Originally Posted by Brian Ratliff
I don't currently have an ebike system, but I'm toying with the idea of designing a hybrid bicycle and playing around with it. Is there a system on the market with a 100W motor and weighs ~5 lbs including batteries? I figure 100W is roughly half of the power I am putting into the pedals at 20mph. The battery would be sized like a hybrid car battery, IOW, it'd provide a boost on acceleration and hills, and drag slightly on the flats and especially downhills to charge the battery, so the battery pack would be significantly smaller than the normal (from what I can see) ebike system.
The way I figure, it'd be plugable, but it could also work as a closed system that never requires charging, like a hybrid car. Is there a system like that on the market or in someone's garage?
SPARC by SRAM and the discontinued Sinclair Zeta III are probably the closest systems to what you describe.
Here is a pic of the 172 W Zeta III which was still available about a year ago at this site:
http://www.zapworld.com/ZAPWorld.aspx?id=2242 a pic is still visible although they seem to have cleared them. They pop up on ebay occaisionally. About 9 mph, 10 lbs, you also have a headlight out of the package. It uses a friction belt drive which is vastly superior to the roller friction drives.
SRAM SPARC has 2 100W motors embedded within a S5 internal gear hub, system with batteries adds about 10 lbs. also. Pricey, close to $1000 dollars. Like the Zap DX, runs the current through the motors in series for low speed and in parrallel for high speed.
You could probably get a 100 W scooter and make that conversion for a lighter system.
If you are doing 20 mph, you are probably putting out much more than 100 W though.