Customized your bicycle yet? (to electric...)

Has anyone already customized, or plan to customize, your bicycle by putting an electric motor on it? I'm researching how I can weld a flat hub motor in the middle of my mountain bike. I want to weld two sprockets (1 small, and 1 large) to the end of the drive shaft, and run the chain from the back wheel to the sprockets on the motor, instead of the pedals. the smaller sprocket would be for hill-climbing, and the larger for high speed on flat surfaces. And it has to have variable speed control.

Hell, no. One of the things I like about my bike is that it's powered by my legs, whether I'm riding in the mountains or just riding home, after work, up the hills with 20 lbs of kack in my bookbag.

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A bike like I'm talking about allows you to move the chain from the electric motor back to the pedals below it. So I'm actually talking about a customization issue and not an enjoyment issue. You would have the best of both worlds with the design I'm talking about.