number1cruncher said:
Modifying John's idea a bit, would it be terrible if one were to attach a 5mm high X 30% arc scoop on the backside of the vent hole to catch the wind and direct it into the hub? It would create some drag, but I would think minimal. I'd have to spend some time at my playground(Home Depot) to find something appropriate to use, but I am envisioning something that would clamp to the hole wall.
Intake holes are closer to the center of the cover. Jeremy crunched some numbers showing any exterior scoops will to little. Plus anything you do on the exterior will be subject to the complex dynamics of being mounted on a moving wheel, not a stationary wheel spinning. eg when a hole is at its lowest position it is actual traveling at 0mph relative to the ground just like your tire when it is touching the ground, and the speed relative to the outside environment is constantly changing. Plus you have wind effects too, and take any fan outside in the wind or move it around and output goes to hell.
The only thing I would put on the exterior if I was so inclined would be a reversed scoop in front of each hole at the perimeter to deflect away the outside influences and debris, which would also create a low pressure region behind it, stimulating more flow out of the hole. The problem is that you want those holes at the very perimeter of the interior of the motor. That's where the windings and the magnets are, and you don't want that fresh air you worked hard to get into the motor to flow out before it passes over the part you're trying to cool. At the very perimeter you're forced to use small holes which means a lot of them to maximize flow.
Holes at the very perimeter near the air gap is another reason I put intake holes near the axle only on one side. At first it was just to avoid debris and gunk from the chain going in the intake, but also with intake on one side but air exiting both perimeters air can only get to that other side by flowing through the holes in stator spokes and through the air gap between the magnets and end of the stator. The pressure differential makes it go via both routes and I like air through the gap to help cool the magnets and the end of the stator. I'm even going to plug 4 of the 6 1" holes in my 9C stator to force more air through the gap. I'm leaving 2 open because I do want some fresh air reaching that side of the stator before the gap.
WRT air gap flow and a single side fresh air intake, there's an issue with Xlyte motors. The laminations are splayed creating angled channels between the stator teeth. With a moving air flow created by the magnets passing so close in one direction this will create a natural flow in one direction, and trying to flow air in the other direction would be counter productive. On my X4, that natural flow is right to left, so a one sided intake on the left side would be a mistake. I don't know if all the Xlyte motor have their stators angled in the same manner, so check yours first. That flow may account for some of the X motors high power handling even when completely sealed, because not only do they get spinning air at the sides of the stator, but air is forced across through the air gap to return back through the stator spokes. It creates air movement in a toroidal manner around the entire stator, which has spread the heat more evenly through all of the air in the motor instead stuck in a hot spot near the perimeter. This has to create at least some better overall cooling. For our purpose though we just want to be aware of which direction that nature flow is, so we don't diminish it by trying to flow air in the other direction.
Ignoring flow restrictions, to maximize air flow we have to get as much of the air spinning at motor rpm as possible. That means more weight spinning and maximum pressure to flow out of the exits. That's the rationale behind Jeremy's suggestion for vanes inside the motor covers. There's plenty of space, at least till we get close to the stator.
In addition to flow amount, we care about where the air flows. We're not trying to blow leaves; we're trying to cool the stator and magnets. I mentioned the air gap flow earlier. We also don't want the vast majority of the air just following along the smooth side covers and out of the holes. We want turbulent flow at the stator. I haven't addressed that on my 9C covers yet, but on my last completed motor I put blades on each cover. They're angled to stimulate spinning and flow toward the perimeter, AND they are angled in relation to the cover so they throw air off the ends of the blades at the stator. My intake holes are behind the blades, which is good because that action creates a negative pressure region behind the blade, just like any fan blade.
Sorry for the long post, but I've spent a bunch of time on this issue and it's made an increasingly beneficial difference on each motor I've modified, learning and adapting with each. I think the only further big improvement would be to get rid of a drum brake and use that stationary cover to install a high pressure high volume ducted fan there to force tremendous amounts of fresh air through the motor and out the perimeter vent. Maybe some day when I have a powerful enough controller to shoot for 20kw through one of my hubbies, but if the fan shuts down, I would instantly fry my motor just like I did a controller when I forgot to turn the cooling fan on and it blew as soon as I hit my first big hill.
John
It did help the temps and I think on my rebuild an internal fan may be the way to go with my cooling holes.
