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Old 01-24-2006, 11:22 PM   #1
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Question Motor sizes - what do the numbers mean?

I'm new to electric flight - bought a copy of Bob Aberle's Getting Started in Backyard Flying (2002 www.backyardflyer.com) as my introduction, but found he doesn't explain what the motor size numbers mean, and I haven't yet tracked down any thread in this Forum which explains them.

So, just what is a 180 size, a 280 size, a 370 size, a 400 size, etc? Is there any standardisation? Why do only some manufacturers use these numbers?

Thanks!

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Old 01-25-2006, 04:26 PM   #2
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Welcome to my world!! I just got started in electric flight last spring and I was just as confused. Near I as I find out, the numbers are arbitrary, but relate to each other. As those numbers increase, the power output and the current required increase. Best bet is to start with the plane you want to fly and it's weight. I only do park flyers, 36" wingspan or less because I only have parks to fly in, so I started with a geared 370 inrunner e-flite park 370. It draws a max of 7 amps. 7 amps times 11.1v from my Li-poly battery gives 77.7 watts. Moved my 14 oz Great Planes Basic Light Trainer with authority. Takeoffs in less than 3 feet, flying at 1/4 to 1/2 throttle. My Great Planes Lil Poke was 16oz flying weight and would barely fly with the same setup. Moved up to a e-flite Park 400 outrunner and sized the prop for the max of 10amps. 10 amps times 11.1v gives 111 watts. Nice comfortable park flying, takeoffs in about 6 feet, flying at 1/2 throttle, but not aerobatic capable at all. Now moving up to an e-flite Park 480 (got on feebay) which draws 20 amps max. That results in 222 watts, which, with the proper sized prop, should make it totally aerobatic. Oh yeah, I replaced the three channel polyhedral wing with a scratch built aileron wing also. Building a new fuse (also scratch built) and stronger tailfeathers to take the added pressures. FUN!!


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Old 01-25-2006, 08:40 PM   #3
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Red face I'll take a stab at that...

Originally Posted by velojet View Post
So, just what is a 180 size, a 280 size, a 370 size, a 400 size, etc? Is there any standardisation? Why do only some manufacturers use these numbers?
You know, I could be wrong, but I bet the origin of motor sizing is related to the grams of aircraft it was intended to fly and/or the thrust it was designed to produce. So, a 400 motor was intended to fly a 400 gram, or ~14 ounce airplane. A 480 would fly a ~17 oz plane, etc.

Since most aircraft manufacturers recommend underpowered setups, this power level only provides medeocre performance, generally not enough for 3D acrobatics. This would have been in the days of brushed motors, and I would guess the lines have blurred considerably with the introduction of brushless motors a few years ago.

Then again... this could all be BS...

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Old 01-25-2006, 10:03 PM   #4
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The basics for brushed motors are here :
http://www.ezonemag.com/pages/faq/a414.shtml

The rest of the FAQ is worth reading too.

Unfortunately brushless motors are different again. There are no real standards.

Steve
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Old 01-26-2006, 03:52 AM   #5
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Thanks to all for your responses (and for your welcome, flyranger). Slipstick pointed to the best answer I'm going to get on this - that "if you measure the length of a standard ferrite electric motor in mm and add a 0 you have its approximate Speed xxx designation". Some scheme! So I guess the length does bear some rough relationship to power, but certainly nothing even as equivalent as TManiac suggested (or, naive novice that I am, I expected).

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Old 01-26-2006, 04:25 AM   #6
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Unhappy

Oh well, shot down, but it sounded good, huh?

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Old 01-26-2006, 07:08 PM   #7
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Originally Posted by TManiaci View Post
Oh well, shot down, but it sounded good, huh?
Sure did! Most ingenious, and certainly more ingenious than the actual method!

John Velojet - the Flying Kiwi
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