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Royal P-38 Electric

Old 07-10-2011, 03:25 PM
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Default Royal P-38 Electric

Sorry for the double post, but I originally posted this in the elec to glow fourm by mistake.

I am thinking about building a Royal P-38 this fall, and would like to try electric motors. After a few hours of browsing, and trying to understand the various parts of an electric power system, I am a little confused.

I picked a motor and battery, and reviewed their specs to see if I could make sense of all the information avaible. I'm hoping I can get some answers.

If I look at an AXI 282610 outrunner, the following information is supplied.
Kv = 920
Volt Range 11.1V to 19.2V
Max Amps 40A
Suggest battery 3-5s

For a battery, I looked at a Prolite V2 4 cell 2600 mah, 14.8V
C = 20
Continuous current = 52A
Max current = 104A

Motor rpm is calculated by multiplying 14.8 x 920 to get 13,616 rpm

Here is where I get a little confused

Motor volt range is 11.1 to 19.2
Why is there a range?
Will an battery over 19.2 damage to motor?

Max motor amps is 40A
Will a battery feeding more than 40A damage the motor?
What is the difference between continuous and max amps?
The max battery current is listed at 104A which 2.5 times greater than the listed motor current of 40A
How do you calculate the power in watts of this system (V*A) but I don't know which numbers to use.

I just chose these two items in an attempt to understand the math. I may have made a bad coice.
Would this battery kill the motor?
would two these power a 12 pound p-38.

I would appreciate any answers or suggestions. I'm a litte confused about all the numbers that turn up.

Thanks, Keith
Old 07-10-2011, 07:14 PM
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Default RE: Royal P-38 Electric

I am by no means an expert here, but I ran the numbers you listed, AXI 2826/10, 4s battery, and I put an APC 11X6 prop on it. It shows 87 ounces of thrust. So this is a twin so double that to 174 ounces or 10.8 pounds of thrust. That seems a little lite on power. It might fly, but will be very scale like and have no reserve power.

I switched motors to the Monster power, Eflite clone 32 sized motor, 13X6 prop, same 4s battery and a 60 amp ESC. I get 108 ounces of thrust, * 2 is 216 ounces or 13.5 pounds of thrust. I increased the prop to a 14X6 and it goes up top 250 ounces or 15.6 pounds of thrust

I think that would be a better natch for this plane.

Here is the calculator I am using.


It took me some time to figure out how the battery and prop can really effect the power you get out of the motor.

Old 07-21-2011, 12:33 PM
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Default RE: Royal P-38 Electric


Electrifly has an awsome power system calculator on their website. Please don't take this as a brand endorsement, but the calculator is GREAT! You put in the lbs/prop size/amount of power/number of cells you want to put in a given plane and they give you their recommendations as to what you should be using. I find after flying a number of warbirds including a B-25 and Mosquito on electric power, that 100 watts per pound is a good place to be. No 3D verticals, but good, solid power on take-offs and half throttle flying. For a twelve pound twin, you'll need at least 600 watts a side to get what you're looking for. You can use the calculator and then apply the result to any comparable brand of electric motor. Good luck!!

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