Why do people say a brushless motor runs cooler than brushed?

[CoolRunning]

This is for crawling speeds.

Same can size (lets pick 550) and same motor quality on 3S with same gearing in the same truck.

I imagine if the motors were geared for the task, shouldn't both stay a similar temp?

I know high speed can increase brushed motor temps with more brush friction and arcing and the brushless motor will rev harder but why would brushless supposedly run cooler for slow stuff?

If you're applying similar levels of torque I would have thought in this example it would be similar enough not to be an easily noticeable difference.

 

[Meatwad]

The allure of brushed motors is not torque.

 

[mikemcE]

Friction is a bitch.


Hang up and Drive

 

[WHITE-TRASH]

Friction is a bitch.

Indeed it is and brush drag & arcing creates heat.

 

[Greatscott]

Brushless systems are capable of more power than their brushed counterparts. Because of this, brushless systems do not have to work as hard to produce the same amount of torque/speed, because they are not working as hard, they generate less heat. This is a very over-simplified explanation, the BL systems have to balanced for the size of the RC and what it will be used for.

 

[badhoopty]

in my now oldschool c2, i have a tekin pro4 3300 that hasnt been rebearinged or anything other than cleaned and lubed for the past 5 years. maybe longer... long enough ago i cant really remember how old it is. "thumbsup"

 

[EeePee]

long enough ago i cant really remember how old it is. "thumbsup"

You got that just last week, yo! You're the one that's old.

 

[CoolRunning]

Yes but we're talking nearly the same efficiency and motor speeds where friction is clearly not a major factor like a high speeds. I've looked around and there is nothing that seems to describe what everyone is saying about how a brushed motor generates all this excess heat vs a brushless one at the same RPM, load and gearing.

Many countless motors in many countless appliances going for how many long years have been brushed. I understand the possibilities of brushless like more rpm, longevity and lack of maintenance but the heat thing I'm not following.

The brushless motors I've used seem too get nice and warm going slow just the same as their brushed counterparts. I'm generally curious about why this is the case as if it's true it give some credence to throwing $400 at a brushless system if you crawl a lot.

 

[Meatwad]

Efficiency and service life is enough of a justification of the cost.

 

[mikemcE]

A high end Holmes Brushed is not " inexpensive " but I don't run them. I don't want to constantly check and adjust brushes and comm.


Hang up and Drive

 

[crawlinwithacat]

I know squat when it comes to motors but my first intuition is that since brushless motors use electromagnets I would assume that under load they are cooler since it is just a magnet with more current being pumped through it. Where as a brushed motor has an arc that is active for a longer period of time when under load. (I think) Like I said this is probably totally wrong but maybe someone who actually knows a thing or two about motors chime in.

Sent from my SAMSUNG-SM-J120A using Tapatalk

 

[Hardcoretam]

Yes but we're talking nearly the same efficiency and motor speeds where friction is clearly not a major factor like a high speeds. I've looked around and there is nothing that seems to describe what everyone is saying about how a brushed motor generates all this excess heat vs a brushless one at the same RPM, load and gearing.

Many countless motors in many countless appliances going for how many long years have been brushed. I understand the possibilities of brushless like more rpm, longevity and lack of maintenance but the heat thing I'm not following.

The brushless motors I've used seem too get nice and warm going slow just the same as their brushed counterparts. I'm generally curious about why this is the case as if it's true it give some credence to throwing $400 at a brushless system if you crawl a lot.

It comes down to simple physics.
Brushes create friction which increases heat
Brushes create arcing which increases heat

As brushless motors don't have brushes, it a brushed motor was built to perform the same as a brushless motor and have the same amp draw and put under the same load then after some time the brushed one would have higher temps. If you're frequently in binds, then you'll have heat issues regardless of brushed or brushless and the difference in time they would take to heat up under abuse would be minimal.

 

[Col_Sanders]

Yes but we're talking nearly the same efficiency and motor speeds where friction is clearly not a major factor like a high speeds. I've looked around and there is nothing that seems to describe what everyone is saying about how a brushed motor generates all this excess heat vs a brushless one at the same RPM, load and gearing.

Many countless motors in many countless appliances going for how many long years have been brushed. I understand the possibilities of brushless like more rpm, longevity and lack of maintenance but the heat thing I'm not following.

The brushless motors I've used seem too get nice and warm going slow just the same as their brushed counterparts. I'm generally curious about why this is the case as if it's true it give some credence to throwing $400 at a brushless system if you crawl a lot.

IIn my experience, brushless runs much cooler when crawling, has more torque, and quite a bit more wheel speed.

I had a 2300kv Roc 412 in my C2 comp rig and was running a 12t pinion. I could run through 4000+mah of battery and the motor would get warm but nowhere near hot. I swapped in a HH 16t Crawlmaster Expert and went down to an 11t pinion. Less than 850mah and it was too hot to touch. Dropped down to a 10t and still got hotter than I like. Not its down to a 9t and still hotter than my old Roc 412 would get. This was all during fall/winter.

The truck is Toyzuki V2 so the front is overdriven quite a bit. It has big tires (Hyraxes or RBXLs) and its no lightweight. I am about to install one of the new Castle sensored motors and see how that works out

 

[fyrstormer]

Friction is only a minor source of heat in a brushed motor. The brushes are constantly lubricated by graphite powder embedded in them. The major source of heat (aside from the electrical resistance of the coils, which brushless motors also have to deal with) is the electrical resistance of the brush/commutator interface. In a high-load/low-RPM scenario, the battery is shoving several amps through a chunk of copper and graphite that contacts another chunk of copper via an interface that is riddled with microscopic flaws *and* constantly changing position. Both of those factors significantly increase the electrical resistance and heat-generation of that interface. If the brush shunts are screwed-on instead of soldered-on, that adds a second interface with lots of microscopic flaws to increase its electrical resistance. Brushless motors don't have either of those high-resistance electrical interfaces, and thus they run cooler.

I have several 12-turn brushed motors, some running copper brushes and some running silver brushes, which are installed in touring cars with various gear ratios. The slower cars have gear ratios on the order of 9:1, and despite the motors turning 35,000rpm at top speed, they barely get warm to the touch when I do speed-tests. If friction between the brushes and commutator were a major source of heat, those motors would be painfully hot after a couple passes at such high RPMs.

 

[CrawlinMike]

I switched to brushless in 90% of my RC fleet for the simple matter of convenience. Many years I dealt with brushes and having a motor fail when I was at an area miles from home to play. I make sure to get an appropriate kv for the application just like you would turns in brushed. And in my trail/crawler slow control I have gotten sensored. In my 6x6 I have a brushed but keep a couple non rebuildable cheapo rc4wd throwaway motors on hand. I believe the brushless has an efficiency advantage and runs cooler. I'm sold on them anyways. Not sure if my post helps any more than what's been said already, but my .02 is in now too. Cheers

 

[fyrstormer]

They are more convenient, to be sure...but I enjoy tinkering.

 

[Greatscott]

https://www.youtube.com/watch?v=Y7nQI2xM2as

 

[robert@castle]

https://www.youtube.com/watch?v=Y7nQI2xM2as

The graphic a 1:09 is the real key to heat. Brushless motors are more efficient. 5-15% may not sound like a lot but that means that 5-15% less of your energy is being wasted as heat.

Lets say you are running 3s and pulling 20amps of load. 12.6V * 20amp = 252watts. If you are using a 90% efficient motor you are only generating 25.2 watts of heat. If you are using a 75% efficient motor you are generating 63 watts of heat.

And really the advantage of the brushless motor would be even higher than that. That is comparing 2 setups with equal input current. A better example would be saying a setup needs 200watts of rotational power to operate. A 90% efficient brushless motor would draw 222.2 watts of power from the battery, and a 75% efficient brushed motor would draw 266.6 watts of power from the battery. So to produce the same amount of output power, the brushed motor would be wasting 3x as many watts to heat. So not only will the brushless motor run cooler, you'll get 19.9% longer battery life.

These are full throttle efficiencies, but the same applies at slower speeds. Brushless motors are more efficient at all throttle percentages.

All castle motors are around 90% efficient and some are even as high as 93%.

 

[fyrstormer]

Yes, I agree. I was talking about *why* brushless motors are more efficient.

There is one thing in the video that is obviously incorrect: They claim that brushed motors lose efficiency from constantly connecting and breaking electrical connections to the wire coils. Brushless motors do this as well, they just do it electronically inside the ESC instead of mechanically at the surface of the commutator. Both types of motors suffer from inductive reactance when the coils are powered-up, because inductive reactance is a property of ANY circuit capable of generating an electromagnetic field -- it doesn't matter if the coil is spinning or stationary. The lower efficiency of brushed motors is the result of the high electrical resistance of the moving mechanical interface between the brushes and the commutator.

 

[losikid]

Yes, I agree. I was talking about *why* brushless motors are more efficient.

There is one thing in the video that is obviously incorrect: They claim that brushed motors lose efficiency from constantly connecting and breaking electrical connections to the wire coils. Brushless motors do this as well, they just do it electronically inside the ESC instead of mechanically at the surface of the commutator. Both types of motors suffer from inductive reactance when the coils are powered-up, because inductive reactance is a property of ANY circuit capable of generating an electromagnetic field -- it doesn't matter if the coil is spinning or stationary. The lower efficiency of brushed motors is the result of the high electrical resistance of the moving mechanical interface between the brushes and the commutator.

Technically, a brushless motor requires 3 phase power and there is absolutely no switching involved if pure sine waves are being pumped into the motor. But we have to convert DC power into 3 phase AC so there are some losses in switching the mosfets.

However, the switching losses in a brushless esc are similar to the losses inside of a brushed esc. The mechanical commutation of a brushed loss is significantly more than the pwm switching losses in an esc.

Both brushed and brushless esc's switch the power on and off inside of them. There are some recovery losses during this process, but there are nearly lossless snubber circuits that can be used instead of a flyback diode. But efficiency gains are usually not worth the effort to design/tune such a snubber circuit.

Brushed motors will also suffer more electromagnet losses compared to a brushless motor because a brushless motor keeps the rotor closer to the generated magnetic field and realizing most of the power and minimizing reactive power.