UBC Undergraduate Research

Front-wheel friction drive electric bicycle motor Chen, Oliver; Ghoussoub, Mireille; Zhou, Cherry Apr 3, 2013

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata


52966-Chen_O_et_al_ENPH_459_2013.pdf [ 1.2MB ]
JSON: 52966-1.0074490.json
JSON-LD: 52966-1.0074490-ld.json
RDF/XML (Pretty): 52966-1.0074490-rdf.xml
RDF/JSON: 52966-1.0074490-rdf.json
Turtle: 52966-1.0074490-turtle.txt
N-Triples: 52966-1.0074490-rdf-ntriples.txt
Original Record: 52966-1.0074490-source.json
Full Text

Full Text

FRONT-WHEEL FRICTION DRIVE ELECTRIC BICYCLE MOTOR     Oliver Chen Mireille Ghoussoub Cherry Zhou       Project Sponsor: Dr. Andrej Kotlicki       Project 1316 Engineering Physics 459 Engineering Physics Project Laboratory The University of British Columbia April 3rd 2013 Executive Summary   Many cyclists are seeking easy solutions to bring electric power to their bikes. Having an electric motor that can be switched on to get a boost going uphill, to go faster, or to simply take a break from pedaling can be very useful. With these motivations, we sought to develop a front-wheel friction-drive motor system that could be easily mounted and removed from any adult-sized road bike. The objective was to develop an easily mountable solution containing the motor, controller, battery pack, and throttle that could be installed within minutes.   Friction-drive motors are a cheaper, lighter alternative to the more common hub motors that must be permanently attached to the wheel of the bike.  Indeed, the motor mechanism component of our design weighs 1.45 kg, and the total weight of our design does not exceed 3 kg (depending on the size of battery pack used). The design of our solution was based on goal of keeping the installation as simple as possible, whilst ensuring that the mechanism could tolerate the strong rotational forces introduced by the motor. Our solution mounts at the handlebars by means of two snap-on clamps, as well as at the fender holes, located at the hub of the front wheel of the bicycle. The design can be adjusted at two locations: by changing the angle between a horizontal and a vertical cantilever, as well as by changing the height of the supporting rods. The motor is attached to a pivot point, such that is has sufficient room to engage and disengage with the front tire. Blocker pieces are located strategically to ensure that the motor does not swing too far back and get stuck in the wheel.   The mechanical aspect of our solution has proven to be successful. We were able to mount the mechanism to five different bicycles, all of which varied greatly in handlebar shape and tire size. In all these cases, our solution was easily installed in under two minutes.    Installing a user-friendly throttle proved to be very challenging. The most successful attempt entailed running the controller by means of a purchased servo tester circuit; however, our throttle setup was not functioning in time for us to do test ride our solution. We therefore cannot present meaningful results as the electrical efficiency of our system.   We recommend three important actions to be taken to ensure that our solution be safe and fully-functional. First, all electrical parts should be protected in a water-proofed enclosure. Secondly, a push button throttle should be installed along with the servo tester circuit. Finally, we recommend that an emergency brake be installed to ensure the safety of the user in the case where the throttle or controller fails.  TABLE OF CONTENTS ABSTRACT?????????????..???????????????..?ii LIST OF FIGURES?????????????????.????????...?iv LIST OF TABLES????????????????????????..??.....v 1.0 INTRODUCTION?????????????????????????...7  1.1Background??????????????????????????.7  1.2 Objectives??????????????????????????..7  1.3Scope and Limitations?????????????????????.....7  1.4Organiztion??????????????????????????.7 2.0 DISCUSSION??????????????????????????.?..8  2.1 Theory????????????????????................................8  2.2 Methods and Testing Protocol??????????????????....9  2.3 Mechanical and Electrical Components??????????????..14  2.4 Results???????????????????????????..16  2.5 Discussion of Results?????????????????????...17 3.0 CONCLUSION???????????????????????????18 4.0 PROJECT DELIVERABLES?????????????????????..18  4.1List of Deliverables??????????????????????...18  4.2 Financial Summary??????????????????????..18  4.3 Ongoing Commitments by team members?????????????..19 5.0 RECOMMENDATIONS???????????????????????.20 6.0 APPENDICES???????????????????????????.21 Appendix A. SolidWorks Drawing of Key Components????????????...21 Appendix B. Electronics Schematics????????????????????.25 Appendix C. Cost of Materials of the Project???????.?????????...27 7.0 REFERENCES?????????????????????????.......28  LIST OF FIGURES  Figure1. Friction-drive Mechanism Figure2. Handlebar Clamp Figure3. Supporting Rod Figure4. Joint between Horizontal and Vertical Cantilever  Figure5. Slots on the Tip of the Supporting Rod Figure6. Motor Blocks Figure7. Servo Tester Device Figure8. 3D Printed Throttle Attached to Pot Figure9. Hall Sensor Throttle Figure10. Jump Cable Circuit Figure11. Examples of Successful Mounting Cases Figure12. All-in-one Units in A Bike with Fender Figure13. Weight Comparison between Hub Motor and Our Design Figure14. Whole Set of All-in-one Units Figure15. Solidworks Design of Fully Assembly Figure16. Solidworks Design of Clamp Figure17. Solidworks Design of Motor Attachment Figure18. Solidworks Design of Vertical Cantilever Figure19. Solidworks Design of Horizontal Cantilever Figure20. Solidworks Design of Blocker Hole Zoom In Figure21. Solidworks Design of Supporting Leg Figure22. Solidworks Design of Fender Hole Attachment Figure23. 555 Timer Figure24. Electrical Schematic     LIST OF TABLES  Table1. Financial Summary Table2. Cost of All-in-one Units Table3. Industry-standard Benchmarks 1.0 INTRODUCTION  1.1 Background  As demonstrated by their popularity, bicycles are one of the most practical, cheap, and sustainable transportation solutions around the world. However, the physical exertion required to travel uphill or to go faster poses a disadvantage to many riders. Keeping in the spirit of sustainability, we built an electric friction-drive motor that can easily attach to the front wheel of a typical touring bike. The system allows the rider to engage the motor when they wish to go faster, or take a break from pedaling. The reasons for opting to build a friction-drive motor, instead of a hub motor, lie in their easier installation, lower costs, and higher power to weight efficiency. While there currently exists solutions on the market, most come in the form of incomplete kits, and it falls to the user to customize the system to their bike. Our design offers an all-inclusive package that can easily attach to any touring-style bike. The purpose of this report is to communicate the results of our friction-drive motor design, as well as to provide recommendations for future improvement of the solution.  1.2 Objectives  Our aim is to build a removable, all-in-one unit, including battery pack, motor, controller, and throttle, which may easily attach and adjust to the front wheel of any touring-style bike. Specifically, the motor and battery should run for at least 40 minutes, with the bike moving at an average of 15 km/h. We are not developing a very powerful electric bike motor, but rather one that may be easily transferred between different bicycles.   1.3 Scope and Limitations  This report primarily addresses the mechanical aspect of our solution. It will present all features of our mechanical design, the reasons behind our choices, and our design's ability to mount to different bikes. It does not include information on the riding experience or on power considerations, as we were unable to obtain sufficient test riding data. These serious limitations are due to last-minute failures to produce a correct throttle signal to run the motor, and they will be further addressed in the discussion section of this report.  1.4 Organization  Our recommendation report is comprised of four main sections: Discussion, Conclusions, Project Deliverables, and Recommendations. The Discussion section covers the physical theory behind our mechanism, the methods undertaken to construct an easily-mountable device, the attempts to develop a user-friendly throttle, and the results of our solution.    2.0 DISCUSSION 2.1 Theory  Theory behind the friction-drive mechanism In a friction-drive setup, the spinning motor comes into contact with the tire, and causes it to spin. The motor is attached to the bike such that it can pivot under the impact of its own angular momentum, thus engaging with the bike wheel. Once it is in contact with the bike wheel, the high coefficient of friction between the two surfaces prevents it from disengaging. In order to achieve maximum power transfer from the motor to the wheel, the motor must engage just enough with the tire to prevent it from slipping without deforming the tire.  Figure1. Friction-drive Mechanism  2.2 Methods and Testing Protocol  Methods of constructing an easily-mountable device  In order to make solution that could be adjusted to fit different bicycles, we considered all possible locations to which the motor could be mounted. These options included the handlebars, the head tube, the hub, and the front-wheel forks. Our selection was based on which locations would best support the forces introduced by the motor mechanism, whilst minimizing the number of places where the user must attach the device. Based from Tao Wang's 479 project recommendation report, we chose not to use the fork blade curvatures to mount the motor, as they proved to weaken under the force of the motor. We selected instead to mount the mechanism at the handlebars and the hub of the front wheel, and this proved to be successful.  Mount Testing Protocol To test the quality of our solution, we attempted to mount the mechanism to different bicycles at the UBC Bike Kitchen. These attempts allowed us to identify the weaknesses in our design, and it took several reiterations of certain parts before our current solution was achieved. To ensure that the testing provides meaningful insight, we purposely tested on bikes of varying handlebar width and shape, and of different tire size.  2.3 Mechanical and Electrical Components ? Handlebar mounts  The mechanism attaches at the handlebars by two polyethylene clamps. The pieces were waterjet-cut, and are flexible enough to accommodate handlebars of 2 to 3 cm in diameter. A bolt screws through each clamp to ensure rigidity. The clamps snap onto the handlebars from the under, rather than over (see Figure 2), and this setup avoids interference from gear cables, which often lie directly in front of the handlebars.   Figure2. Handlebar Clamp  ? Hub mounts  It quickly became apparent that the mounting at the handlebars alone could not withstand the rotational forces of the motor mechanism, and therefore made it necessary to include an attachment at the hub of the front wheel. We initially designed two rods that mounted to the hub; however, the difference between quick release and nut-type wheels made it difficult to find a solution that would fit all. From surveying the bikes available at the UBC Bike Kitchen, we found that roughly 50% of the bikes were of the quick-release-type, and 50% of the nut-type. Fortunately, during the survey we observed over 90% of the bikes have fender holes at the end of fork. Thus we decided to choose fender holes as the supporting point of the hub mount  ? Fender Hole mounts  As fender holes are designed to attach fender to the bikes, they have standard size of diameter, which fit to either M5 or M6 metric bolts. Using this advantage, we design our supporting rod as shown below: two holes are used to connect to the fork, and the rest for the fender if needed.  Figure3. Supporting Rod  ? Adjustable designs   There are several designs in the mechanism to fit different bikes; they together ensure a rigid mount and perfect distance between motor and the tire.  ? Joint between horizontal and vertical cantilever  The joint has one pivot point and a circular slot so that the angle between two pieces can be adjusted continuously from 0? to 90?.    Figure4. Joint between Horizontal and Vertical Cantilever  ? Slots on the tip of the supporting rod  These slots provide multiple level of height the motor can be mounted so that the motor is close enough to engage when running but not too close that it hits the tire when not running. The distance between the top slot and the bottom slot is 9 cm.  Figure5. Slots on the Tip of the Supporting Rod  ? Motor blockers  Motor blockers are used to block the motor from over engaging, in which case the motor get stuck with the tire. Multiple holes were included should the user wish to relocate the blockers fit the specific blocking angle required for their bike.   Figure6. Motor Blocks  ? Throttle  The controller can run from a purchased servo tester circuit (see Figure 7). The device can operate in three modes, one of which allows the user to manually turn a potentiometer-knob to change the signal's duty cycle, and thus control the speed of the motor.   Figure7: Servo Tester Device ? Attempt 1: 3D Printed Thumb Throttle  Although the knob allows for smooth control of the motor speed, it is awkward to use whilst cycling. For this reason, we designed and 3D-printed a thumb throttle that mounts to the potentiometer knob (see Figure 8).   Figure8. 3D Printed Throttle Attached to Potentiometer knob  ? Attempt 2: Hall Sensor Throttle  Still, we were not satisfied with this solution as we were unable to implement a spring that would make the throttle bounce back once the user ceases to press. The reliability and robustness of the throttle is critical to the safety of the user, and we therefore decided to use a purchased thumb throttle (see Figure 9). This throttle was actually a hall sensor throttle, which produces a signal varying linearly from 0 to 5 V with the angle of rotation. We then tried to control the output of the servo tester circuit by attaching the hall sensor throttle to its input. Following the advice of hobbyists online, we removed the potentiometer and jumped a cable on the servo tester circuit; however, this failed to control the duty cycle of the signal.   Figure9. Hall Sensor Throttle  Figure10. 555 Timer Circuit  ? Attempt 3: On/Off Switch  We tried to implement a simple On/Off switch button onto the servo tester circuit. However, the changes we made to the circuit in our previous attempt seemed to have caused some damage, and output signal gave too small a duty cycle to have the motor speed be high enough to engage with the wheel.  ? Attempt 4: 555 Timer Circuit  In another attempt, we built a circuit to generate a square wave pulse that we could control by an on/off switch. The circuit uses a 555 Timer, and the duty cycle and frequency of the square wave output can be determined by the choice of resistor and capacitor values. Since this circuit can only produce square waves of duty cycles from 50% to 99%, we added an inverter to the output to obtain our desired duty cycle of 12%. The circuit generated the correct output signal when powered from a voltage supply. Previously, the servo tester circuit was powered by 5 V from the controller; however, we were unable to power our 555 Timer circuit this way. 2.4 Results Results of Test Mounting  The motor unit can be successfully mounted to different bikes with different kinds of handlebar designs. Three adjustable designs are discussed above to ensure the flexibility of the mounting.      Figure11. Examples of successful mounting cases   We even managed to mount our all-in-one units to a bike with a fender as shown in Figure 12.   Figure12. The unit attached to a bike with a front-wheel fender   In testing our solution, we measured the time taken to mount the motor unit to each bicycle. In every case, the time was under 2 minutes. An Allan key is the only tool required by the user to mount the mechanism.  The weight of our friction drive motor unit is 1.45 kg (not including controller, battery, and throttle), which is significantly lighter than a typical hub motor (see Figure 13).    Figure13. Weight Comparison between Hub Motor (5.32 kg) and Our Design (1.45 kg)   2.5 Discussion of results   In mount testing on a total of 7 bikes, 5 of them work perfectly, 1 of them could work after lowering down the handlebar, and the other one would not work due to fender hole is located on only one side of the fork. More testing can be performed to find other limitation and constraints of our design.   Speed testing has not been performed yet due to the problems we encounter with the electrical design. Test rides would be performed after electrical design is fixed.   Figure14. Motor unit  3.0 CONCLUSION  Based on the results, our solution has succeeded in being easily adjusted to fit a variety of road bikes. Its ability to fit onto a variety of handlebar shapes and sizes, and to accommodate different types of fender holes, indicates that it is a practical solution for people seeking a non-permanent electrically-powered motor solution for their bicycle. The two cases in which the unit failed to fit to the bike are exceptions that do not undermine the success of our solution. In the instance where the bike offered only one fender hole was considered to be rare by bike mechanics at the UBC bike kitchen. In the case where the distance from the handlebars to the front-wheel tire was too long, the handlebar stem was adjustable and could have been lowered to accommodate the motor mechanism.   Given the circumstances of our throttle circuit, we were unable to perform test rides, and therefore cannot provide information as to the electrical efficiency of our solution. This task will remain an ongoing commitment of all our team members.   4.0 PROJECT DELIVERABLES  4.1 List of Deliverables  The primary deliverable is the motor mechanism, comprising of the motor unit, and the supporting rods, and a controller and servo tester are provided for speed control.  4.1.1 Motor Unit The motor unit is comprised of the cantilever mechanism, as well as the two supporting rods. As mentioned previously, the unit will attach at the handlebars by means of clamps. The unit has the ability to adjust to various heights along the mount in order to achieve the optimal location for any bike. The batteries, controller, and cables are velcroed compactly to the unit.  4.1.2 Throttle A servo tester device serves as the throttle and should be attached to the handlebar mount where user can easily reach. Our current solution does not include a fully-functional throttle; however, our team is committed to ensuring that this deliverable will be ready by April 19th.    4.2 Financial Summary  # Description Quantity Cost Purchased By: Funded By: 1 Brushless DC Motor 1 $75.77 Bernhard Project Lab 2 Programming Box 1 $9.91 Bernhard Project Lab 3 Controller  1 $73.58 Bernhard Project Lab 4 Battery 1 $45.00 Bernhard Project Lab  5 Hall Sensor Throttle  1 $15.00 Bernhard Project Lab  6 Servo Tester Device 1 $4.15 Bernhard Project Lab 7 Water jet cut pieces  10 $20.00 Bernhard Project Lab  Total Cost  $243.41   Table1. Final Summary  4.3 Ongoing commitments by team members   Our team remains committed to ensuring that our bike motor is fully functional, and wish to include a working throttle as part of our final design. Our target date for this goal is, and we will turn in all our project deliverables to our sponsor, Andrzej Kotlicki, by Friday, April 19th.    5.0 RECOMMENDATIONS  Despite the success of our solutions' ability to mount to different bikes, it still lacks some important features that prevent it from being fully functional. The following is a list of recommended actions that should ensure that our final deliverables meet the original project objectives:  1. Waterproofing  We recommend that the controller and battery sit in a water-proof enclosure, underneath the metal frame.  2. Throttle Installation  Given that the only success in running the motor came from using the servo tester circuit, we recommend using this, along with a an ON/OFF push button. The servo tester circuit should operate in manual mode, with the potentiometer knob set to a position that ensures a duty cycle of at least 12%, to  ensure that the motor speed is high enough to engage with the tire. The COM port of the push button should connect to the input of the servo tester. The NC port should connect to the controllers ground signal, and the NO port to the controller's 5V signal. This setup should allow the user to activate the motor by pushing the putton, and deactivates it when the button is released. The user still has the option of adjusting the motor speed by changing the potentiometer knob on the servo tester circuit, as one speed may not be optimal for all bikes.  3. Emergency Brake  To ensure the safety of the solution, an emergency brake should be installed in case the throttle or the controller fails. The brake should therefore break the circuit between the battery and the controller, and the brake throttle should be mounted at an easily-reachable location.  4. Bicycle Basket  While our final recommendation is more a matter of personal preference, we would like to recommend that a basket be fit around our current mechanism. Aside from improving our design aesthetically, a basket would provide space to the controller and battery.   As mentioned earlier, our team members are commitment to the ongoing improvement of our solution, and we hope to have carried out the recommendations (notably 1 and 2) by the time the project deliverables are handed to our project sponsor.    Appendix A SolidWorks Drawing of Key Components   Figure15. Full motor mechanism assembly   Figure16. Handlebar clamp    Figure17. Motor attachment piece  Figure18. Vertical Cantilever    Figure19. Horizontal Cantilever  Figure20. Blocker Hole Zoom In     Figure21. Supporting Rod     Figure22. Fender Hole Attachment Appendix B Electronics Schematics   Figure23. 555 Timer Circuit  The frequency and the duty cycle can be adjusted by selecting appropriate resistor and capacitor values for R1, R2, and C1.  THigh  Time for which the signal is high, s TLow Time for which the signal is low, s F Frequency, Hz  THigh = 0.693*(R1+R2)*C TLow = 0.693*R2*C F = 1.44/[(R1+R2)*C]  At its maximum duty cycle, the PWM signal generated from the servo tester circuit has THigh = 2.10 ms, TLow = 14.3 ms, and F = 61.5 Hz. For the purpose of calculating R1 and R2, we assign the value of THigh to  TLow and vice versa, since the output of the 555 timer is then inverted. Resulting component values:  C = 47 ?F R1 = 360 ? R2 = 62 ?    Figure24. Electrical Schematic   Appendix C Cost of Materials for the Project  Removable all-in-one Units of Friction Drive Electric Bike Motor Material  Price  Weight/time  Cost  Aluminum  $8-10 /lb 174 g $3.84 Polyethylene $3-9 /kg 45g $0.45 Water-jet  $1/min  5min $5 Friction Motor  SK3-6374-149KV $75.77 N/A $75.77 Controller $73.58 N/A $73.58 Battery $35 N/A $35 Other Cost $20 N/A $20 TOTAL COST $213.67  Table2. Cost of All-in-one Units  The information of the Industry- Standard Benchmarks as shown in following table   Table3.  Industry-standard Benchmarks  REFERENCE Analytic Cycling (2012). Forces on Rider. Retrieved December 10, 2013. From  http://www.analyticcycling.com/ForcesPower_Page.html  Bicycle Design (2013) Retrieved January 10, 2013. From  http://bicycledesign.net/wp-content/uploads/2012/09/Footloose-assembly-pair-49 8x343.jpg  BikeFanatic (2010). Eboost-kepler friction drive Review and Testing.   Retrieved March 20, 2013. From    http://endless-sphere.com/forums/viewtopic.php?f=4&t=22026  Commuter Booster (2013) Retrieved January 9, 2013. From  https://sites.google.com/site/commuterbooster/photo-album  Eboost Power Assist (2013) Retrieved February 15, 2013. From  http://www.eboo.st/index.php?main_page=product_info&cPath=9&products_id1 &zenid=hv5n2hrgclcklqji52ejmlud91  MIT (2012) The Copenhagen Wheel. Retrieved September 29, 2012. From   http://senseable.mit.edu/copenhagenwheel/gallery.html  MIT (2013). Understanding D.C. Motor Characteristic. Retrieved November 19,  2013.  From http://lancet.mit.edu/motors/motors3.html  Rainer Pivit (2/1990). Drag Forces in Formulas. Pp.44-46. Retrieved November 18,  2013. From http://sheldonbrown.com/rinard/aero/formulas.htm  


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items