Some years ago a design student solicited help for a class project to design the bicycle of the future. He needed a new propulsion system that would allow new design freedoms.
I found this challenge very exciting.
I proposed eliminating the mechanical chain and gearing system with electronics. The pedals would connect directly to a generator that would drive two hub motors. There would no longer be the constraints of a chain connecting from the pedals to the rear wheel. The braking would be accomplished by turning the hub motors into generators and storing the energy in a small battery or capacitor. This would greatly enhance the safety of city driving. There is always the temptation to coast through stop signs and lights. Now you could stop without hesitation and when it was safe and legal to proceed get right back up to speed by releasing the energy stored in the battery or capacitor.
I built a tabletop display model with pedals you could turn by hand and two hub motors and a small rechargeable battery to demonstrate the concept. Cranking the pedals would spin the wheels, and then when you applied a brake, which was simply a switch that turned the hub motors into generators, the wheels stopped turning. Then when you pressed another button, the energy stored in the battery would spin the wheels again to a good fraction of the speed they were at before.
I am leaving out the details of the electronic control system but for now I'll just say that I consulted with experts in the then re-emerging field of electric cars and was definitely do-able in their opinion.
The student built a full size realistic looking but non functional model. A picture of it and other student’s proposals was featured in "Bicycling" magazine. And that was the end of it as far as the design student's project. (We are in the photo.)
But I wanted to take the concept further. Instead of replacing expensive precision mechanical bicycle components with expensive electronic ones for a purely human powered bike, suppose you cheated and used cheaper motors and generator and components and made up for it with batteries. You would dial in the percentage of assist you would get from the batteries but you go only in proportion to how much you pedaled.
Bicycle commuters could use the bike as an exercise platform in the evening and store the energy for the morning commute. Or one could make exercise equipment that would charge your bike's battery.
I also thought handicapped could use it. Arm strength could be multiplied by the electronics to drive a wheelchair.
I applied for a grant and nearly won but the proposal was sent to an expert in the field who said his company was already working on a better version. It turned out it was nothing like I proposed. I'd like to take another shot at it perhaps with the help of the electric vehicle club here at Caltech.