kiyohime. Originally I used a fatass lifepo4 ping battery and a stock 9c hub. I ditched the big saggy battery, built a lipo pack, modded the 9c hubbie, and reassembled everything. The result is a bike that tops out at 50mph, but weighs so little it can be lifted with one hand and handles like a top tier mountain bike. It was a lot of work, but most of the "work" was learning all the skills needed to push stock components so far. Some cool things about this bike:
Check out this video I had a lot of fun making and
I started by mocking up the box in google sketch up. This was very helpful in figuring out how many batteries I was able to fit. If I could do it again, I would build the battery pack first and then build the box around that. I also used sketch up to come up with the clamping dropout.
The batteries are secured using high quality tyrap zip ties. The high voltage meanwell 12v dc-dc is not shown in this picture. The wiring harnesses for monitoring each of the 22 cells were custom made for this project. I also made my own parallel boards out of strip boards to parallel the balance leads.
The waterproof box houses all the switches and monitoring widgets. I use the temperture monitor from hobby king to watch the heat build up in the motor. Running at 5kw it gets up to 100c around the ten mile mark. I don't like getting it much hotter than that as the motor performance becomes very boggy and inefficient. To monitor the battery pack I use 3 LVC adjustable lipo alarms. They were $3 each on ebay. They aren't terribly accurate and tend to put the packs out of balance so I typically run with them turned off. I use a st4p switch to break the ground connections for all of the widgets.
I can also unplug the lipo alarms and balance the cells from the harnesses. The yellow plug is to connect to one of my chargers. I have a mobile 3a charger that takes about 2 hours to charge, and a massive charger at home that charges in less than an hour.
The ventilated hub motor and no-nut clamping dropouts. (thanks to dogman and john in cr for the help building this!)
114a * 90v = ~10kw peak!
I took this picture after a good ride in the rain. The moisture kept the hub nice and cool! You can also see the taillight I made.
Overall I'm very pleased with this build. The bike is a blast for trail riding and tearing around town. The handling is great and the bike is visually very impressive. I already have 1000 miles on it and I suspect I could put another 10,000 miles on it with out problems. However, I know I won't. The battery pack is anemic for commuting, and since the box doesn't have enough room in it for more batteries it's a bit of a lost cause for anything but recreational riding. Even If I did upgrade the pack the motor is still woefully small and pressed to it's absolute limits already! I'm already considering an x5 or magic pie 2 as an upgrade! Additionally more voltage would be nice, but that requires +100v components.
For more information check out the build thread on ES.