SO much I *love* about your "project"!
MY first experience with battery assist two-wheelers were on the Currie® Phat Flyer SE Electric kick Scooter (watt had "extra kick" via a chain-drive motor and two 12V 10Ah SLAs in series...)
AND PLUS ONE on the idea to offer a conversion kit rather than to "reinvent the wheel" as manufactured electric bikes are starting to flood into the markets... (at least in North America...). And how many bikes, etc are already "out there" where a "low cost" conversion kit will be an attractive option for millions...
AND... Friction drive too??? Extra nice, simple approach... Some folks will say "not perfect", but watt is? Still wayyy better than pedal (kick) -only for urban travels as entertainment.
BUT. (but, but, but...) Laws local to me ie Canada actually require that our "power-assisted" bikes on roads have operable pedals. [Sigh...]
So like lots re your conversion kit as friction drive, however any chance you'll EVer have a more "bike-friendly" option that'll fit a more "generic" bike?
ES changed my life (for the waaaaay better).
Eff. June, 2014 Phoenix Ebike Promotions
(Current ride? High speed lawn chair.)
Phoenix Ebike Promotions conversion kit (work in progress. More drink holders, etc etc)
Joined yer local chapter of EA yet?
(Ebikers Anonymous - Where we're all miserable failures, but the parties are hilarious...)