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Brushed to Brushless conversion

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Old 08-12-2007, 06:16 PM
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Default Brushed to Brushless conversion

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?
[sm=confused.gif][sm=frown.gif]

Somebody please help me out real soon.
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Old 08-13-2007, 09:11 AM
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Default RE: Brushed to Brushless conversion

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.
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Old 08-13-2007, 11:38 PM
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Default RE: Brushed to Brushless conversion

Ok thanks much but one more question... How do i figure out how many Watts the prop pulls?
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Old 08-14-2007, 08:35 AM
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Default RE: Brushed to Brushless conversion


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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Old 08-14-2007, 08:56 AM
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Default RE: Brushed to Brushless conversion


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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Old 08-14-2007, 01:32 PM
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Default RE: Brushed to Brushless conversion

Ok thanks and is the higher the "Kv" the better?
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Old 08-14-2007, 02:46 PM
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Default RE: Brushed to Brushless conversion

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.
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Old 08-14-2007, 02:48 PM
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Default RE: Brushed to Brushless conversion

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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Old 08-14-2007, 04:49 PM
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Default RE: Brushed to Brushless conversion

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.
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Old 08-14-2007, 04:59 PM
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Default RE: Brushed to Brushless conversion

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).
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Old 08-14-2007, 05:15 PM
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Default RE: Brushed to Brushless conversion

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
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Old 08-14-2007, 05:34 PM
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Default RE: Brushed to Brushless conversion

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/UNITEDHOBBI...idProduct=4700
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Old 08-14-2007, 05:36 PM
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Default RE: Brushed to Brushless conversion

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.
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Old 08-14-2007, 05:38 PM
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Default RE: Brushed to Brushless conversion

See my edited post. You could even go up a bit in size and get two genuinely 200W motors for not much more.
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Old 08-14-2007, 05:43 PM
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Default RE: Brushed to Brushless conversion

Hey thank you so much!!! Thanks!!!![sm=regular_smile.gif]

And whats the stock number of the other ones that are better? They should work for the elight P-38 right?
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Old 08-14-2007, 05:46 PM
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Default RE: Brushed to Brushless conversion

If you want a lot more power (certainly 200W, maybe 250W) try this (still lighter than your 65g monster): http://www.graysonhobby.com/catalog/...97f97cb3cb949a
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Old 08-14-2007, 05:51 PM
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Default RE: Brushed to Brushless conversion

Ok and so that requiers a 11x5.5 prop. are there any that counter rotate that you know of?? Or can 10x8 work? Thanks

And what about the following specs for an ESC?

Specifications:

· Weight: 18g / 0.63 oz

· Size: 32 x23 x7 mm / 1.26X0.91X0.28 inch

· Constant Current:20A

· Max Current:25A (for ten seconds)

· FET: 12

· BEC: Yes, 2A

· PWM: 8 KHz

· Input: 2 to 3 Li-Po, or 6 to10Ni-MH/Ni-Cd

sorry for asking so many questions[]
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Old 08-14-2007, 11:34 PM
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Default RE: Brushed to Brushless conversion


Quote:
ORIGINAL: Dr Kiwi

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.
That is a good (obvious) point. My brainfart move for not bringing that up in the first place.
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Old 08-14-2007, 11:44 PM
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Default RE: Brushed to Brushless conversion

http://www.graysonhobby.com/catalog/...97f97cb3cb949a - careful using anything larger than say a 10x5 with that motor. It is spec'd. at 1400 kv, a ton of rpm's to be running a prop. as large as a 10x8 or 11x5.5. Plus, they only recommend a 9x5.

Or if you are looking for a bargain, check E-Bay for a motor that is very similar to the specs. of the Park 450 - 14 amps continuous, 18amp burst and around 890kv with a watt output of around 150-175 total.

On that ESC, the GH2217-09 Brushless Outrunner Motor that Dr. Kiwi mentioned has a max. of 30 amps and a continuous that could get as high as 27amps, the ESC you are looking at only gets up to 25amps max. and 20amps continuous, you want the ESC to exceed the demand of the motor.
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Old 08-15-2007, 12:35 AM
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Default RE: Brushed to Brushless conversion

Hey thanks for the help but the only prob is the p-38 comes with counter rotating props(10x8) and do you know any where that has counter roatating props thath are around 9x5-10x5? I found counter rotating props that are 10x4.5.
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Old 08-15-2007, 09:10 AM
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Default RE: Brushed to Brushless conversion

If you have not already, check out Towerhobbies, they carry just about everything. There will not be that much of a difference between a 10x5 and a 10x4.5. They are very, very close.
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Old 08-15-2007, 07:05 PM
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Default RE: Brushed to Brushless conversion

I couldnt find any in tower hobbies. So what would happen if i got 10x4.5?
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Old 08-15-2007, 07:51 PM
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Default RE: Brushed to Brushless conversion

It would just have a little less thrust or acceleration than a 10x5, but really just barely, maybe not even enough to notice. Also, if you are going with that bigger, more powerful motor. the extra power the motor is going to provide should compensate for the very little difference in prop. pitch.
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Old 08-15-2007, 07:54 PM
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Default RE: Brushed to Brushless conversion

So with that bigger motor this plane (eflight P-38) is prob going to fly pretty fast?
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Old 08-16-2007, 10:22 AM
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Default RE: Brushed to Brushless conversion

Theoretically ...which sometimes means nothing .....it should. That motor that Dr. Kiwi mentioned a while back will get up to a 30 amp burst, the Park 450 that is specified for the P-38 only gets up around an 18 amp burst......big difference in power. Which will equate to more thrust and top speed as long as the prop. combination works out.

The best thing for you to invest in is a wattmeter, voltmeter or powermeter. They connect in-line with the power system and tell you how many amps your motor/prop. combination is drawing, how many watts it is producing, etc.....it is a must to precisely know how your system is running.
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