Cooling Direct Drives

Hey guys!

I have a bunch of ideas, but rarely follow through… i’d at least like to document and maybe model the idea, and get your thoughts.

For a bit of background, my TBDDs pulling 160 amps get hot. They cool down slowly, enough to still have plenty of power with a bit of rest… but i’d like to close that gap if I can.

First dumb idea: a 3D printed air funnel filled with dry ice… scoop up air and blow cold air over the motors.

Second maybe not so dumb idea, and plenty of ways to implement it: a peltier cooler like this would fit perfectly on the hangar’s heat sink portion. To take it a step further, a CNC’d metal block that fits around the hangar and into the fins, with TIM between the hangar and shaped metal block, and TIM between the block and the cold side of the peltier cooler. From here, a low profile heatsink for the hot side, or a small 40mm water block connected with flexible tubing to some low profile radiators and a rugged reliable water pump.

Any other ideas? I have been considering putting thermal paste between the hangar/motor interface, i’ve just been lazy, and the hangar already gets almost as hot as the motors judging by touch, so this might be useless.

Final idea: Just a cooling block that interfaces with the hangar to give the hangar more thermal mass, more cooling fins, etc! simple.

Question, if motor heat is generated by the windings (?) would it be more beneficial to cool the hangar/axles (with TIM between hangar/motor) or would it be more beneficial to cool the cans themselves?


And water cooling? Or with mineral oil?

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IF the water cooling, than water. I hear mineral oil is not as good of a heat conductor.

It is nearly as effective as water and on top it’s non conductive though, if it’s submerged into that, like PC are doing.


Here are my 2 cents from having tried some stuff with Peltier coolers, thermal compound and thendoing some extensive browsing on the liquid cooling :

  • peltier modules have terrible efficiency and power consumption, it’s perfect for closed isolated environment + active air or water cooling for the hot part. There’s a thresold to aim for in order to manage the cooling effect : you must allow the hot side to build some heat but you cannot let it overtake the cold side either… This might be useful eventually for a fully enclosed waterproof ESC box + isolant instead of motors cooling (motors will get hot way quicker) but it’s not practical nor reliable… So let’s go to solution 2

  • Water cooling our liquid cooling ; it’s great if you manage to have a pump on board to circulate water from heat source toward a cooling area (metal tube exposed to direct air? Fan on top of the tube? This kind of stuff) though it will be heavy. Mineral oil works also, but the heat dissipation is achieved through same process. In short, just having “still” liquid without circulation will saturate at some point and become a hot trap… Definitely doable with proper process tho. Last option then

  • more thermal transfer : this is useful If you cool down the good area… The can itself isn’t the main source, it’s the stator. Cool down the windings and you gain everywhere : power, efficiency, reliability. Your best bet is experimenting with thermal compound to add patch between metal and your windings. Just like you’d do for a cpu.

Hope this will help you a bit :beer:


Just paint them white. Problem solved.


Your best bet

The problem of using the hanger to cool it is that the steel of the stator is not a good thermal conductor, and the section the heat has to travel is small, with Statorade you transform the whole can in a heat sink, the results in eBike hubs are impressive


that seems too good to be true. Nice catch


But also quite logical really. For the can to properly start radiating the stator already needs to be hot as balls. At that point the cooling effect is lost.

If you could extract the head straight into the can right away it should work wonders?

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I think it simply gives a thermo conduction between the parts filling up the air. Only problem is if you need to open up the motor. Must be mess afterwards. Ptobably we need like 1-2mm statorade so not that bad.

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I don’t open motors. If they make a single strange noise I just leave them on the side of the road for diy peasants to find and fix.


ahahahah ok then perfect I would say

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I’m eager to test it, just don’t have a motor to test

As they say on the description is not that you just cool the motor, you can greatly increase the power

power because internal resistance increase with heat. So the power is due to keep it lower. I might give it a try. I do not have problem with overheating motor but the more efficient the better.


@Pedrodemio @Brenternet @Vanarian

I’ve used ferrofluid (statorade) in my ongoing ebike build - Yes you need to open the motor. Either fully open, or drill a small hole and inject, then plug the hole afterwards.

It’s surprisingly not-messy. The magnetic nature of the ferrofluid means it sticks tightly to the magnets - very little goes anywhere else. You do need well-sealed motors, because any particle ingress will contaminate the statorade, and any gaps around the perimeter may allow statorade to leak out over time at high speed (centrifugal effect). A big ebike hub motor (3KW and 12" diameter) takes about 8ml of statorade to achieve full effect.

Another addition seen on ebike motors is hubsinks - curved heatsinks attached to the outer circumference of the motor between the spokes, to better dissipate the heat moved there by the statorade. With statorade+hubsinks, a 3KW motor can be run at ~10KW without overheating. I bet something similar for DD cans is possible. Even on hubs, the inner and outer faces could have fins added to increase dissipation with statorade.


since I make the direct drives for me I do not have problem to access the motor. I have strategic premade threaded holes. I am really thinking of try it out. Thanks for the review!


That site also mentioned specifically eboard motors and because we typically run higher rpm the centrifugal force basically makes it less effective…

well if well filled up should still do plenty.

If you’re gonna fill it up (more than a couple ml), then it would be just as effective (and far cheaper) to use automatic transmission fluid. The advantage of ferrofluid is you can get away with a tiny amount because it stays stuck to the magnets. Ebike users have used ATF too, but it tends to add more resistance (viscous drag) and get everywhere more easily than ferrofluid.


There is a big topic in endless sphere about the Statorade, and somewhere Justin tested in Inboard hub motors, didn’t have much effect due to the hub nature of being isolated, but there was some drag tests and how much to fill