The challenge was to retrofit Citibikes with weatherproof universal charging doc, so Citibike users can charge the bike while they ride. We were able to utilize the already existing and overpowered Shimano hub as a power source and feed the 7v provided though a custom designed step-down (buck) converter to wrangle the voltage to be consistent with USB. After some testing, we decided to insert a 5v battery pack in-between the buck converter and phone to regulate voltage and allow the relay battery to charge, even when the rider does not have a phone with them.
