Hyena wrote:That's some crazy thick casting in the middle of those hubs John! I guess being made for scooters they're designed to take a heavier load. Did you ever weigh one ?
The covers are heavy, especially the side with the huge moto disc brake mount. The bike weighed 40kg including batteries last time I put it on the scale. I bet the motor and wheel are half of the weight.
Hyena wrote:What are your thoughts on having both intake and exhaust holes on each side cover ? I tend to have intake on one side and exhaust on the other. I also have mixed feelings on the size and placement of the holes. I usually do it the same as you (albeit with fewer, bigger exhaust holes) but part of me says go with bigger holes right over the windings to have more air blowing directly over the hot spot and to allow more heat to radiate out when going slowly (or stopped)
Until Hubmonster I've only done dual sided exhaust. I like the idea of intake on one side and exhaust on the other if it means getting flow through the magnetic gap, which is why I'm trying it. I haven't been able to get it past slightly warm at the magnet backing ring, and it doesn't look like I have enough controller to get it much more, so I'm up in the air right now regarding a preference.
I've got a pretty strong opinion about big holes in general. They don't allow you to get to the very perimeter, so I doubt much air can get through the gap. I proved to DocBass in his X54 thread that radiation is low enough to be ignored at these temps. My biggest problem with holes at the windings is that the flow is going to take the path of least resistance, so I see much of the air flowing along the side cover and out the holes, bypassing the end windings on the way out.
Instead of holes I put fan blades there. The idea behind that is to direct air away from the cover where it will do little good and at the stator. At the very least those blades, which are within a few mm of the end winding must push a quite turbulent flow at the windings. Even at just 25mph that puts a blade passing close to every point on the end windings over 2,000 times per minute, which must add a lot of turbulence there. Turbulence is critical to good convective heat transfer. It's not like a liquid such as water or oil where it only needs to touch the heat source for really good heat transfer. Air requires a turbulent flow just to get decent heat transfer. The blades are probably a significant part of my success with passive ventilation. I've put some kind of blades in all of them so far. For some reason I didn't take a pic of the 9C covers after I put the blades. Here's one of the covers of the motor (equivalent to a 2 turn Xlyte HS40) my son has been using for the past year and for the last month or so really blasting up the mountains at high power.