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Old Aug 25, 2012, 03:34 PM
Crash test dummy....
mattthomas78's Avatar
United States, TN, Waynesboro
Joined Mar 2012
110 Posts
Help!
I need a powerful 3S motor

I am building a plane out of foam for R&D to be later built out of wood/fiber glass.... The all up weight is estimated at 15lbs or 240oz or 6803g, however you want to look at it... The projected wing span will be 108" or 2.74 meters.... The fuse will be 60" or 1.524 meters in length, pusher prop.....

I am looking for a powerful motor in the 1500watt or more range that will get this thing off the ground and run off of a couple 3S lipos in parallel..... I want to use 3S lipos if at all possible because not only do I have many of them but they are cheaper to replace...

I also need a max prop dia for said motor somewhere in the 12-16in range.... I am not looking to set any kind of speed records..... Looking to keep the cruising speeds to around 35 MPH

Any suggestions will be greatly appreciated!!!

Matt
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Last edited by mattthomas78; Aug 25, 2012 at 04:05 PM.
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Old Aug 25, 2012, 05:00 PM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
5,179 Posts
What's the wing area?

At that low voltage you will need a high Kv motor, and an ESC which can handle at least 150A. Here's Motocalc's estimate for a Neu 1530/1Y driving a 14x8 prop.

Motor: Neu 1530/1Y (est); 1100rpm/V; 2A no-load; 0.015 Ohms.
Battery: Turnigy nano-tech 6400mah (40C); 3 series x 2 parallel cells; 6000mAh @ 3.85V; 0.001 Ohms/cell.
Speed Control: Castle Creations ICE LITE 200; 0.003 Ohms; High rate.
Drive System: Aeronaut Folding 14x8 (ba); 14x8 (Pconst=1.18; Tconst=0.995) direct drive.
Airframe: mattthomas78 Pusher 108"; 1100sq.in; 240oz RTF; 31.5oz/sq.ft; Cd=0.05; Cl=0.51; Clopt=0.75; Clmax=1.17.
Stats: 103 W/lb in; 82 W/lb out; 27mph stall; 34mph opt @ 53% (51:25); 41mph level @ 63% (35:36); 1463ft/min @ 29.7; -246ft/min @ -4.8.
Conditions: Sea Level, 101.0kPa, 20C

Static WOT:
AirSpd (mph) = 0.0
Motor Amps = 142.5
Motor Volts = 10.9
Input (W) = 1554.1
Loss (W) = 322.0
MGbOut (W) = 1232.1
MotGb Ef(%) = 79.3
Prop RPM = 9649
Thrust (oz) = 183.5
PSpd (mph) = 73.1
Time (m:s) = 5:03

Cruising @55% throttle:
AirSpd (mph) = 35.0
Batt Amps = 13.6
Motor Amps = 25.2
Input (W) = 154.2
Loss (W) = 21.0
MGbOut (W) = 133.2
MotGb Ef(%) = 86.4
Prop RPM = 6321
Thrust (oz) = 19.2
PSpd (mph) = 12.9
Prop Ef(%) = 62.6
Total Ef(%) = 53.1
Time (m:s) = 52:58
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Old Aug 25, 2012, 05:50 PM
Crash test dummy....
mattthomas78's Avatar
United States, TN, Waynesboro
Joined Mar 2012
110 Posts
The wing span 108"Lx12"W so the wing area will be 1296 square inches.... And the batteries will be nano-tech 8400 40-80C...... I just downloaded the program you used and it's looking very promising for using a power 32 e-flite or Hyperion Zs4020-12, unless i did something wrong on the program.... Which is highly possible with me
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Old Aug 25, 2012, 10:25 PM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
947 Posts
Quote:
Originally Posted by mattthomas78 View Post
The wing span 108"Lx12"W so the wing area will be 1296 square inches.... And the batteries will be nano-tech 8400 40-80C...... I just downloaded the program you used and it's looking very promising for using a power 32 e-flite or Hyperion Zs4020-12, unless i did something wrong on the program.... Which is highly possible with me
Ok, which prop and how many cells in series with the E-flite 32 motor?

In sticking with the Neu motors, the 1521/.5Y might also do the job on 3 cells, just not while pulling in 1500 watts!

Michael
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Old Aug 25, 2012, 10:54 PM
Crash test dummy....
mattthomas78's Avatar
United States, TN, Waynesboro
Joined Mar 2012
110 Posts
I've always been told 100watts per pound.... The power 32 770kv in the motocalc was setup on a 3S 3200mah I didn't have the option for an 8400mah 3S, a 12x8 prop, but for some reason it keeps putting the empty weight at 120oz ( no motor,ESC,batteries) when I am putting it in at 160oz...... 108"WS 1296" wing area..... It's showing 3 batteries in series and 4 in parallel, so now I'm all cornfused..... I'm trying to come up with a power plant that will operate on 2 nano-tech 8400mah 40-80C batteries in parallel so I can keep it in the air for extended periods of time for photography/videography..... And as cheaply as possible.... My maximum expected weight will be 15lbs, most of the time it will be around 10lbs....
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Old Aug 25, 2012, 11:06 PM
The 6 P principle works for me
elecfryer's Avatar
Ventura CA
Joined Aug 2007
947 Posts
Many planes fly very well on less than 100 watts (in) per pound RTF.

In motocalc make sure in the battery area the series cells reads "3" and the parallel cells reads "2". You can enter the number manually or by using the + or - buttons.

As far as the other issues, motocalc does work, just keep at it!

Michael
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Old Aug 26, 2012, 04:05 AM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
5,179 Posts
Quote:
Originally Posted by mattthomas78 View Post
I didn't have the option for an 8400mah 3S, a 12x8 prop, but for some reason it keeps putting the empty weight at 120oz ( no motor,ESC,batteries) when I am putting it in at 160oz
Don't use the Motowizard, enter all parameters manually. Any components which are not already in the database can be added, but you need to know their specs.

Battery weight is per cell, so take the 3S weight and divide it by 3. You can change the measurement units in Options to flick between metric and imperial while entering specs. The end result should look like the pictures below. Don't forget to save each component after entering it!

Quote:
most of the time it will be around 10lbs....
10lbs AUW? In that case the empty weight should be about 106oz (depends on weight of the motor, battery and ESC).
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Old Aug 26, 2012, 08:01 AM
Crash test dummy....
mattthomas78's Avatar
United States, TN, Waynesboro
Joined Mar 2012
110 Posts
Ahhhh, battery weight is per cell!!! Now we're getting somewhere!!! Couldn't have done it without you guys!!!

Yes estimated AUW most of the time will be 10lbs but I just want to ensure that I can add additional video/photo gear weight when/if needed....
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