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All Forums >> Electric Aircraft Universe >> Brushed/Brushless motors, speed controls, gear drives >> Brushed to Brushless conversion
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Brushed to Brushless conversion - 8/13/2007 12:16:41 AM   
DAL4215


 

Posts: 22
Joined: 8/13/2007
From: Pleasant Grove, UT, USA
Status: offline 		Im trying to learn how to convert from brushed to brushless and choose the right brushless motor, when i switch to a brushless motor do i keep the same prop that was on the brushed motor? Any one know a good website that explains al of this stuff? I know there are motors that are brushless that say for ex. 4oo brushless to replace a 400 brushed. But there are websites that dont say that and only give me the specs so how should i be able to tell if its the right one? Also ive noticed the motor is down and to the right why?


Somebody please help me out real soon.

< Message edited by DAL4215 -- 8/13/2007 4:27:57 AM >
       Post #: 1

RE: Brushed to Brushless conversion - 8/13/2007 3:11:44 PM   
ADChobbystore



Posts: 1540
Joined: 5/16/2006
From: Rancho Santa Margarita, CA, USA
Status: offline 		You will most likely NOT be using the same prop. when you convert to brushless.

The most precise way to convert over is to use the flying weight and style of the plane. Everything in regards to electric power is based on total watts, which then converts to watts per pound of aircraft. Trainer/slow flying models require 70-90 watts per pound, sport/aerobatic models require 110-130 watts per pound, and 150+ is for 3D and High Performance models. The total watts of a power system is calculated by multiplying the voltage input from the battery, times the amp draw of the prop/motor combination.

Example: Let say you have a 3lb aerobatic/sport plane - 3.0lbs x 120watts per pound (middle of the road) = 360 total watts required of the system to acheive the proper performance level. Now that you have a requirement, you can start looking at motors and batteries. Most likely, you will be using a 3 cell 11.1 volt LiPo, unless you have a 4lb. + plane. So, if total watts = voltage from battery x amp draw of motor....... 360 total watts = 11.1volts x amps = 32amps required of the motor in order to acheive the desired performance level. So in this example, you would be looking for a brushless motor that can handle a 3 cell LiPo, with a max. watt output at or above 360watts, and can handle a continuous amp draw of 32amps +

I know.......seems confusing if you have not gone thru this process before ......but this is the most precise way to nail down a power system.

< Message edited by fliprob17 -- 8/13/2007 3:13:17 PM >

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RE: Brushed to Brushless conversion - 8/14/2007 5:38:10 AM   
DAL4215


 

Posts: 22
Joined: 8/13/2007
From: Pleasant Grove, UT, USA
Status: offline 		Ok thanks much but one more question... How do i figure out how many Watts the prop pulls?

(in reply to ADChobbystore)
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RE: Brushed to Brushless conversion - 8/14/2007 2:35:11 PM   
Dr Kiwi


 

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From: Chattanooga, TN, USA
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quote:

ORIGINAL: DAL4215

Ok thanks much but one more question... How do i figure out how many Watts the prop pulls?



Most motors come with manufacturer's specs which give you an idea of what the max amps/max watts ratings are. Usually a range of props is recommended.

You can use a calculator program like Motocalc to try different combos.

Or, you can use a Whattmeter and test the motor yourself.

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RE: Brushed to Brushless conversion - 8/14/2007 2:56:19 PM   
ADChobbystore



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quote:

ORIGINAL: DAL4215

Ok thanks much but one more question... How do i figure out how many Watts the prop pulls?


As Dr. Kiwi stated, most manuf. have a specified range for prop. sizes. The larger or higher you go on that range, the closer you will get to the MAX. BURST rating of the motor. The safest way to determine the correct prop. size is always to test it yourself. Using a wattmeter, voltmeter, powermeter..... there are a bunch of different options out there now. It basically connects to the battery on one end, and the ESC on the other, so it sits in-line and measure the current draw the system is demanding. They generally display, amps, watts produced, battery voltage, mah used, and some show RPM's as well.

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RE: Brushed to Brushless conversion - 8/14/2007 7:32:31 PM   
DAL4215


 

Posts: 22
Joined: 8/13/2007
From: Pleasant Grove, UT, USA
Status: offline 		Ok thanks and is the higher the "Kv" the better?

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RE: Brushed to Brushless conversion - 8/14/2007 8:46:18 PM   
ADChobbystore



Posts: 1540
Joined: 5/16/2006
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Status: offline 		Not necessarily......it depends on the application. The higher the kv, the smaller the prop must be to avoid over taxing the motor and possibly overheating it. Generally, the safe bet is to stay around or under the 1100kv number when running direct drive on an Outrunner style motor......at least that has been my experience. The highest kv Outrunner I have is a 1250, running direct drive.

< Message edited by fliprob17 -- 8/14/2007 10:50:05 PM >

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RE: Brushed to Brushless conversion - 8/14/2007 8:48:42 PM   
DAL4215


 

Posts: 22
Joined: 8/13/2007
From: Pleasant Grove, UT, USA
Status: offline 		So an Outrunner 1000Kv is ok? I am looking into buying the Eflight P-38 and it requires a 450 outrunner 890 Kv and i have an outrunner 1000Kv.

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RE: Brushed to Brushless conversion - 8/14/2007 10:49:29 PM   
ADChobbystore



Posts: 1540
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quote:

ORIGINAL: DAL4215

So an Outrunner 1000Kv is ok? I am looking into buying the Eflight P-38 and it requires a 450 outrunner 890 Kv and i have an outrunner 1000Kv.


That should work out ok. You may have to change the prop dia. or pitch a tad, but it should work. I am sure you are aware of this, but if not, the P-38 is a dual prop/motor/esc setup. It requires (2) motors and (2) ESC's.

< Message edited by fliprob17 -- 8/14/2007 10:50:26 PM >

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RE: Brushed to Brushless conversion - 8/14/2007 10:59:47 PM   
Dr Kiwi


 

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quote:

ORIGINAL: DAL4215

So an Outrunner 1000Kv is ok? I am looking into buying the Eflight P-38 and it requires a 450 outrunner 890 Kv and i have an outrunner 1000Kv.


All motors are not equal:
You need to look at the amps/watts rating of that mystery 1000Kv outrunner of yours. The E-flite 450 (890Kv) is rated at 14A/18A burst... so lets call that about 150W max....can your 1000Kv outrunner cope with that (or do better)... if it matches up then you can have the same power as the suggested 450....if your motor is rated at say only 10A/100W then you see the problem.... you'd have 200W (twin) when the recommended power system is 300W (twin).

< Message edited by Dr Kiwi -- 8/14/2007 11:03:48 PM >

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RE: Brushed to Brushless conversion - 8/14/2007 11:15:46 PM   
DAL4215


 

Posts: 22
Joined: 8/13/2007
From: Pleasant Grove, UT, USA
Status: offline 		Dang so these specs would most likely not work for the P-38;

Weight:65g

Size:Ф31X62.0

Output Axis:M3

Current:8.2A/12.7A

BATTERY: 3-4 cells Lipo

KV:1000

What about these other specs;

2-3cells 7-20A 1570KV
Φ30x23 mm /1.18X0.91 Inch
Φ3mm 68g / 2.4oz

< Message edited by DAL4215 -- 8/14/2007 11:18:17 PM >

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RE: Brushed to Brushless conversion - 8/14/2007 11:34:08 PM   
Dr Kiwi


 

Posts: 1194
Joined: 12/4/2002
From: Chattanooga, TN, USA
Status: offline 		That's a heck of a heavy motor (65g) to be only good for 8A or so! There have got to be better motors out there? I mean, you need two motors...right? I would not buy a second lousy motor when there are so many good, cheap options out there. You'd be better to put your money into two good 150-200W motors.

These are cheap ($16.95) and work well if you keep 'em at no more than 15A. http://unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=4700

< Message edited by Dr Kiwi -- 8/14/2007 11:38:07 PM >

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RE: Brushed to Brushless conversion - 8/14/2007 11:36:11 PM   
DAL4215


 

Posts: 22
Joined: 8/13/2007
From: Pleasant Grove, UT, USA
Status: offline 		Yes i kno i just noticed the same thing but the thing is i cant afford 2 $65 motors + $130 for the kit. You know what i mean? i cant find any good cheap ones.

(in reply to Dr Kiwi)
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RE: Brushed to Brushless conversion - 8/14/2007 11:38:58 PM   
Dr Kiwi


 

Posts: 1194
Joined: 12/4/2002
From: Chattanooga, TN, USA
Status: offline 		See my edited post. You could even go up a bit in size and get two genuinely 200W motors for not much more.

< Message edited by Dr Kiwi -- 8/14/2007 11:39:45 PM >

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RE: Brushed to Brushless conversion - 8/14/2007 11:43:21 PM   
DAL4215


 

Posts: 22
Joined: 8/13/2007
From: Pleasant Grove, UT, USA
Status: offline 		Hey thank you so much!!! Thanks!!!!

And whats the stock number of the other ones that are better? They should work for the elight P-38 right?

< Message edited by DAL4215 -- 8/14/2007 11:45:32 PM >

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