Table of Content

Electric Assisted BicycleElectric Assisted Bicycle

Table of Contents

1ACKNOWLEDGMENT

ABSTRACT21 INTRODUCTION3Electric Propulsion Trends3Environmental Benefits3Electric Efficiency42 PROBLEM STATEMENT6Design Issues62.1 Tasks Assigned to Individual team Members:8Joe LaPointe:8Gregory Huh:93 DESIGN CRITERIA114 DETAILS OF DESIGN12Motor Controller13Regenerated Braking14Solar Panels15Hardware Development16Schematic of System16Software Development17Analog To Digital Converter17Pulse Accumulator18Output Compare184.1 Final System:184.2 Socio-Economic Issues:20Cost Proposal20Cost of Time20Product Pricing21Economic Benefits and Societal impacts214.3 Safety Issues:225 TEST RESULTS AND DISCUSSION256 CONCLUSION266.1 Executive Summary:277 REFERENCES29

ACKNOWLEDGMENT

This project would not have been possible if not for the valuable support and funding from the Center for Engineering Education and Practice, College of Engineering and Computer Science, University of Michigan-Dearborn.

The authors also wish to thank Associate Professor Dr. Natarjan Narasimhamurthi and Graduate Advisor Dr. M. Shridhar for their help and advice throughout the development of the project, and for their critical review of this report.

ABSTRACT

Increasing demand for non-polluting mechanized transportation has revived the interest in the use of electric power for personal transportation and also reduced reliance on automobiles. A low cost alternative to an automobile is a bicycle. However, the use of bicycles has been limited to very short trips or as a recreational activity. This report describes the design of an electric assisted bicycle that will extend the range of a typical rider. The system consists of three source of power. The human effort of the rider pedaling the bicycle, and electric motor running off a 12-volt lead-acid battery, and a solar panel that can charge the battery when there is adequate sunlight. The power module is controlled by a microprocessor, so that one can operate the bicycle at a preset speed (cruise control). The power control module on the motor will reverse the current in the motor if the speed of the bicycle is more than the desired speed. This current reversal charges the battery, and thus provides regeneration not only when braking as well as when going down hill, or when the rider pedals harder than the set speed. The final system has features that will appeal to a broad spectrum of users. Those who ride the bicycle for exercise can do so either by disabling the electric assistance, or if they chose, by exerting more effort to generate electric power and charge the battery. Those, who would otherwise not use the bicycle to move around the city, can do so, confidant that there will be power assistance when they grow tired, or when facing an uphill climb. The constant speed operation will also provide a sense of comfort, especially when coming down steep slopes.

1 INTRODUCTION

The worlds car usage is booming. Cars are polluting the worlds cities, dumping increasing amounts of carbon dioxide and other climate-altering greenhouse gasses into the atmosphere, and consuming vast quantities of petroleum. The alarming reality is that the automobile usage is growing at a much faster rate than the human population, with saturation nowhere in sight. If present trends continue, over 3 billion vehicles could be in operation by the year 2050, exceeding 20 cars per 100 people. Even then, world car ownership rates would fall far short of current U.S. rates of 70 cars per 100 people.

Electric Propulsion Trends

Electric vehicles cost more and perform worse than their gasoline counterparts. This is mainly because gasoline cars have benefited from a century of intensive development; electric cars have been virtually ignored for over seventy-five years. Even today, gasoline cars profit from billions of dollars of research every year while electric vehicles receive a tiny fraction of that.

Environmental Benefits

The primary premise for government support of electric vehicles has been air quality. The sole legal justification for the EV mandate is controlling the pollution. Electric vehicles will not disappoint on this count. But air quality alone is not sufficient justification to mandate electric vehicles. The single biggest advantage of electric vehicles is that the electric power is produced in a centralized location where the pollution can be better monitored and controlled.

Electric Efficiency

Electric vehicles do, however, offer other strong benefits that are ignored by the marketplace. One is the dramatic reduction in oil consumption and petroleum imports that their widespread use would bring about. Much less oil would be needed because only a tiny proportion of electricity is generated from oil-less than 5 percent in the United States. The other major nonmarket benefit would be lower greenhouse gas emissions.

The energy efficiency advantage is due to several factors. First, the overall system efficiency taking into account the production of electric power, transmission and distribution, local storage in batteries and conversion of electric power to mechanical motion is estimated to be approximately 50%, while combustion engine vehicles are 15 to 25 percent efficient. Second, about 10 percent of the energy used combustion engine vehicles is during idling; electric vehicles consumes no energy during idling. Third electric vehicles can recapture heat energy lost during braking. About one-third of the energy used by a motor vehicle is lost during braking; electric vehicles can recover up to half that energy with regenerated braking.

2 PROBLEM STATEMENT

The problem to be solved is that of increasing the range of a human-powered bicycle by equipping it with an electric motor running off a lead-acid battery. The department of Electrical and Computer Engineering presently has mountain bike equipped with an electric motor and battery kit manufactured by Zap World. The kit consists of a permanent magnet DC motor, directly driving the rear wheel of the bike, a 17 Ampere-hour lead acid battery and a battery charger that connects to a standard wall outlet. This kit has been used in previous semesters for senior design projects. An earlier project had designed a computer controlled power management system. However, their design did not include a full regenerative braking, and it was decided to redesign the power control module that can provide regenerative braking. Also, the ease of integrating microprocessor-based control was a primary goal of this project.

Design Issues

Motor control

In simplified terms, its terminal voltage controls the speed of a permanent magnet motor. An efficient technique for controlling the terminal voltage is by using a pulse-width modulation. Also, as the vehicle slows down, such as when braking, the terminal voltage of the motor will be less than the battery voltage. To absorb the kinetic energy of the vehicle and convert it to electrical energy and charge the battery, some form of a DC-DC boost converter circuitry must be used. This boost converter will transfer power from a low voltage source to a higher voltage sink.

Solar Energy

Since a bicycle would normally be used in daylight, it would be advantageous to tap the solar energy to charge the battery. The solar panel used to convert the solar power must have a high level of energy output without being too big and cumbersome. One of the design goals was to size the solar panel so that the battery can be charged in less than 4 hours while parked in bright sunshine. The solar panel can be connected to the charging connector of the battery so that the battery can also be charged from an electrical outlet using the battery charger that is part of the kit.

2.1 Tasks Assigned to Individual team Members:

Joe LaPointe:

Research different components in implementing the electric bicycle hardware applications. This was mainly done by searching the Internet, researching books and getting input from the faculty advisor.

Write cost proposals to obtain funding from the College for the project.

Research and incorporate EMC into the design.

Design and built a motor controller circuit (without regenerated braking).

Test/simulate electrical circuits on Electronics Workbench and P-Spice.

Test and simulate first stage designs, with actual components.

Visit motorcycle dealers in search of parts for the project.

Work on the wiring interface for the 68HC11.

Identify a commercial motor controller. Perform calculations for incorporating the controller. Design techniques to modify the commercial controller

Devise different approaches to implementing the variable speed controller.

Mounting and assembling of the electrical hardware on the bicycle.

Built a circuit for manual override of the microprocessor.

Gregory Huh:

Study different options for electric vehicles, such as an electric automobile, Go-Cart, Scooter and the Bicycle.

Researched different approaches of controlling the vehicle. Mainly, using different controller chips from Motorola and Unitrode in implementing the design.

Called and obtained free samples of the controller chips from Motorola and Unitrode.

Researched solar panels and made choices of the most suitable panel for the project.

Wrote numerous cost proposals in order to obtain funding from the Dean for the project.

Ordered components and solar panels, through Karen.

Designed a system for implementing the project through software.

Chose which interrupts to use and how to best implement the design through software.

Researched the possible methods for writing and utilizing the EEPROM into the design.

Wrote a test program for moving and storing data into the EEPROM.

Wrote a program to convert from Analog to Digital. This program controlled the motor accordingly based upon the voltage input (Speed Control), through the 68HC11.

In charge of the wiring of the bicycle, mainly minimizing the number of wires running along the bike frame.

3 DESIGN CRITERIA

The goal of this project is to design and build an electric bicycle, powered by a 12-volt battery, with an operating range between 28 to 33 miles. This goal can only be attained by adding features designed to minimize the power consumption of the system. All of the components used for obtaining the goal of the project must be small enough to fit on the bicycle.

The first feature is to add pulse width modulation. The advantage of pulse width modulation over the use of adding gears to the system is the fact that with gears the gears, torque is gained, but distance efficiency is lost. Pulse width modulation allows the motor to operate at a variety of speeds.

In order to obtain the pulse width modulation a microprocessor can be used to trigger the motor. Since the microprocessor puts out a 5-volt signal at 2 mA, and the motor runs off of 12 volts at a current of 20A, a motor controller must be obtained to handle the voltage and current specifications.

Another feature of the design to add distance to the electric bike is regenerated braking. Regenerated Braking is a system designed to recharge the battery as the bike is braking or slowing down.

Another method of increasing the distance is to include solar auxiliary power. Solar power is relatively free, except for the initial cost of the panels, and it is a reliable source of energy. All these feature of the design must be within a cost range of under $500.00.

4 DETAILS OF DESIGN

To control the speed of a D.C. motor we need a variable voltage D.C. power source. However if you take a 12v motor and switch on the power to it, the motor will start to speed up: motors do not respond immediately so it will take a small time to reach full speed. If we switch the power off sometime before the motor reaches full speed, then the motor will start to slow down. If we switch the power on and off quickly enough, the motor will run at some speed part way between zero and full speed. This is exactly what a p.w.m. controller does: it switches the motor on in a series of pulses. To control the motor speed it varies (modulates) the width of the pulses - hence Pulse Width Modulation.

If the motor is connected with one end to the battery positive and the other end to battery negative via a switch (MOSFET, power transistor or similar) then if the MOSFET is on for a short period and off for a long one, as in A, the motor will only rotate slowly. At B the switch is on 50% and off 50%. At C the motor is on for most of the time and only off a short while, so the speed is near maximum. In a practical low voltage controller the switch opens and closes at 20kHz (20 thousand times per second). This is far too fast for the motor to even realize it is being switched on and off: it thinks it is being fed from a pure D.C. voltage. It is also a frequency above the audible range so any noise emitted by the motor will be inaudible. It is also slow enough that MOSFETs can easily switch at this frequency. However the motor has inductance. Inductance does not like changes in current. When implementing the system with a microprocessor an RC circuit will be used it as a buffer between the microprocessor and the controller circuit.

Motor Controller

Specifications

Supply voltage 10v to 60v - 48v version

Supply current 20mA (at zero speed)

Output voltage0 to 100% full speed

Output current (typical) 100A (cold), 75A (hot)

Braking current80 A (cold), 75 A (hot)

Voltage drop at 20 Amps140 mV

Switching frequency 20 kHz approximate

Size: (board only) 122mm x 55mm x 30mm

Size: (with heatsink). . . 180mm x 55mm x 35mm

Weight 100g 35 and 70 models

Input1k to 100k pot.

Input voltage0v to full speed

Full speed input adjustable 3v to 20v

Features

High speed MOSFET chopper circuit

Half Bridge

Fast current limit on drive and regeneration.

Adjustable gain

Regenerative braking

Current limit on drive and regeneration

CR type ramp

Heatsink is adequate for normal motor use (i.e. intermittent operation at maximum output). The integral heatsink may be bolted to an additional heatsink if required. The current limit reduces automatically if the controller gets hot, reducing the danger of failure.

Circuit can be used to drive loads such as lamps, which will work off a chopped d.c. supply.

Regenerated Braking

Regenerated braking will be incorporated into the motor controller circuit. The best way of thinking about it is that the controller is supplying a voltage to the motor to drive it, and the motor is generating a back emf, proportional to its speed. If the motor goes faster, its back emf rises and the current (caused by the difference between the controllers output voltage and the motors back emf) falls. If the motor gets fast enough, the current falls to zero, as back emf equals controllers output. It the motor goes even faster then the current must go negative (feeding back into the controller), as the back emf is now greater than the controllers output voltage. So braking starts to occur. The controller has to do something with this current. Crude designs simply dump it as resistive heating but it is more efficient (and not difficult) to feed the current back into the battery.

Solar Panels

Electrical Specifications

MODEL KC40

Maximum Power40 Watts

Maximum Power Voltage 16.9 Volts

Maximum Power Current2.34 Amps

Open Circuit Voltage21.5 Volts

Short-circuit Current 2.48 Amps

Length 526mm (20.7in.)

Width652mm (25.7in.)

Depth52mm (2.0in.)

Weight 6.0kg (13.2 1bs.)

The conversion efficiency of the Kyocera solar cell is over 14% These cells are encapsulated between a tempered glass cover and an EVA pottant with PVF back sheet to provide maximum protection from the severest environmental conditions.

Hardware Development

The following schematic represents the hardware design of the system. The schematic represents the outputs and inputs to the 68HC11, the output power from the solar panel and the power going into the motor.

Schematic of System

The first step in the hardware design is to design the motor controller so it takes a pulse from the microprocessor in order to drive the motor. The 2Qd controller circuit was modified to take an input from 0 to 5 volts. This was achieved by the addition of components to the 2Qd circuit. The values of these components were calculated and configured into the controller circuit.

The solar panel was mounted and connected to the system with a diode to protect the solar panel from receiving any back current. The solar panel was also connected to a shunt regulator in order to receive current readings and voltage output readings. This also provided a reading for the power provided to the system by the solar panels.

An infrared sensor was attached to the front tire of the bicycle. This allowed the HC11 to keep track of the amount of revolutions pre second. The count of revolutions per second is used in controlling the bicycle once cruise is activated.

Another controller circuit was designed and built to allow manual operation of the bicycle or microprocessor driven operation during cruise control.

Software Development

The software for the project is written in Assembly language. The program is interrupt/event driven. It utilizes three interrupts: A/D which gets the input from the grip throttle/pot, Output compare, which is the signal input to the PWM signal to the motor controller, Pulse Accumulator for obtaining the RPMs for the cruise control.

Analog To Digital Converter

The analog-to-digital or A/D converter in the 68HCI I makes 8-bit unsigned numbers representing external DC voltages. The A/D converter, by using an 8-channel multiplexer, can read voltages from eight different pins on the 68HC II package. Port E is the collection of the eight input pins for the A/D converter. An A/D converter normally reads signals from analog sensors. Typical sensors measure temperature, pressure, or position.

An analog-to-digital converter makes a binary number that is proportional to an unknown DC voltage. A digital-to-analog converter makes a DC voltage proportional to a binary number. Generally, an A/D converter is much more complex than a D/A converter, which is relatively simple and inexpensive.

Pulse Accumulator

The pulse accumulator either counts pulses on a pin or it counts cycles of an oscillator to make a timer. The pulse accumulator operates in two modes called the external-event-counting mode and the gated-time-accumulation mode.The primary hardware in the pulse accumulator is an 8-bit up-counter. The port A pin PA7 controls the counter.

Output Compare

The output-compare hardware normally controls the timing of changes in output bits. Usually the output signal is nearly periodic; for example, a pulse-width modulated waveform. However, almost any kind of timing can be achieved.

The 68HC II has five output-compare registers. Output compare I has characteristics very different from those of output compares 2 through 5.

4.1 Final System:

In order to produce this design into a final product that can be marketed to the public fabrication issues need to be addressed. The first step is to set up suppliers to manufacture the necessary parts needed to build the electric bike. These parts will include a wiring harness, which will be able to contain all weirs leading form the microprocessor in the front of the bike to the motor controller circuit and from the motor controller circuit to the battery. Clips must be manufactured to hold the wiring harness tightly to he frame so that the bicycle riders will not get hung up o the wirers thus the system will be aesthetically pleasing. A motor controller cover should be ordered to contain the motor controller circuit. Along with this cover there should be a battery cover to prevent electrical shock hazard. The Solar panels will require a mounting frame system so that during a rough ride the solar panels will be secure.

Once the proper parts have been fabricated then an assembly factory must be acquired in order to produce the finished product. In order to assemble the bike the plant will need a staff off workers and supervisors. Also an administrative staff must be put in place to oversee the business side of the operation. A marketing team will also be needed to advertise and promote the product. Since the European and Asian markets are more receptive to electric bicycles. It is in the companys best interest to set up international marketing schemes.

The software aspect of the product is immensely vital to the proper operation of the system. The software needed to properly run the bicycle will be burned on to a memory chip. This chip will be mounted on a circuit board that will compose of a microprocessor, the 68HC11. The memory and the processor unit will be VLSI circuits. Due to the high current in the rest of the controller hardware, VLSI will not be possible and larger components and wires will be used.

4.2 Socio-Economic Issues:

Cost Proposal

Parts and Price List

PartQuantity Price (Total)

Microprocessor

Motorola 68HC12 1$160.00$160.00

Metal Box (EMF)1$20.00$20.00

Ribbon Cable1$10.00$10.00

Solar Panels

KQ 401 $295.00$295.00

Custom Made Frame1 $40.00$40.00

Motor Controller Circuit

Power Transistors 12 $5.00$60.00

Power Diodes6$4.00$24.00

Power Resistors 10$2.00$20.00

Bread Board2$15.00$30.00

Cables1 $10.00$10.00

Relays4$5.00$20.00

Misc. Parts--$50.00$50.00

Controller Chips

Unitrode 36783$4.00$12.00

Control Mountings

Grip Accelerator 1$50.00$50.00

Misc. Mountings--$40.00$40.00

Sub Total

$1037.00Tax, Shipping and Handling

Tax6%$93.36$93.36

S&H--$120.00$120.00

Total part Cost

$1250.36

Cost of Time

Student/Faculty TimeRateTotal

Joe LaPointe15hrs./Week $10.00

Total30 weeks,450 Hours

$4,500.00

Greg Huh15hrs./Week $10.00

Total30 weeks,450 Hours

$4,500.00

N. Narasimhamurthi5hrs./Week $100.00

Total30 weeks,150 Hours

$15,000.00

Total Team1050 Total Hours

$24,000.00

Fringe Benefits at 30% of Total Hourly Cost$7,200.00

Total Cost of time

$31,200.00

Facility Rental

500 hours @ $10/hour$5,000.00

Total Cost $37,450.36

Product Pricing

In order to recover the initial investment capital and production cost, we would have to sell the following amount of units at the designated price.

Number of units to be sold: 500 units

Unit price:

$1,100.00

Profit Margin after all expenses including Production,

Shipping and Marketing

$100.00

Revenue

$550,000.00

Profit

$12,549.64

Economic Benefits and Societal impacts

This project involves the implementation and studies of the electric vehicle. This is of primary importance because of current world trends. Oil and gasoline is being consumed at a much higher rate than it is being produced. In some countries gasoline prices are as high as 4 dollars per gallon. This is an outcome that the United States will eventually face and one that will get worse before it gets better.

Differences that exist between electric motors and gasoline motors include the following. Although a gasoline motors can put forth much power with a small engine they are only about 30 to 40 percent efficient. Electric motors on the other hand are around 90 percent efficient. Another important fact is that oil takes millions of years to produce and is limited resource electricity can be spontaneously produced and is not considered to be a limited resource. One more advantage that electricity has is that it poses very little threat to the environment.

4.3 Safety Issues:

There are many safety issues that in tail this project. The first is that of bicycle safety itself. When one is riding on a road or traffic filled street unless the bike can keep up with the speed of that street they should ride along the shoulder of the street. It is recommended that when riding on the shoulder of the street that one rides against the flow of traffic. If something should occur there is more reaction time for the bicyclist. One can also be aware of whether drivers are aware of your presents. Also when riding a bicycle and even more important when riding an electric bicycle, a bicycle helmet should be worn. And when riding on city or country roads always obey the traffic laws.

Another safety concern of this electric bicycle is that it should not be driven in the rain. If the motor controller circuit gets wet it may fry the MOSFET transistors. Although a protective cover is placed over the circuit, in heavy rainwater could still make its way up into the circuit. It is also recommended that the electric bicycle be not ridden through puddles or wet terrain because of the tires tendency of throwing water up onto the bike.

When servicing the bicycle only authorized personnel should do so. Since the motor takes a 20 amp current when the battery is fully charged there is a risk of electrocution. Small children should not be allowed to ride the bike. It is our recommendation that the age requirement be 12 years and older in order to operate the bicycle.

5 TEST RESULTS AND DISCUSSION

The tasks and goals of the design team were all accomplished. These included: variable speed control, microprocessor control, cruise control, and solar panel auxiliary power. The bicycle worked in both modes of operation, manual or automatic.

Although some tests were performed on the system, such as solar power output and power consumption by the bicycle at full speed. The power produced by the solar panels is tested to be relatively close to the manufacturer specifications. Our tests produced 15.6 Volts and a current of 2.16 Amps in direct sunlight. These figures translate into a power supply of 34 Watts. The maximum power consumption of the bicycle is tested to be at 20.5 Amps at a voltage of 11.56 volts. This gives a power consumption of 237 Watts.

There was not enough time to perform the extensive testing that would be necessary in order to fully state bicycles capabilities. This inability to fully test the system was mainly due to time constraint placed on the team.

6 CONCLUSIONDuring the past two semesters the electric bicycle project has provided an opportunity to grasp the full scope of what it means to Design a product. This opportunity allowed an initial idea/goal to be realized in a team environment.

The idea developed as research and various other information on the topic was obtained.

The project evolved and changed as the team limitations and financial constraints were realized. Due to a lack of funding, the initial design of an electric go-cart was downsized to the current project, the electric assisted bicycle.

The initial design, of the electric assisted bicycle, carried along with it constraints that had to be worked around. The constraints were mainly financial in nature. They represent pieces of equipment in the design that had to be carried over from other semesters. The constraints on the equipment consisted of the battery, motor, and the bicycle frame. The motor bicycle relationship could not be altered, mainly due to the type of mounting on the motor. These constraints limited, but did not totally restrict the teams ability to design a new system.

Once all constraints were known, the goals for the design were clearly identified. The goals were divided among the team members. In order to meet the deadline for the final project, progress was monitored weekly and individual goals were readjusted as needed.

With communication between the team, and hard work, the final objective was obtained. The design project provided the team with valuable experience in design and teamwork. It allowed the team members to develop skills that will be useful in future endeavors.

6.1 Executive Summary:

1.Name and academic rank: Gregory Huh, Senior at University of Michigan2. Degrees with field, institutions and dates: Diploma 1994, Axtell High School (College Prep.)

3. Number of years of service at University of Michigan: 3 years

4. Other related experience: Lab Proctor ECE 373 1/01/99 12/12/99Intern at Dearborn Group 1/6/99 9/9/99

1.Name and academic rank: JOE LAPOINTE, Senior at University of Michigan2. Degrees with field, institutions and dates: Diploma 1982, South Lyon High School (College Prep.)

3. Number of years of service at University of Michigan: 2 years

4. Other related experience: Interfaced musical hardware systems.

7 REFERENCES

1) Adle S. Sedra/Kenneth C. Smith, Micro Electronics Circuits, Fourth Edition, Oxford university Press, 1998.2) Motorola, M68HC11EVB Evaluation Board Users Manual, Motorola, 1986.3) J. David Irwin, Basic Engineering Circuit Analysis, Prentice-Hall, Upper Saddle River, New Jersey, 1996.4) Daniel Sperling, Future Drive, Electric Vehicles and Sustainable Transportation, Island Press, 1995.5) 4QD, Motor Controllers, http://www.4qd.co.uk/prod/2qd.html6) Fredric M. Cady, Software and Hardware Engineering, Oxford University Press, 1997

7) Gene H. Miller, Microprocessor Engineering, Prentice-Hall, 1993

8) Mazzae, Elizabeth N; Barickman, Frank S. Intelligent transportation Systems (ITS) Research, Vehicle Research and Test Center, http://www.nrd.nhtsa.dot.gov/vrtc/ca/its.htr9) Occupational Safety and Health Adminisration OSHA Regulations for Motor Vehicles http://www.osha-slc.gov/OshStd_data/1910_0303.htrr10)United States Patent Office, Patent Search, http://www.ibm.patent.com EMBED CorelPhotoHouse.Document

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