they should be able to get through it all without destroying any motors.

Jack
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Old Sep 25, 2012, 10:06 PM
just Some Useless Geek
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Hmm. I like to design to continuous maximum power output instead of peak or burst power ratings, so I tend to be a little conservative. However, if the manufacturer says a particular motor is capable of a lot more power than seems reasonable then we need some means of determining what's real and what's hype.

On the other hand, those small Turnigy SK3 motors are rated at about half the continuous power they are capable of delivering. How are we supposed to handle that?
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Old Sep 25, 2012, 10:19 PM
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Quote:
Originally Posted by THOMASJONES View Post
Hi guys,

I bought the Suppo 2217K/6T and ran it with the watt meter attached. I got 27Amps draw with 317Watts of a 3S 11.1V LiPo. (8x4 prop)

I was looking at Dr.Kiwi's test results (link below) and he got max 19.3Amps and 206 Watts with his 8x4 prop. I'm not sure why there is such a large discrepancy??

http://www.flybrushless.com/motor/view/194
I really can't explain the vast discrepancy, except that you are getting 11.74v under load (those must be fantastic batteries), whereas I was using 10.7v... but are you using 8x4 GWS HD?... if you have an 8x4 APC E that will draw a LOT more than the GWS prop.
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Old Sep 25, 2012, 10:22 PM
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On the other hand, those small Turnigy SK3 motors are rated at about half the continuous power they are capable of delivering. How are we supposed to handle that?

I must say that the tiny SK3s do seem to be rated fairly conservatively (2W-2.5W/g)... but as size increases so does over-optimism of power handling capacity... 3536-1400: weight 110g, rated power 590W = 5.36g/W
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Old Sep 25, 2012, 11:05 PM
just Some Useless Geek
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Yeah, nobody seems to want to stick to the 3.5 watts/gram that is the industry average. Or am I wrong that the mode average power density appears to be on the rise across the board? Isn't everybody producing motors with more oofta these days?
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Old Sep 26, 2012, 01:49 AM
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Quote:
Originally Posted by Dr Kiwi View Post
I really can't explain the vast discrepancy, except that you are getting 11.74v under load (those must be fantastic batteries), whereas I was using 10.7v... but are you using 8x4 GWS HD?... if you have an 8x4 APC E that will draw a LOT more than the GWS prop.
AHA!.... that's that it is... the prop! Good observation Dr.Kiwi. I went back and looked at the photo you had on the site and noticed that your prop was more rounded around the edges. I am using a APC prop, which would explain for the discrepency. Given the above information, here are my 2 questions:

1) compared to the GWS prop you are using, how much more thrust do you think I'm getting with my APC? How can I calcuate it?

2) What are the main differences between GWS and APC props?

EDIT: I'm going to have to add a 3rd question on here. I bought this motor for my Bixler FPV since the thrust level is so high... which prop (APC or GWS) would be better suited for my needs if I'm looking to get minimal amp draw with max thrust.?


Thanks in advance.
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Old Sep 26, 2012, 06:19 AM
Jack
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In the test you posted the link to he tested the GWS HD 8 x 4 and the APC E 8 x 6 at 3S voltages and you can see there is a huge difference in the current draw (19.3A versus 36.7A) but also more thrust of course (988g versus 1114g).

The interesting part is the difference in the efficiency, 83% for the GWS and 67% for the APC.

You could probably interpolate numbers and guesstimate the APC E 8 x 4 to have about half of that gain in thrust?

Jack
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Old Sep 26, 2012, 02:32 PM
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Quote:
Originally Posted by A Useless Geek View Post
Yeah, nobody seems to want to stick to the 3.5 watts/gram that is the industry average. Or am I wrong that the mode average power density appears to be on the rise across the board? Isn't everybody producing motors with more oofta these days?
Being cynical... with competition for sales increasing, maybe everyone is simply over-stating their motors' capabilities!

Perhaps I don't do 'em justice.. maybe they are winding better with heavier gauge wire.. and so increasing their motors' ability to cope with higher currents/power.
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Old Sep 26, 2012, 02:39 PM
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Originally Posted by THOMASJONES View Post
AHA!.... that's that it is... the prop! Good observation Dr.Kiwi. I went back and looked at the photo you had on the site and noticed that your prop was more rounded around the edges. I am using a APC prop, which would explain for the discrepency. Given the above information, here are my 2 questions:

1) compared to the GWS prop you are using, how much more thrust do you think I'm getting with my APC? How can I calcuate it?

2) What are the main differences between GWS and APC props?

EDIT: I'm going to have to add a 3rd question on here. I bought this motor for my Bixler FPV since the thrust level is so high... which prop (APC or GWS) would be better suited for my needs if I'm looking to get minimal amp draw with max thrust.?

Thanks in advance.
Give me the RPM for your 8x4 APC E and I can tell you the thrust.

GWS HD appear to be more efficient than APC E in terms of g/W... but one must remember that pitch speed comes into the equation.. many of us feel that the pitch printed on GWS HD props is higher than it really is... e.g. a 7x3.5 is probably closer to 7x2.5, an 8x4 might be only an 8x3..... so though they generate a lot of thrust they'll do so at lower pitch speed than do APC E (where we tend to think the pitch printed on the prop is fairly accurate).
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Old Sep 26, 2012, 07:20 PM
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There is a calculator on FlyBrushless that will give you an estimated thrust based on an RPM.

Follow this link and then select the prop from the list and enter the RPM. It uses the actual test data from the site to find the best fit for the data and uses that to estimate the thrust.

http://www.flybrushless.com/tools/thrustCalc

Robert
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Old Sep 26, 2012, 08:04 PM
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Originally Posted by Dr Kiwi View Post
Give me the RPM for your 8x4 APC E and I can tell you the thrust.

GWS HD appear to be more efficient than APC E in terms of g/W... but one must remember that pitch speed comes into the equation.. many of us feel that the pitch printed on GWS HD props is higher than it really is... e.g. a 7x3.5 is probably closer to 7x2.5, an 8x4 might be only an 8x3..... so though they generate a lot of thrust they'll do so at lower pitch speed than do APC E (where we tend to think the pitch printed on the prop is fairly accurate).
I don't have a gadget that can give me the RPM. I tried counting the RPM's visually and it didn't work ...LOL... Just kidding! What tool should I get to get the RPM? Thanks
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Old Sep 26, 2012, 08:57 PM
Jack
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Originally Posted by THOMASJONES View Post
I don't have a gadget that can give me the RPM. I tried counting the RPM's visually and it didn't work ...LOL... Just kidding! What tool should I get to get the RPM? Thanks
Well, a tachometer of course.

But why set you sights so low? With a eLogger data logger, and the optional brushless RPM sensor and Power Panel LCD display, you can see the RPM, Volts, Amps, Watts, two temperatures, and add optional sensors to see a lot more things too. And you can give it an ride in an airplane (only weights 30 grams or so) and get all that data recorded in flight. And then you can look at it all on a PC later too!

As questions arise, instead of getting tools one at a time for each answer as the questions arise, you can get all the answers all the time and just look at them whenever you want.

Jack
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Old Sep 27, 2012, 06:31 AM
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Originally Posted by THOMASJONES View Post
I don't have a gadget that can give me the RPM. I tried counting the RPM's visually and it didn't work ...LOL... Just kidding! What tool should I get to get the RPM? Thanks
This is the one I've always used: http://www3.towerhobbies.com/cgi-bin...P?I=LXPT32&P=8
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Old Sep 28, 2012, 10:27 AM
just Some Useless Geek
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...maybe they are winding better with heavier gauge wire.. and so increasing their motors' ability to cope with higher currents/power.
I am wondering if there isn't a rising tide floating all boats; that is, the industry overall is going to better magnets, better wire, better bearings, better coil winding machines, etc. Remember how totally craprodica those E-max motors used to be? Now people are telling me they have their act together with motors that will actually last more than a week. Could be, but I'm not risking any of my money to discover the truth of it.

Anyway, we need to gather empirical data somehow to validate the longevity of some of the wilder P/W ratio claims. For instance, if these EDF motors can really produce 8W/g continuous then somebody must be running them as such and can verify that they do this. Otherwise I'm thinking that a call of bologna (see, censors? See? I'm proper.) is not out of order.
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