Regenerative braking on bicycles to power LED safety flashers

Abstract

This work develops a method for capturing some of the kinetic energy ordinarily lost during braking on bicycles to power LED safety flashers. The system is designed to eliminate: (a) battery changing in popular LED flashers, and (b) the "generator drag" associated with battery-less human-powered bicycle lights and flashers. System sizing, mechanical design considerations, potential end-user factors, and a model for braking frequencies in urban settings are discussed. With the urban commuter cyclist in mind as a potential user of the regenerative braking system, custom direct-pull brake calipers (or "V-Brakes") were designed and manufactured to include both conventional friction pads in addition to a DC motor to be used as a generator for kinetic energy capture. The energy captured by the DC motor during braking is passed through a full wave bridge to a bank of Nickel-Cadmium batteries at an efficiency of 79%. The output of the full wave bridge and the batteries are connected in parallel with a step-down switching voltage regulator, which insulates the LED safety flasher from voltage spikes due to braking at high cycling speeds. The performance of the final prototype was evaluated at cycling speeds ranging from 8 to 19 mph and braking frequencies ranging from 2 to 8 operations/stops per mile of travel.

(cont.) From the mean power flow (charging) into the batteries per unit distance of travel and the power required by LED safety flashers, the effectiveness of the system at each speed and stopping frequency is examined. For cyclists traveling at average speeds of 10 mph or higher, the LED safety flashers can be powered continuously for stopping frequencies of 8 times per mile and semi-continuously (> 50% of the time) for stopping frequencies of at least 4 times per mile. As such, the system is determined to be potentially useful to urban commuter cyclists, who frequently perform braking operations at regularly spaced intersections and traffic signals, and who regularly travel by bicycle in low-light conditions (dawn or dusk), though usually less than 50% of the time.