ME 102B

FAST BIKE BRAKE PROJECT WEBSITE

SPRING 2005

CONCEPT DESCRIPTION

The Fast Brake is an automatic bicycle braking system designed to minimize rear wheel slippage during emergency stops. The angular velocities of both the front and rear wheels are determined using proximity sensors, the output of which are connected to a Texas Instruments Digital Signal Processor (DSP). If the DSP detects rear wheel slippage during heavy braking, a linear actuator reduces the braking force, thereby optimizing stopping effectiveness.

MOTIVATION

When encountering a dangerous situation while riding a bicycle, the most natural reaction is to pull the brake levers as hard as possible. However, doing so can “lock” the wheels and induce tire slippage, a potentially dangerous condition that increases stopping distances and decreases the bicycle’s overall stability. The probability of tire slippage increases when riding on wet or icy roads, loose dirt trails, downhill slopes, and at high velocities. We believe that an automatic bicycle braking system such as the Fast Brake can decrease emergency bicycle stopping distances by 20%.

TECHNICAL OVERVIEW

Mechanical Components

Text Box: The majority of mechanical components lies in securely mounting the brake line control system, which is comprised of a linear actuator and pulleys as seen in Figure 1. Brackets for the proximity sensors and DSP board must be machined.

Linear Actuator - A linear actuator will be purchased in order to control linear motion of the system with electrical current. A pull-style actuator will be used to reduce the effective length of the rear brake line. A mounting bracket for the actuator must be designed and machined to fit on the bicycle.
Pulley System - Three pulleys designed to fit standard brake line wires must be purchased in order to align the linear actuator with preexisting brake line positions. Mounting one pulley to the tip of the actuator and the other two to the bicycle frame must be done by hand.
DSP System Box - A box must be designed and machined to safely house the DSP board, batteries, and other electronic components. The box will be weather-proof and secured with rubber mounts to the bicycle frame in order to eliminate damage due to vibrations.
Proximity Sensor Mounts - Mounting brackets for the proximity sensors must be designed and machined to position the sensors on the front and rear forks of the bike. They must be adjustable to allow for sensor calibration.

System Layout

Figure 1 - The Fast Brake system is initialized once the rear brake lever is pulled. Tire slippage is detected by comparing the angular velocities of each wheel, which is determined by two proximity sensors mounted on each fork. The signal is sent to the DSP, which is mounted to the bicycle frame, and directs the linear actuator to move upwards. This motion slackens the brake line and decreases braking force, allowing for a controlled braking sequence.

System Control Overview

The following block diagram shows the overall control path of the system:

Below is a preliminary sampling sequence for the Texas Instruments DSP board.

Text Box: Sensor Components

In order to accurately measure the angular velocity of each wheel, inductive proximity sensors will be mounted to both the front and rear fork. These sensors operate by detecting metallic parts and translating this motion into a change in a DC load, which can be configured in NPN or PNP transistor modes. In order to compare the angular velocities of each wheel, we have chosen to mount two proximity sensors within 1 cm of the rotating wheel spokes. In addition to two wire used to power the sensor, there is a single analog output which will be connected to the DSP A/D converter.

Basic Dynamic Modeling

Rear tire slippage is of particular concern for bicycle velocities above 7 MPH, or 4.91 rev/sec for a standard 26 inch diameter wheel. If twenty spokes on each wheel are detected by the proximity sensors, the system sample rate is approximately 100 samples/sec. A bicycle speed of 20 MPH would allow for a sample rate of 280 samples/sec. Emergency braking occurs within 4 seconds from start to finish, so the system must be able to operate the solenoid within .1 second intervals for fast response times. The brake cable may be adjusted to accompany a desired tension, but the linear actuator must be able to induce a 10 lb force at a minimum for safety reasons.

Cad Models

Link to Movie

Class Website: www.http://me.berkeley.edu/ME102B_S05/

Written by: Carlos Torres, Abel Flores, Andrew Cardes, Gustavo Gonzalez

May 14, 2005