Design a DC/DC converter + micro-controller for a stationary bike - repost

The project is consist of a stationary bike, a DC/DC generator with a micro-controller and a battery. As the cyclist pedal of the bike, the energy is transferred from mech. to elec. and is uncontrollably stored in the battery. At this stage, The bike, bike stand generator and battery are already purchased. The generator is a 24V DC generator and the battery is 12V. The generator is in touch with the back wheel of the bike. as the bike's back wheel's rotate, it rotates the rotor of the generator. The work is designing the DC/DC converter with a micro-controller to control the rate of charge of the battery. it is desired to avoid over charging the battery. Also it is desired to have the option of changing the degree of difficulty of pedaling by changing the current/torque produced. this could be done by having a potentiometer for the user to change it.