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alienx
04-24-2007, 08:26 PM
I am a big fan of APC slow-flyer props. But you need a Kv below 1000 or so (in most of my cases anyway). I've been swapping a motor or two for some higher RPM Chinese motors, but this is forcing me to use the "E" props. I just don't like the flight characterisitcs I get with them. I guess I should mention that I am scale-minded, and even my warbirds feel better with a slo-flyer on them than an APC E.

What I am learning though is that I must be in the minority because when I started to look around for a motor for a new plane I want, there were VERY FEW motors with a Kv below 1000. I guess I am trying to understand why?

Certainly, there are two ends to the motor/prop spectrum. Why is the choice of motors that can turn a big, slow prop so limited?

The e-flite Park 480 (lower Kv one), and the AXI 2217/20 seem to be the only two motors that make around 200-250 watts and spin slow enough to turn a SF prop. I looked at Hacker too (and Scorpion), and there just don't seem to be any options there.

Any opinions??

Dr Kiwi
04-24-2007, 08:57 PM
I'm guessing that it is difficult to get enough turns into a small motor, to obtain a low Kv. You'd have to use a lot of very fine gauge wire, so resistance would increase and efficiency would suffer. To wind a "hot" motor you might use only 6 turns of very thick wire - that's a very different story.

The Axi 2212/34 is 740Kv, there is a Himaxx at 650Kv [but neither of 'em can do 200+W]. You a right - small/medium low Kv motors are hard to come by!

Once you get into really big motors low Kv is a breeze!

alienx
04-24-2007, 09:27 PM
I'm guessing that it is difficult to get enough turns into a small motor, to obtain a low Kv. You'd have to use a lot of very fine gauge wire, so resistance would increase and efficiency would suffer. To wind a "hot" motor you might use only 6 turns of very thick wire - that's a very different story.

The Axi 2212/34 is 740Kv, there is a Himaxx at 650Kv [but neither of 'em can do 200+W]. You a right - small/medium low Kv motors are hard to come by!

Once you get into really big motors low Kv is a breeze!

Excellent! That is very insightful.

So is there any motor in the slightly below 1000 Kv that I might be able to check out? I don't think I need to go down to 600-700. I just hoped to stay away from anything over 1000.

Let me ask another question too. Let's say I have a particular motor that makes 200 watts while pulling 15 amps using a 9x6SF prop. If I swap to an APC E prop that makes exactly the same numbers, but takes maybe a 10x8E to do it, what happens to the flight characteristics???

I guess I am trying to decide if it is the prop or the RPM that I don't like.

Thanks. Andy

skiman762
04-24-2007, 10:41 PM
Here's the limits

apc slowfly props 65000/prop dia= max rpm
apc glow and thin electric props 190000/prop dia=max rpm

skiman762
04-24-2007, 10:49 PM
Andy
At least your trying something that only cost a few dollars
I don't have anything using slow fly props anymore if you do the math on max rpm for a 10 inch props it's 6500 rpm your looking at a 1000kv motor on a 2s lipo
I have always said props are like voodoo magic they never seem to make sense that's why most people in the hobby have a big collection

paranoia
05-02-2007, 01:27 AM
that's why we have gearboxes.....

get a inner at say 2500 rpm/v and run it on 6.6:1 gearbox

that's ~379rpm/v :) is the slow enough?

so on 11.1 that's 4207rpm :)


or you could try other ratios....... There are alot of nice gearboxs with changable gears out there.



or you could just power back.




ps when you are flying with a ‘slow prop’ with a powerful motor and you start exceeding the props rpm limit they make a loud humming. Then you just bring the power back until the humming stops….

alienx
05-02-2007, 02:02 AM
Sorry guys. I'm not getting any email notices anymore for some reason.

I think I really am at the point where I am going to have to make a thrust stand. You juts can't tell the difference in performance between props with a watt meter alone (specially different brands or types!).

Thanks for the feedback.

ron_van_sommeren
05-02-2007, 06:12 PM
You wanted low Kv? Low Kv is what you're going to get :D
http://groups.yahoo.com/group/lrk-torquemax/messages/10836?o=0&xm=1&l=1 --> message #10836 "larger motors"



Excellent motor building articles by Brian Mulder, a must read, will prevent you from asking a lot of questions you even did not know you were going to ask ;) ;)
http://www.southernsoaringclub.org.za/
-> Articles by SouthEasterners.
-> Electric Motors - part 1-5

Do-it-yourself motor homepages, manuals/tutorials, checks and tests in this motor builders tips and tricks thread. The checks and tests may save you from frying your controller or motor. Thread is active, bookmark it for future reference and subscribe to it:
http://www.rcgroups.com/forums/showthread.php?t=240993 (sticky thread, at top of subforum)

Two instructive motor winding/assembly videos, 14 & 10Mbyte respectively.
http://www.utahflyers.org/
-> Motor Winding #1 & #2


Vriendelijke groeten ;) Ron
• diy motor building tips & tricks (http://www.rcgroups.com/forums/showthread.php?t=240993)
• diy brushless motor discussion group (http://www.yahoogroups.com/group/lrk-torquemax)
• Drive Calculator (http://www.yahoogroups.com/group/D-calc/) download & discussion group
• int. E fly-in & diy outrunner meet (http://home.hetnet.nl/%7Eronvans/), Aug.26 2007, Nijmegen, the Netherlands

Kiiski
05-02-2007, 10:27 PM
Take a look at the Hyperion Z-3013-16, 985 Kv, 2-3 cells 27 amps. Bishop power products has them.
Kiiski

mysticplayer
05-03-2007, 12:06 AM
Really enjoying the Rimfire 35-30-950 on 3s for my Formosa I. Certainly in the power range you are looking for and this is a very well built motor.

It come with a 1/4" prop adapter so not really SF prop friendly. Not sure if you can get a prop save attachment to work. I have run GP and APC SF props on this motor by opening up the hub.

Jerry

alienx
05-03-2007, 12:33 AM
Really enjoying the Rimfire 35-30-950 on 3s for my Formosa I. Certainly in the power range you are looking for and this is a very well built motor.

It come with a 1/4" prop adapter so not really SF prop friendly. Not sure if you can get a prop save attachment to work. I have run GP and APC SF props on this motor by opening up the hub.

Jerry
I'll check these out. Thanks guys.

I thought the 4mm shaft on my eflite's were 1/4" on the output side of the adapter?? I could be wrong.

flieslikeabeagle
05-03-2007, 11:16 PM
This issue (excessive Kv) is one of the reasons why I think the widespread adoption of outrunners has been a bit of a step backwards for our hobby in some ways.

It's not just being unable to use Slow Flyer props - excessive Kv forces you to use propellers that are smaller than optimal on many models. Small propellers are less efficient than big ones operating at the same power level. A propeller operating at only 50% efficiency because it is too small is throwing away 20% of the power from the motor. If you had a bigger propeller operating at 70% efficiency you could get that 20% back.

I agree with Paranoia - gearboxes still have their place. Outrunners are convenient, but in many cases gearing down and using a bigger propeller will provide substantially better performance.

I'm no expert on outrunners, but I do know Maxwells equations that describe all electromagnetic phenomena (including electric motors). To lower Kv, you either need more turns of wire, a stronger and bigger magnetic field, or more poles. None of these options are very practical in a small motor. So I don't think we will see extremely low Kv small outrunners with good efficiency any time soon.

Of course, gearing down an outrunner with a gearbox can be an interesting way to get really low effective Kv. ;)

I have a Slow Stick with a 13x9 propeller spun by an Astro 010 geared about 7:1 at only about 70 W full throttle. Performance is stronger than some Slowsticks with 100 W but only a 9" prop.

A flying buddy experimented with a similar setup geared even deeper using gears from a small GWS helicopter. His Astro 010 swung a 15" prop on his Slow Stick. Top speed was limited, but performance was phenomenal - his SS accelerated to full speed in a heartbeat and would go full speed in any direction including straight upwards. With a 15" prop and no ailerons, torque reaction was also extreme. I think my friend found the upper limit to practical prop size on an overpowered SS with his experiment!

No real mystery here, a look at the Froude equations for propellers tells you that a big prop gently accelerating a large volume of air is more efficient than a small prop violently accelerating a small volume of air.

-Flieslikeabeagle

alienx
05-04-2007, 05:33 AM
I guess intuitively, that's exactly why I want the lower KV direct drives. Just not too many out there for the reasons you guys point out.

Bill G
05-04-2007, 05:59 PM
I'm guessing that it is difficult to get enough turns into a small motor, to obtain a low Kv. You'd have to use a lot of very fine gauge wire, so resistance would increase and efficiency would suffer. To wind a "hot" motor you might use only 6 turns of very thick wire - that's a very different story.

The Axi 2212/34 is 740Kv, there is a Himaxx at 650Kv [but neither of 'em can do 200+W]. You a right - small/medium low Kv motors are hard to come by!

Once you get into really big motors low Kv is a breeze!
That pretty much sums it up. Folks look at the power ratings, and find that the higher kv motor in the same motor size has more power. Most folks being POWER freaks::o , they buy it, whether whether they need it or not.

Bill

tom1968
05-04-2007, 07:13 PM
Here's what I have in my database of mostly smaller motors:
Brand Model Kv Amps
<TABLE style="WIDTH: 209pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=278 border=0 x:str><COLGROUP><COL style="WIDTH: 75pt; mso-width-source: userset; mso-width-alt: 3657" width=100><COL style="WIDTH: 73pt; mso-width-source: userset; mso-width-alt: 3547" width=97><COL style="WIDTH: 28pt; mso-width-source: userset; mso-width-alt: 1353" width=37><COL style="WIDTH: 33pt; mso-width-source: userset; mso-width-alt: 1609" width=44><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; WIDTH: 75pt; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" width=100 height=17>MP Jet</TD><TD class=xl31 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; WIDTH: 73pt; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" width=97>AC 28/7-35D</TD><TD class=xl30 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; WIDTH: 28pt; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" width=37 x:num>950</TD><TD class=xl30 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; WIDTH: 33pt; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" width=44>8-12</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>Hacker</TD><TD class=xl32 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent">A20-22L</TD><TD class=xl32 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" x:num>924</TD><TD class=xl32 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent">6-19</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>Electrifly</TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">28-30-750</TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent" x:num>750</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent"></TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17></TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">28-30-950</TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent" x:num>950</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent"></TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17></TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">35-30-950</TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent" x:num>950</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent"></TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>Esskay</TD><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff">400XT</TD><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff" x:num>950</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" x:num>10</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17></TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent">450XT</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" x:num>950</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent">13-16</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; HEIGHT: 12.75pt; BACKGROUND-COLOR: #ccffff" height=17>Dualsky</TD><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff">XM2826CA-18T</TD><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff" x:num>980</TD><TD class=xl28 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff">10-14</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17> </TD><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff">XM2830CA-12T</TD><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff" x:num>980</TD><TD class=xl28 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff">13-17</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17> </TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">XM3536CA-8T</TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent" x:num>990</TD><TD class=xl26 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">21-32</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17> </TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">XM3536CA-9T</TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent" x:num>890</TD><TD class=xl26 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">20-30</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17>TowerPro</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent">BP-12Y</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" x:num>790</TD><TD class=xl24 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" x:num>9</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; HEIGHT: 12.75pt; BACKGROUND-COLOR: #ccffff" height=17>Emax</TD><TD class=xl29 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: yellow">CF2822</TD><TD class=xl27 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff" x:num>950</TD><TD class=xl28 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver 0.5pt solid; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: #ccffff">12</TD></TR><TR style="HEIGHT: 12.75pt" height=17><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver 0.5pt solid; BORDER-BOTTOM: silver 0.5pt solid; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" height=17> </TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">2215/22</TD><TD class=xl25 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent" x:num>800</TD><TD class=xl26 style="BORDER-RIGHT: silver 0.5pt solid; BORDER-TOP: silver; BORDER-LEFT: silver; BORDER-BOTTOM: silver 0.5pt solid; BACKGROUND-COLOR: transparent">15</TD></TR></TBODY></TABLE>

A number of these will pull 200W in bursts of 30 seconds with no trouble, and a couple will run at 200-250W all day. Admittedly "a couple" of low-Kv 200W motors is still not a lot - but we just need one or two good ones really.

Dr Kiwi
05-04-2007, 07:16 PM
But a higher Kv motor can only handle the same amount of power (W) as a lower Kv version of the same motor [since they weigh the same and are the same physical size, their ability to dissipate waste heat will be exactly the same] - the only difference is that the higher Kv one can cope with higher amps (but to keep within the max watts limit, it would need to be run at lower voltage).

If both motors are 200W max - the high Kv one might manage 28A @ 7v, while the low Kv can do 20A @ 10v.

alienx
05-04-2007, 07:26 PM
But a higher Kv motor can only handle the same amount of power (W) as a lower Kv version of the same motor [since they weigh the same and are the same physical size, their ability to dissipate waste heat will be exactly the same] - the only difference is that the higher Kv one can cope with higher amps (but to keep within the max watts limit, it would need to be run at lower voltage).

This is exactly my problem. I have a couple Chinese 1150kv (or so) and they can draw about 20 amps versus my Park 450, which is 14 amps. But they both make reasonable close to the same power.

That's why I think I need a thrust stand because I can't tell how much actual power I am making with these smaller size, thinner bladed, E props vesus the Slow Flyers.

tom1968
05-04-2007, 09:08 PM
I hate to argue with Dr. Kiwi who has taught me a lot - but isn't it true that the electrical power that is turned to heat in the motor depends on current, not voltage, and so isn't just a function of the watts? Power dissipation is the P=I^2*R formula. That's why motor manufacturers rate their motors for max amps, not watts. I believe the high Kv motors are rated for higher current mainly because they use a thicker wire with lower resistance and therefore turn less of their input power into heat to start with.

So a high Kv motor turns less power into heat, so more power goes to the prop - but then you're turning a smaller prop and you lose all that efficiency again.

Pretty soon I'll be talking myself into buying inrunners and gearboxes...not going there :)

alienx
05-04-2007, 09:33 PM
I hate to argue with Dr. Kiwi who has taught me a lot - but isn't it true that the electrical power that is turned to heat in the motor depends on current, not voltage, and so isn't just a function of the watts? Power dissipation is the P=I^2*R formula. That's why motor manufacturers rate their motors for max amps, not watts. I believe the high Kv motors are rated for higher current mainly because they use a thicker wire with lower resistance and therefore turn less of their input power into heat to start with.

So a high Kv motor turns less power into heat, so more power goes to the prop - but then you're turning a smaller prop and you lose all that efficiency again.

Pretty soon I'll be talking myself into buying inrunners and gearboxes...not going there :)


I feel like I just chugged a whole Slurpee!::o

Bill G
05-08-2007, 09:26 AM
But a higher Kv motor can only handle the same amount of power (W) as a lower Kv version of the same motor [since they weigh the same and are the same physical size, their ability to dissipate waste heat will be exactly the same] - the only difference is that the higher Kv one can cope with higher amps (but to keep within the max watts limit, it would need to be run at lower voltage).

If both motors are 200W max - the high Kv one might manage 28A @ 7v, while the low Kv can do 20A @ 10v.
According to some of the ratings, some show different total power capabilities with different winds of the same motor series number. Then again, I don't trust anyone's ratings very far.


Bill

flieslikeabeagle
05-08-2007, 10:55 AM
But a higher Kv motor can only handle the same amount of power (W) as a lower Kv version of the same motor [since they weigh the same and are the same physical size, their ability to dissipate waste heat will be exactly the same]
I'm not sure this is true. I agree with the second part - same physical dimensions equals the ability to dissipate the same amount of heat. But it seems the higher Kv motor almost always has higher efficiency due to the lower winding resistance - and that changes the amount of power needed to generate the same amount of heat in the two motors.



As an example, consider two motors of the same physical size, a low Kv one at 80% efficiency, and a higher Kv one at 85% efficiency. If you were to put 100W of power into each motor, the first one would turn 20W of that power into heat. The second would turn only 15W of that power into heat. That doesn't seem like much of a difference at first sight.

However, if both motors were capable of dissipating, say, 40 actual watts of heat, the first one would be at its limit with 200W of input power, 40 W of heating, and the remaining 160 W to the propeller. The second motor would be at its limit with 266.67 watts of input power, 40 W of heating, and 226.7 W of power to the propeller.

Imagine that - a 5% change in efficiency allows the higher Kv motor to put 67 more watts into the propeller while dissipating the same amount of heat. That is almost a 42% power increase!

There's a reason many people are willing to pay for Steve Neu's motors. A few percent increase in motor efficiency can make a big difference to the amount of power you can put to the propeller. As motors approach 100% efficiency this effect is more and more striking. After all, a 100% efficient motor could handle an infinite amount of power...which is infinitely more power than a 99% efficient motor can!

We're not likely to see 99% efficient motors anytime soon, or 100% efficient motors ever, but as you can see, the effect is quite strong even at typical 80% - 85% efficiencies which are quite achievable by good brushless motors used in our hobby today.

-Flieslikeabeagle

flieslikeabeagle
05-08-2007, 11:00 AM
Pretty soon I'll be talking myself into buying inrunners and gearboxes...not going there :)
I never stopped buying inrunners and gearboxes - at least at power levels and sizes that will fit into GWS gearboxes. The plastic GWS gearboxes are light enough to not take away the weight advantage of inrunners, and the efficiency gains from lowering the Kv and using a big prop are too big for me to throw away all the time.

I do use small outrunners on some models for convenience, but I always feel a little twinge of shame when I do. :)

When the power level and motor size goes beyond what will fit in a GWS gearbox, things start to look a bit different. The bigger outrunners can be had with lower Kv, while bigger gearboxes tend to be all-metal, heavy, and expensive. So at some point in the size continuum the outrunner starts to look pretty good, and the advantages of the inrunner are not so pronounced any more.

-Flieslikeabeagle

Dr Kiwi
05-16-2007, 02:53 AM
I'm not sure this is true. I agree with the second part - same physical dimensions equals the ability to dissipate the same amount of heat. But it seems the higher Kv motor almost always has higher efficiency due to the lower winding resistance - and that changes the amount of power needed to generate the same amount of heat in the two motors.



As an example, consider two motors of the same physical size, a low Kv one at 80% efficiency, and a higher Kv one at 85% efficiency. If you were to put 100W of power into each motor, the first one would turn 20W of that power into heat. The second would turn only 15W of that power into heat. That doesn't seem like much of a difference at first sight.

However, if both motors were capable of dissipating, say, 40 actual watts of heat, the first one would be at its limit with 200W of input power, 40 W of heating, and the remaining 160 W to the propeller. The second motor would be at its limit with 266.67 watts of input power, 40 W of heating, and 226.7 W of power to the propeller.

Imagine that - a 5% change in efficiency allows the higher Kv motor to put 67 more watts into the propeller while dissipating the same amount of heat. That is almost a 42% power increase!

There's a reason many people are willing to pay for Steve Neu's motors. A few percent increase in motor efficiency can make a big difference to the amount of power you can put to the propeller. As motors approach 100% efficiency this effect is more and more striking. After all, a 100% efficient motor could handle an infinite amount of power...which is infinitely more power than a 99% efficient motor can!

We're not likely to see 99% efficient motors anytime soon, or 100% efficient motors ever, but as you can see, the effect is quite strong even at typical 80% - 85% efficiencies which are quite achievable by good brushless motors used in our hobby today.

-Flieslikeabeagle


This would have been my argument - but then I read something from Steve Neu himself! Why does the very reputable Medusa Research show exactly the same max watts limit for every wind/Kv of motor in each size series????

watt_the?!
06-09-2007, 10:02 PM
I hate to argue with Dr. Kiwi who has taught me a lot - but isn't it true that the electrical power that is turned to heat in the motor depends on current, not voltage, and so isn't just a function of the watts? Power dissipation is the P=I^2*R formula. That's why motor manufacturers rate their motors for max amps, not watts. I believe the high Kv motors are rated for higher current mainly because they use a thicker wire with lower resistance and therefore turn less of their input power into heat to start with.

So a high Kv motor turns less power into heat, so more power goes to the prop - but then you're turning a smaller prop and you lose all that efficiency again.

Pretty soon I'll be talking myself into buying inrunners and gearboxes...not going there :)

Seems like this thread is going a little bit off on a tnagent and talking about high V versus Low V setups.

remember that not only does P= I^2*R, its also P=IV. One of the RC myths has revolved around purely dropping I as people have incorrectly correlated drop in performance with high relative (relative to their ESC and battery setup) current. Their fix has been to step up their voltage which of course allows I to come down and all of a sudden their system runs cool and doesnt bog. This is more to do about their setup now being relatively oversized for their new parameters than any form of "efficiency" gain. If one were to compare apples, their new higher V setup with lower Amps would now need less battery mah and a lower amp ESC to have the same ''relative'' overheads that their original setup had. Then when the comparison is done theyd find the same relative power losses as before...ignoring the new losses that would be inherent in this different setup of course.

Thats why its erroneous to consider just amps as the driving factor- and thats why it depends on Power. Which is expressed via Ohms law. The losses are more to do with other factors like the stress ratio of the electrical and electronic components (the actual load versus the rated load).

SPeaking on that also- a component's actual rated capacity may vary from that marketed by the manufacturer....unless you can get a bill of materials from the PCB design youll never actually now. It's good practice to derate your product either in design or via marketing so it will run efficiently and for a long time. However the penalty is that higher rated components cost more.

This is why i think that the term ''Quality" is subjective in RC as it is referred to more as an item's ability to operate and keep operating than actual ''Quality''- which is virtually impossible for the user to make judgement on. Its more a process and organisation related characteristic.

An example to me would be that users often report product types like Axi and Mega as being able to run at significantly higher ratings than they are marketed as....how could this be?...i mean a rating is supposed to describe an item's cieling- not to be passed...or it will fail.. at least thats the industry and engineering definition as this is essential in parts selection for design by engineers.

but in RC its different- i have no doubt. You can run certain items WAY over their rating because their marketed rating is much lower than their real, component rating.

oh ok i see im now going OT...bit of a pet subject of mine..brought about one day when i was at the field and questioned a high V setup and was virtually laughed at by other pilots as to why i ''didnt seem to get it''...yet it was so simple for them that a drop in current = better performance...

flieslikeabeagle
06-11-2007, 09:01 AM
Why does the very reputable Medusa Research show exactly the same max watts limit for every wind/Kv of motor in each size series????
Dr Kiwi, I have no answer for you other than (a) advertising and marketing rarely make any logical sense, and (b) physics and thermodynamics trump advertising and marketing any day. :D

In other words, I don't think there's much doubt about the science. As to why Medusa chose a one-size-fits-all policy, I have no idea, and honestly, I don't care a whole lot!

I'm curious as to your comment re Steve Neu - what did the motor maestro himself have to say?


-Flieslikeabeagle

qmulus
06-13-2007, 07:45 PM
FWIW, I use a Rimfire 35-30-950 in my E-Flite Mini Pulse XT with a 10x8 Master Airscrew prop. They rate it at 296W constant (20A constant, 28A max). Here in Denver it pulls a static 17A at full throttle with a 3S 2100mAh Lipo with the MA 10x8. So far, I really like the performance and flight times average about 20 minutes, with lots of full throttle.

A 10x7 APC SF prop bolts on to the included prop adapter with no issues, but I haven't flown with it or checked power.

alienx
06-13-2007, 08:10 PM
I have that motor. I made about 250 watts with an APC 10x7SF and drew nearly 22 amps. I down propped to a 10x4.7SF and now only draw about 18 amps and make 220 or so watts. My particular plane flys great on both. I can usually tell the difference with the smaller pitch down-propping, but in this case, it doesn't really seem "underpowered."

My motor get's pretty hot. How about yours?? Another thing is that it makes some terrible noise at two distinct spots around half throttle. Imagine if the electric motor had pistons and connecting rods and it broke one of the rods!! It is loud enough to hear at altitude and make me power up or power down to get out of that spot in the throttle curve. I can't say if it is the motor or maybe something else like the ESC, but it is something I am going to have to figure out!

Otherwise, I think I like the motor. ertainly fits the kV range I was after.

qmulus
06-13-2007, 10:39 PM
I haven't noticed excessive noise or heat with mine, but then mine isn't very accessible, so unless I take off the spinner and cowl I can't touch the motor. What plane are you flying?

I may try the 10x7SF and see how that compares to the 10x8 Master Airscrew. I've liked the performance of other APC SF props compared to the MAs in my trainer, but I liked the way the MPXT flew with the MA prop so much that I haven't done any experimentation yet. Due to the altitude at our field, I will be drawing less static current than you will be in NJ.

alienx
06-13-2007, 11:33 PM
I haven't noticed excessive noise or heat with mine, but then mine isn't very accessible, so unless I take off the spinner and cowl I can't touch the motor. What plane are you flying?

I may try the 10x7SF and see how that compares to the 10x8 Master Airscrew. I've liked the performance of other APC SF props compared to the MAs in my trainer, but I liked the way the MPXT flew with the MA prop so much that I haven't done any experimentation yet. Due to the altitude at our field, I will be drawing less static current than you will be in NJ.
I have it in a hobby lobby Super Miss. Some of my heat may be coming from something rubbing in the motor I guess!?

I tested a few MAS props on different planes, and I always prefer the APC SF's to them (and to the APC E's too). If you can keep your amps to around 20, I think you will be very happy with the APC, especially because you seem to feel the same as I do about the choices.

To be honest, the 10x7 wasn't so high an amp draw'er on my plane that I would have down-propped, I was just worried about the hot motor. My battery and ESC are only mildly warm.

Let me know how you make out!

Andy

qmulus
06-14-2007, 03:03 AM
Well, looking at the Super Miss on HL's site, it looks like there is no cooling provided for the motor. When you are pulling that much current, you are going to be generating a fair amount of heat, which needs to be dissipated by some air flow.

As for the noise, have you verified the balance of the prop? An out of balance prop will resonate at different RPMs, causing a fair amount of noise and vibration. IME, the APC props tend to be pretty good straight out of the bag, but I still have needed to do a little work to balance them, though not as much as the MAs. You would be amazed at what just a tiny bit of imbalance will do.

There was a little more wind than I was comfortable to fly my Mini Pulse in today, but if it is nice tomorrow, I will give the 10x7 SF a try.

alienx
06-14-2007, 03:14 AM
As for the noise, have you verified the balance of the prop? An out of balance prop will resonate at different RPMs, causing a fair amount of noise and vibration. IME, the APC props tend to be pretty good straight out of the bag, but I still have needed to do a little work to balance them, though not as much as the MAs. You would be amazed at what just a tiny bit of imbalance will do.



I do balance the props as best I can tell. I have one of those magnet balancers.

Matt Kirsch
06-14-2007, 05:28 PM
Is the noise a sort of screeching sound? That's a timing issue. Check all your connections and make sure they're clean, bright, and tight. If the ESC has adjustable timing settings, try one that's different from the one you have now.

alienx
06-14-2007, 05:40 PM
Is the noise a sort of screeching sound? That's a timing issue. Check all your connections and make sure they're clean, bright, and tight. If the ESC has adjustable timing settings, try one that's different from the one you have now.No, it really does sound like a magnet or somethign metal fell off on the inside and is being hammered by the other parts.

I'm going to swap the ESC (sooner or later) and try to rule that out.

mysticplayer
06-14-2007, 06:01 PM
alienx, as you know I am using this outrunner too and in a mosa. Not running the power it should but that's a pack problem (other post).

I took my spinner off so that the air flows directly into the motor can. 1 1/4" hole. There are also venting from under the cowl into the plane to cool the batt/ESC as well as a bottom vent to ensure all that hot air can get out.

When the plane is throttled up, you can feel the warm air blowing back.

Now that the summer temps are here. I have added another vent in the cowl. This really helps keep things cool. Have expanded the air inlets to both the batt and ESC too. Now have a look at the cowl exits.

I read somewhere that even with vent holes in the cowl, unless the air is allowed to circulate or directed to/through/over the motor/engine, it will not be affective. Also, the venting out of the cowl must be several times larger then the inlet due to hot air expanding/better circulation - slight vacuum drawing in more cold air.

If the motor can is hot to the touch, the windings inside are burning up. Not good for long life or power production.

Jerry

alienx
06-14-2007, 06:10 PM
My plane is tail heavy by 2oz. I think I am going to put the motor in front of the firewall. This will let me move the battery up another inch or more as well. Hopefully, that solves a couple problems. This one is just a little tricky because the canopy wraps around the front of the nose over the firewall. It took me a while to figure out how to mount the battery and still be able to get to it. One good thing is I have 4 landings (and one ROG) and it has not nosed over on me yet! Short of that, I have to cut a lot of holes in it.

violind
06-15-2007, 04:13 AM
Wait till high temperature superconducting wire is available, the motor heating problem will be solved.

B.L.E.
06-15-2007, 01:45 PM
No it won't be solved. We would still need zero hysteresis iron to eliminate hysteresis losses and also non conducting iron to eliminate eddy currents in the stator laminations.
Winding resistance is only one of a motor's losses.

alienx
06-15-2007, 02:13 PM
No it won't be solved. We would still need zero hysteresis iron to eliminate hysteresis losses and also non conducting iron to eliminate eddy currents in the stator laminations.
Winding resistance is only one of a motor's losses.
I was gonna say that!

Bill G
06-15-2007, 10:28 PM
Is the noise a sort of screeching sound? That's a timing issue. Check all your connections and make sure they're clean, bright, and tight. If the ESC has adjustable timing settings, try one that's different from the one you have now.
Check for cold solder jobs too, on the motor connectors. Make sure one of them dosen't bust off,:eek: like what happened to me the other day.::o

Why no low kv?
My LHS says their convinced many folks just think bigger is better, and go for the larger numbers.

dcs191919
06-16-2008, 07:58 PM
I have been running a park 480 1020kv on a 3s 2100mah. The prop is 12 x 3.8 slow flyer. The safe speed is 5,416 rpm. I have been turning them at 10,000+ with no problems.... Didnt know about the rpm limitations????

flieslikeabeagle
07-07-2008, 06:05 AM
I have been running a park 480 1020kv on a 3s 2100mah.
<snip>
The safe speed is 5,416 rpm. I have been turning them at 10,000+ with no problems..
5416 rpm is safe for what? :confused:

It can't be the motors rpm limit, certainly. A motor with a Kv of 1020 rpm running on a 3S lipo pack at 10.5 V (typical voltage freshly charged at full load) will reach an rpm (with no load on the motor) of approximately 1020 x 10.5, or 10710 rpm. Since the Park 480 is designed to be quite capable of running on 3S lipo, it most certainly has been designed to be safe at well over 10000 rpm.

Under load the motor will drop to 75% - 80% of the unloaded rpm, but even this will be in excess of 7500 rpm, still well over 5416 rpm.

-Flieslikeabeagle

qmulus
07-07-2008, 04:54 PM
5416 rpm is safe for what? :confused:

It can't be the motors rpm limit, certainly. A motor with a Kv of 1020 rpm running on a 3S lipo pack at 10.5 V (typical voltage freshly charged at full load) will reach an rpm (with no load on the motor) of approximately 1020 x 10.5, or 10710 rpm. Since the Park 480 is designed to be quite capable of running on 3S lipo, it most certainly has been designed to be safe at well over 10000 rpm.

Under load the motor will drop to 75% - 80% of the unloaded rpm, but even this will be in excess of 7500 rpm, still well over 5416 rpm.

-Flieslikeabeagle

That would be safe RPM for an SF prop; the motor is not the issue. From APC's website http://www.apcprop.com/html/rpm_limits.html (http://www.apcprop.com/html/rpm_limits.html):

Maximum RPM=65,000/prop diameter (inches)

I personally had two slow fly props fail when I tried to spin them too (way) fast. One lasted two flights before it cracked at the root, the other came apart on take-off.