A heated discussion about cooling down

Here’s something that I have wondered about that I feel like I’m missing something.

Why don’t most eskate use any kind of active cooling on the motors and ESC?

The background story is: I see many comments and discussions about going to bigger motors, 80xx etc, for more torque/power, hooked up to battery + escs that can’t even sustain half of what the motor is capable of handling. Huge, bulky motors capable of 6-8kWs each that theoretically would require 20p+ packs with watercooled ESCs. Since motor torque is directly related to amperage, increasing motor size at the exact same power input would only realistically only increase torque by a very low amount, at the expense of a motor 2-3x the weight. The only conclusion to me then is that the bigger motor can sink more heat due to more material before losing efficiency and torque to overheating.

Obviously heat is a big issue with any electrical drive system, almost all electric cars use some type of fluid cooling on the motors and even battery. Liquid cooling is a bit inhibiting for eskate, but why not forced air cooling? The brushless out runners we use originated from RC things, yet there are companies like scorpion motors making outrunners in the 40mm can size that can hold sustained wattages higher than most 63xx eskate motors. The difference is 1: trading torque for RPMs, then gaining the torque back through high gear reductions (disregard the erpm limit for now), and 2: machining a centripetal fan into the motor casing to pull a lot of airflow through the core.

Now why does no eskate motor use the can as a fan to eject heat? Or any kind of active airflow for cooling? (including the esc? My RC cars have fans on the esc, why not eskate?). A smaller motor can achieve similar power outputs as a large one (to a reasonable extent) as long as the smaller motor can stay cool. Dust/waterproofing is not an excuse here. Outrunners are surprisingly resilient to dust/water ingress as long as the vents are of reasonable size. And ESCs can be waterproofed with protruding heatsinks and fans attached. If a $60 RC esc with an active cooling fan can be driven underwater, there’s no reason for eskate escs and motors to have the same?


Ngl I didn’t read past the first paragraph, but I’ll toss my 2c in, sorry if I repeat you 🤷

the only ‘worthwhile’ powered cooling system would be an aluminum block with fans attached on the Inside of the enclosure, and even that has issues.

The best we can do without power, using large thermal masses and mounted plates for exterior cooling, is probably the perfect amount of cooling for the avg user.

I’ll always opt for this over something powered, or something that rotates, or introduces water into the system. It’s easy, cheap, proven to work very well, and hasn’t been the cause of any* ESC failures

* as I know, I could have missed a thread somewhere

1 Like

Almost all active cooling systems either require liquid or generate condensate liquid. That’s why I wouldn’t consider it.


Obligatory link to past discussion about cooling direct drives with statorade, a liquid that would transfer heat from the stator to the outer motor can:


Most boards at most has an exposed aluminum plate, almost none have fins of any significant size to increase air contact area.


A large heatsink with a fan is also active, the motors themselves can be used as fans since they already spin.

Yeah, I never said otherwise :slight_smile:

That’s my preferred method. @3DServisas needs to collaborate with @jeffwuneo to make some Heatsinks for those new vescs :wink:

We already make :smiley:


Go to bed Jeff! :joy::joy:


I back to work already :slight_smile:


Wow, sounds busy :0

my god :scream:

1 Like

The thing is, to draw any conclusion we need to perform a lot of tests, whats better, a smaller motor that heats up a lot and we need to cool down or a bigger one that doesn’t get hot? Temperature is not a measure of loses, a good parameter to look is phase resistance, but that is only valid for motors of the same Kv, and while loses other than resistive ones are small on most motors we use, going bigger may not continue this trend

Another important point, a motor doesn’t produce ever growing torque for increasing phase current, I don’t know if we are close or not to saturation in the typical settings most user run for 63XX motors, but I know from some tests that 50XX motors at 40 A phase current is beginning to saturate, so this is a case where cooling doesn’t matter that much

That is a old discussion on ebikes forums, people fill they’re hubs with Statorade and heat sinks and run crazy power in them, while ignoring that the motors are well above saturation and are running crazy inefficient, you have a heater, not a motor

Justin Lee did some test that can easily be reproduced for our motors, that should give a clue if the currents we run are already too high, or only heat is the limiting factor, and if we manage to cool them down, we can pump way more current for a linear torque increase



Active cooling plus, you know, water cooling on rainy days.

Also, the whole casing is made from an aluminium block.


Many cars are air cooled, like first edition of the WV Beatle or Citroen 3cv, their performed well under hot weather, but sometimes need to stop for a while to cool down and keep going…By the other hand, new tech became more affordable, and water-cooled cars has became more reliable to perform under really hot weather; but the expense was more space taken at the motor compartment, and higher cost to the buyer…My thoughts, for now we are at the middle of the Citroen 3cv stage and different cooling methods, but future it is promising and surely we will achieve the goal of an extreme performance machine under all weather conditions…It is a matter of time, and if you think so, things are changing fast…

1 Like

Is anyone here a crazy/fast enough rider to make their motors hot? I ride around the park and the liquor store. Never even had my motors or esc get warm.

@nickw1881 Yes lot of us. For example my motors goes easily up to 70 deg C while outside is only 5deg C. I’m little worie how it will be during summer. And actually I’m thinking how to do active cooling.

@moestooge has fans cooling his escs. They stay on inbetween runs. I felt the inrunners cans after his laps at the evolve World Cup and they were barely warm.

I use passive heat sinks on my escs and hit avg 50a over 5-6 miles,150a peak. They might get warm.

You are on 4wd. Do your cans get hot after a sprint on urethane?

My cans see maybe 140F at the very most, usual is in 120f.

My biggest thermal concern is the lipos. If a 7lbs pack is hot, 80f-100f, you need to chill (literally) or decrease your max battery draw.

I spent a few hours looking at the performance scorpion gets out of their outrunners. It’s impressive, but they aren’t really impact resistant? Would you roll on 1.2k$ (300$ x 4) of their special edition 40mm series capable of 5-6k watts peak each?

Not a rhetorical question, It might be worth it, at least their motors are serviceable.

1 Like

in regular use no, but to get those pictures i went up to 84 degrees celsius


Those are good points, I guess ultimately cooling doesn’t matter if it never gets to saturation. Heat on the ESC has not really been an issue to me, passive plates gets warm at most, but in my hilly area with non-stop up/down steep hills, after half an hour the motors get hot enough that I don’t want to keep my hands on them. Not scorching hot, maybe 140-150f on the can on a hot summer day, I wonder if there is any efficiency gain if the motors ran cooler.

The scorpion motors are definitely interesting, too expensive but would be kind of fun build to roll around on a couple 40mm cans with some really high gearing. erpm might be an issue though with vsec. their 500+ kv motors are pushing past even vsec6 limits. Although they make some in-house 14s ESCs that they claim can take 16s without voiding warranty. but no regen braking so that’d be interesting.