MECH 4010 – Senior Design Project – Winter 2011
Winter Term Report
Lab Group Number/Name
#8 – InfiniCycle
Group Member Names
Donald MacIsaac, Michael Ramsis, Daniel Verner, Kellen Wadden
Group Supervisor
Submission Date
Dr. Lukas Swan
8 April, 2011
MECH 4020
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Group 8
InfiniCycle
Executive Summary
There is a need to reduce the amount of greenhouse gases produced from conventional means of
transportation such as gasoline powered automobiles. A common alternative for this mode of
transportation is the bicycle. Commuting by bicycle is a clean mode of transportation. However,
many people choose not to ride a bicycle because of the effort required. Throttle actuated electric
bicycles reduce the effort required from the rider and essentially transform a standard bicycle into
a moped, which eliminates the physical benefit of riding a bicycle. This report presents a solution
proposed to bridge the gap between the standard bicycle and the electric bicycle.
The design solution is the InfiniCycle, an electric bicycle which assists the rider by providing a
multiple of the power the rider outputs through an electrical motor. The riders input pedalling
power is measured continuously while riding and the motor outputs a multiple of the measured
input power. The design requires the rider to continuously pedal to use the electrical assistance;
thus, the rider can physically benefit from the pedaling action associated with riding the InfiniCycle.
The power output from the rider is determined by measuring the torque applied to the pedals and
the angular speed of the pedal crank arm. The applied torque is calculated by continuously
measuring deflection of the chain using a linear potentiometer, which is indicative of the amount of
torque the rider is applying to the pedals. To minimize error, a speed measurement is made at the
same location as the torque measurement. An idler sprocket meshes with the chain at this location
and is mounted on a shaft connected to an incremental encoder to measure the rotational speed.
A rechargeable battery pack is installed on the bicycle to power the motor that provides electrical
assistance. A controller modulates the output of the motor using the power measurement obtained
by combining the torque and speed measurements. The controller is also used for regenerative
braking to restore some of the energy that would otherwise be lost using mechanical brakes.
Mechanical brakes are also available on the bicycle and can be used in emergency stops.
The InfiniCycle is capable of providing electrical assistance for a minimum of 10 km on a single charge in
urban conditions, such as a Halifax city commute, while riding at an average speed of 20 km/h. The
batteries can be fully charged in 4.5 hours if charged simultaneously or in 9.0 hours if charged
successively and can be charged from a 110 V 60 Hz standard outlet. In accordance with the Nova Scotia
Motor Vehicle Act, the electrical motor will be shut off if the speed exceeds 30 km/h.
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Table of Contents
Executive Summary....................................................................................................................................... 2
List of Figures ................................................................................................................................................ 4
List of Tables ................................................................................................................................................. 6
1.
Introduction ........................................................................................................................................ 7
2.
Design Requirements.......................................................................................................................... 8
2.1.
2.2.
3.
Preliminary Testing ............................................................................................................................. 9
3.1.
3.2.
4.
Design Constraints ...................................................................................................................... 8
Design Criteria ............................................................................................................................. 8
Aerodynamic Drag Testing .......................................................................................................... 9
Rolling Resistance Testing ........................................................................................................... 9
Design Selection Process .................................................................................................................. 10
4.1.
Power Measurement ................................................................................................................ 10
4.1.1. Linear Potentiometer ......................................................................................................... 10
4.1.2. Strain Gauges ..................................................................................................................... 12
4.1.3. Load Cell ............................................................................................................................. 13
4.1.4. Comparison ........................................................................................................................ 15
4.2.
Motor & Controller ................................................................................................................... 16
4.2.1. Motor ................................................................................................................................. 16
4.2.2. Controller ........................................................................................................................... 17
4.3.
Regenerative Braking ................................................................................................................ 18
4.4.
Energy Storage .......................................................................................................................... 19
4.4.1. Lead-Acid ............................................................................................................................ 19
4.4.2. Nickel Metal Hydride .......................................................................................................... 20
4.4.3. Lithium-Ion ......................................................................................................................... 20
4.4.4. Comparison ........................................................................................................................ 21
5.
Proof of Concept ............................................................................................................................... 22
5.1.
Battery Testing .......................................................................................................................... 22
5.1.1. Theoretical calculations...................................................................................................... 22
5.1.2. Experimental results........................................................................................................... 22
5.2.
Potentiometer Testing .............................................................................................................. 26
5.2.1. Theoretical Calculations ..................................................................................................... 26
5.2.2. Experimental results........................................................................................................... 29
6.
Selected Design and Components .................................................................................................... 31
6.1.
Power Measurement ................................................................................................................ 31
6.1.1. Linear Potentiometer ......................................................................................................... 31
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6.2.
6.3.
6.4.
6.5.
7.
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InfiniCycle
6.1.2. Spring.................................................................................................................................. 31
6.1.3. Encoder .............................................................................................................................. 32
6.1.4. Housing............................................................................................................................... 32
6.1.5. Component Connection ..................................................................................................... 34
6.1.6. Encoder Attachment .......................................................................................................... 34
6.1.7. Sprocket.............................................................................................................................. 35
Signal Processing ....................................................................................................................... 35
6.2.1. Signals ................................................................................................................................. 35
6.2.2. Systems used to process signals......................................................................................... 36
6.2.3. LabVIEW program............................................................................................................... 37
Motor and Controller ................................................................................................................ 42
Energy Storage .......................................................................................................................... 45
Regenerative Braking ................................................................................................................ 48
Final Testing ...................................................................................................................................... 49
7.1.
7.2.
7.3.
7.4.
7.5.
7.6.
7.7.
7.8.
Preliminary Motor Tests/Calibration ........................................................................................ 49
Motor Cut-Out .......................................................................................................................... 51
Motor Top Speed ...................................................................................................................... 51
Range ........................................................................................................................................ 52
Regenerative Braking ................................................................................................................ 53
Weight ....................................................................................................................................... 53
Hill Test...................................................................................................................................... 54
Summary ................................................................................................................................... 55
8.
Future Recommendations ................................................................................................................ 56
9.
Conclusion ........................................................................................................................................ 57
10.
References ........................................................................................................................................ 58
Appendix A
- Technical Drawings .......................................................................................................... 59
Appendix B
-........................................................................................................................................... 68
Appendix C
Time Line ............................................................................................................................ 69
Appendix D
- Design Modeling Spreadsheets ........................................................................................ 70
Appendix E
- Power and amp-hour curves of the battery..................................................................... 71
List of Figures
Figure 1- Potentiometer diagram ............................................................................................................... 10
Figure 2- Strain gauges on pedal crank arm ............................................................................................... 12
Figure 3- Load cell locations (fix labels) ...................................................................................................... 14
Figure 4- Nine Continent 2807 Hub Motor ................................................................................................. 17
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Figure 5- 20A Infineon Controller ............................................................................................................... 18
Figure 6– Variable resister circuit diagram ................................................................................................. 23
Figure 7 – Variable resistor circuit for test ................................................................................................. 23
Figure 8- Variable resistance configurations .............................................................................................. 24
Figure 9 – Power curve of the battery subjected to 500W load ................................................................. 25
Figure 10 – Battery performance vs time, subjected to 500W load ........................................................... 26
Figure 11- Chain displacement nomenclature ............................................................................................ 27
Figure 12- Potentiometer assembly............................................................................................................ 27
Figure 13- Chain deflection vs. Input torque, Linear approximation .......................................................... 29
Figure 14- Linear potentiometer testing..................................................................................................... 30
Figure 15- Cross-Section of power measurement system .......................................................................... 33
Figure 16 – National Instruments USB-6008 (National Instruments website) ........................................... 36
Figure 17 - LabVIEW program written to process the input signals ........................................................... 37
Figure 18 - Program used to convert potentiometer input to torque reading ........................................... 38
Figure 19 – Graph showing the linear proportionality of torque to voltage. ............................................. 39
Figure 20 - Program used to get speed of the front sprocket and speed of the bicycle ............................ 39
Figure 21 – Program giving power and Torque signal to the motor ........................................................... 40
Figure 22 - Program used to convert torque to a voltage output .............................................................. 41
Figure 23 - limits for output range .............................................................................................................. 42
Figure 24 – Motor Specifications ................................................................................................................ 43
Figure 25 – Motor Power Output Limit vs. Theoretical Required Output .................................................. 43
Figure 26 – Motor Torque Output Limit vs. Theoretical Required Output ................................................. 44
Figure 27- Yardworks 20V (6Ah) Lithium-ion Battery (Canadian Tire website) .......................................... 45
Figure 28 – Original battery bracket design ................................................................................................ 46
Figure 29- Batteries attached to bracket on bicycle rack ........................................................................... 46
Figure 30 - Custom electrical connections .................................................................................................. 47
Figure 31 - Full assembly of the battery bracket ........................................................................................ 48
Figure 32- Approximation of displacement vs. input torque ...................................................................... 50
Figure 33- Measurement of displacement vs. input torque ....................................................................... 50
Figure 34- Motor cut-out testing ................................................................................................................ 51
Figure 35- Bike Route (Google Maps, 2011) ............................................................................................... 53
Figure 36 - Model of the electrical systems of the bicycle ......................................................................... 70
Figure 36- Power vs. Time (250W Test) ...................................................................................................... 71
Figure 37- Voltage, Current, and Ah vs. Time (250W Test) ........................................................................ 71
Figure 38- Power vs. Time (125W Test) ...................................................................................................... 72
Figure 39- Current, Voltage, and Ah vs. Time (125W Test) ........................................................................ 72
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List of Tables
Table 1 - Motor Summary ........................................................................................................................... 17
Table 2- Summary of Energy Storage Methods (Information provided by Dr. L. Swan) ............................ 21
Table 3 – Resistances used to simulate motor load ................................................................................... 23
Table 4- Summary of values collected during endurance test ................................................................... 52
Table 5- Summary of the recorded times during the hill test..................................................................... 54
Table 6- Summary of testing ....................................................................................................................... 55
Table 7- Design Requirements vs. Actual Performance .............................................................................. 57
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1.
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InfiniCycle
Introduction
Commuting by bicycle can be physically challenging, especially for long distances and changes in
elevation. Although commuting by a bicycle can be as quick as commuting by a car or public transit
in large congested cities and it is more environmentally friendly due to the lack of exhaust, many
people choose not to ride a bicycle because of the effort required and the condition in which they
arrive at their destination. An alternative to conventional bicycles is electric throttle actuated
bicycles. The purpose of these bicycles is to provide electrical assistance to the rider on demand
through a throttle. However, riders tend to use them as a moped and continuously use the throttle
instead of pedaling for propulsion, which eliminates the physical benefit of riding a bicycle. Our
solution is an electric power multiplier bicycle which provides electrical assistance by providing a
multiple of the power the rider delivers to the bicycle.
The benefit of using the electric power multiplying bicycle is that it requires the rider to
continuously pedal in order for the bicycle motor to provide power. The bicycle measures the
torque input by the rider and the speed at the same location where the torque measurement is
being made, and combines the two measurements for a power measurement. This power
measurement dictates the amount of voltage that is sent to the controller. This voltage will specifiy
power output of the motor. If the rider is not pedaling (the rider is putting out 0 W), the motor will
supply 0 W. This ensures that the rider cannot use the power assistance without pedaling so that
the rider is always physically benefitting from the exercise associated with riding a bicycle.
A battery pack on the bicycle powers the motor through a controller. The controller will use the
power signal supplied by the torque and speed sensors to modulate the power supply to the motor.
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2.
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InfiniCycle
Design Requirements
The design requirement memo was submitted on 5 October 2010. The purpose of this memo was to
outline the problem and specifically state the criteria and performance goals for the project.
2.1.
Design Constraints
Performance
1. Must be as functional as a conventional bicycle.
2. Motor can only be utilized to power the bicycle when the rider is pedaling.
3. The bicycle must be capable of charging with a standard 120 V, 60 Hz electrical outlet.
Design
1. All mechanical/structural components added to the bicycle must be designed by the team.
2. A torque/speed measuring device will measure the rider input power.
3. The bicycle frame must be made of steel alloy or aluminum alloy.
4. The bicycle must incorporate 2 wheels.
5. The bicycle will accommodate one rider.
6. The bicycle will allow conventional riding position.
Safety
1. The batteries must charge safely according to manufacturer/supplier specifications.
2. There must be an emergency shut-off switch for the motor.
3. The additional weight of equipment plus the rider cannot exceed the manufacturer’s weight
restrictions.
4. All electrically charged components must be insulated for safety.
Cost
1. The total cost of the bicycle must be under $2000.
2.2.
Design Criteria
Performance
1. The bicycle should incorporate regenerative braking.
2. The bicycle should be able to achieve a top speed of at least 30 km/h.
3. The bicycle should have a minimum range of 10 km in urban conditions
4. The braking system must be able to switch between regenerative braking and manual
braking.
Design
1. The bicycle’s total weight should be less than 35 kg.
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3.
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InfiniCycle
Preliminary Testing
The first stage of the design process was to determine the energy and power requirements to meet
the specified performance of the bicycle. On 23 October, 2010, testing was conducted to determine
the aerodynamics of the bicycle and rider and also to find the rolling resistance of the bicycles tires.
With the aerodynamics and rolling resistance of the bicycle we could then begin an analysis of the
all aspects of the bicycle to determine the kind of equipment we would need for our bicycle.
3.1.
Aerodynamic Drag Testing
The first test that was done was to determine the aerodynamics of the bicycle. This was done by
having the rider peddle the bicycle up to 25 km/h and then stop pedaling and allowing the bicycle
to coast. Time was recorded for every 5 km/h interval from 25 km/h down to 5 km/h. With this
data we were able to use Microsoft Excel and equations from the Bosch automotive handbook
(Bosch) to determine the coefficient of drag on the bicycle and rider.
In this test, rolling resistance was assumed to be negligible and the coefficient of drag 𝐶𝐷 was
determined to be 0.894. The drag is proportional to the square of the velocity as shown in the
equation:
1
2
𝐹𝐷 = 𝐶𝐷 𝜌𝐴𝑅 𝑉 2
3.2.
(1)
Rolling Resistance Testing
The second test that was done was to determine the rolling resistance of the tires on the bicycle.
This was done by pedaling to a certain speed and recording this speed at a point A. Then the rider
stopped pedaling and again allowed the bicycle decelerate to a point B where the speed of the
bicycle was recorded again. Using Microsoft Excel again and equations from the Bosch automotive
handbook (Bosch) we were able to determine the rolling resistance of the tires on the bicycle.
After this testing was completed it was determined that the rolling resistance coefficient, μ was
0.015. The rolling resistance force was proportional the amount of normal force that was being
exerted on the bicycle according to the following equation:
𝐹𝑅 = 𝑁𝜇
(2)
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4.
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InfiniCycle
Design Selection Process
Different designs and components were considered to ensure optimum quality. The different
designs were weighed based on longevity, ease of maintenance and cost. The following sections
include the details of the different considered designs.
4.1.
Power Measurement
The torque/speed-measurement system is integral to the effectiveness of the bicycle. Design
Constraint 2 states that the bicycle must be able to measure torque effectively. The three designs
that were considered are detailed in the following sub-sections.
4.1.1.
Linear Potentiometer
When a rider applies torque to the crank assembly there is a resulting change in the tension of the
chain. As the torque increases, the tension in the chain increases, and as the tension increases a
positive vertical displacement occurs against a spring as shown in Figure 1. The linear
potentiometer will utilize this change in displacement to cause an analog change in electrical
output. This system consists of a single linear potentiometer, with a spring wrapped around its
actuation shaft and an idler gear inserted in the journal bearing at the end of its actuation shaft, as
shown in Figure 1.
Figure 1- Potentiometer diagram
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The potentiometer consists of an actuated shaft, which will vary the effective resistance across it
when there is a change in the linear displacement.
Normally, there would be a very small change in vertical displacement, which would cause difficulty
tuning the controller. The spring integrated into the system can be pre-tensioned to create a
vertical displacement in the chain, which increases the range and allows the controller to be tuned
more easily and accurately. Figure 1 shows that the spring will cause more deflection in the chain
and the larger deflection will be easier to tune. The change in resistance across the potentiometer
will cause a change in the measured voltage.
The linear potentiometer actuation shaft will be attached to an encoder bracket. The bracket will
allow for a shaft to run through it. An idler sprocket will be mounted on the shaft and connected to
an encoder. The idler sprocket meshes with the bicycle chain to allow for a speed measurement to
be made and to allow for a smoother contact point between the linear potentiometer and the chain.
A speed measurement has to be made at the same location as the torque measurement to minimize
error when calculating the total power.
A linear potentiometer would meet all of the relevant design requirements, as it could readily
measure the input torque from the rider. The amount of displacement caused by the notches in the
chain (around 5 mm) would be considerable with respect to the total deflection in the chain. It
would be very difficult to filter out that large amount of noise because the amplitude is relatively
large with respect to the displacement of the chain. The idler gear drastically reduces the amount of
noise that affects the potentiometer and allows it to only be affected by the displacement in the
chain. This system does not require information to be sent from the rotating shaft to the main frame
of the.
The main disadvantage of this particular system is that it can be influenced by disturbances that are
caused by outside forces. If the bicycle was to go over a speed bump or hit a pothole, there would be
a large displacement of the chain, which would cause a torque ripple. This would cause large,
undesired input torque that would be difficult for the ride to control. Since this is so important to
the life-span of the bicycle and the safety of the driver, it is addressed with the spring.
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4.1.2.
Group 8
InfiniCycle
Strain Gauges
When a rider is pedaling, the input torque produces a bending stress in the pedal crank arm. This
design would utilize a set of strain gauges attached to the pedal crank arm to measure the amount
of strain that the bending moment is producing on the shaft. By using multiple strain gauges we will
be able to compensate for the strains produced by temperature difference and lateral forces, and
isolate the strain due to bending. The strain gauges will be attached to the top and bottom surfaces
of the crank as shown in Figure 2. By measuring the stain, the stress due to bending can be
calculated, which is proportional to the amount of torque that the rider will be inputting into the
bicycle. We will be able to use the controller system to send a signal to the motor to multiply the
amount of input torque.
Figure 2- Strain gauges on pedal crank arm
The strain gauges would be connected to a wheatstone bridge to produce an output that can be
measured by our controller. Since the crankshaft is rotating, the signal from the wheatstone bridge
will have to be passed from the rotating crank arm to the stationary frame of the bicycle where the
controller will be mounted. This is a disadvantage because it becomes more difficult to send a signal
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from a rotating measuring device than it would be to use a measuring device that could be
stationary on the bicycle.
There are a number of methods that could be used to send a signal from the measuring device to
the controller; two methods have been considered. The first method would be to use slip rings to
transfer the signal from the rotating crank arm to the stationary frame. The advantage of this
method is that it is a proven method of transmitting a signal from a rotating shaft to a stationary
receiver. The disadvantage of using slip rings is that they use brushes to transfer the signal from a
rotating object to a stationary one. This connection would be difficult to maintain and protect from
the harsh outdoor environment. The average price of a single strain gauge is approximately $10 to
$20 (reference) and the slip rings are approximately $50 to $150 each (reference). The second
method is to use a wireless signal transmitter that would transmit the voltage signal output from
the wheatstone bridge and send it to a receiver connected to the bicycles controller. The advantage
to this method is that no brushed devices would have to be used to transmit the signal. Also, since
part of the system will be wireless, there will be less covering over electronic parts on the bicycle. A
drawback to a wireless system is that it would need a power supply for the transmitter. This could
be done by adding a small battery pack to the crank arm of the bicycle but this would add
undesirable weight to the crank arm and increase operational costs and maintenance. The
rotational speed of the sprocket can be made by attaching the sprocket shaft to an encoder.
The overall benefit to using the method of strain gauges to determine the torque input by the rider
into the bicycle is that it is a very well established method used to measure torque. This would
suggest that the method of using strain gauges could work for our application on the bicycle. Also,
due to the size of the stain gauges, they would add a negligible amount of weight to our bicycle
which is an important design criterion for the bicycle.
4.1.3.
Load Cell
The load cell option would incorporate a compression measurement, taken by a load cell having an
output conditioned by a wheatstone bridge. The load cell would be rated for a 90 to 100 kg
compression reading. The location of the cell is very important when considering where the torque
could be measured most accurately and simply. Two options have arisen for the location of the load
cell for optimal torque measurement:
(1) The compressive force of the rider pressing on the pedal would be measured by a planar load
cell mounted directly on top of the pedal surface. This is shown as first location sensor location in
Figure 3.
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(2) Within a customized two piece key installed along the shaft that runs through the bottom
bracket. One piece would be rigidly connected to the pedal crank set, while the other piece would
be rigidly connected to the bottom bracket shaft. A slot would be machined at the surfaces where
these two pieces meet to allow the load cell to be installed (as shown as second location in Figure
3).
Figure 3- Load cell locations (fix labels)
When the pedal crank arm is subjected to a force (and thus a torque, via the distance from the pedal
to the center of the bottom bracket shaft) the two pieces would create a compressive force on the
load cell at the point where they meet which would be detected and measured by the load cell.
The rotating pedal crank arm prevents the use of direct wiring to the controller because the wiring
would eventually become wound around the shaft. For this reason, the output signal from the load
cell must be sent to the controller using an electrical slip ring. The slip ring utilizes brushes to
maintain contact (and thus signal transmission) with the stationary member where the signal is
going and the rotating member from which the signal is being sent.
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There are several advantages to using this system of measurement: The measurement accuracy
would be quite high, as the torque measurement would be taken from one of the earlier locations of
energy transmission in the bicycle system. The load cell would be directly measuring a compressive
force related to the torque by the distance from load application to the center of the axis of rotation
of the pedal crank arm. In contrast, other systems such as the linear potentiometer have significant
calculation and tuning difficulties related to converting the linear displacement measurement of the
potentiometer to the input torque. Another advantage of the load cell design is that the load cells
are quite small (approximately 4 cm diam. x 0.5 cm thickness) and very lightweight (approximately
100 grams). This fits with the design criterion of 35 kg for the complete electric bicycle. The
rotational speed of the sprocket can be made by attaching the sprocket shaft to an encoder.
Although there are some enticing advantages of this design, there are several major disadvantages.
The load cell output signal would require a slip ring to send the signal to the controller. The slip
rings have inherent disadvantages described in Section 3.1.2. Also, for load cells rated for
approximately 90 kg (200 lb), the price is high- $400-600 per cell (Omega). Finally, for the case of
the customized two-piece key with a load cell installed within it, the bottom bracket shaft would
require significant effort to ensure safety and structural stability after installation/modification.
4.1.4.
Comparison
The linear potentiometer was chosen as the design for our torque measurement system because of
its relatively low cost, easy maintenance, long life expectancy and feasibility. Although the strain
gauges cost relatively little per unit, the equipment needed to route the signal back to the controller
(slip rings) is expensive and complex. The only additional equipment that would be needed for the
linear potentiometer would be extra wiring to route the signal to a ballast circuit and then to the
controller. The linear potentiometer provides the easiest maintenance since both of the other
options require slip rings. Since slip rings are mounted on the bottom bracket shaft, the entire shaft
would have to be taken apart to repair them. The linear potentiometer can easily be disassembled
from the bracket if it is need of tuning or repairs. The strain gauges would require modifications to
the crank shaft to allow spacing for the slip ring. The load cell system was deemed the least feasible
because of its high cost and modifications that would be needed to be made to the bicycle. The load
cell would require modifications to the crank shaft to create additional spacing for the slip ring.
However, the crankshaft must be modified further to account for the additional space that the load
cell would require. These modifications would be difficult and could change the rider’s position.
Overall, the linear potentiometer system was deemed to be most feasible of the three systems.
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4.2.
Group 8
InfiniCycle
Motor & Controller
The motor and controller system is the next step after the torque measurement system sends its
signal. Once the rider begins to apply an input torque, we need a system to add a percentage to that
output. The design selection for the motor and controller are detailed in the following sub-sections.
4.2.1.
Motor
In order to determine the optimal motor required for the InfiniCycle, power requirement models
were developed to examine how much power was needed from the motor to allow the bicycle to
achieve different speeds at different inclines, especially the top speed goal of 30 km/h. Simulations
were done for flat ground and several grades of incline and decline. Substantially higher power was
required from the motor to reach 30 km/h on higher grades. Based on 30 km/h on flat ground, the
approximate power output required from the motor is 300 W if the multiplier value was set to
200% - the motor outputs two times the riders input power. To achieve a speed of 30 km/h on a 2
degree incline however, the motor would need to output approximately 500W based on 200 %
power multiplier. Finally, the Motor Vehicle Act of Nova Scotia (2009) (”Bicycle,” Chapter 293)
dictates that the maximum power rating for an electric motor on a bicycle cannot exceed 500 W,
therefore the design was limited to 500 W to meet these regulations.
Based on the chosen battery pack- 40V, 6 Ah, The motor would need to be rated for 36-48 volts. Due
to small decreases in battery output voltage upon higher current draws, it was determined that the
motor should be specified for 36 V, thus being able to use the motor to its potential rather than
under utilize a 48V motor.
Upon determination of the motor power requirements, the next step was to find manufacturers of
electric bicycle hub motors and to determine what options were available. Initially, three motor
suppliers were identified as the best options as they all had a large customer base and a large
selection of motors available. The three companies were Crystalyte Motor Company, Golden Motor
Company, and Nine Continent (distributed by Grin Technologies). After some market research, Nine
Continent and Crystalyte motors emerged as the best suppliers for the motor as they had proven
track records of high quality products. A summary of the different motor choices can be seen in
Table 1.
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Table 1 - Motor Summary
Motor
Crystalyte 408
Nine Continent 2807
Nine Continent 2806
Torque
Medium
Medium
Low
Speed
Medium
Medium
High
The Crystalyte 408 motor is unable to provide torque output under speeds of 5-9 km/h (Crystalyte,
2010), which significantly reduces the InfiniCycle’s proposed operating range of 0-30 km/h. The
Nine Continent 2807 motor can provide torque at very low speeds (nearly 0 km/h) which suits our
operating requirement better than the Crystalyte 408 motor. Finally, the Nine Continent 2806
motor is classified as a high speed motor, and therefore is able to achieve higher speeds but
provides less torque in the low speed range. The 2807 has ample speed to match our requirements
(NineContinent); therefore, it is not justifiable to choose the 2806 which would limit our low speed
torque with no speed benefit. Since all motors considered were capable of regenerative braking
this was not a concern in the final motor selection process.
Figure 4- Nine Continent 2807 Hub Motor
4.2.2.
Controller
The linear potentiometer will produce an analog signal and the rotary encoder will produce a
digital signal. These signals will be processed and converted into an analog signal which will be sent
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to the controller. The controller will receive this signal, which will be used with the selected
multiplier to limit the amount of voltage and current that is sent to the motor.
The InfiniCycle controller will act as an inverter which will convert the DC power (received from
the battery) to AC power which will drive the hub motor. The main design consideration for the
controller is the current limitation. Assuming a motor and controller power system with 70%
efficieny (eBikes) approximately 715 W would be supplied to the controller to have a motor output
of 500 W. This corresponds to a 20 A maximum for 36 V from the batteries . Also, calculations were
performed based on the battery testing detailed in Section 5.2 to determine the maximum amount
of current that the controller will have to handle, we determined this to be approximately 21 A.
From this, it was decided that the required controller current limit must be between 20 A and 25 A.
In addition, compatibility between the hub motor and controller are very important in order to
ensure the motor operates as expected within its voltage and current limits. For this reason, the
controller options were narrowed down to the 20 A/25 A options. Infineon controller (for the Nine
Continent hub motor) and the 36 V-20 A Crystalyte analog system controller (for the Crystalyte hub
motor). Both controllers are able to operate within 36 V and 48V.
Figure 5- 20A Infineon Controller
4.3.
Regenerative Braking
Regenerative braking is a system that is used to convert kinetic energy into electrical energy while
slowing down a vehicle. This system can be used to increase the efficiency of the electric bicycle. A
regular braking system converts the kinetic energy into heat which cannot be stored or re-used.
The electric motor that is used to multiply the power input can also be utilized as a generator. When
the motor is used as a generator, the potential difference across the terminals of the motor induces
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resistance to motion which causes braking. As the kinetic energy is transferred from the wheel to
the batteries through the motor, the bicycle slows down.
In addition to the increased efficiency, a regenerative braking system is also a safety feature as it
disconnects the motor from the power supply once it is engaged. This can be used instead of a
motor shut off switch to satisfy the safety design requirements. The benefit of using the
regenerative breaking system in place of a shut off switch is that it does not require any additional
action in an emergency; instead, the rider simply engages the brakes as one normally would on a
normal bicycle.
In addition to regenerative braking, the bicycle will also utilize the friction braking system. The
braking system will be designed so that the break lever would control both of the regenerative and
frictional brakes. Enough slack will be placed in the brake cables so that the manual brakes will not
be actuated right away, but rather will activate regenerative braking. Once the lever is pulled past a
certain point the manual braking will also be engaged along with the regenerative braking. This
precaution is to ensure that very quick braking is made possible in emergency situations.
4.4.
Energy Storage
Selecting an appropriate battery type and size is important to the success of the bicycle. The energy
storage unit must have sufficient power and energy capability while remaining within a reasonable
mass and volume. A rechargeable battery was chosen as the best method of energy storage to avoid
replacing the battery after it is depleted. Based on the predicted 10 km minimum range of the
bicycle, a rechargeable battery system with a life of time of an average Li-ion battery (about 1500
life cycles) would need to be replaced after every 15,000 km. This will drastically decrease
maintenance costs for the user, which will make the bicycle more appealing as a product on the
market. A rechargeable battery would also allow the user to charge the bicycle at home before
leaving. The chemistries considered were Lithium-Ion, Lead-Acid and Nickel Metal Hydride. A brief
description of advantages and disadvantages of each of the three types of batteries can be found
below along with selection of the most suitable type for the bicycle.
4.4.1.
Lead-Acid
A lead acid battery was utilized on the previous electric bicycle design project in 2008 as the energy
storage system (Dal Mech Eng, Group 8, 2008). Lead-Acid is a very popular type of industrial use
battery due to its wide availability and low cost. Lead-Acid batteries have good performance at high
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and low temperatures; however this is not a major concern for this purpose, as the bicycle will most
likely only be used in moderate temperatures (5oC-30oC).
The main disadvantage of Lead-Acid batteries is that they have a very low Energy and Power output
per unit mass and volume. The cycle life of lead acid batteries is low compared to other
rechargeable batteries. Another major disadvantage of Lead-Acid batteries is their tendency to
succumb to sulfation or corrosion when placed in long term storage in a discharged state. In the
case of this project, the bicycle would likely not be used in the winter. This would mean that the
Lead-Acid batteries could potentially corrode and would have to be replaced.
4.4.2.
Nickel Metal Hydride
Portable Nickel Metal Hydride batteries have advantages over the Lead-Acid batteries because of
their higher energy density, longer life cycle, and longer shelf life. The higher energy density allows
for higher energy storage for the same added weight. The longer life cycle reduces operating costs
for the user. The longer shelf life is very important in colder countries because most bicycle users
store their bicycles during the winter and using a battery with a short shelf life would require more
frequent replacements which would increase maintenance cost.
The main disadvantages of Nickel Metal Hydride batteries are availability and cost. The cost of NiMH batteries approaches Li-Ion while the power density is more comparable to lead acid.
4.4.3.
Lithium-Ion
Lithium Ion batteries were selected as the optimal choice for the InfiniCycle. One of the main
advantages of Li-Ion batteries is that they have a very high energy and power output per mass and
volume. Table 2 shows that Li-Ion has over 300% more energy per mass of the Lead-Acid and 60%
more than NiMH. It would also have the largest cell voltage of the considered batteries (3.3V/Cell).
The advantages of Li-Ion also include long cycle life and shelf life, which reduce operating costs for
the user, good retention of charge, which increase driving range, and rapid charge capability, which
would make it possible for the bicycle to be used more frequently.
The main disadvantage of Li-Ion batteries is the initial cost. Although Li-Ion batteries cost more
than Lead-Acid per unit mass and volume, the cost of energy ($/Wh) is less, so longer driving
ranges can be achieved for the same or less cost with decreased weight addition.
Another
disadvantage of Li-Ion batteries is that they lose capacity when overcharged but that can be offset
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by specifying the manufacturer’s estimated time required for charged so that the user will not
overcharge the batteries.=
4.4.4.
Comparison
The Lithium-Ion battery was chosen as the energy system for our electric bicycle. Lithium-Ion
batteries were lighter and occupied a smaller volume than the Lead-Acid or Nickel Metal Hydride
systems. Since Lithium-Ion batteries have both higher Energy per mass and Power per mass values
than the Lead-Acid and Nickel Metal Hydride (as illustrated in Table 2), we will have a much
smaller weight addition to the bicycle. The Lithium-Ion batteries also have a longer lifespan, with
the number of life cycles being greater than 300% more than that of Lead Acid and 50% more than
Nickel Metal Hydride. Although Lithium Ion batteries may be more expensive, they have significant
performance advantages relating they their energy density and lifetime. It was concluded that the
Lithium Ion batteries were the most advantageous energy system to use for the project.
Table 2- Summary of Energy Storage Methods (Information provided by Dr. L. Swan)
Energy
Battery Type
Wh/kg
Pb-Acid
Li-Ion
25
80-85
NiMH
50
Power
Wh/L
55
165
110
W/kg
100
1000
150
Dalhousie University- Dept. of Mechanical Engineering
W/L
210
1000-3000
300
Longevity
Cost
Life Cycles
$
400
1500
$150
$450
1000
$300
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5.
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Proof of Concept
To ensure that the selected design is functional, two prototypes were built. The first was built to
simulate the loading conditions of the batteries and the second was built to examine the range and
practicality of the torque measuring mechanism.
5.1.
Battery Testing
Dr. Lukas Swan graciously allowed the usage of a Yardworks Li-ion battery, which allowed us to test
the battery chemistry that had been selected. These batteries eventually became the batteries that
were selected for the energy storage system. This will be discussed in section 6.4-Energy Storage.
We needed to determine the number of batteries we would need to use and the actual output that
could be expected from these batteries. The main considerations for this testing were:

Amp-hour (Ah) capacity compared with battery rating

Current draw compared with theoretical

Voltage drop (depression due to high current)
The theoretical limitations of the batteries based on the manufacturer specifications were analyzed
and compared with the experimentally determined limitations.
5.1.1.
Theoretical calculations
A spreadsheet was developed to model the battery performance based on motor power
requirements (See Appendix D). From this model, the theoretical Ah (current draw over time) and
distance that could be achieved under a certain motor load could be determined. By using this
model along with the power and energy storage modeling spreadsheet (which will be discussed in
section 5.2, we were able to model the amount of energy storage required to meet consumption
rates based on multiple variations of riding conditions (speed, distance, gear ratio, etc.). These
models were used to determine the number of batteries, and their appropriate sizes &
specifications for optimal performance.
5.1.2.
Experimental results
The theoretical models provided an approximation of how the batteries would perform. The next
step was to examine how the batteries would respond to motor loads representative of common
scenarios in our application. To do this, a resistive circuit was used to discharge a Yardworks
battery identical to that which will be used on the InfiniCycle, using rates that are similar to those
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expected while riding the bicycle. The circuit diagram of our system and the experimental system
that was used for this test are show in Figure 6 and Figure 7 respectively.
Figure 6– Variable resister circuit diagram
Figure 7 – Variable resistor circuit for test
The battery was tested at 500 W, 250 W and 125 W to simulate our motor running at a 50%, 100
and 200% power multiplier corresponding to a 250 W human power input. We calculated the
resistance needed using Equation (1):
V2
P
R=
(1)
Where P is the motor load in watts, V is the battery voltage output, and R is the resistance in ohms.
The results are detailed in Table 3.
Table 3 – Resistances used to simulate motor load
Power simulated
125W
250W
500W
Resistance used
3.2Ω
1.6 Ω
0.8 Ω
Figure 8 illustrates the different resistor clamping configurations which were used to achieve the
total resistances of 3.2 Ω, 1.6 Ω, and 0.8 Ω.
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Figure 8- Variable resistance configurations
A 4 Ω power resistor was used for the testing. The resistor was rated for 1000 W across its full
length. To simulate the 3.2 Ω, 1.6 Ω, and 0.8 Ω resistances, a clamp was positioned along different
lengths of the coil directly proportional to the resistance ratio. Equation (2) illustrates the
relationship between the resistance and the clamp length:
𝑅𝑡𝑒𝑠𝑡
𝑅𝑡𝑜𝑡𝑎𝑙
𝐿
= 𝐿 𝑡𝑒𝑠𝑡
(2)
𝑡𝑜𝑡𝑎𝑙
For example, if 𝑅𝑡𝑒𝑠𝑡 =3.2Ω, 𝑅𝑡𝑜𝑡𝑎𝑙 = 4Ω, then 𝐿𝑡𝑒𝑠𝑡 =
3.2
×
4
𝐿𝑡𝑜𝑡𝑎𝑙
Once the battery was connected and the appropriate connections were made to the coil to give the
correct resistance, we began the test. By using a Fluke 87 V true RMS multimeter (DAL L.S. #1) we
were able to measure the current that was being drawn from the battery. Instead of breaking the
connection of the battery and the rest of the system to find a measurement of current, we used an
EMPRO DHSE1 (Date stamped: 7/95) shunt resistor.
The shunt resistor in our tests had a
calibration of 1 mV per Amp which made it possible to measure the current across the shunt
resistor by measuring the voltage drop. Finally we used a Fluke 336 true RMS (DAL L.S. #2) clamp
meter to measure the voltage of the battery across the battery terminals. By using a solenoid
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switch, we were able to make the connection of the battery to the rest of the resistive system. This
allowed us to connect the battery to the circuit prior to testing, thus simplifying the start of the
testing process with the closing of a switch. The voltage and current measurements were recorded
at 30 second intervals around the start and end of the test because the voltage and current drop
were much greater at this time. The recording intervals were reduced to 1 minute during mid-test
times as the voltage and current were more steady. From this test we were able to calculate the
power and amp-hours of the battery when subjected to each load. Graphs of the power and amphours of the battery are shown in Figure 9 and Figure 10.
For a load of 500 W, the load on the battery started at 500 W and then quickly dropped to a steady
state at approximately 320 W. From Figure 9 we see that the battery is completely discharged after
approximately 12 minutes. We concluded that if one battery module can produce 310 W of power,
when two battery modules are used on the bicycle, it will allow for a power output much closer to
the 500 W continuous desired.
Power (W)
Power (Watts)
500
400
300
200
100
0
0
2
4
6
8
10
12
14
Time (min)
Figure 9 – Power curve of the battery subjected to 500W load
Figure 10 below shows the voltage, current, and amp-hour profiles of the battery when subjected to
a 500W load. It is apparent that the battery can produce approximately 4 Ah in this situation. Also,
we see that the current that is produced as the battery comes to a steady state at approximately 20
A. Since this experimental test shows that approximately 20 A can be drawn from our batteries, this
helps to confirm that our selection of using a 20 A controller is valid. The results of the 125 W and
250 W tests can be found in Appendix E.
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30
25
20
Current (A)
15
Voltage (V)
10
Amp Hours (Ah)
5
0
0
5
10
15
Time (min)
Figure 10 – Battery performance vs time, subjected to 500W load
5.2.
Potentiometer Testing
On November 30 through December 1, 2010, testing was carried out to satisfy the torque
measurement portion of the proof of concept. The testing demonstrated that the torque input
would cause enough deflection of the chain to be measured by a linear potentiometer.
5.2.1.
Theoretical Calculations
A relationship has been determined between the tension in the chain and the amount of torque
input of the rider for fixed sprocket sizes. The deflection in the chain will be measured by the linear
potentiometer and converted to a voltage signal which will be sent to the controller.
As the rider applies torque to the pedal crank arm, the torque gets transferred to the chain through
the sprockets as tensile forces which act along the direction of the chain. The linear potentiometer
(represented on the drawing by a spring) is mounted vertically, which puts it at a certain angle with
respect to the chain, as shown in Figure 11. θ1 and θ2 are the angles between different parts of the
chain and the horizontal; θ1 is measured clockwise from the positive x-axis and is the angle
between the portion of the chain connected to the big sprocket and the horizontal and θ2 is
measured counter-clockwise from the negative x-axis and is the angle between the portion of the
chain connected to the small sprocket and the horizontal.
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Figure 11- Chain displacement nomenclature
The tension forces in the chain act on the meshing teeth of the transducer sprocket in two opposite
directions, along the direction of the chain and towards each sprocket. As a result of the angle
between the chain and the linear potentiometer, each force has two components, a vertical
component and a horizontal component. The summation of the vertical components of the two
forces acts on the linear potentiometer and causes a deflection that is proportional to the spring
constant and deflection, as shown in Figure 12. The linear potentiometer outputs a voltage signal
that is proportional to the amount of vertical deflection in the chain. The voltage signal will be
processed by the controller and converted to a torque value which will draw a corresponding
amount of current from the batteries to power the motor.
Figure 12- Potentiometer assembly
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The horizontal components of the tensile forces will have a resultant that is not equal to zero, due
to the fact that θ1 and θ2 are not equal. To make sure that the linear potentiometer is always
vertical, guides will be installed to counteract the horizontal resultant force.
The values of θ1 and θ2 change as the value of input torque changes. Depending on the spring
constant of the linear potentiometer, at a certain amount of torque, the value of θ2 will go to zero
and then start increasing in the opposite direction. This will cause the vertical component of the
tension force, contributed by the smaller sprocket, to be opposing the direction of vertical
component of the tensile force contributed by the larger sprocket. This has two disadvantages:
First, it will require two different relations to be defined in the controller between the amount of
displacement and torque applied, one when θ2 is positive and another when θ2 is negative; and
second, the amount of resulting displacement in response to applied torque will decrease
significantly, which will reduce the sensitivity in the higher input torque range. To avoid such a
situation, the maximum displacement in the linear potentiometer will be limited to the value of the
radius of the smaller sprocket. This will constitute the value of the spring constant of the linear
potentiometer.
Since the vertical resultant force acting on the linear potentiometer is dependent on the values of θ 1
and θ2, the displacement in the linear potentiometer in response to the torque is not going to be
linear.
However,
when
the
displacement
Dalhousie University- Dept. of Mechanical Engineering
was
modelled,
as
shown
in
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Figure 13, it was noted that over the operating range, the system can be approximated as linear
with a maximum error of approximately 5% over 75% of the operating range and 10-12% over the
remainder 25% of the range.
Figure 13- Chain deflection vs. Input torque, Linear approximation
5.2.2.
Experimental results
To approximate this system we used a position transducer, a bracket, a digital multimeter and a
spring (k=34.02 N/mm, experimentally determined). The bracket was used to hold the spring in
place, as well restricting its lateral movement. Both position transducers and linear potentiometers
operate under the same principles; varying resistance based on a change in displacement. The
position transducer consisted of a thin cable with a small press fit attachment on the end of it,
which was connected to the bottom of the spring.
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Figure 14- Linear potentiometer testing
After the set-up was complete, different input torques were evaluated to determine both the
deflection of the chain and the resulting change in resistance across the transducer. The transducer
was resting on the floor and was attached to the multimeter by the input and ground wires. The
nominal resistance across the transducer was found to be approximately 468.5 Ω. To show the
maximum amount of input torque that could be administered to the system was estimated by
allowing the rider to input as much force downward as they could while the back wheel was fixed.
This was carried out by a rider with a mass of approximately 90 kg. The maximum chain deflection
that was achieved was 11 mm. This maximum deflection corresponded to a resistance of 526.4 Ω
across the position transducer, which is a change in resistance of 57.9 Ω. Another test was carried
with approximately half of the original input torque, deflecting the chain 6mm. This torque
corresponded to a resistance of 499.7 Ω across the position transducer, which is a change in
resistance of 31.2 Ω.
When approximately half of the original torque was applied, the amount of deflection was
approximately half the original amount of deflection. These results validated the design decision to
assume that the deflection is a linear function of the amount of input torque.
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6.
Group 8
Infini-Cycle
Selected Design and Components
6.1.
Power Measurement
As discussed in section 4.1.1, the speed and torque measurements have to be made at the same
location to minimize error. The bracket has been designed to fit in the tight spacing of the bike and
allow for the torque and speed measurement to be made at the same location. A cylindrical housing
for the linear potentiometer is clamped to the bicycle frame. This housing allows for a secure
attachment method for the linear potentiometer and can be easily removable to allow maintenance
and replacement. The design constraints included the size of the linear potentiometer, available
space, positioning, and wiring.
An encoder bracket has been designed to allow for a direct attachment to the linear potentiometer
actuation shaft. A shaft runs through two journal bearings which are press fit into the bracket. The
shaft is coupled to an encoder, which is attached to the encoder bracket to secure it in place. A
protective sleeve is also attached to the top of the encoder bracket to eliminate lateral forces
induced by the chain. Due to the limited strength of the linear potentiometer actuation shaft, the
protective sleeve is necessary to increase the longevity of the components of the bicycle and reduce
maintenance costs.
Spring caps and seats have been designed to prevent longitudinal motion of the spring and secure it
in place. Multiple adjustable seats have been fabricated to allow for tuning the tension in the
system.
6.1.1.
Linear Potentiometer
The linear potentiometer selected was an Omega LP804-01 which has a range of 25 mm and a 9.53
mm diameter. The expected maximum deflection in the chain under maximum torque input is 22
mm. The 25 mm range of the potentiometer will cover the expected distance of travel and the small
diameter was suitable for the limited space available so the model was selected. The linear
potentiometer also has an expected life of 1 billion operations which is very advantageous since a
longer life would reduce maintenance costs. The stock bicycle chain only allowed for about 10 mm
maximum deflection so it was replaced with a longer chain to take advantage of the full range.
6.1.2.
Spring
As mentioned in section 5.2.1, a model has been built to predict the performance of the torque
measuring mechanism and an optimum spring constant of approximately 3.0 N/mm was required
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to allow for a deflection of 20 mm at maximum torque input. Limitations to the spring selection
included the length of the spring and the inside diameter, as the spring would have to be wrapped
around the linear potentiometer casing and the protective sleeve. Since a custom spring could not
be made, an off-the-shelf spring had to be selected. The spring selected had a spring constant of
2.75 N/mm which is the closest match to the required constant and dimensions. The spring that
was selected was placed around the outer housing and was pre-compressed by spring caps, which
will we discussed in Section 6.1.4.
6.1.3.
Encoder
The encoder that was selected is a TRD-NH360-RZWD medium duty incremental encoder sourced
from Automation Direct. The encoder has a rate of 360 pulses-per-revolution and it is equipped
with a hollow shaft and two set screws, as an attachment point. The encoder would be attached to a
custom shaft where the sprocket would be attached by means of the two set screws.
The 360 pulses-per-revolution rate produces approximately 65 pulses per second at 2 km/h and
1070 pulses per second at 30 km/h. The next available rates were 100 and 500 pulses-perrevolution. The 100 pulses-per-revolution encoder would have produced about 18 pulses per
second at 2 km/h which was considered to be too coarse and the 500 pulses-per-revolution
encoder would have produced approximately 1486 pulses per second which was considered to be
too high and may require additional unnecessary storage space for the measured data. The 360
pulses-per-revolution encoder was selected as the most suitable for our application. The hollow
shaft geometry allowed a custom shaft to be fabricated to fit both the selected sprocket and the
encoder, which facilitated the design process.
6.1.4.
Housing
There were some major considerations with the LP804 Linear Potentiometer. Firstly, the lateral
strength of the actuating shaft and secondly the strength of casing. The shaft was only 1/8” in
diameter; it was believed that this would fail at a high torque. The casing was only 3/8” in diameter.
A more robust potentiometer was originally chosen, however this potentiometer did not fall within
the budget constraints.
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Figure 15- Cross-Section of power measurement system
It was decided that the best design would utilize concentric hollow cylinders which would provide
enough lateral strength to protect the potentiometer while still allowing for the potentiometer to
easily slide up and down while measuring the rider’s input torque. As shown in Figure 15, the
power measurement design utilizes two concentric shafts, one for the potentiometer housing and
one for the outer housing (pictured in red and turquoise respectively). The potentiometer (shown
in dark blue) in encased within a cylindrical housing. The cylindrical housing has a 3/8” bore size
that the potentiometer will fit down and 3/16” walls. The relatively thick walls provide the lateral
strength that will protect the potentiometer’s body.
Another concentric hollow-cylinder slid over the potentiometer housing, which was called the outer
housing. This cylinder had an outer diameter of ¾” and an inner diameter of 1/16” walls. The outer
housing must have an outer diameter less than 0.77”, so that the selected spring can fit around the
outside of the outer housing. Spring caps (shown in dark green in Figure 15) were constructed to
allow the spring to be pre-compressed before there is any torque input. The spring caps were made
up of 8 removable caps that could be easily added to or removed from the outer housing.
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6.1.5.
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Component Connection
The connection of the power measurement system to the bicycle frame was very important. The
frame could obviously not be altered in any way so as not to affect the structural integrity of the
bicycle. Therefore, the only viable option was to develop a clamping mechanism that would clamp
onto the seat stay and remain rigidly attached. Early iterations of the power measurement system
included a clamp consisting of two pieces that were fixed together by means of 4 ¼” bolts.
Unfortunately there was too much eccentricity in the bore holes and the potentiometer housing
could never be rigidly secured by the clamp.
The solution to this problem was to weld the potentiometer housing into one half of the clamp
assembly. This would allow the potentiometer attachment to be rigidly attached as well as
providing enough lateral strength. There was also an additional concentric bore made on the same
angle (45o) that allowed the potentiometer to still be removed easily. This would ensure that the
power measurement assembly would still be easily assembled and disassembled and that the
potentiometer could be accessed.
The other critical connection point was the custom stud which allowed three components; the
linear potentiometer actuating shaft, the outer housing and the encoder attachment to be connected
at the same point. To achieve a smooth measurement of torque, the potentiometer’s actuating shaft,
the outer casing, and the encoder attachment needed to move as one synchronous object. To ensure
that this would occur with minimum eccentricity, the potentiometer was connected to the outer
housing and the encoder attachment by means of a custom stud. The stud had a 3/8” UNF thread on
the outside and #4-40 thread on the inside. This allowed for the stud to be able to connect the
potentiometer’s actuating shaft and outer housing in one object.
The outer housing and the potentiometer’s actuating shaft could now be connected to the encoder
attachment, which would complete the arrangement of the system. However, it also allowed for
these components to be easily assembled and disassembled. This stud removed the need for a
single component to be made or for several components to be welded together. This is an essential
design feature for a prototype as many of the components would be checked throughout testing to
see if they were working correctly.
6.1.6.
Encoder Attachment
The encoder attachment threaded into the custom stud. The encoder attachment incorporated two
bearings to ensure the exact position of the custom shaft as well as taking some stress off of the
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shaft. The sprocket is attached to the custom shaft via set screws. The set screws allow for easy
realignment of the sprocket with the chain. This is very important as the sprocket would need to be
re-aligned several times during testing. The encoder that was used was a hollow shaft incremental
encoder which attached to the custom shaft via set screws. As the sprocket would turned, the
encoder would turn via the custom shaft and produce an output which would be sent to the DAQ for
processing.
6.1.7.
Sprocket
Selecting the sprocket depended solely on the specifications of the bicycle chain. A 1.34” sprocket
with a pitch of ½” was selected. After multiple testing, some vibrations were noted so the sprocket
was grinded down slightly to allow for smoother meshing and reduce vibrations. The sprocket was
purchased from McMaster-Carr and initially had a width of 7/8”, however the distance between the
walls of our encoder attachment is only 1”. The width of the teeth had also become an issue as they
were too wide to mesh with the chain of the bicycle. The width of these teeth was machined down
to 0.97” and the hub also had been reduced to ¼” width. This allowed for the sprocket to be aligned
with the chain easier.
6.2.
Signal Processing
With all of the physical components in place, the final step is to create a way to compile all the
signals. This requires a combination of the linear potentiometer and the encoder signals to output a
final combined signal. As it has been previously stated, the signals coming in would be a torque
measurement from the linear potentiometer and an angular velocity from the encoder which
needed to be combined together to give power. From this power measurement, using a program, a
final proportional power output to the motor. To move through this process it is easiest to break
everything down into separate parts.
6.2.1.
Signals
As mentioned in the preceding section there would be three signals which are:



Analog input from the linear potentiometer
Digital input from the encoder
0-4 volt analog output signal
The analog and digital signals need to be combined to eventually output a 0-4 volt signal that can be
sent to the motor. A system is needed to acquire these two signals and output a signal which will be
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discussed in the following section. The signals that would need to be acquired would include a 0-5
volt analog signal from the potentiometer and a digital count from the encoder.
6.2.2.
Systems used to process signals
In order to process the signals, a Data Acquisition system (DAQ) was needed. For our design it was
decided to use a National Instruments USB-6008 which is shown in Figure 16 below. The USB-6008
is a multifunction DAQ device that consists of:




1- 32-bit, 5 MHz counter
8- analog inputs at 12 to 14 bits
12 - digital input and output (I/O) lines
2 - analog outputs at 12 bits
For the encoder the 32 bit, 5MHz counter input was used. This would provide a digital count that
could be manipulated to give an angular velocity. Next, for the linear potentiometer one of the
analog inputs was used. This would provide a 0-5 volt analog signal that could be manipulated to
give a torque input. Finally, to provide a 0-4 volt output to the motor, one of the analog outputs was
used.
Figure 16 – National Instruments USB-6008 (National Instruments website)
With the DAQ providing a way to acquire data from the mechanical components, the next step is to
have a way to program and give the data acquired a purpose. By combining the USB-6008 with the
National Instruments programming software LabVIEW (Laboratory Virtual Instrumentation
Engineering Workbench) the two inputs could be programmed to give the desired output.
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LabVIEW program
Figure 17 shows the LabVIEW program that was used to process the inputs and give a final output.
In the diagram each piece of the program is called a block and is connected by branches or wires.
Figure 17 - LabVIEW program written to process the input signals
The program can be broken into sections for further understanding. The first section that will be
looked at is the input of the potentiometer converted to give a torque reading. This is shown in
Figure 18 below.
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Figure 18 - Program used to convert potentiometer input to torque reading
To begin, the DAQ first brings in the signal from the linear potentiometer and outputs the data from
the first block called Potentiometer. The potentiometer block will output 5 volts when it is fully
extended and 0 volts when fully compressed based on its design. For the purpose of the bicycle, it
is desired to have the full extension of the potentiometer output 0 volts instead of 5 volts. To solve
this problem the signal is multiplied by -1 and then 5 is added using the two numeric math blocks.
This gives an output from the potentiometer block ranging from 0 volts when the potentiometer
was fully extended to 5 volts when compressed.
Since this 0 to 5 volt signal does not represent a torque reading the results needed to be calibrated
to give a torque reading. To do this, a simple calibration test was done. Multiple sized weights were
placed on the pedals of the bicycle to act as a torque input. Based on these torque inputs the voltage
output was recorded. These outputs were then graphed to determine the constant that would
relate the voltage to the torque (this is shown in Figure 19 below). By graphing the data it was
found that the voltage was proportional to the torque giving a multiplier of 11.652 which is shown
in the program in the orange block in Figure 18 above. This converts the 0 to 5 volt input to a
torque output.
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35
y = 11.652x - 4.4723
R² = 0.99
30
Torque (Nm)
Infini-Cycle
25
20
15
10
5
0
0
0.5
1
1.5
2
Voltage (volts)
2.5
3
3.5
Figure 19 – Graph showing the linear proportionality of torque to voltage.
The next input is from the encoder, which will be used to give an angular velocity of the bicycle and
front sprocket. The program that was used is shown in Figure 20 below.
Figure 20 - Program used to get speed of the front sprocket and speed of the bicycle
The encoder input was connected to the DAQ at the counter input port which outputs a continuous
count. The first thing that needed to be found was how many counts were being made for as certain
amount of time to give a velocity. This was done by using a while loop that surrounds the entire
system which is shown in Figure 17 as the gray border around the entire system (as well as the
gray vertical lines on the far left and right of Figure 20). By subtracting the initial count signal from
the signal out of the while loop the number of counts will reset every second. The encoder reads
360 pulses per revolution so the next step was to divide the output by 360 to give the number of
pulses per second. The readout would now give a reading of velocity with units of pulses per
second. Since the velocity is needed in radians per second the final step was to convert the units of
pulses per second to radians per second by multiplying by the constant 2π.
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The preceding steps provide the velocity of the encoder, but what is needed is input speed of the
rider. This can be done by finding the ratio that relates the speed of the encoder to the speed the
rider is inputting. A simple way to do this is to determine the ratio of the teeth on the sprocket
attached to the encoder and the teeth on the front bicycle sprocket. The ratio found for the bicycle
was determined to be 7/32. This is shown as constant blocks in the program.
The final step in determining the speed in radians per second is to divide the radians per second
that has been calculated with the sample time of the program. The sample time used was 100
milliseconds.
The speed of the bicycle was also found using the encoder, which will be used later in the program.
To do this, the rotations of the encoder were compared to the rotations of the back wheel in order
to find a multiplier that could relate the speed of the bicycle to the speed of the encoder.
The final big step in the program was to determine the output signal needed to control the motor.
This is done by combining the torque and speed input by the rider to find power and then dividing
this power by the speed of the bicycle to give an output of torque that can be sent to control the
motor. This is shown in Figure 21 below.
Figure 21 – Program giving power and Torque signal to the motor
The torque signal is the final signal needed to control the motor. The output from the DAQ can only
range between 0 to 5 volts and the motor needs a 0 to 4 volt signal to run. The current signal for
torque does not output in this range so the output needed to be calibrated. To calibrate the torque,
the maximum torque that could be sent to the motor was found and scaled between 0 and 4 volts.
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With the torque scaled between 0 and 4 volts the signal could now be sent to the DAQ to be output
to the motor. The program used to convert torque to voltage output is shown in Figure 22 below.
Figure 22 - Program used to convert torque to a voltage output
An extra feature to the program to insure that the output falls between the range of 0 and 5 volts is
shown in the middle of Figure 22 (and again in Figure 23 below for clarity). To do this, a “true or
false” statement was used that would send true if the output value was greater than 4 and false if
the output was less than 4. If the signal was true then a constant 4 volts would be output to the
motor but if the signal was less than 4 it would output the torque 0 to 4 volt signal. This insured
that the output could not increase over 4 and shut down the motor due to interference in the signal.
Finally, an “if” statement was added to the program which would output the 0 to 4 volt torque
signal if it was greater than 0 and output 0 if the torque signal was less than 0.
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Figure 23 - limits for output range
Each of these steps can be seen combined together in Figure 17. By using this program, the signals
from the linear potentiometer and the digital encoder can be combined and used to control the
bicycles motor.
6.3.
Motor and Controller
The motor chosen for the InfiniCycle is a 500W Nine Continent 2807 Brushless 36V DC motor. This
motor will be mounted in a 26” spoked front wheel hub and is delivered from the manufacturer as
an assembly. The Nine Continent 2807 motor shown in Figure 4 is rated for 36 V (and capable of
operation up to 72 V) which will meet our power requirements. The load on the motor will be up to
36 V and 20 A under the most strenuous conditions. Assuming the efficiency of the power system
(motor and controller) to be 70% (Hub Motor Simulation), this will yield as peak power rating of
500 W, thus meeting the NSMVA requirements (Electric Bicycle Laws). The hub motor will have a
mass of approximately 5 kg which is an average mass compared to other hub motors having similar
specifications (Hub Motor Simulation).
To fully determine if this motor would meet our specifications we compared the motor
specifications provided on the manufacturer’s website (Hub Motor Simulation) with our theoretical
output of power and torque that will be required. The manufacturer’s specifications are shown in
Figure 24.
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60
1200
50
1000
40
800
30
600
20
400
10
200
0
Power (W)
Efficiency x 10(%)
Torque (N-m)
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Torque (N-m)
Efficiency(%)
Power (W)
0
0
10
20
30
Speed km/h
40
50
Figure 24 – Motor Specifications
To determine if the theoretical power outputs required from our motor would fit the motor
specifications, power curves for a 50 %, 100% and 200% power multiplier of the riders input were
superimposed on the motor’s power specification curve as shown in Figure 25. From this we
determined that based on power we can theoretically achieve the 30 km/h that we are looking for
on flat ground with the Nine Continent 2807 motor.
600.00
50% Power
Multiplier
Power (W)
500.00
400.00
100% Power
Multiplier
300.00
200% Power
Multiplier
200.00
100.00
Motor
Power Limit
0.00
0
10
20
30
40
Speed (km/h)
Figure 25 – Motor Power Output Limit vs. Theoretical Required Output
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Similar to the power specifications, the torque required from the motor was also superimposed on
the graphs of the motor’s specifications. This is shown in Figure 26. From this we determined that
the torque that would be required to reach a speed of 30 km/h could theoretically be achieved with
the Nine Continent 2807 motor.
60
Torque (Nm)
50
100% Power
Multiplier
40
50% Power
Mulitpler
30
20
200% Power
Multiplier
10
0
0
10
20
Speed (km/h)
30
40
Motor Torque
Limit
Figure 26 – Motor Torque Output Limit vs. Theoretical Required Output
Compatibility between the hub motor and controller are crucial in order to ensure the motor
operates as expected within its voltage and current limits. Since we have decided upon using the
Nine Continent 2807 Brushless 36 V DC motor, we have chosen the 20 A Infineon controller
because it meets our 20 A current limit specification, 36 V operation specification (rated for 36-48
V), and is compatible with the Nine Continent 2807 motor.
To complement the Infineon controller that we have chosen for the bicycle, we will also be utilizing
the Cycle Analyst (Cycle Analyst Information). The Cycle Analyst is a digital read out device that will
provide the rider with information about the bicycle. It will monitor the speed of the bicycle, the
distance the rider has traveled, the voltage of the batteries and the current being drawn from the
batteries. In addition, it can limit the bicycle speed as well as the voltage and current to the motor.
By limiting the speed of the bicycle, we will be able to prevent the motor from assisting the rider
over 30 km/h to abide by the Nova Scotia Motor Vehicle Act (Electric Bicycle Laws). The Cycle
Analyst will limit the voltage to a cut-out limit so that the batteries will not be discharged too
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deeply or experience sudden surges in voltage that could exceed the motor limitations. Finally, by
limiting the current being drawn from the batteries we can protect the controller and the motor
from dangerously high currents.
6.4.
Energy Storage
As mentioned in design selection, Lithium-Ion batteries were the battery chemistry chosen for the
energy storage system. The type of battery that was chosen was the 20 V (6 Ah) Yardworks
Lithium-ion battery shown in figure 26. By using two of these batteries we are able to achieve a
total voltage of 40 V, a capacity of 6 Ah, and energy storage of 240 Wh.
Figure 27- Yardworks 20V (6Ah) Lithium-ion Battery (Canadian Tire website)
One of the main advantages of using the Yardworks Lithium-Ion batteries is that they are readily
available and can be purchased at hardware stores including Canadian Tire. This is an advantage to
a rider because when the Lithium-Ion batteries have passed there useful lifetime, it is simple to
purchase a new set of batteries.
To mount the batteries on the bike, a design was chosen that would incorporate the already existing
mounting clip system incorporated within the batteries. This clip system is used to mount the
batteries on the charger. To do this, we wanted to design a bracket system that would allow the
user to slide and lock the batteries in place on the back rack of the bicycle. This would ensure that
the batteries will be securely attached when the rider is using the bicycle and will allow for easy
connect/disconnect. The original battery bracket design was a horizontal system that would allow
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the rider to clip the batteries in the bracket from the side of the bike. The original design is shown
below in Figure 28.
Figure 28 – Original battery bracket design
It was determined that this design had a few problems. First, this design would place the battery
release clips facing down towards the ground and the electrical connections coming from the side
of the bike. This is not an ergonomic design as it would be difficult for the rider to locate the release
clips and the electrical connections would be protruding from the side of the bike in an undesirable
way.
To solve both of these issues, a new vertical design was proposed which is shown in Figure 29. This
new design would allow the rider to have full view of the clips for easy release from the battery
bracket. Also, this design would allow all of the electric connections to be placed toward the seat of
the bike and run down toward the controller instead of to the side, as in the original design.
Figure 29- Batteries attached to bracket on bicycle rack
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With the problem on how to connect the batteries to the bike solved, the next step was to design an
electrical connection point. A custom electric connection was design from aluminum and is shown
in Figure 30.
Figure 30 - Custom electrical connections
These connections were made by machining aluminum into the appropriate shape to fit into the
battery terminals and also connect to a terminal block. This terminal blocks could then be wired to
the bikes main controller. Each connector was covered by heat shrink to insulate and color code
each of the connections (red +, black -). These connections are a relatively simple design and are
effective in meshing with the design of the batteries.
Also incorporated into the electrical connections was a 20 Amp fuse, which was placed between the
positive terminal of one battery and the negative terminal of the other. This 20 Amp fuse is used as
a safety measure to protect our controller from receiving a current of greater than 20 A. On a figure
of the full battery bracket assembly shown in figure 30, the 20 Amp fuse is the orange connector
coming from the negative connector on the terminal block.
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Figure 31 - Full assembly of the battery bracket
6.5.
Regenerative Braking
For regenerative braking, the EbrakeEzee brake lever was selected as it matched all of the design
requirements. The brake lever controls both of the regenerative and frictional brakes and is
connected directly to the Infineon controller. Enough slack is placed in the brake cables so that the
manual brakes will not be actuated right away, but rather regenerative braking will be activated if
the lever is slightly pulled. As the brakes are further applied, the manual brakes will begin to
engage. This will allow the rider to come to a stop much quicker in the same fashion as a
conventional bike.
Another key feature of the EbrakeEzee brake is that when the brake is applied, power is
disconnected from the motor. By disconnecting the power from the motor, the brake is effectively
a kill switch for the system. This kill switch meets our safety criterion set out in the design
requirements of incorporating a kill switch onto our bike.
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Final Testing
The testing was used to prove that the bicycle that was constructed had met the design
requirements that had originally been set out. We performed several small scale preliminary motor
tests to ensure that the motor would engage. To verify the motor shut off at high speeds the bike
was elevated and the maximum signal (4V) was sent to it. The most critical part of our testing was
the range test, which consisted of a 10 km simulated commute; this tested the battery life as well as
the components ability to withstand extended components of stress and vibration. We also
performed some testing on the regenerative testing, in which we were able to measure what
percentage of the power we were able to achieve during braking.
7.1.
Preliminary Motor Tests/Calibration
Preliminary tests performed were performed by connecting the encoder and potentiometer to
measure the output voltage across the DAQ. Once it was determined that a constant voltage could
be produced by processing the signals from the potentiometer and the encoder, testing and
measurement needed to be performed to calibrate the components. Torque was calibrated by
placing weights on the crank arm, measuring the displacement and relating them to the subsequent
output voltage. The power output was then measured and scaled to a voltage output that was
within a usable range (0V-4V signal). The control system was also written such that the signal being
sent to the motor could not be a negative voltage and could not exceed 4 V.
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Figure 32- Approximation of displacement vs. input torque
Figure 33- Measurement of displacement vs. input torque
During the calibration of the system we were also able to validate our earlier assumptions about
approximating the system as linear. These results are shown in Figure 32 and Figure 33.
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7.2.
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Motor Cut-Out
The motor was programmed to cut out when it reached a speed of 30km/h. This was programmed
into our CycleAnalyst using a feature that would cut out the motor once 30km/h had been reached.
To prove that this requirement would be met before the bike was allowed to be ridden outdoors, an
indoor test was performed. The hand actuated throttle that came with our motor set up was used to
input the max signal (4V) to the controller, causing the motor to output as much power as it could.
The front wheel was lifted off of the ground to allow for the wheel to spin freely. The speed of the
wheel was monitored on the CycleAnalyst, as shown in Figure 34. The maximum overshoot that
was observed during this testing was at a value of 31.8 km/h, which would correspond to an over
shoot of 6%.
Figure 34- Motor cut-out testing
When the motor would receive its maximum signal it would quickly ramp up to 30 km/h then dip
slightly below 30 km/h then would again slightly eclipse 30km/h. This test proved that we were
limiting the speed of the bike.
7.3.
Motor Top Speed
The maximum speed that was required for the bicycle was 30km/h. During a flat ground test on
March 17th, testing performed to show that the bicycle could reach 30km/h on flat ground and that
the motor would at that point disengage. The maximum speed was reached easily with the
assistance of the electric motor at which point the electric motor cut out according to our speed
limiters control. This is in accordance with the Nova Scotia Motor Vehicle Act (“Bicycle,” Chapter
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293) which dictates that electric bicycles cannot be electrically assisted for speeds exceeding
30km/h.
7.4.
Range
The design requirements dictated that the bicycle must be capable of completing a 10km trip on a
single charge. The endurance test was intended to show that the electric bicycle was capable of
being able to complete a long bike ride on a single charge. We deemed 10 km to be a reasonable
commute for a rider in Halifax.
This test was performed to ensure that the batteries chosen could provide sufficient power over an
entire 10 km commute. In addition, to the test that would ensure that the battery life could hold up
over a 10 km commute, it was useful to validate that the torque and speed measurement devices
could withstand the test. This test would subject the components to extended durations of
continuous stress and vibration. Preliminary battery testing had been performed to ensure that the
batteries were correctly sized, and the results of this test showed that they worked exceptionally
well in our application as well. The test was a complete success with the measurement components
and their brackets both being able to withstand the long ride and not showing any signs of stress on
components. This was a very important achievement in this test, as the components had not been
subjected to an elongated ride prior to this.
This test was performed on March 30, 2011; the route that was selected is shown in Figure 35. The
route begins at Dalhousie University (Point “A” in the figure) starting on Barrington then continues
down Morris Street, South Park Street, Bell Road, and Quinpool Road before reaching the Armdale
Rotary (Point “B” in the figure). This route combines both busy streets and side streets and features
different portions that have quite a steep gradient. The steep gradient portions allowed for the
torque and speed measurement components to be tested while the rider was inputting a large
amount of torque. Parts of the route, namely Bell Road through to South Park Street have bike
lanes; however the rest of the route does not have bike lanes. This route was deemed to be a good
approximation of the difficulties of commuting in Halifax.
Table 4- Summary of values collected during endurance test
Initial Voltage (V)
Final Voltage (V)
Distance (km)
Time (mm:ss)
41.5
39.9
10.54
34:21
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Figure 35- Bike Route (Google Maps, 2011)
The entire trip was measured as being 10.54km long by the cycle analyst. The initial and final voltages of
the batteries prior to and after testing were 41.5 V and 39.9 V respectively. The voltages measured are
the open circuit voltage. Table 4 shows a tabulated summary of the results taken after the endurance
test was completed. When this is compared to the battery testing that was performed in the first term
we can state that we have used approximately 30% of our battery life. The battery testing is shown in
Appendix E.
7.5.
Regenerative Braking
The design requirements dictated that the bicycle must be capable of utilising regenerative braking.
This was utilized by the use of a lever which was connected to a switch that began regenerative
braking as soon as it was pulled. However, when the lever is pulled harder the mechanical brakes
engage. Over the range test of 10.54 km, we were able to sustain approximately 7% regeneration as
dictated by the Cycle Analyst. This would essentially mean an increase in available energy from the
battery pack of 7%.
7.6.
Weight
The design requirements dictated that the total mass of the bicycle could not exceed 35 kg and that
the weight of the components must not exceed the manufacturers specified weight limit. The
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bicycle and all of its components were weighed using the scale in the Civil Engineering building. The
total weight of the fully-assembled bicycle was 30 kg, well below the limit of 35 kg dictated in the
design requirements. This weight included the bicycle, all torque and speed measurement devices,
computer, National Instruments DAQ and all wiring. Kona does not specify weight limits on their
bicycles; however, the weight that is on the rear rack is 6.1 kg which is under the weight limit of
11.4 kg specified by the manufacturer.
7.7.
Hill Test
A qualitative test was performed to see the difference between a conventional bicycle and the
InfiniCycle electric assist bicycle in a hill situation. This test involved one rider on a normal bicycle,
and the other rider on the InfiniCycle. The InfiniCycle motor was first shut off and the two riders
rode up the same hill in the same gear, pedalling the same speed, and it was seen that both riders
had a hard time reaching the top of the hill and reached it at the same time. Subsequently, the
InfiniCycle motor was turned on and the riders repeated the same hill with the same pedalling
speed and in the same gear. The result was that the InfiniCycle was seen to be traversing the incline
with ease, whereas the conventional bicycle rider still had a hard time.
Table 5- Summary of the recorded times during the hill test
Donald (Normal Bicycle)
Dan (InfiniCycle)
No Motor (s)
8.76
9.02
Motor Engaged (s)
8.56
6.45
Table 5 shows that the rider of the InfiniCycle can travel up a steep hill at a much faster rate than a
rider on a conventional bicycle. During the original test, the InfiniCycle was slightly slower, which
can be attributed to its increased mass relative to that of a normal bicycle. However, in the second
test the InfiniCycle climbs up the hill at a much faster rate and the InfiniCycle’s rider (Dan) while
exerting much less effort than the normal bicycle’s rider (Donald).
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7.8.
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Summary
The testing was very successful. The tests that were performed showed that the bicycle was able to
meet all of the design requirements that had originally been set out. The bicycle’s measurement and
control system was adequately calibrated and could send a signal to the motor. The motor cut-out
test allowed for the bicycle to prove that it was able to meet the standards set in place by Nova
Scotia’s motor vehicle act. The bicycle also made the weight restriction with a weight of 30 kg,
which was far under the required 35 kg. We also performed an additional hill test t illustrate the
difference between the InfiniCycle and a normal bicycle. The testing results are summarized in
Table 6.
Table 6- Summary of testing
Test
Preliminary Motor Test
Motor Cut Out
Range Test
Regenerative Braking
Weight
Hill Test
Constraint
Calibration?
Measurements?
Motor Engaged?
Validate linearity assumptions?
Limit signal to 0-4 V
Motor Cut-Out?
Minimize overshoot?
10 km
Final Voltage > 32 V
Components safe?
Engage when lever pulled?
Regen %
< 35kg
Faster than normal bike?
Time difference
Dalhousie University- Dept. of Mechanical Engineering
Result
Yes
Yes
Yes
Yes
Yes
6%
10.54 km
39.9 V
Yes
Yes
7%
30 kg
Yes
2.57 s
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Future Recommendations
This is the first year in the development of the InfiniCycle, the concept of measuring the rider’s
input power is an interesting one allowing for many opportunities for different avenues of design.
For this reason, we have several recommendations for future developments on this project: (1)
Integration of a microprocessor onto the bicycle that can handle both digital and analog inputs, and
output an analog signal. Ultimately, this would eliminate the need for the rider to wear a backpack
containing the DAQ card and laptop. (2) Alterations to the location of the power measurement
system (potentiometer and encoder), so as to eliminate the need for a longer pedal bar and prevent
bumping. In addition, explore alternative measuring devices such as using an angular
potentiometer with a pivot point near the back axle of the bike, this would eliminate lateral stress
issues encountered using the linear potentiometer. (3) Signal filtering from the power
measurement system to smooth any torque spikes or “jerk” in the motor’s power output
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9.
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Infini-Cycle
Conclusion
The InfiniCycle performed exceptionally is all aspects sought after during the design process. We
were able to reach or exceed all of our design requirements as shown in Table 7. The bicycle
achieved and surpassed the 10 km minimum range by 5 km (15 km total) and was 5 kg below the
35 kg weight requirement, allowing riders to commute to school, work, or wherever they may
desire with ease and comfort. In addition, safety features built in such as the regenerative braking
lever kill switch, and maximum speed limit of 30 km/h were essential to provide the rider with the
utmost safety and security.
Table 7- Design Requirements vs. Actual Performance
Criteria
Requirement
Actual Performance
Requirement Met?
Top Speed
30 km/h
30 km/h
Yes
Range
10 km
15 km
Yes
Weight
35 kg
30 kg
Yes
Regenerative Braking
Yes
Yes
Yes
Charge with standard outlet
Yes
Yes
Yes
Innovation was prevalent in the power measurement system which proved to be a difficult design
task, but was successfully implemented through the hard work and design skill of the InfiniCycle
team under the strong guidance of their supervisor. Also, the ergonomically designed battery
mount allows the rider to easily insert and remove the batteries for charging/riding, while offering
a durable and reliable way to attach the batteries to the bicycle.
Finally, much was learned and improved by the team members during the design and construction
of the InfiniCycle, from teamwork, interpersonal skills, and perseverance, to electronic component
familiarity, fabrication/machining skills, and overall experience in the design process.
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10. References
1. About the Project: Innovative Transportation Solutions – Dalhousie Mechanical Engineering
Department (n.d.). Retrieved April 3, 2011, from
http://poisson.me.dal.ca/~dp_08_08/index.htm
2.
“Bicycle”, Chapter 293: Motor Vehicle Act of Nova Scotia (n.d.). Retrieved April 7, 2011, from
http://nslegislature.ca/legc/statutes/motorv.htm
3. Bosch, Robert. (2004). Bosch Automotive Handbook. (6th ed.). London, UK: Professional
Engineering Publications.
4. Cycle Analyst Information: ebikes.ca, online home of Grin Tech (n.d.). Retrieved April 3, 2011,
from: http://www.ebikes.ca/drainbrain.shtml
5. Hub Motor Simulator: ebikes.ca, online home of Grin Tech (n.d.). Retrieved April 3, 2011,
from http://www.ebikes.ca/simulator/
6. Load Cells: omega.ca® (n.d.). Retrieved April 3, 2011, from
http://www.omega.ca/shop/subsectionSC.asp?subsection=F03&book=Pressure
7. Yardworks 20 V (6 Ah) Lithium-Ion Battery: Canadian Tire (n.d.). Retrieved April 7, 2011,
from:
http://www.canadiantire.ca/AST/browse/2/OutdoorLiving/PowerEquipment/LeafBlower
VacAccessories/PRDOVR~0602181P/Yardworks%252B20V%252B%2525286Ah%25252
9%252BLithium-ion%252BBattery.jsp?locale=en
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Appendix A -
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Infini-Cycle
Technical Drawings
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Infini-Cycle
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Appendix B -
Component
Kona Bike
Motor/Controller
Batteries
Potentiometer
Bearings
Springs
Charger
Aluminum
Encoder
Terminal Block
Hardware
Quantity
1
1
2
1
2
2
1
1
1
2
3
Unit Price
$340.00
$496.00
$150.00
$313.00
$15.00
$20.00
$34.00
$74.00
$239.00
$2.50
$9.20
Total Cost
Dalhousie University- Dept. of Mechanical Engineering
Price
$340.00
$496.00
$300.00
$313.00
$30.00
$40.00
$34.00
$74.00
$239.00
$5.00
$27.60
$1,898.60
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Appendix C - Time Line
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Appendix D -
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Design Modeling Spreadsheets
Figure 36 - Model of the electrical systems of the bicycle
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Appendix E -
Infini-Cycle
Power and amp-hour curves of the battery
Power vs. Time (250W Test)
300.00
Power (W)
250.00
200.00
150.00
Power (W)
100.00
50.00
0.00
0
5
10
15
Time (min.)
20
25
Figure 37- Power vs. Time (250W Test)
Voltage, Current, and Ah vs Time (250W Test)
25.00
20.00
15.00
Current
10.00
Voltage
Ah
5.00
0.00
0
1
2
3
4
6
8 10 12 14 16 18 19 20 20 21
Time (min.)
Figure 38- Voltage, Current, and Ah vs. Time (250W Test)
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Power vs. Time (125W Test)
120.00
100.00
Power (W)
80.00
60.00
Power (W)
40.00
20.00
0.00
0
20
40
Time (min.)
60
80
Figure 39- Power vs. Time (125W Test)
Current, Voltage and Ah vs. Time (125W Test)
25.00
20.00
15.00
Ah
10.00
Current
Voltage
5.00
0.00
0
10
20
30
40
Time (min.)
50
60
70
Figure 40- Current, Voltage, and Ah vs. Time (125W Test)
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