Automatic Bicycle Gear Selector

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1. INTRODUCTION

1.1 Purpose
Bicycles are among the most widely used inventions in the world. Designing an
automatic bicycle gear selector system for a common multi-speed bicycle would have a
huge market of consumers. The Automatic Bicycle Gear Selector will be implemented as
a modification to an already existing 18-speed bicycle. This system would automatically
determine and select the most comfortable gear to be riding in. Ideally, the system will
allow the rider to pedal at a constant rate on any degree of inclination.



2. DESIGN PROCEDURE
2.1 Power system

The power system was set up to allow for the entire system to be self sufficient. Our
initial idea was to have the generator power the entire system. A battery would be
included in the system so that it would be able to run when the bike was stopped or
moving too slowly. The generator we found was a typical ac bicycle generator that was
attached to the rear wheel. During testing of the generator, we found that the generator
did not output the required voltage at a normal riding pace. Because of this, we modified
the design to have the generator charge the battery and have the system run off the
battery. The generator voltage was boosted using a boost regulator to obtain the required
values to charge the battery.



Mechanical system
The mechanical system consisted mainly of the motor. One of the design challenges was
to find a good place to mount the motor. Because the derailleur is controlled by a cable,
there is a chance that the cable can become stretched either by stress or by temperature.
This required that we mount the motor as close to the derailleur as possible to prevent
possible noticeable error in the system. We mounted the motor towards the middle of the
frame of the bike as seen in Figure 2. This location allowed for the motor to be close
enough to the derailleur that it would not be ill-affected by cable slack, but still far
enough from the rear cluster and rear wheel that it would not become soiled and/or
damaged from normal wear and tear. The cable was then secured to the shaft of the
motor.

Sensor system
Our initial design was to have both pressure and speed sensors on the bicycle to measure
both the rotation of the wheel and the pressure on the pedals. Since we were unable to
secure price effective pressure sensors, we chose to use one magnetic sensor mounted
close to the crank to measure the speed at which the rider is pedaling as shown in Figure
- 3 -
3. A strong magnet was attached to the crank such that it would trip the sensor every time
it went by. This allowed us to signal the microcontroller that one revolution of the crank
has occurred.