post mortem v1 - ensc.sfu.cawhitmore/courses/ensc305/projects/2008/dpost.pdf · this post mortem...

December 16, 2008 Dr. Andrew Rawicz School of Engineering Science Simon Fraser University Burnaby, British Columbia V5A 1S6

Re: ENSC 440 Post Mortem: Cyclic Technologies Anti‐lock Braking System (ABS)

Dear Dr. Rawicz:

Attached with this letter is the Post Mortem for Cyclic Technologies ABS System. We have developed an ABS system for bicycles that would enable riders to maintain more control and stop faster during hard braking events. The ABS system will improve rider safety by enabling cyclists to maintain better control of their bicycles and avoid accidents.

This Post Mortem outlines the requirements and goals specified in the functional and design specification that the current state of our product has deviated from or not met. In addition, this document outlines the strategies for future development of our product. An outline of the experience gained in the process of development of the ABS is also provided here.

Cyclic Technologies consists of five dedicated, resourceful, and enthusiastic engineering students: Zack Blair, Amir Tavakoli, Rahm Lavon, Datis Danesh, and Milad Gougani. Our team brings together people with different skill sets and experience which will help Cyclic Technologies to achieve its goals.

Should you require additional information or would like to meet us in person, please feel free to contact us at cyclic‐[email protected].

Sincerely,

Cyclic Technologies

Enclosure: Post Mortem for Cyclic Technologies Anti‐lock Braking System

Submitted to: Dr. Andrew Rawicz – ENSC 440

Mike Sjoerdsma – ENSC 305

School of Engineering Science

Simon Fraser University

12/16/08

Post Mortem

Project team:

Milad Gougani

Rahm Lavon

Datis Danesh

Amir Tavakoli

Zack Blair

Contact person: Amir Tavakoli

cyclic‐[email protected]

Bicycle Anti‐lock Braking System

Bicycle ABS Post Mortem

Copyright ©2008, Cyclic Technologies ii

Table of Contents

Table of Contents .............................................................................................................................ii

List of Figures .................................................................................................................................. iii

Glossary ........................................................................................................................................... iii

1. Introduction ............................................................................................................................. 1

2. Current State of the System .................................................................................................... 1

2.1 Data Acquisition ............................................................................................................... 3 2.2 Brake Actuation ................................................................................................................ 3 2.3 UI ...................................................................................................................................... 3

3. Deviation of the System .......................................................................................................... 3

3.1 Overall System .................................................................................................................. 4 3.2 Sensor ............................................................................................................................... 4 3.3 ECU ................................................................................................................................... 4 3.4 HCU ................................................................................................................................... 5

4. Future Plan .............................................................................................................................. 5

4.1 Overall System .................................................................................................................. 5 4.2 Sensor ............................................................................................................................... 6 4.3 ECU ................................................................................................................................... 6 4.4 HCU ................................................................................................................................... 7

5. Budgetary and Time Constraints ............................................................................................. 7

5.1 Budget .............................................................................................................................. 7 5.2 Time .................................................................................................................................. 8

6. Inter‐Personal and Technical Experiences............................................................................. 10


Copyright ©2008, Cyclic Technologies iii

List of Figures

Figure 1: System overview ............................................................... Error! Bookmark not defined.

Figure 2: System Block Diagram ....................................................... Error! Bookmark not defined.

Glossary

ECU Electronic Control Unit

HCU Hydraulic Control Unit

NEMA National Electrical Manufacturers Association

FCC Federal Communications Commission

UI User interface

GPS Global Positioning System


Copyright ©2008, Cyclic Technologies 1

1. Introduction The Cyclic Technologies ABS system is a one‐of‐a‐kind electromechanical braking system used on bicycles, making them safer, reliable, and more practical than ever before. The system looks for acute deceleration during brake operation and regulates the force applied on brake caliper utilizing a 3 way valve and a pump to prevent the wheels from skidding. This operation prevents wheel lock‐up thereby minimizing the distance required to stop and enabling riders to maintain better control of their bicycles and avoid accidents.

During the last 14 weeks our team has faced numerous challenges in design and integration of our product. To a bitter end, we have learned that Hydraulic Systems are extremely hard to work with and smallest imperfection would lead to operational malfunctions. The biggest challenge Cyclic Technologies had faced in this process is the hydraulic fittings for the HCU and the power circuitry for high power inductive loads (the hydraulic valve and pump). These challenges have risen due to the fact that we are dealing with extremely high pressures at very low volumes.

2. Current State of the System Cyclic Technologies ABS system is composed of an Electronic Control Unit (ECU), two wheel speed sensors (one for each wheel), and a Hydraulic Control Unit (HCU) as shown in Figure 1.

In addition, Cyclic Technologies' system provides the user with the ability to easily customize the braking system’s performance using a menu‐driven user interface on an LCD display.



Figure 1 ABS Subsystems [1]

The ECU constantly collects data from rear speed sensors. When it senses that there is an acute differential deceleration (i.e. wheel lock), it will actuate the valve to reduce the pressure applied to the caliper. This effectively reduces braking force on the disk brake the wheel then turns faster. A fraction of a second later, the pressure is reapplied. The system is expected to continuously execute the process up to 10 times per second. The Cyclic Technologies’ ABS system can be modeled at high level as shown in Figure 2.

Figure 2 System Block Diagram

Our speed sensor is composed of a stationary handmade pickup coil attached to the bicycle frame, and 12 neodymium permanent magnets spaced evenly around the circumference of the



disk brake at 45 degree intervals. As the wheel turns, the magnets fly by the pickup coil, inducing a train of pulses in the pickup coil.

The ECU:

• Monitors bicycle speed and actuates the brakes to prevent the wheels from slipping for a prolonged period when braking

• Provides an interactive UI that displays bicycle speed and other information in real time

• Stores configuration data, even when power is removed

These tasks are done through the modules summarized below:

2.1 Data Acquisition Using a Schmidt trigger stage, the induced pulses from the speed sensor are converted into a digital signal that is appropriate for processing by the microcontroller.

2.2 Brake Actuation To drive both the valve and the pump, a power MOSFET is utilized to apply the 12 volts DC according to the control signal form the microcontroller. Due to the high capacitance at the input of the power MOSFET a driving circuit is used to couple the micro controller to the MOSFET. Furthermore, the valve and the pump are inductive loads so fly back diodes are utilized to mitigate the surges.

2.3 UI

The user interface includes a 20 x 2 Char (5 x 8 dots) LCD module. It displays bicycle speed, distance traveled, average speed, maximum speed.

2.4 HCU The Hydraulic Control Unit (HCU) contains a valve that disconnects the pressure feed to the calipers and a pump to release the existing pressure while forcing the oil back into the master cylinder. The hydraulic fittings of the HCU are a combination of thread fitting and pressure fitting. The pressure fitting are used for hydraulic line connection and the tread fitting are used for T‐connections and bras lines connecting the valve and the pump.

3. Deviation of the System Summary of the overall system deviation is listed below.



• Current system cannot be retrofitted

• System is not autonomous meaning that the battery is not charged on board

• The weight of the system is heavier than anticipated

• Pressure sensor to avoid a flip over was not implemented

We also planned to integrate both front and rear wheels in our ABS system. But due to lack of resources and time the system is only functional on the rear wheel.

The plan was to integrate both front and rear wheels in our ABS system. But due to lack of resources and time the system is only fictional on the rear wheel.

The Cyclic Technologies' ABS system was planned to be an autonomous and retrofit braking system.

3.1 Overall System

3.2 Sensor The wheel speed sensors were to double as induction generators, recharging the batteries inside the ECU which operates the system. Although, the current model produces up to 3 volts peak to peak, due to higher than expected power consumption of the system, it cannot provide the required power. It should be mentioned that this feature can be implemented by using more turns on the coil and a more efficient core material along with stronger magnets.

Furthermore the permanent magnets of the speed sensor were planned to be mounted on the disc brake to be coupled with the braking system. The existing model has the magnets glued to the rim of the wheel instead. This configuration is much easier to work with and provides a much higher voltage which was planned to be utilized as a battery recharger. The only drawback is that it cannot be considered as part of the bicycle braking system.

3.3 ECU

The ECU was originally intended to control both the front and rear braking systems. However, due to time constraints, we have focused only on the rear wheel. In reality, the rear wheel is the one that is by far more likely to lock up in a hard braking situation, because as one brakes, the weight of the bicycle shifts onto the front wheel.



Additionally, we had originally intended to base our ECU around the Atmel ATtiny2313 microcontroller, but we later chose a much more powerful microcontroller of the same family: the Atmel ATmega162.

Using the more powerful microcontroller, we were able to implement some features that we didn't originally plan to implement. For instance, using one of the microcontroller's built‐in pulse‐width modulation (PWM) generators, we were able to control the backlight intensity of the LCD programmatically, and have it configurable from within the UI. Configured values can be stored within its built‐in EEPROM memory so that they are retained, even if the battery is removed.

The Cyclic Technologies original plan was to have one integrated valve and pump driver utilizing a dedicated signal for each of the loads. However the original driver chip stopped working during our testing stage. Therefore, the team came up with an alternative design to control the pump. The current system uses one control signal from the microchip. This signal is fed the original driver chip and actuates the valve. The same signal is delayed through a 555 timer to drives the pump.

3.4 HCU The power consumption of the HCU is much higher than expected due to the use of an industrial valve and a pump that uses a 12 V dc motor. Since we have high pressures throughout the system the use of a high voltage valve and pump was unavoidable.

Cyclic Technologies' mechanical team was able to build a low voltage, high pressure valve. Super glue was used inside the unit; hydraulic fluid melted the glue and destroyed the valve. Due to time constraint the team was not able to prepare a new unit. Having this experience though, the engineering team is confident that they can utilize a light, high pressure, and low voltage valve in the prototype ABS system.

4. Future Plan

4.1 Overall System

The milestone for Cyclic Technologies' system is to have a light weight, autonomous, and intelligent anti‐lock braking system. In that front, some plausible improvements of system modules are summarized below.



4.2 Sensor

• Double as induction generator this can be done by having more turns of wire on the coil and using a more efficient core material along with stronger permanent magnets.

• Portable the whole unit can be designed and coupled as part of the disc brake to be retrofitted on traditional hydraulic brakes. This way, the sensor is also shielded making it more reliable and robust.

• High resolution higher resolution can be achieved by having more magnets placed next to each. Although there is a physical constraint on how close the magnets can be placed.

4.3 ECU

• Lower Power Consumption The single largest source of power consumption for the ECU is the LCD display's backlight. One easy way to reduce power consumption would be to purchase a different LCD display that is clearly visible without a backlight during the daytime. A light‐dependent resistor (LDR) could be incorporated into the casing of the ECU to periodically measure the ambient light and turn on the LCD backlight only when necessary (e.g. at night).

• More Features Although we initially planned to use an Atmel ATtiny2313 microcontroller at the heart of our ECU, we later found this device's memory specifications (primarily its limit of 2 kiB of program memory) to be insufficient. Thus, we upgraded our microcontroller to the much larger ATmega162 ‐ a 40‐pin device with 16 kiB of program memory. With this much more capable microcontroller, we have ample room for future software and hardware enhancements. Additionally, a real‐time clock could be incorporated easily using the ATmega162's I2C communication peripheral to communicate with a small real time clock chip (e.g. the DS1307). This would enable us to record trip durations and other information for the bicyclist to review. By including information about trip time, it would then be trivial to calculate statistics like average speed and maximum speed, also, making our ECU competitive with bike computers currently on the market, like the Sigma BC 400



(http://www.sigmasport.de/us/service_center/produkt_support/bikecomputer/fragen/?jahrgang=1&produkt=41&gruppe=1&sprache=2&typ=bikecomputer).

• PC Interface Open‐source implementations of the USB protocol exist for the ATmega162, including the popular “AVR USB” library available at “http://www.obdev.at/products/avrusb/”. If we were to incorporate this into our ECU, and provided a USB port, we could allow users to download trip statistic information from the ECU to their PC's for review. This is already done by some bike computers currently on the market. Additionally, a USB interface coupled with some additional circuitry and software to run on the PC would enable users to update the firmware on their ECU's. This might be hard for users that wish to write their own firmware, or for distributing bug fixes after a device has been put into use.

4.4 HCU

• Light Weight The hydraulic unit can be made much lighter by using a smaller valve. Cyclic Technologies mechanical team has already started this process and it is in the early stages of making a light, high pressure valve.

• Reduced power consumption Power consumption of the unit can be reduced by using a more efficient pump. It should be noted that there is a limit on power consumption, since the system is dealing with high pressures at very low volumes.

• Portable The HCU can be coupled with the caliper unit of the traditional hydraulic brakes making them easier to be retrofitted.

5. Budgetary and Time Constraints

5.1 Budget

Table 1below lists and compares the initial tentative prices with the actual costs of our proof of concept prototype. The items listed in red are not used in our final product as they do not meet our needs. However, the items displayed in blue color were required by our final design and we had to purchase them even though they were not considered in our initial budget planning.



Table 1Estimate v.s. Actual cost

Required Items Estimated Price Actual Price Notes

Enclosure $5.00 $7.34Circuit Board $2.00 $5.00Microcontroller $5.00 $11.00Crystal $1.00 ‐ Not used LCD Display $15.00 $25.00LCD Enclosure $5.00 ‐ Not used Resistors, Caps, etc $1.00 $68.46Tactile Switches $3.00 $3.00Power switch $1.50 ‐ Not used Speed Sensor / Generator $60.00 ‐ Not used Solenoid / Actuator $40.00 ‐ Not used Rechargable batteries $20.00 $12.50Battery holder $1.00 ‐ Not used Misc Items $15.00 $86.54Hydraulic Brake ‐ $229.20Pump ‐ $236.70Valve ‐ $80.71Mechanical Parts ‐ $52.99Magnets ‐ $30.73Bleed Kit $100.00

Total $174.50 $949.17

As it is clear Table 1, in the planning stage we had a different concept design based on our knowledge of the project at the time. Later we realized that a single solenoid is not able to handle 400 psi pressure due to the hydraulic system on the brakes. To provide pressure for the handle bar we had to use a pump to push out the oil from the brake caliper to the master cylinder so the rider will be able to apply brakes on the lever and will prevent the lever to bottom out. We also had to use a valve to disconnect the flow of oil from the master cylinder to the brake calipers, so we are able to disengage the brake in the event of wheel lock up. In our estimated budget we have not included the price of the bicycle as it is not part of our finished product; however, we had to purchase the hydraulic brake system to integrate with our system. The hydraulic brake system alone has attributed 50% of our total expenditure and this cost could have been extremely higher, hadn't we purchase and assemble the unit separately. The other cost saving effort in our project was in the process of speed sensing through utilizing magnets and coil as opposed to purchasing a speed sensor with twice the cost.

5.2 Time The table below compares the Gantt chart of our expected and actual time lines.



Table 2 Gantt chart comparison of expected (blue) VS. actual time lines (green)

As it is clear from the graph we have spent twice the time we had anticipated for the research and it is due to the fact that we had miscalculated the amount of pressure and force required in our system in the planning stage. The extension in the research phase of our development has propagated through the other phases and has pushed back the demo time in our project from December 10th to December 16th. We also had to adjust our Design Specification document to account for the new features and designs integrated into our project and as the result our Design Specification document has been delayed for three days.

In the assembly of the modules phase of our project we had to wait to receive two of our primitive components, namely pump and valve to start putting together all the modules. This has contributed significantly to our deviation from schedule and delayed our Assembly, integration and testing phases; however, we have managed to keep the duration of all the phases the same as the original plan.



6. InterPersonal and Technical Experiences Zachary Blair I worked primarily on the ECU, writing software for the microcontroller and designing some of the circuits surrounding it.

Some of the good choices made when developing the ECU were:

• Choosing microcontroller that had a free, high‐quality C compiler available for it

• Leveraging previously tested open‐source libraries like the AVR Libc library.

• Managing our source code using CVS (Concurrent Versioning System)

• Collaborating on design and documenting our design using a Wiki

Some of the poor choices made when developing the ECU were:

• Initially choosing a microcontroller with too little program memory

• Not adequately researching some aspects of the microcontroller (like interrupt handling and PWM) before trying to use them.

• Not using in‐circuit programming instead of a separate device programmer.

Datis Danesh

Working on this project was an amazing experience! First and foremost, it was very interesting idea to integrate an ABS system onto bicycles with four other students to simulate a start‐up company, and to design and implement a piece of the technology from scratch. The scope and magnitude of this project is definitely not like anything done previously in other courses. This project was also a challenge since most of us had little or no exposure to the mechanic details of the project. However, we overcome this challenge by dedicating our time and more than half of the project timeline to R & D. At the end we deviated a bit from the time line and had to rush to finish some of the minor phases of the project but overall we are all proud of our achievement.

In this project I learned from basic soldering techniques to setting up a motor deriver circuit and pre planning to setup breadboard circuitry onto the vector board. I also realized that taking care of and tracking down the financial spending of a team is a brainstorming task!



Amir Tavakoli

My contribution to Cyclic Technologies has span across all disciplines as the quality control engineer of the company. I collaborated with Rahm Lavon on developing the HCU and helped Milad Gougani and Datis Danesh developing the control and power circuitry.

This project was my first exposure to Hydraulic systems. Through this project I have learned that the Hydraulic Systems are extremely power full and have many advantages camper to mechanical systems; however, they are extremely hard to implement especially at high pressures.

Electrical components easily get defected. One working on a R&D project should take this factor into count and be prepared. When sourcing and ordering components always give the possibility that components can arrive defected or you may break them during the integration and testing stage, always order spares. I also learned that one can learn much more though mistake of building a circuit board that trying to design the circuit on paper.

Overall, my experience with Cyclic Technologies team has been grant. I am extremely pleased with all the group members and everyone has contributed equally. I look forward to work with my team members in the future and commercialize this product.

Rahm Lavon

This project was originally inspired by an understanding of automotive dynamics, coupled with a can‐do attitude. Injuries which both my friend and I suffered while losing control of a bicycle made me take up a passion with this project. Our team was incredibly motivated, and we worked diligently to complete each section of the system we built.

At first my main focus was the Hydraulic Control Unit. My years of mechanics experience and knowledge of systems design helped me design, construct, and then reconstruct a system, out of parts that were initially not intended for the application we required. I successfully rebuilt a high‐precision instrument valve to handle the extreme pressures, and unforgiving environmental stresses it would face, while exceeding our power and spatial requirements. I then had to build a manifold that would interface our parts to the brake lines of the bicycle, and the high‐compression gear pump. Hydraulic leakages were a very troublesome hurdle we had to overcome, as we began to integrate these discrete components. I learned many important lessons from this part of the project, including the importance of engineering safety into life‐critical components, making the system fail‐safe.



Debugging the electronics and firmware components of the system took place as a last push to the demonstration deadline. We had to be quick to debug circuitry that didn’t seem to work for no apparent reason. I got a real feel for how hands‐on practical knowledge helps to get the job done faster and better than a by‐the‐book analysis of the circuit’s operation. I can’t emphasize enough how important the need is for our lab experience. The knowledge we gained by working on this project, as a whole, is priceless.

Milad Gougani

Through undertaking the ABS system project, I had the opportunity of working with a group of credible and responsible students in school. Throughout the project I used years of theoretical knowledge and course work and realized how rewarding it can all be. ENSC 440 is what you could say SFU’s Engineering program is all about!

Electronics:

Being involved in the design and development of the HCU driver circuitry, I became more familiar with power MOSFETS, Schottky diodes, Opto‐couplers, and 555 timer ICs‐just to name a few. Although I manage to destroy a few components, gaining hands on experience enabled me to have a better understand of operations and limitations of electronic components.

My involvement in the design of the A/D module of the speed sensor helped me understand various Analog to Digital signal conversion schematics and operations. Finally, having sourced some of the ICs for this application helped me realize the endless options in the market for specific applications.

Mechanical:

I was also involved in the ABS system’s mechanical design which was a good opportunity for me to learn about operation of hydraulic systems, valves and pumps. I was responsible for sourcing both the valve and pump used in the HCU. Since the ABS system was designed to be used on road bicycles, the main challenge in this case was to hunt down the smallest and lightest valve and pump that could stand pressures of up to 1000 psi.

Social Experience:



Being involved in an R&D project of this magnitude, it is critical to learn how to be patient with one another as you try to understand and complement each other’s ideas. Listening skills are vital.

It is important not to take any criticism personally, and not to give any personal criticism unless it is really affecting the project.

Having weekly group meetings, team members had an opportunity to communicate on project progress and eventually work together and easily integrate the final project. Last but not least, you cannot have a successful project without support and trust of group members.

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