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Old Jun 08, 2014, 10:24 AM
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United States, CT, Southington
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1/4 scale BUSA Cub Conversion-91FS equivalent?

Hey All, This has, I am sure been covered in other threads, but I wanted specific questions answered if possible by the electric experts. I have been flying my Balsa USA 1/4 Scale Cub on a Saito 91 spinning a 15x4 wide blade APC prop. I fly the Cub pretty aggressively with the 91 being able to pull it through rolling circles and pretty much sustained knife edge on a cool day. I would like a bit more power. Maybe the equal to a Saito 100. This would give me just the right amount of power for warm days as well. I usually fly about 10 to 15 minutes at a time. What combination would give me that much power and duration? Now I fly a combination of aerobatics and a bunch of slow flight, not just WOT all the time. Right now I have two 6s 3000mah that I can combine for 6s and 6000mah from an electric chopper. Can I use these batteries for the Cub as well? I was looking at the Firepower Sport 80 (5065-04) from heads up RC. Am I on the right track? Thanks a bunch for any and all help you guys can give as I am a longtime glow guy with minimal electric experience. Thanks,,,,,,,,Jeff D
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Old Jun 11, 2014, 02:42 PM
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United States, CA, San Diego
Joined May 2004
471 Posts
Hi,

I built a BUSA 1/4 cub using a scorpion 40mm motor and 10s. To do what you are after is going to require more cells than your current available batteries. With my 10s 5000mah setup I draw ~55 amps and can comfortably fly for 8 minutes. It has plenty of power to do the aerobatics your are interested in.
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Old Jun 11, 2014, 06:02 PM
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Canada, ON, Newmarket
Joined Jul 2013
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Jeff,

Combining two 3 cell, 3000mah lipo batteries in series will give you a 6 cell (22.2 nominal volts), 3000 mah battery - not a 6000 mah size battery (no free lunch, smiley)

My suggestion is that you learn a little about the relationship and tradeoffs between KV rating, number of lipo cells, prop size and plane speed in the electric model world.
eg. lower KV = more low end torque, larger prop, slower plane speed
eg. higher KV = higher rev'ving prop, smaller prop size

The firepower house brand of motor is not on free electric power calculation programs like 'eclac', but Firepower 5065 and 6354 size powers are similar to brands that are on that program so you can substitute similar motors and 'play around' with number of lipos, prop size, plane weight, etc. to get some sense of how rearranging these factors change plane speed and power to weight ratios.
Firepower is a "hobby" grade of electric motor with poorer efficiency (more power going to wasted heat) than a competition grade motor such as Scorpion, Hacker, etc. Nothing wrong with that grade, but to produce the same power with a hobby type motor you probably want to tick up to a slighter bigger motor.

Also, there are a lot of online threads of electrified quarter scale cubs that you can google to get ideas of what has worked for others.

good luck,

Michael
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Old Jun 13, 2014, 04:33 PM
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United States, CT, Southington
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Thanks for your replies, I am combining two 6S 3000mah lipo's to get a 6S 6000mah battery. This is a parallel setup as you must know. I am not trying to get a FREE LUNCH. From what I have learned about electrics in larger planes, the glow setup is still quite a bit lighter than electric. Especially if I want to get something similar in performance to what I am used to right now. By my rough calculations, the electric cub would be about 2 pounds heavier to get near the flight time I now enjoy. And the cost of two sets of batteries buys me a whole bunch of glow fuel. I really love the nice quiet flight electric would give me! I already have a great charger if I do go electric on the Cub. Thanks again..... Jeff D
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Old Jun 13, 2014, 05:36 PM
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Canada, ON, Owen Sound
Joined Oct 2008
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I'd use either a Scorpion 4020-16 or 4025-12 with props from 16/10 up to 17/10 on 6s.
Either motor is very efficient in the 50-60a range and should give you the power you need.
fwiw Doug B
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Old Jun 13, 2014, 06:31 PM
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United States, CA, San Diego
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I should have posted a video of my electric setup. I meant to but the brain quit early. I can't remember how much it weighs.

Electric Balsa USA Cub Maiden Flight (2 min 15 sec)
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Old Jun 14, 2014, 03:04 PM
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Letchworth, Great Britain (UK)
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Quote:
Originally Posted by rv4pilotone View Post
... From what I have learned about electrics in larger planes, the glow setup is still quite a bit lighter than electric. ...
That's not my experience; all my conversions, up to 1.20-size Extra, have come out less than when they were glow-powered with a full tank of fuel. Usually, in fact, the electric ready-to-fly weight has been about the same as the glow model with half a tank of fuel.

My 1/5 scale Cub flew with an OS91FS, and now has an AXI 4120/14 with a 16x10 prop on 3S LiPo. The motor's good for 6S, so plenty more power available for your 1/4 scale
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Old Jun 14, 2014, 08:21 PM
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I should have posted a video of my electric setup. I meant to but the brain quit early. I can't remember how much it weighs.
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Old Jun 19, 2014, 06:39 PM
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United States, CT, Oxford
Joined Jan 2009
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rv4pilotone

Here is a video of the 2nd flight of my 90" P-38 using Scorpion 4025-12 on 6S with APC 15.75x13x3.
These props are a little too big, but you can get an idea of the power they have. That motor should pull your cub around quite nicely

Nitro Planes 90" P-38 2nd flight (5 min 37 sec)
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Old Jun 19, 2014, 07:43 PM
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Just re-read original post. Yes you can connect two same # cell batteries together in parallel to increase capacity

Since you are flying that prop, thinking you can get away with a lower KV motor (or less cells)
with a larger diameter, higher pitch prop. Similar performance, less amps. Spinning low pitch props uses power
How about a Tacon 110 on 6S with a 18 or 20" prop?

That is a 8S-10S motor, but since you are not after speed, might work just fine

Since I have no idea what the 15x4 is spinning, going to guess it is spinning at 11000RPM. That would give you roughly 12# static thrust and a 41MPH prop speed

The Tacon with a 20x10 prop would give you 14# static thrust and 52MPH prop speed....rough numbers.
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