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Old Aug 19, 2014, 06:49 PM
Registered User
Joined Aug 2014
1 Posts
Why brushless motor?

Hi guys!
I am absolute noob on r/c world and a new member here as well. I have been through some basic info and have understandings of fundamentals though (motors, ESC, battery, servos etc). I wonder, why brushless motors are used for r/c? I do understand that they run analogue and hence the wavelength can be changed. Is that the reason behind using brushless motors for r/c or something else? A bit more explanation will surely be highly appreciated . Thank you all for your time regarding my post.
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Old Aug 19, 2014, 10:51 PM
Submarine or Target?
ericbphoto's Avatar
United States, SC, Piedmont
Joined Jul 2013
527 Posts
One major advantage is that there are no brushes to wear out and therefore, no conductive carbon dust to build up inside the motor. With a good quality ESC, there is potential for better low end speed control. I am sure there are other details. There are some people on this list who have extremely strong bias towards one type over all others. The truth is that each motor type (brushed, brushless outrunner, brushless inrunner) has strong points and weak points. Choosing the right one depends on your application, your personal preference and your budget. Don't let anyone convince you that there is only one type worth using. do your research and learn as much as you can from multiple resources.

I personally like the idea of using brushless because of my experience with industrial 3 phase motors. But the first electric boat I am building will have a brushed motor in it. My second boat will be receiving a steam engine.
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Old Aug 20, 2014, 04:52 AM
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Blackpool, Lancs
Joined Feb 2006
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The big advantage of brushless comes from their favourable power to weight ratio in performance boats plus their better efficiency running fast. For the most part, if close control at low speed is required, the potential mentioned remains just that, potential. i have a feeling that at low speeds, the efficiency of brushless evaporates, so there is plenty of potential for both families of motor depending on the model.
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Old Aug 20, 2014, 08:46 AM
Vita ex Machinis
patmat2350's Avatar
Motor City
Joined Dec 2004
12,841 Posts
+1 to all of above.

Another big plus for brushless: The brushless motor makers all seem to be hobby oriented, and they publish one of the the most important specs- the kV value (how fast an unloaded motor will spin per applied volt).
Brushed motors are almost all "found" motors" from high volume production applications, and with unknown specs... you have to guess at, or test, to determine just what they are.

A downside for outrunners: All motors "ring" when hit with the pulsed output of an ESC. Outrunners have a semi-open can that is shaped like a bell, and these ring even louder.
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Old Aug 22, 2014, 02:42 AM
Naval gazing
United States, MA, Boston
Joined May 2008
1,232 Posts
Why do people prefer to run LIpo batteries with brushless motors and would there be a problem running a non-LIpo battery on the , like worse run time, or in my case worse performance than the equivalent brushed motors would be getting from the same batteries?

Also how does one figure determine comparative motor power output when you want to replace a brushed motor with brushless?
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Old Aug 22, 2014, 04:17 AM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
5,131 Posts
Hi spacephrawg,

In general, a motor doesn't care where the juice comes from, Lead, NiMH, Lipo, as long as the battery can deliver the current the motor will take under load.

The preference for Lipo's over NiMH comes from the high current speedboat set-ups; less weight and more runtime from Lipo's versus NiMH.

Also the discharge current of Lipo's is much flatter than NiMH, so if you're racing, the boat will run at (virtually) the same topspeed until the LVC cut's in, where you see the speed drop gradually when running NiMH.

I see no problems when you power a large tug with brushless motors and use SLA for their dual porpose, powersource and ballast, as long as the ampdraw of the motor(s) in question can be easily met by the batteries.

Replacing a brushed with a brushed equivalent isn't always simple, as a brushless motor with the same power output will be considerably smaller than the brushed motor, which may result in a different bolt pattern to get it to fit in the existing motormount.

I either make a fitting new mount, or, if the old one isn't accessable without major surgery, I take a larger motor diameter that will fit the original mounting holes and live with the fact I now have five to ten times more power installed than the model in question will ever need.

My smaller semi scale models all run on Lipo's nowadays due to the much better weight to capacity rate.
My 60 cm tug, powered by a brushed 5 pole motor, can run up to two hours full throttle continuously before the (8000mAh) lipo's are depleted.

My larger 110 cm MAS runs on 9600mAh Lipo's, has a 4250 800Kv outrunner (a lot lighter than the brushed Fan motor I was originally going to use) and can run way over two hours, mainly at walking speed with the occasional full throttle sprint at 25+mph.

Regards, Jan.
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