Ben said:
I think they need the vents to cool the batteries. It seems like they could get awfully hot in there.
The wireless throttle is interesting as well, but it's just another thing that needs batteries.
GCinDC said:
jsmay311, here's another pic. but why the holes/openings in the hub? dumb me: wouldn't that let water in?:
from:
http://web.mit.edu/newsoffice/2008/biking-1010.html
more research, from
http://www.greencarcongress.com/2008/10/mit-bringing-sm.html, someone else's thinking, fyi:
If these batteries (I count 16) are A123 26650 cells then you would have a 13,2 V / 9.2 Ah battery pack (4S4P), capable of helping the bike at 120 Watt, during 1 hour. That is a serious amount of "push" and could make a daily 16 kilometer (10 mile) commute a lot easier. The battery would weigh just 1 kilo / 2 pounds.
I don't think the vents are there specifically for the batteries, though it certainly would cool them whilst the bike was moving in warm weather. In fact, I would be surprised if the batteries are not isolated from the rest of the components with a dipped epoxy coating or some waterproofing method, as these would be what I would be afraid of getting wet. Especially considering their position on the perimeter and the effect of centrifugal force in this area.
The A123 cells do not get so hot in normal use to *require* any cooling. At least not on my bike and they are in a plastic case, packed tightly together and even shrink wrapped!
Yes, the vents will let the water in to the hub, BUT it will let it back out as well. I think the venting serves three purposes, not to trap water, help dry the insides while using or setting and cooling air for components.. Being brushless, I think it should work good this way. Especially with centrifugal force, the heat and the air from the vents, it probably dries quick and has no chance to develop corrosion. Unless you put it away wet outside in a rainstorm. Otherwise, I think it would dry up. This is a problem with Crystalyte motors, they trap water, then this creates rust and then failure. You can read about this at ebikes.ca. They claim this is their biggest headache keeping up on customer support for these motors. They even have some photos if I am not mistaken, showing a waterline of rust inside a unit.
Also, the charger, controller and the winding in this motor need the ventilation I am sure, as they do shed a lot of heat. Again, on my eBike, these components get hot and either have heat sinks or are connected to a good mass of metal to transfer heat. The plastic case on my cheap on board chargers have even warped from heat. So, I leave the battery case open during use to get some air movement.
So, as a good engineer, (and if you can get into MIT you are a GOOD engineer) he will provide that function and at the same time reduce weight. I have found when working with electric motors, they can get wet. I even have seen them run underwater at 480 volts. Water is a poor conductor. But, I have seen trapped water corrode and destroy a motor. We now always drill a hole in the motor lead cover to let water out as we gave up trying to stop it coming in.
I also assume this motors innards are epoxy coated or something of that nature. I would be more concerned about the contaminants in the water from the street such as road salts and fertiliser-another salt. But, maybe you can actually hose this thing out! :lol: :wink:
And pedaling your ass off to charge it? 
Oh sure, it can be done, but I'd rather just tie a brick to my bike and drag it.
