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Power Systems Talk about motors, ESC speed controllers, gear drives, propellers, power system simulators and all power system related topics

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Old 12-28-2005, 03:38 AM   #1
rattusrex
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Default Understanding motor specs

I'm a long-time R/C flier (35+ years) - but always glow-powered.
Now I want to get into electrics but I am baffled by all the different motors and controllers - not to mention batteries and new chargers.

Does anyone hav some good, reliable sites that I could use to get a better understanding of the electric motor/controller/battery scene?

Thanks.
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Old 12-28-2005, 04:35 AM   #2
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You will probably have a whole lot better luck posting your questions in the "Power System" section. This is the testing section.
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Old 12-28-2005, 01:40 PM   #3
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Default Understanding motor specs

I'm a long-time R/C flier (35+ years) - but always glow-powered.
Now I want to get into electrics but I am baffled by all the different motors and controllers - not to mention batteries and new chargers.

Does anyone hav some good, reliable sites that I could use to get a better understanding of the electric motor/controller/battery scene?

Thanks.
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Old 12-28-2005, 01:43 PM   #4
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Thanks. I have taken your advice and re-posted in the Power system section.

Mike (AMA L695)
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Old 12-28-2005, 02:28 PM   #5
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Old 12-28-2005, 03:29 PM   #6
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Default Understanding Motor Specs

Hi Mike, welcome to E-Flying!
I wish I knew one site or reference to give you that explains all the different motor designations. If such a place exists, maybe some kind reader will post it here!
I believe Graupner (Hobby-lobby.com) started a "benchmark" of sorts with the Speed designation, Speed 400, Speed 500. etc. Later motor-makers added their own "labels" like can diameter, number of winds, can length and so on. There's been lots of suggestions for a standard table of sizes but so far, nothing. It may be too late to install one now!
I learned about 1/2 of what I know about motor sizes from the Hobby Lobby catalog; They list comprehensive plane specs, motor, battery, prop sizes and upgrades for every plane they sell, and that's a lot of planes! So if you have a plane in mind, find a similar size and weight aircraft in the catalog and use their recommended motor.
The most common motor size is Speed 400. This is a brushed, inexpensive ( $ 10.00) motor. Until recently, with the advent of very high output, lightweight LiPoly batteries, 400 sized planes were the vast majority of kits, ARFs, RTFs and plans available. In glow terms, a Speed 400 on direct drive (no gearbox) with 7-8 cell NiMh or 2-3 cell Lipo would swing a 5.5" x 4.5" prop around 7,000 to 9,000 RPM. About like a 1/2A, right? The planes for that power system looked like 1/2A's, too, maybe slightly bigger and with somewhat lighter construction. Now comes the part a lot of people have problems with; Put a 4:1 gearbox (reduction gearing) on the 400 and it will really wind up, 20,000, 30,000 or so and turn a 10" x 6" prop 1/4 of the RPM, enough thrust to easily fly a 2 meter powered glider! Not a 1/2A anymore!
So there's Direct Drive and Geared motors, depending on the type of flying you intend to do. Little, fast planes like pylon racers would use Direct drive, small props, short duration flights.
Geared motors would be for larger, slower planes like 3D models, sailpanes and models that were intended to swing a larger prop. "Park Flyers".
Just about all of this applies to Brushless motors, but they've added another type of motor; Outrunners, also called "Rotating Cans" or "LRK's" in Great Britain. With this type, the outside case (can) has the magnets attached to the inside and the entire "can" rotates, also driving the prop shaft. The result is tremendous torque in a small motor, the ability to swing a much larger prop without the complexity of a gearbox. So in the Brushless catagory there are Direct Drive, Geared and Outrunners.
About the only site I can direct you to that might give you better idea on motor/gearbox/battery combos (besides Hobby Lobby) would be a free "Moto-Calc" program, http://brantuas.com/ezcalc/dma1.asp.
Just scroll the batteries, pick one out, pick a motor, prop. Anything will do to start; Hit "Calcuate" and watch what happens. Now change one factor, like go from 7 cell NiCad to 8 cell Nicad, hit "Calcuate" and compare the result. After a few of these, you'll get an idea of how these factors effect each other. It may seem like voodoo at first but hang in there. You have a BIG advantage in having flown R/C glow before. Wing loading, airspeed, power-to-weight, thrust are not any different from what you've already learned. The big difference is what turns the prop, and the "Lingo"
There is a lot of good info here at Wattflyer, keep reading the posts, especially "Beginners" and "Power Systems".
Wish I could help more, but that's all I know! Ron
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Old 12-28-2005, 05:12 PM   #7
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Thank you, Ron, for your informative reply.
I'll try the Hobby Lobby site and the "Moto-calc" program.
Mike
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Old 12-29-2005, 06:44 AM   #8
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IMHO, the Hobby Lobby website, and others that show example applications, will be infinitely more useful to an electric newbie than Motocalc. Motocalc is a fine tool, but like any tool, it's only useful if you know how to use it and interpret the information it generates.

Examples of electrified planes are tremendously useful in that you can almost always find one that's a close match to the plane you want to power. It's a simple matter of taking the same power system and installing it in your plane.

On the other hand, if you just let Motocalc run wild as someone new to the electric arena tends to do, it's going to give you some funky results. It'll recommend motors and battery technology that are either obsolete or out of production. What you would need to do with motocalc is set limits on battery size, battery type, and motor brand to make Motocalc's data more useful.
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Old 12-29-2005, 01:56 PM   #9
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Default Moto Calc

Hi Matt, I agree that Moto-Calc can and does give some oddball results occasionally and is not as up-to-date as it could be. That's hard to do with motors and batteries coming out every week!
I recommended Mike try it more as an example of how factors change results; A slightly bigger prop, more or less cells (volts) etc. Rather than make my post any longer than it already was, I believed that instead of just reading an opinion, an interactive program might help him (or anyone, for that matter) feel more a part of the process. It shows, better than I could ever explain, factors like "efficiency" changing with different props, gearing, etc. It changes "Thrust", both static and in-flight, when another factor is changed. "Watts in/out" ,"KV (rpm/volt) or (inozamp) etc. I don't think it's the final word on selecting a motor or power system, but it will get you close. My suggestion was in hopes that, by using the "Calc", Mike would become familiar with the terms, what they mean and how they change results.
As far as selecting an exact system, I recommend he (and anyone else starting out in electric) use all the resources available, including the HL catalog, "Moto-Calc", advice from other e-flyers, mag columns and of course, Wattflyer!
Happy New Year All! Ron
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Old 12-30-2005, 01:08 AM   #10
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Electric motors are sort of backwards from glow engines, going to a bigger propeller increases power, just the opposite of your typical glow engine. I found this the hardest part to understand when I started in electrics.

Read this series of articles to understand the basics.
part 1: http://www.rcgroups.com/links/index.php?id=3385
part 2: http://www.rcgroups.com/links/index.php?id=3389
part 3: http://www.rcgroups.com/links/index.php?id=3393
part 4: http://www.rcgroups.com/links/index.php?id=3398
part 5: http://www.rcgroups.com/links/index.php?id=3402
part 6: http://www.rcgroups.com/links/index.php?id=3597

These will give you enough knowledge to do your own "motocalc" calculations. The only other thing you need are motor constants. Download them from www.motocalc.com -> new data -> motors

There are some good general electric flight articles here: http://members.aol.com/kmyersefo/page3.htm#TOP
especially this one: http://members.aol.com/kmyersefo/scale.pdf

Hans
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Old 12-30-2005, 01:52 AM   #11
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Default Brushless motors

Ratt,
Check out this Horizon Hobbies site: http://www.horizonhobby.com/Shop/ByC...D=AP&CatID=APK . As you key on each thumbnail picture of a motor it will devote a full page to that particular motor. All the specs, what weight range of plane the motor will handle and etc.! You can learn a lot right there! Pay special attention to the "Outrunners".
It's all about brushless motors, which is the way to go if you're just getting into electrics. Brushed and brushless parts and pieces don't mix very well, so don't invest in a lot of brushed motors and speed controls and then discover brushless! It's the coming thing!
Check it out!
Dick
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