using a motor as a generator

I have a project with an electric bicycle and want to get longer range for long distance travelling (25 miles or so) im too cheap to go past
leadacid technology and a small hybrid generator set up really speaks to the geek in me. im thinking a small 3 hp 2 stroke engine hooked up to a pmdc generator or an alternator. Im planning to use a pic to monitor voltage and throttle the engine accordingly (and even have it where if im not riding the bike it will do a proper absorbtion charge rise to 14.5-hold-then drop to 13.65 , or if im riding try its best to maintain 13.65, i think itll just have to pegged wide open if im riding anyways). Problems are im not too sure what the thermal capability of most motors are. Im going to assume a 540 mabuchi motor will burn up even though some of them are supposed to be able to throw out a half horse i cant imagine an 8 ounce motor dissipating that much heat. Another promising approach is the 35 amp mini alternators but then ill have to play with field voltage and throttle at the same time maybe better maybe not but its definetely more complicated(ill do it if its more efficient)/I might just throw down another 275 bucks for the same drive motor im using on the bike and spin that seems logical but i want to ask the experts (i am but a young'n). I know the people around here seem not to like the hybrid drive thing, but if its good enough for toyota its good enough for me.
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