Flyzone J3 cub, new power system, am I doing this right? - RC Groups
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Oct 15, 2010, 02:04 AM
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Flyzone J3 cub, new power system, am I doing this right?

From this thread..

And then I read some more. I bought the wrong second plane. I haven't even flown it yet, it looks so pretty.

The plane

Soooo... Today I went about buying some components that I think will make this heavy slow pig better. To make it worse I live at over 4000ft of elevation, which I know can't help.

I hope this isn't in the wrong forum. I'm a beginner, probably a bit less than a beginner.

I read the power system sticky up top. Reading the battery setup thread closely.

Here is what I did, I think I did it right, I think, though this is new, so I may have messed it all up. BTW, I tried to keep it CHEAP!!

GWS Brushless Outrunner Motor. High Quality CNC Machined. Great for Craft 20oz or Less. For use with a 4"-8" prop and 2-3 cell Lipo. Our prop of choice is Either a 7x3.5 2 Blade or even better the 6x3 3 Blade both with a 3 cell Lipo. The 2 Blade will run about 20oz thrust on 12 amps and the 3 blade will put out more thrust ~22oz on only 10amps. A 4.5" prop will run 20,000 rpms on 3 Cells. A 8" prop is only recommended for 2 cell lipo. Motor Comes with a back plate mount optional prop saver mount and all mounting hardware.
New speed control. Same place. Same brand, 15 amp.
15 amp Weight .6oz 17g 2amp BEC
What the heck does BEC mean? Its a breakout to run the receiver on the same battery????

Prop, GWS again. 6X3X3.

Battery. E-bay. I bought 2 of 'em. It was all I could find that would fit, and dropping the mAh seemed logical going from brushed to brushless.

# 3 cell Li-Polymer 900mAh battery pack.
# 10C continuous discharge rate of 9 amps with 12 amp bursts in accordance with our "Real Flight Rating" method.
This knocks the motor weight down from 3oz to less than 1 (obviously I need to cobble something up to mount it), and the battery from 5.5 oz down to 2.5 oz. A full 5 ounces off the plane, about a 25% reduction. Should bring her to about 1 pound, with 180 square inches of wing. 11.25 ounces per sqft. Theoretically 22 ounces of thrust.

The battery should handle it for short bursts. Speed controller shouldn't have a problem.

Now the questions.

Did I match this correctly? I'm just looking to fly around in circles and figure 8's at half throttle. I'm looking for some power to pop up quick from the ground, clear the grass and cactuses (cacti???) real quick. Plenty of nice open sky, 20+ acres and all the empty land around. 100's of acres.

Did I do my homework correctly, will this work?

Except for the connectors for the motor and the battery, this should work plug and play style, hopefully????

One thing that does concern me. The motor has a KV of 2160. Will I have a problem throttling her down and running her slow? At 12volts(11.1lipo) thats almost 26000 rpms, 6X3 prop, thats almost 74 mph. I'm guessing the stall is going to be well under 20mph(she went on a diet and is only about a pound now). Am I going to be able to click in just 3 or 4 volts? Keep her cruising nice and slow? With the tactic radio that came with it.

A Spektrum D6???? is on the way, but I'm pretty sure that will require a new receiver.

Any help, advice or general "that was stupid" is appreciated. I've only been into this for about 6 weeks or so. I'm having an absolute blast, my wallet is getting a little PO'd at me though.
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Oct 15, 2010, 08:34 AM
If in doubt, add accelerant
Lberry.88's Avatar
I think you may need a bigger esc to begin with, why have you decided to upgrade the powertrain before you have even flown it? I read your first thread, i would suggest you just get flying first, I imagine your morale is quite low, so just get some airtime- before spending too much $$$ on upgrades.

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