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brushless confusion!!

Old 06-19-2006, 01:33 PM
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drbenz
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Default brushless confusion!!

Does anyone know of a website that explains how to figure out what gearbox goes with rpm motor goes with what size prop goes with what weight plane goes with what C rating battery, etc..etc..
I started i glow RC 20 years ago, but just started in electric and I am finding it very confusing.
Old 06-20-2006, 10:39 AM
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WhtBronco
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Default RE: brushless confusion!!

I don't know that you'll find a site that answers all those questions. That's just too many variables. The best way to look at it is to determine how many what's you want for a particular plane. Many planes list the suggested range of power in watts now days. For 3D flight you're gonna want 150+ watts per pound. Then find a motor that can provide that. The motor manufacturer will suggest a range of props just as the glow engines do. Then find a battery that will provide the voltage and amps the motor will pull. It's not really as tough as it sounds.

I built a plane that has a projected weight of 14 oz. Based on that and the plan to fly it only in 3D flight I knew wanted atleast 150 watts, the 150watts per pound rule. So I went looking for a motor and settled on a 200 watt motor(more power is always better), the Hacker A20-20L which is direct drive(no gear box) outrunner motor. I don't like gear boxes and they are not necessary to get high power. Hacker says to use a 10x4.7 prop on it when using a 3 cell li-po battery and that it will pull up to 18 amps. Now I did the math on batteries. My batteries have a max discharge rating of 15C, 15 times the rated capacity. My Thunder Power 3S(3 cell) 1320mah batteries at 15C discharge can handle 19.8 amps so they are good. My TP 3S 730mah li-po can only handle an 11 amp discharge rateso they will not work.

You might poke around the Hobby Lobby website as they do have some good info on motor, battery, prop etc selection based on Axi motors.
Old 06-20-2006, 04:11 PM
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lwatson
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Default RE: brushless confusion!!

As you can see from WhtBronco's response, there are some very knowledgeable people here. So another approach is to just post what plane and the estimated All Up Weight, and everyone will pitch in their recommendations.

Larry
Old 06-20-2006, 05:41 PM
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Wazmo
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Default RE: brushless confusion!!

[link=http://www.motocalc.com]MotoCalc[/link] is a great program that will help you determine a good starting point. Until you get some experience, you may need to tweak gear ratio and/or prop size a little to get the power in the range you want.
Old 06-20-2006, 07:00 PM
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drbenz
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Default RE: brushless confusion!!

thanks all for your responses. as soon as i get another plane, i will ask for recommendations.

Thanks again
Old 06-20-2006, 07:45 PM
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Default RE: brushless confusion!!

Dr benz

I didnt even ask the forum members

Just listened to a few greats( posts) such as Tman and others,, and and put together a very enjoyable package , good flying
Old 06-21-2006, 02:34 AM
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stockdaddy
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Default RE: brushless confusion!!

On the hacker site, they do a pretty good job of telling explaining details for each motor:
http://www.hackerbrushless.com/motors_a20.shtml

And their motor are plug and play so you won't have to buy motor mounts, prop adapters, bullet connectors, or extra shafts.
Old 06-21-2006, 08:46 AM
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WhtBronco
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Default RE: brushless confusion!!

I agree, I am very impressed with my Hacker motor as I have been with my HiMax motor. Both motors came complete with mounts and prop adapters, the HiMax with both firewall mount and stick mount.

All I did was start looking at this forum and read most of the posts for a while and I figured it out. I just got into modern electrics 2 years ago, but I love them. Convenient, quiet, powerful but expensive.
Old 06-21-2006, 09:02 AM
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WhtBronco
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Default RE: brushless confusion!!

Oh and 1 other thing, I downloaded and tried to use MotoCalc or something similar to it and after about an hour I gave up. I could not figure it out. It sure seemed simple enough, but no matter what numbers I put in I could not get output anything close to what I had verified I have in my plane. I am a Network Engineer by profession and generally have no trouble figuring out software programs.

I used the published numbers for the electronics equipment I am using on my plane and the output was way, way, way off. Had I used that program to select the electronics equipment on my new plane I'd have ended with an unflyable airplane IMO. In this arena nothing works like experience.
Old 06-21-2006, 10:23 AM
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Troy-RCU
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Default RE: brushless confusion!!

P-CALC free online calculator with many popular motors and batteries
http://brantuas.com/ezcalc/dma1.asp

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