The signals of an electric eel: piezoelectric power generation on a high-tech bicycle

In the Department of Mechanical, Automotive and Aeronautical Engineering at the University of Applied Sciences in Munich, students are working on an innovative vision of a bicycle. In the
”Electric Eel“ project, the lightweight material carbon is combined with piezoelectronic ceramics from the field of intelligent materials. Vibrations in the frame of the bicycle produce electrical charge transfers as a result of mechanical deformation (the piezoelectric effect).

The electrical energy generated in this way can be used for various applications, without additional power sources. The principle is similar to that of an electric eel, that emits current impulses through electric organs.

Two topics of investigation

Using a CRP (carbon fiber reinforced plastics) rear swinging fork with piezoelectric ceramics, the electrical signals generated by the uneven ground should control the dampers in the chassis frame of full suspensions.
In the stem, a system for monitoring the loads on the forks and the handlebars was examined. The signals of the piezoelectric modules are used to register overloads. Warning lights on the handlebars indicate, for example, when the bicycle has to be inspected.

"Against a background of safety and warranty aspects, the importance of load monitoring systems will increase drastically in many areas of machine and vehicle construction, as will optimization of maintenance cycles.

Various sensors are suitable, depending on the application. Whereas currently, investigations are carried out for mechanical engineering applications with strain gages, the benefit of the piezoelectric effect for a bicycle is primarily to avoid heavy batteries" Prof. Dr. Alexander Horoschenkoff, Project Leader at the University of Applied Sciences in Munich

Deformation determines placement

Before attaching the piezoelectric modules, we measure the deformation of the components under different loads (hopping, out-ofsaddle riding, braking) with linear strain gages and strain gage rosettes. The carbon components are carefully polished with 220-grit sandpaper until the first carbon fibers come to the surface and the strain gages can then be installed with the cold-hardening adhesive, Z70. Two Spider8 amplifiers with catman® software are used to record the deformation on the forks and handlebars.

Test bench

To develop the chassis, the students planned a roller type test bench to allow them to investigate the control of the damping valve. The deformation of the CRP rear swinging fork, the displacement during deflection and the piezoelectric signal are all measured.

HBM strain gages, displacement transducers, force transducers and measuring amplifiers as well as software are used here.

The chassis of the "electric eel"…

…is a complex, mechatronic system that should not require any outside power sources. The erection of the roller-type test bench is a prerequisite for informed investigation of the interaction between the deflection, the valve switching and the damping effect.