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You big scale electric guys; kindly compare these 2 stats and pick a motor....

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You big scale electric guys; kindly compare these 2 stats and pick a motor....

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Old 11-18-2015, 03:31 PM
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rustyrivet
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Default You big scale electric guys; kindly compare these 2 stats and pick a motor....

I'm new to this, but these two motors look to be very close in power if I'm reading the stats properly. They are of similar Amps, props, etc. What puzzles me is that the Suppo motor can fly an 11 lb AstroHog with authority in that video, while the AXI motor is listed as only good up to 169 ounces (10.5 lbs) The Altitude Hobbies people say the Suppo compares to the AXI 4130/16 too.


I'm preferring to buy and use the AXI in my own 11Lb AstroHog. I trust the AXI name while nobody knows much about a "suppo". I'm hoping perhaps the AXI people are just being modest with their 169oz limit. (??) Or do you experienced guys feel the Suppo is actually a stronger motor and more capable of the AstoHog aerobatics, and the AXI is just not? Not to confuse you, the ASTRO HOG video shows a just-go-fly 4130/6 motor in that plane........which is actually a Suppo 4130/6 at less $. Your input please....should the AXI work in that Hog....or go with the Suppo?
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AXI 4130/16 motor;

http://www.hobbyexpress.com/brushles...32987_prd1.htm
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Suppo 4130/6 motor;

http://www.altitudehobbies.com/suppo...v-suppo-4130-6
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The Suppo motor in action in an 11 lb AstroHog;


https://www.youtube.com/watch?v=XXywDbHx1Zs



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Old 11-21-2015, 01:58 PM
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11 lb seems a bit heavy for an AstroHog. I thought that would be more in the 8 lb range. What size prop our you planning to run? With a 385 Kv on the Axi motor, I am assuming you will be in the 14-16" range. Assuming a 16-10 prop, you will get about 1000 watts (according to eCalc http://www.ecalc.ch/). This would be marginal on an 11 lb plane, but would be fine if you were closer to 8 lbs.

I have a Hog Bipe on the bench now and selected a Cobra 4130/12 motor. http://www.cobramotorsusa.com/motors-4130-12.html This motor has a 540 Kv, so I will be running a bit small prop. With a 6S battery and a 13-8 prop, I will get about 1200 watts (on the upper limit for this motor). I am expecting this build to come in around 8 lbs, so this gives me a very generous 150 watts per lb, so I shouldn't need to running full throttle. I may step down to 13-6.5 prop to start (which should pull about 1100 watts) which keeps me well in the safe zone for the motor.
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Old 11-21-2015, 02:54 PM
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Aymodeler,

I have decided against both the AXI and the Suppo motor in the last couple of days.I can get a NIBox AXI for $50, but will not buy it because of the lack of replacement shafts, and I am particularly annoyed with Altitude Hobbies for not providing a phone number on their websight, and instead making me wait until next week before they are good and ready to answer my simple email question I sent them about shipping. I would have ordered the Suppo Motor and Gecko ESC Thursday already if not for such piss poor correspondence! (.....lack of it) Well......that was a blessing in disguise, because I completely overlooked Cobra by accident not seeing the 4130 motors on their 12 pages of motor listings. I prefer their bolt on prop adapters, their quality motors, and their answering their phone and providing good customer service for me in the past. A company shouldn't have me waiting a week for a reply as to whether I can use UPS instead of USPS while I have my finger waiting on the enter button ready to place the Altitude Hobbies order. I had overlooked their ignoring my email a few months back asking them when they were going to receive a backorder. I now see that was not an isolated incident but a pattern with them.


Ok....back to the stats;
I would not doubt if a Hog can weigh 11 lbs if it is glassed, painted, has an optional aluminum landing gear, and carries 2.5 lbs of 5000mah battery, esc, and motor. But I plan to first use the motor on a 10lb Hobbistar 60 trainer with a 71" Semi symetrical wing. I will then use it later for the AstroHog when I've become a proficient pilot. I'm still learning about electrics, and the only thing I know to do is to use Cobras very thorough prop charts when deciding which motor to buy. Right now my choice is a Cobra4130/14 450KV. http://innov8tivedesigns.com/parts/b...s-motor-kv-450 The propeller chart for the Cobra 4130/14 motor shows me; APC 16x8E prop on 5S @ 142oz of thrust....and, an APC 15x6E prop on 6S @155oz of thrust. I have no preference of any one APC prop size, and anything up to 16" will fit. I'd prefer a 6s battery (so I can use two 3S batteries in series) but can settle with a 5S battery. Is there any reason to doubt these numbers that the Cobra chart is showing, and am I choosing the right motor and props for my purposes?

As for your choice of motor and prop for your Bi-hog, my question is this; I see that you can go to a 15x4E and get 176oz of thrust (and still be within Cobra's green zone on the prop chart) vs the 13-8 or 13-6.5 you chose @ 141oz of thrust. Why are you skipping that 15" prop and all that extra power in the green as an option? Is it that the prop is too large.....or is there some other reason I don't understand being a newbie?

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Old 11-21-2015, 04:16 PM
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Originally Posted by rustyrivet View Post
Aymodeler,
As for your choice of motor and prop for your Bi-hog, my question is this; I see that you can go to a 15x4E and get 176oz of thrust (and still be within Cobra's green zone on the prop chart) vs the 13-8 or 13-6.5 you chose @ 141oz of thrust. Why are you skipping that 15" prop and all that extra power in the green as an option? Is it that the prop is too large.....or is there some other reason I don't understand being a newbie?
It is classic speed vs. force trade. Both props will crank out about the same power ~1100-1200 watts. The 13-8 has a pitch speed of 77 mph, while the 15-4 will be down around 38 mph. With a 540 Kv, the 15-4 prop is sort of like driving around in first gear all the time (lots of pull, but limited speed).
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Old 11-21-2015, 08:08 PM
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Originally Posted by aymodeler View Post
It is classic speed vs. force trade. Both props will crank out about the same power ~1100-1200 watts. The 13-8 has a pitch speed of 77 mph, while the 15-4 will be down around 38 mph. With a 540 Kv, the 15-4 prop is sort of like driving around in first gear all the time (lots of pull, but limited speed).
Ahhh....! I learned something else just now. I now know that I need to start checking out pitch speed when I'm making comparisons, and not just focus on amps, watts, and thrust. Thanks.
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Old 11-22-2015, 06:43 AM
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Motor/Battery/Prop selection really is a good example of classic engineering trade-offs where you need to find a balance between competing factors. I typically use the following approach when spec'ing out a new setup:

1) Determine how much power I need. I like to start with an assumption of 125-150 watts/lb knowing that what I end up with in the "real world" will probably be closer to 100 watts/lb
2) I determine what size battery I need to deliver that power while keeping current draw reasonable (typically under 60 amps). Again, I tend to discount the inflated manufacturer "C" ratings
3) I figure out what prop will fit the plane (diameter), and what pitch speed I would like to obtain
4) Last but not least, I find a motor with a Kv rating (which determines RPM) that will give me the desired pitch speed I want and that can handle the power needed at the current required

I use eCalc (http://www.ecalc.ch/motorcalc.php?ecalc&lang=en) to play around with various combinations and iterations of the above process.

There is a small subscription fee (~$6/yr), but it you can play with all the combinations of batteries, motors, props, etc to narrow your choices down. It will also give you an overall assessment of how your selection will work for critical parameters such as power limit, thrust, pitch speed, flight time, motor temperature, etc. Of course this is all based on some theoretical calculations, but at least you can get some kind of idea of how your combination will work.
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