The Issue / Background

The question being addressed by this project is: "Are we able to make a fully functioning bike dynamo capable of charging a cellphone, from scratch?" This project should prove to be fairly complex requiring the cross of electrical engineering and mechanical engineering disciplines to complete our tasks. Furthermore, each part is relatively difficult to create a working model of on its own, let alone functioning as a cohesive whole.

Current bike dynamos on the market consist of mechanical units that either attach to the axle of one of the wheels or replace the hub of the wheel itself.

Figure 1- Basic parts of a touring bicycle. Bicycle Touring Pro

A parts diagram of general bike parts can be seen in figure 1. The mechanical energy of the wheel causes a magnet to rotate within the dynamo which contains copper wiring. The turning permanent magnet induces a charge in the wires and the charge feeds into a battery or capacitor mounted elsewhere on the bike. The battery or capacitor is then able to produce a steady flow of electricity to the load of the circuit. This may include headlights/taillights, GPS charger, phone charger, etc.

There are three common forms of dynamos. The first, as seen in figure 2, affixes to the axle and has a part that makes contact with the tire or rim. As the wheel rotates, this physically turns the dynamo as described before. The second type of dynamo replaces the hub of the wheel itself and mounts onto the axle.

Figure 2- Bike dynamo. BBC

As the wheel turns, the dynamo rotates about the part of itself that is securely attached to the axle. The third common dynamo design is mounted to the fork of the bike and has a component that wraps around the axle and attaches to the hub/wheel. As the wheel turns, it rotates a series of gears within the arm of the dynamo, eventually rotating magnets within the dynamo. An example of this design can be seen in figure 3.

Figure 3- Hub replacing dynamo. Instructables

Figure 4- Gear driven dynamo. The Nology