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Geoff_Gino
11-09-2005, 06:54 AM
Hi All

I have just completed a Phoenix Rainbow 60" ARF and I will be powering it with an Axi 2814/10 motor using a 35 amp CC ESC and a 3,5 Amp LiPo.
Having trouble choosing the correct prop to limit my current draw to 30 Amps. Recommended prop is a 9,5"x5.
Is anyone using a similar setup on a plane weighing 1,9 Kgs.

Geoff

qban_flyer
11-09-2005, 11:03 AM
Hi All

I have just completed a Phoenix Rainbow 60" ARF and I will be powering it with an Axi 2814/10 motor using a 35 amp CC ESC and a 3,5 Amp LiPo.
Having trouble choosing the correct prop to limit my current draw to 30 Amps. Recommended prop is a 9,5"x5.
Is anyone using a similar setup on a plane weighing 1,9 Kgs.

Geoff

Say Geoff,

Why don't you e-mail L.A. Johnston at Hobby Lobby? He's their Sr. Tech and if anyone can answer your question he is the one.

Mike Parsons
11-09-2005, 02:56 PM
Geoff,
A great site that has blazed the trail on some of the most popular setups is http://www.flyingmodels.org. Click on the "Great Electric Motor Test".
Or you can download the PDF version http://www.flyingmodels.org/motortest/pdf/TheMotortest_5.pdf

Are you using 10 cells or 3S?

They

Matt Kirsch
11-09-2005, 03:34 PM
According to www.modelmotors.cz (http://www.modelmotors.cz), AXi's website, you would be drawing 27 Amps on a 7-cell NiMH or a 2S LiPoly. If you're running a 3S LiPoly, the current will be roughly proportionallly higher, around 35 Amps. You'll need to drop down in prop size to get the draw to 30 Amps.

AXi's website shows an 8.5x6 drawing only 22.5 Amps on a 2S LiPoly. Again, going to a 3S will increase the current roughly proportionally, so it'll be right around that target of 30 Amps you're shooting for.

batman
11-09-2005, 08:06 PM
I don't think that motor will be enough for that plane. I have one of those motors and 60 inch span will probably be too much for it. Tho I am not familiar with the plane I would imagine that there will not be enough power to fly it.

Geoff_Gino
11-10-2005, 05:43 AM
Hi All

Thanks for the replies.

Mike
The chart at Flying Models suggests a 9,5"x5 with 10 cells, however I have fitted a 3S LiPo. Last night I fitted an 8,5"x6 and had to limit my throttle travel to 20% to stay at 35 Amps. This gave 2 lbs thrust and the AUW is 1,6 kgs. Perhaps I should go for a 2S Lipo or try a 10"x4. 2 lbs of thrust should fly 1,6 kgs without a problem.

Any more thoughts.
Geoff

Geoff_Gino
11-11-2005, 05:59 AM
I don't think that motor will be enough for that plane. I have one of those motors and 60 inch span will probably be too much for it. Tho I am not familiar with the plane I would imagine that there will not be enough power to fly it.

Hi All

Tried various props last night and this is what I came up with:-

Plane:- Phoenix Rainbow 60"
AUW:- 1,6 kgs
Motor:- Axi 2814/10 (recommended on the box)
ESC:- CC 35 Amp
Batt:- 3S1P 3,5 Ah

Prop I settled for is 10"x4 which gave me 1,05 Kgs of thrust and draws 34 Amps.

A little bit worried that I had to set my throttle travel to 33% on my Tx to stay below 35 Amps. :confused:

Any thoughts?
Geoff

Matt Kirsch
11-11-2005, 01:34 PM
Don't forget that each time you unplug the battery from the ESC, it "forgets" the throttle ATV (EPA, depends on the transmitter what it's called) setting on your transmitter. The next time you plug it in, it auto-calibrates to whatever the throttle is set at on your transmitter. You would have to reset your throttle ATV (EPA) to 100%, plug the battery into the controller, reset your throttle ATV back to 33% without unplugging the plane, and THEN go flying. What a pain in the butt...

Limiting throttle to limit current draw is a bad method anyway. ESCs operate on a simple ON/OFF cycle. The current is either on at "full throttle" or off, and it does this thousands of times per second. What you're reading at the battery is the average current draw, but if you could slow down time, you'd see that the momentary current draws are the same as the "full throttle" current, perhaps even higher.

What I'm getting at is that rather than burning up your ESC in one fell swoop, you're causing "death by 10000 cuts" so to speak. It's slowly burning up a millisecond at a time. You need to set your peak current at full throttle.

That said, your prop is too big. Way too big. Way way way too big... The bigger the prop is, in diameter OR pitch, the more current the motor will draw. You need to go smaller, much smaller, to get it to where you can go to 100% throttle and keep the Amps within your 30-35 Amp target.

Matt Kirsch
11-11-2005, 01:43 PM
What worries me is that you're getting higher-than-expected current draws. That tells me one of two things:

1. There's something wrong with the motor.
2. You're operating beyond the motor's physical limitations.

ModelMotors.cz claims that this motor can handle a 3S LiPoly, but they don't show any 10-cell or 3S LiPoly applications in their chart. That could very well be because the motor doesn't deal well with the higher RPMs and loses a LOT of efficiency.

Geoff_Gino
11-11-2005, 02:22 PM
Hi Matt

Thanks for your replies.
Wow confusion reigns supreme at the moment. The Axi 2814/10 is what is reccommended by the plane's manufacturer and I bought the ESC to match.
I am now worried that I am doing something wrong as the smaller props were giving me consistantly higher current draws, and what you say is true. I need a smaller prop.
With an 8,5"x6 prop I was drawing 32 amp with only 650 grams of thrust, but that is understandable because it is a smaller prop and I am worried that it will not fly well with 650 grams.

Geoff

FinnFlyer
11-11-2005, 03:08 PM
Try an 8x6, that is what I run on my 28/14/10.

qban_flyer
11-11-2005, 03:32 PM
Hi Matt

Thanks for your replies.
Wow confusion reigns supreme at the moment. The Axi 2814/10 is what is reccommended by the plane's manufacturer and I bought the ESC to match.
I am now worried that I am doing something wrong as the smaller props were giving me consistantly higher current draws, and what you say is true. I need a smaller prop.
With an 8,5"x6 prop I was drawing 32 amp with only 650 grams of thrust, but that is understandable because it is a smaller prop and I am worried that it will not fly well with 650 grams.

Geoff

Hello Geoff,

I believe 650 grams of thrust will fly the model propely, though it won't set any records. It all depends on what you want to use the model for.

A Boeing 747's thrust to weight ratio is something in the neigborhood of 35% and it flies perfecly well.

Geoff_Gino
11-14-2005, 05:31 AM
Try an 8x6, that is what I run on my 28/14/10.

Hi FinnFlyer

Thanks for the heads up. Will try that this evening.
Are you using a 3S Lipo?

Geoff

Geoff_Gino
11-14-2005, 05:36 AM
Hi Bert

The plane is distincly between a Rascal and Cub and I am definitely not looking for 3D but more scale.
Flew it Saturday with the 10"x4 prop after checking that my current draw stayed below 35 Amps WOT.
It flew very well and giant loops were no problem what so ever and managed 2 torque rolls in the vertical.

Must agree that 650 grams thrust should fly pretty well.

Thanks all for the info.
Geoff

FinnFlyer
11-14-2005, 05:47 PM
I'm sorry, My battery is a Kokam 3S1P, 2000mAh, 15C discharge. Hope that helps.:)

Geoff_Gino
11-15-2005, 05:58 AM
I'm sorry, My battery is a Kokam 3S1P, 2000mAh, 15C discharge. Hope that helps.:)

Hi FinnFlyer

Yes it does, thanks.

Only difference is mine is 3,5 amps and although not stated on the battery at least 15C if not 20C. (Happens when you buy cheap?? batteries)

Got to admit that I am happy with the set up and will heed Matt's words and check the current each time I power up.

Geoff

A10FLYR
11-15-2005, 04:02 PM
I'm running the /10 in a Sweet Stick, .40 size plane on 6S, 11X7 APC, and a CC 45 amp ESC. Not wide open all the time.....but NICE when you want to!!!
Also, a /12 in a Magic with same setup.

FinnFlyer
11-15-2005, 05:42 PM
I'm running the /10 in a Sweet Stick, .40 size plane on 6S, 11X7 APC, and a CC 45 amp ESC.

I didn't know it was safe to run this motor on 6S!:eek:

Does it get hot?

A10FLYR
11-15-2005, 08:10 PM
I don't see why the windings shouldn't take the voltage.....and yes! it will get hot if you don't slow down once in a while!! All short bursts of max power are followed by a good long glide to cool things off. It has never been to hot touch when the plane landed. The batteries are usually warmer then the motor.

Geoff_Gino
11-16-2005, 05:47 AM
I'm running the /10 in a Sweet Stick, .40 size plane on 6S, 11X7 APC, and a CC 45 amp ESC. Not wide open all the time.....but NICE when you want to!!!
Also, a /12 in a Magic with same setup.

Hi FinnFlyer

What current are you drawing at 50% and WOT?

Geoff

A10FLYR
11-16-2005, 05:56 AM
A LOT!!!

I'll check and let Ya know tomorrow.

Geoff_Gino
11-16-2005, 06:01 AM
A LOT!!!

I'll check and let Ya know tomorrow.

Thanks

Geoff

batman
11-16-2005, 09:17 PM
Didn't realize you were going to use 10 cells, I was going on the max 8 cells recomennded on ModelMotors web site. I only used mine on 8 cells and going on that I doubted it's ability to fly your 60"er. But 2 extra cells will make a big difference.

Geoff_Gino
11-17-2005, 05:27 AM
Didn't realize you were going to use 10 cells, I was going on the max 8 cells recomennded on ModelMotors web site. I only used mine on 8 cells and going on that I doubted it's ability to fly your 60"er. But 2 extra cells will make a big difference.

Hi Batman

I am using a 3S1P pack with a rating of 3,5 amps. Perhaps the 3S is too much and 2S might be the way to go.

To late though as the plane is set up and seems to be OK.

Geoff

CorsairJock
11-28-2005, 02:38 PM
While the link to "Great Electric Motor Test" above may be useful, I noticed that all tests were performed using Ni-Cads, while many of us now prefer Li-Poly.
A much better site is:
http://brantuas.com/ezcalc/dma1.asp

which allows you to 'plug in' any battery type and cell count that you want, while experimenting with different props. Results show current draw, static thrust, motor efficiency as you have set it up, current at max effiecieny with the batteries you have selected (which in turn suggests whether you have too much prop, too little, or just right), and more.

Geoff_Gino
11-28-2005, 02:52 PM
Hi CorsairJock

It's been a while. Thanks for that link. Will definitely check it out tomorrow.

Geoff

Geoff_Gino
11-29-2005, 05:40 AM
Hi CorsairJock

Checked out the site this A.M. Boy great program and it gave me 8x6 for the Axi 2814.

Thanks again
Geoff

qban_flyer
11-29-2005, 08:49 AM
It is by far the most complete e-calculator available, it is updated regularly, it's online, and it is "free". I've been using it for several years now, though it never crossed my mind to post its link here. :o

Glad you had the foresight to do so Corsairjock! :)

CorsairJock
11-29-2005, 01:15 PM
Aw Shucks, Thanks Guys.
I decided to check out the motor myself, and those are surprising results: the (APC) 8 x 6 DOES seem to be the best prop for that motor. Increasing the diameter only decreases thrust, and increases current. And what I saw was just under 30 amps and over 3 lbs (49 oz.) of thrust with the APC 8 x 6.
Notice too that the APC props fare much better than standard Master Airscrews, in terms of efficiency. I would imagine that there are other equally efficient props (as the APCs), such as the Graupner 'Cam' series, and/ or the new Master Airscrew Electric Only series. But the bottom line is: all props are not created equal, and some designs are more efficient than others.

Geoff_Gino
11-29-2005, 01:21 PM
Aw Shucks, Thanks Guys.
I decided to check out the motor myself, and those are surprising results: the (APC) 8 x 6 DOES seem to be the best prop for that motor. Increasing the diameter only decreases thrust, and increases current. And what I saw was just under 30 amps and over 3 lbs (49 oz.) of thrust with the APC 8 x 6.
Notice too that the APC props fare much better than standard Master Airscrews, in terms of efficiency. I would imagine that there are other equally efficient props (as the APCs), such as the Graupner 'Cam' series, and/ or the new Master Airscrew Electric Only series. But the bottom line is: all props are not created equal, and some designs are more efficient than others.

And now to find a LHS which will have said prop/props. I could be so lucky. :mad:

Geoff

qban_flyer
11-29-2005, 04:28 PM
Here is another one of the links I had saved away, an online Propeller Thrust Calculator. Perhaps it could be of some use to others as well.

I know I use it all the time in my pre-design calculations.

http://www.gobrushless.com/testing/thrust_calculator.php