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Brushless vs brush @ energy consumption

Brushless vs brush @ energy consumption

Old 12-21-2009, 02:55 PM
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Default Brushless vs brush @ energy consumption

I was wondering if I take an equivalent brush motor compaired to brushless motor lets say a 17.5 bushless vs a 17.5 brushed with a Lipo battery... which motor is going to run longer? if we give them the same abuse not talking about speed or torque just run time
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Old 12-21-2009, 02:59 PM
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Brushless are reported to run loner. I am not going to state it as absolute fact because I have not done an actual comparison. However, you will notice brushless motors have less resistance than brushed motors. You can see this when spinning the motor shaft with your fingers. In addition, BL have bearings whereas a brushed stock usually does not.
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Old 12-21-2009, 03:09 PM
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Brushless will run quite a bit longer as they are alot more efficient. However, especially in the case that you describe. A 17.5T brushed is a lot hotter than a 17.5T brushless so that would also casue the brushed motor to use more current. 17.5T is stock in brushless. You can't compare them turn for turn.
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Old 12-21-2009, 03:11 PM
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I would guess the brushless would have longer run time since its prob more efficient than the equiv brushed motor.
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Old 12-21-2009, 03:17 PM
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efficiency, runtime, heat, and power all go hand in hand.

Brushed effiecency is around 60%, where brushless is anywhere from 75 to 94%, depending on the motor(94% motors are not available to the public yet)

For runtimes comparing equivilant motors you are looking at a 20% to 35% longer run time for the brushless over the brushed motor.
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Old 12-22-2009, 05:39 AM
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Originally Posted by interplanet View Post
efficiency, runtime, heat, and power all go hand in hand.

Brushed effiecency is around 60%, where brushless is anywhere from 75 to 94%, depending on the motor(94% motors are not available to the public yet)

For runtimes comparing equivilant motors you are looking at a 20% to 35% longer run time for the brushless over the brushed motor.
Do you have an Idea when these motors will become available to us?
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Old 12-22-2009, 05:55 AM
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Talking Brushless and Brushed motors with RPM

The Brushless and brushed motors are not same as RPM with Turns

LRP Eraser Brushless 9.5T with 33,840 RPM

Brushed 17T with 30,00 RPM
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Old 12-22-2009, 06:06 AM
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It's more about the efficiency of the ESC. BL motor's have a very low resistance per phase. Only like .0005 ohms if it's a good one. That means that alot of current can flow through it without being converted to heat. So, yes BL motor are way more efficient. Brushed motors have coils that have more resistance, especially through the brushes. They're also noisier.

-Tony
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Old 12-22-2009, 06:19 AM
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Originally Posted by Tilden View Post
The Brushless and brushed motors are not same as RPM with Turns

LRP Eraser Brushless 9.5T with 33,840 RPM

Brushed 17T with 30,00 RPM
it all depends on how many volts you put through the motor, hence KV, you can multiplie KV by volts to get theoretical rpm. So say the LRP has a kv of 4700,

4700kv x 2s(7.4v) = 34,780 rpms.

Now remember your battery is not going to run a 7.4 constently, and turns and kv's are different between motor manufacturers. Now in theory you can run a more effiecient set up with a lower KV motor and HIger volts to creat the same RPM, with less heat and longer runtimes.

So if you run it with the same motor on 3s it would be like this, and probably not last very long.

4700kv x 3s(11.1v) = 52170 rpms

That would be alot of heat, so to get more efficency and the same general speeds as before you would want a lower kv/higher turn motor.

3000kv x 3s(11.1v) = 33300 rpms

So you end up with longer run times, less heat, and less stress on the esc and motor. But you also have to remember you are adding weight to the car as a trade off. And its all theory, motor companys vary not only from company to company, but from motors to motors.


As for the high efficency motors, it has been done in lab settings so far, just look up brushless motor 94%, I think there is even video somewhere, but people tend to forget how much you lose again through the drivetrain, more if its not setup right.
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