Why ventilate a hub motor? Well, as covered in the temp sensor page it will you allow to push more power through your setup without the motor overheating and destroying itself. Perhaps more importantly though, a cool motor runs much more efficiently. This means a perceivable increase in power and range.


You'll need a power drill, and titanium drill bits. Regular bits work, but not as well. I had to use a standard 3/8th bit for the large holes. A hammer and punch, a vise, a measuring tool, a sharpie, and vacuum also help!

Some theory on how to do this correctly first. Just drilling hubs all willy nilly in the motor does work; it allows heat to easily escape. But there is a much better way. After all, a hub motor is spinning quite fast. And what else spins fast? A fan! And in this case we're going to turn our hub motor into a centrifugal fan.

Like water in a cup being spun in a circle the air in the hub motor is also subjected to centrifugal force. Stock hub motors benefit from this as well as the windings and magnets are on the far edges where the air is densest and can hold the most heat. In the picture above of disc brake rotors you can see how they use vanes to amplify this effect. Some hub motors actually have mini vanes built into them as well.

A test done with a mock up by El Steak in this great thread.

A ventilated hub run underwater. See how water is sucked in near the center and expelled around the perimeter?

So the principle is simple: centrifugal force forces air to the perimeter of the hub motor creating a high pressure zone there and a low pressure zone near the center. All you need to do is drill holes near the center for intake and as close to the perimeter as possible for exhaust. This actively pumps air through; cooling your motor.


In this picture you can see that the drill holes are as close to the center and the perimeter as possible. Remember, you want the air to pass over the hot windings of the motor.
Another thing that helps here is to correctly angle the holes. On the intake you want the holes to make it easier for air to flow in. For the exhaust the opposite is true. Think of it as a cheese grater if it helps. The direction the covers are spinning is very relevant here. This is why I suggest marking the direction each motor cover spins with a sharpie or something. The disc side turns counter clock wise, and the drive side turns clock wise.

First mark with a sharpie your holes. I eye balled the location where I couldn't drill and marked on the vanes it's location. This allowed me to get close to the center. You can measure and get all precise here if you like.

Once I marked all the holes (9 intake and 18 exhaust) I used a hammer and a punch to put a little dent in the metal. This keeps the drill bit from walking around. It's very easy, and saves you a lot of frustration.

I guess we should talk about what drill bits to use now. Titanium coated drill bits! I just used the biggest ones I had. You can go bigger with circle cutter if you have the time and money, although I wonder about the strutural integrity of massive holes since the covers are load bearing. Anyways, since there are less intake holes, I used a bigger bit for those. I actually made a spread sheet to make it easy to match up drill bit sizes and hole numbers so that the area of the intake holes matches the area of the exhaust holes.
I used a 3/8th for intake and 5/16th for exhaust.

With the cover clamped down I used a smaller bit to drill guide holes. It's probably not necessary, but I think it makes things easier.

Since I didn't have a titanium 3/8th bit (for the large intake holes) I drilled them first with the titanium 5/16th and then came back with the slower and duller 3/8th bit.

Once all the holes were done, I came back and angled them. This was a bit trickier and required some playing around to get it right.