The easiest way to see the bike and how I did it is to go Phase I, Phase II, and then Phase III. Also check the videos to see it in action..We are currently planning Phase IV, which is a true gas/electric hybrid as we've envisioned it...
You might want to talk with my friends on this one since they have also accomplished solid hybrid bike designs and can help guide you on your options as well as provide pretty much any thing you need as far as parts whether its a BLDC motor and controls to sprocket and gear design I bought my very first diesel engine years ago from them and they helped me with my initial hybrid designs so you would be in good hands that will also be cost effective!
I have seen similar setups used to provide auxiliary reverse drive for parking maneuvers in motorcycle-based tricycles, but its coupling doesn't sound so safe for a hybrid driveline.
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I bought my very first diesel engine years ago from them and they helped me with my initial hybrid designs so you would be in good hands that will also be cost effective! 
