MadRhino wrote:I believe the lightest that can be done is with a friction drive. This also has the advantage of being very quick to remove, for those who care about using the bike without sometimes.
I have seen one 600w, I believe it's called add-e, that fits very neat with BB mount and weights only 2Kg including the bottle battery. One could easily build something similar, with better power or lesser weight.
A very interesting alternative.
The price seems to be just over a thousand dollars (250 watt version).
I would question the ease of building something similar without access to a good machine shop.