So I know I jumped right into the battery pack and haven't talked yet about much else.Overall goal:
Build an electric bike that's street legal, but doesn't require inspection, insurance or registration. In the Republic of Texas, this means my vehicle cannot weigh more than 100 pounds, cannot exceed 20mph when the operator is not pedaling, and cannot use a motor with a rating that exceeds 750 Watts nominal in rating. SO how do we get around each of these limitations?
100 pound weight limit:
Place batteries in a removable container that is not technically part of the vehicle. By placing straps on this container, I can remove the 28 pounds of batteries from the vehicle as a 'personal item.'
cannot exceed 20mph when the operator is not pedaling:
place an encoder on the pedals that limits motor speed to 20mph when not pedaling. Note that the law does not require the additional energy input above 20mph to come from the operator (i.e. my legs); it just requires that the vehicle cannot exceed 20mph by itself when I'm not pedaling.
750 Watts nominal rating:
Pretty simple. I'm going to buy a 750 Watt nominal 12 volt motor and run 72 volts through it. The law only requires the nominal (i.e. name only) wattage be less than 750 watts. How can I do this without frying the motor? Enter imaginary power. I'm not going to go too much into this, but in short brushless motors are current controlled devices, not voltage controlled. Since EMF is the ultimate driving force here, upping the voltage simply means at the same current we'll get much more power. Mathematically, the motor will still pull 750 watts nominally, but at full throttle it will pull a maximum somewhere around 4500 watts. Obviously, if I did this all day I'd burn up the motor, but for short bursts I'll be just fine.
This leads me to the vehicle itself. I originally liked the idea of a side-by-side 2 seater (above), but this thing is way more than 100 pounds. I then breifly thought about converting Qimikom (my current commuter bike). Now I'm looking at a trike (gay) or a recumbent (not sure yet). In short, I have no idea as of yet what the ultimate bike is going to look like.
