First of all, athletes will not ride very fast. Traffic experts usually set the riding speed at 5KM/H as slow, 10km/H as slow, 15km/H as medium, 20KM/H as fast and 25KM/H as fast. Take 15km/h=4. 17m/s as an example, assuming that the diameter of the forum is 660mm(26 inches), then n=60*4. 17/0.66=379r/min.

Then connect the bicycle shaft with the rotor of a small generator, and the output voltage can be obtained according to the parameters of the generator (minimum speed, magnetic field strength and coil turns):

E = 4.44NKFΦ，f=pn/60

Where e is the generator output voltage, n is the number of turns, k is the constant coefficient (about 1. 1- 1.25), f is the frequency, Hz, p is the number of poles, and n is the rotational speed. φ is the magnetic flux.

Secondly, in order to ensure the stability of the output, there are two ways to solve it. On the one hand, we can try to connect a flywheel with a certain mass to the bicycle wheel, and use the inertia of the flywheel to ensure that the instantaneous speed of the spindle is relatively stable. On the other hand, we can connect a capacitor or inductor in series at the output end of the motor, charge and discharge Li Rong's capacitor and inductor, and add this damping to reduce the fluctuation of generator output current. You can try the bridge if you can.