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Old 11-11-2006, 04:19 PM   #1
p901
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Default Brushless motors

Good morning,
Can someone point me to a good book on AC motors?
How they work, different types, advantages, disadvantages,
speed controls, etc.

Thank you, andrew
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Old 11-12-2006, 02:12 AM   #2
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RC electrics keeps advancing so quickly, that any book that you did find would most likely already be out of date even if written within the past couple of years. Your best bet is to read through the posts here on WattFlyer and ask lots of questions.
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Old 11-12-2006, 05:18 AM   #3
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Default Electric Motor Info

Hello Andrew, Welcome to Wattflyer! Gerald's right, things are changing so fast it's hard to keep up, even if you read W/F every day! There are a couple of online links that are fairly current, the first one is from ScubaSteve; http://www.gobrushless.com/kb/index....01_-_Chapter_1
This next one is slightly older but goes up to Outrunner motors;
http://adamone.rchomepage.com/guide5.htm
Last, a link to one of the best articles I've found on speed controllers;
http://www.rcgroups.com/forums/showthread.php?t=444961
Hope this helps!
Ron
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Old 11-20-2006, 03:23 PM   #4
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Can anyone give me an accepted rule to determine the size motor for the size plane. I'm just getting into electrics and I find this to be a problem. Thanks. Hank
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Old 11-20-2006, 08:38 PM   #5
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Default Motor size?

Hello Hank, Welcome to Wattflyer! Your question is a good one, lots of folks would like to know the same thing: Problem is, there is no standard reference or formula!
Unlike glow engines, there's no "cubic inch displacement" or similar size, volume or any measurable physical dimension that will provide a useful answer.
Generally, electric motors are measured by their power output (in watts) for a given input voltage. This input voltage of course depends on the type and number of battery cells used. Here's the four most common battery "packs" (a number of cells wired in series) and their nominal voltages;
2 LiPoly cells @ 3.7 volts per cell = 7.4 volts
7 NiMH or NiCad cells @ 1.2 volts per cell = 8.4 volts
8 NiMH or NiCad cells @ 1.2 volts per cell = 9.6 volts
3 LiPoly cells @ 3.7 volts per cell = 11.1 volts
When you look at the spec sheet for a given motor it will usually state a power output (again, in watts or occasionally, in ounces of thrust) based on one or more of these input voltage values. If it has a recommended propeller size, it will vary according to the input voltage; As the motor "sees" more input voltage it will try to turn faster, but with a large prop, it can't. As the voltage goes up, the prop size comes down. Volts = RPM, Milliamps = Duration.
Now, if we find a certain motor that produces, say, 125-150 watts of power with a 3 cell Lipoly (3s), what does that tell us?
From past experience I'd say this is a motor that would power a "400" sized aircraft very well. That would be a model about 1/2A to .10 glow size, about 3' wingspan, 250-350 square inches of wing area, and a weight (ready to fly, RTF) of between 16-24 ounces. If we used a smaller model and a small diameter, high-pitch prop, it would have a high top speed; If it was a larger model we might use a somewhat bigger, low-pitch prop and it would fly slower but have more torque, like an aerobatic model.
We could even use a gear reduction drive to turn an even larger prop (at less RPM) to power a much larger model.
If you look at the motor specs and model recommendations from a site like Hobby-Lobby.com it will give you some idea of the range of motors for similar-sized models. Or, if you have a certain model in mind, usually the recommended motor size will power it adaquately. For hop-ups, post the model size here and you're sure to get some recommendations!
Another way to get a "feel" for motor size/output and the effect of different voltages, props, gearing and so on, it a "Motor-Calc". Here's a free one, from DMA; http://brantuas.com/ezcalc/dma1.asp
This is a pretty complicated subject and I've greatly simplified my answer, but hopefully this will get you started!
Good Luck!
Ron
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Old 11-21-2006, 01:04 AM   #6
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Default Selecting proper motor

Thanks Ron,for the info on selecting motors. I'm very grateful for your help. You have me thinking in the right direction.
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