Electric Bicycle Assisted Power



11/29/17righttopFall 2017 40000100000Fall 2017 left250002514600Electric Bicycle Assisted Power900007300Electric Bicycle Assisted Power45148505956935Thomas BallingerJeremy PassaroEvan VasalechSamuel CampoAdvisor: Dr. Rana MitraInstructor: Dr. Cris Koutsougeras00Thomas BallingerJeremy PassaroEvan VasalechSamuel CampoAdvisor: Dr. Rana MitraInstructor: Dr. Cris Koutsougeras-1047756385560ET 493Senior Design I0ET 493Senior Design Iright318135000AbstractAt the beginning of this semester we were tasked with creating a low cost, low profile, assistive power supply that is compatible to almost every bicycle in use. To create such a system, we had to first determine the forces acting on a bike and the force required to overcome any resistive forces. We also had to choose between a gasoline and electric motor. In addition to this, we had to investigate mechanical/electrical controls to safely operate our system. Most importantly, we also had to choose where and how to mount the system to the bike securely.OverviewOur group was tasked with designing a low cost, low profile, adaptable bicycle power aid. This semester we have had many problems as well as many solutions to meet them. After conducting thorough research, we believe we have come up with a solution to this problem by use of an electric motor. At the start of the semester we knew a force analysis was needed in which Thomas worked diligently on until completion. After the force analysis our group split into several different directions. Thomas worked on researching components from his force analysis calculations. Jeremy worked on the circuit and components needed to make this design as safe as possible. Evan and Samuel worked on the design portion of just how this design is going to work and what parts could be found online; opposed to which parts needed to be designed from scratch. From there Evan started working on the rear sprocket mount which was probably our biggest design problem. Samuel started working on a design that would support the battery and motor onto several different styles of bicycles. Together this team has been fairly independent of each other’s work but every advising meeting we come together to brainstorm each other’s problems and offer valuable feedback to one another.The schedule shown in Figure 1 was our original plan to accomplishing our Fall 2017 semester tasks. Once we started to get into our project specifics, we began to encounter problems and delays. Figure 2 is an updated version that shows a realistic process of how the semester’s tasks occurred. As shown in the figures, we extended the time for researching the best methods, the force analysis, the circuit design and component research, and the designing of the mounts. The specifics will be further researched in the Spring 2018 semester.Figure SEQ Figure \* ARABIC 1: Expected schedule of Fall 2017Figure SEQ Figure \* ARABIC 2: Actual progress of 2017Force AnalysisThere were many obstacles and dead ends involved in this portion of the project. It was very much a trial and error process. However, in time, a solution was reached. It was determined that the force required to overcome the maximum theoretical opposing forces to be 110 N. From this, the required power was derived, and found to be about 990 W (1.3 hp). Through conducting an online survey (table found in Appendix page 12) on Academy’s website, Thomas was able to determine an average bicycle weight (36.5 lb). For the purposes of this analysis, a 200 lb rider was also used in order to determine a force that would work for almost any rider. After this, the weight was then converted into SI units in order to make computations easier. I then determined approximately how much of the total weight was acting on each wheel. This value varies with the riders position however can be approximated with a free body diagram. Later on it will be explained that determining the weight distribution for our application was not necessary. The reason it was suspected that it might matter is because bicycles are rear wheel drive systems and a larger normal force on the rear wheel would be expected because friction is a function of normal force, and is also the driving force involved in translating the bicycle and rotating the wheel. Using the equation of static friction,fiction=Normal Force× μswhere μs was equal to 0.8, the force due to friction was computed to be 565 N on the rear wheel.The issue we encountered was this value was far too high and yielded a required power value several times greater than what we anticipated. The reason for this error was that the equation used does not factor in the use of wheels rolling to reduce the work required. The value computed stated that it would require this amount of force to slide the bicycle across the ground with the wheels locked from rotating. The equation and concept of rolling resistance was then introduced into our problem. Using our textbook, Statics and Strength of Materials, we found that rolling friction (rolling resistance) was equal to the coefficient of rolling resistance multiplied by the quotient of the normal force acting on the wheel divided by the radius of the wheel,Fr=Cr(NR) The textbook gives the coefficient for a pneumatic rubber tire on concrete to be 25 mm. because bikes have 2 wheels, there are 2 rolling frictional forces acting on the bike. The sum of both frictional forces will yield the total opposing force due to friction. ThereforeFRtotal=CNrearR+CNfrontRBecause C and R are both constant, they can be factored out.CRNrear+NfrontBy summing the two normal forces, the total normal force (which is equal to weight in this case) can be used to compute the rolling friction and thus void the need to compute weight distribution. Wanting to get the maximum value of rolling friction that may be applied to the bicycle, the smallest standard bike wheel size was used: 26 Diameter. The radius of this wheel is equal to 0.3302 m. by plugging in the known values, the rolling resistance is found to be approximately 80 N total. Next the air resistance value was calculated using the formula:AR=12*Cd*ρ*A*v2where Cd is the drag coefficient, ρ is the air density (averaging at 1.2 kg/m3), A is the cross-sectional area, and v is velocity (20 mph or 8.94 m/s). Using this table found online at (Appendix page 13),A can be estimated to be 0.55 m2 and Cd to be 1.15, using the upright commuting position. By multiplying all of these values and dividing the product by 2, the approximated value for the force of air resistance is equal to 30 N. finally, by adding the rolling resistance forces and the air resistance, the required force to get the bicycle to move at 20 mph is 110 N.From the force, the power can be computed. Power is simply the force applied times the velocity that the object is moving. Both velocity and force are known, therefore the power can be computed, which is found to be 984 W (which is about 1.3 hp). Based on this analysis, it has been determined that our electric motor will be rated for 1000 W and will be a 48 V motor.Circuit Design The circuit design for this project proved to be quite troublesome with the required 21 ampere circuit. Once the motor was picked we decided the battery would have to be a 48V 1000W battery. The voltage is easy to overcome with electronics. The problems come when the scale of current tries to flow through the small switches. After spending a few afternoons with Dr. Drouant we found a snap action switch which met our parameters for the 21-amp circuit. The main circuit breakdown is a series circuit starting from the battery then heading straight to the fuse. The fuse is needed to prevent overcurrent damage to any other component. As small as a fuse is, it is probably the most vital safety feature implemented in the circuit. A one or two-dollar fuse burning up instead of a several hundred-dollar motor will always prevent a headache. After the fuse is the motor, which we figured out to need a 48-volt 1000-Watt DC motor. The motor is not really one of our big concerns this semester as we are not ready to start ordering parts just yet. After the motor comes the speed controller which could come before the motor depending on which method we settle on using. Most motors have a controller built onto them which is why we are waiting to see the exact motor we are going to order to see if this controller is needed or not. The last part of the circuit is the switches. One rocker switch as a main on/off switch for the motor to be activated. The last switch is a snap action switch. The reason we picked this switch for the circuit was because the rider shouldn’t have to think about being safe with our design; that is our job. The snap action switch allows for easy shut off of the motor when the rider presses on the brakes. With the long bar on the snap action switch, pressing the brakes even the slightest amount will shut the circuit down. Next semester our thoughts on advancing the circuit will be finding waterproof brackets for all components. The fuse has a weatherproof holder already for it. The snap action switches we picked was $25 so if rain messes up this switch then it will be problematic very fast. Using heat shrink wrap on every connection made will add to our circuit’s safety. In conclusion of the circuit, we set out to make a simple easy to put together circuit. Looking back over the semester we have made a lot of additions and took away a descent amount of electrical components but we are happy with our electrical progress.Battery AnalysisGiven the required voltage and amperage, we can also determine the specifications for the battery we will need. In order to determine the battery needed, the amp hour rating must be calculated. The formula used to find the required amp hour is given as the product of the amperage and the time the battery will run in hours. The amperage for each case was derived from a minimum power output of 984 W and a maximum of 1000 W. It is recommended that a safety factor of 80% for Lithium-ion batteries be used as well. Because of this the desired amperage is divided by the safety factor 0f 0.8. Based on the numbers produced (Appendix page 12), it is highly unlikely that our product will run longer than an hour. Instead we will focus more on finding a battery with a 26 Ah rating. As far as the type of battery, we have chosen to use a lithium-ion battery for its efficiency and light weight.Mount DesignA bike is a tool that people use to commute to work, race, or even ride on mountain trails. Because of this, we wanted a rugged design that would hold up to just about any cyclist’s lifestyle. Our mount design started with the basic steps of drawing rough sketches of our ideas with pencil and some paper. When the sketch met the necessary criteria, we then began our design in the Computer Aided Design (CAD) software. The CAD programs used to design this mount were Autodesk Inventor and Solidworks. The design process started with a simple sketch of our part, once the workings of the program were learned. While designing, a few learning curves occurred with setup and our part design process. When a problem came up, our team worked together to form a solution, thus successfully completing the task.To ensure that the motor will be secured on the frame, no matter the desired terrain, we decided to have six points of contact (three on each side). The frame clamps are the most important parts to secure our supports to the bike frame. A C-clamp is the type that you will see on most bikes with round frames (Appendix page 14, image 1). They are easy to install and fit snug around the bike frame. Because of this, we are integrating this method into our design. Solidworks was used to design this part. To make this C-clamp, first a semi-circle was sketched to the desired inside radius on the top plane. Then a larger semi-circle was drawn with enough space for the fastening bolt hole. Next a straight line was placed to connect the two semi-circles. Then a feature on Solidworks called Boss-Extrude was used to give the part the width. The feature called Hole Wizard was used to cut the hole where the bolt would go. To do the top part, the bottom part was copied and pasted on a new part file. Then a sketch was made on the top plane of two rectangles with a space in between. Again the Boss Extrude feature was used to extrude these rectangles from the top curved surface. Finally, the two parts were mated in an assembly.The frame consists of six supports. The smaller front two supports will bolt on to a C-clamp mounted underneath the bike seat, the two rear supports will be attached to the axle of the rear wheel on both sides, and the middle supports will be mounted to the frame of the bike so that the weight of the motor is positioned directly above the axle (shown in Appendix page 15, image 4). These will also use a C-clamp to mount to the bike frame. Each rod consists of the same components: an inner threaded rod, and two loop end pieces on each side with outer threading. The Loop end part includes a solid loop that is attached to an outside threaded rod. The specific loop diameter and thread size will be determined in the upcoming semester for our design’s stress analysis. The same stress analysis process goes for the connecting rod part. This part consists of an extruded cylinder that has inner threaded holes bored out at each end. After a sketch of the Loop End part was completed, we then made the part more realistic by using features to make it 3D. Our loop end part and connecting rod assembly can be seen in the Appendix, page 14, images 2 and 3. The next obstacle was creating a universal fit for our sprocket to attach to the rear wheel. Our rear wheel Axle C-Clamp is adjustable and secure. Our clamp is made for easy installment, since it is designed with two separate halves. The clamp is able to be adjusted to fit different diameter axles by adding rubber inserts, for a secure fit for smaller diameter axles. The rubber inserts are the interlocking parts inside the clamp; the black and grey pieces. A variety of rubber inserts could be included in our overall electric bike power aid kit to fit common diameter bicycle axles. The sprocket is attached to the axle clamp by the three horizontal blue bolts. It is locked in place by three corresponding orange locknuts, as well as the three red spacers. The spacer prevents the sprocket from moving and interfering with the tire’s spokes. The locknuts will prevent vibrations from allowing the sprocket to detach from the clamp. The Axle C-Clamp is seen in Appendix page 16 image 5.Restrictions & CostsIn this project, we were given a lot of freedom although there are some requirements. The design must be able to fit onto most bikes, have safety options, and cost effective. Some other requirements we agreed upon are that it be lightweight, cost effective, and be rugged enough to withstand rough terrain. First, we want to make sure we are not adding much extra weight or the bike could be difficult to ride. Second, we had to think about safety. There needs to be some features that will shut off the motor if the rider comes to a sudden stop. A snap action switch will be used to shut off the motor when the operator holds the hand brake. When starting this project, we knew that we needed to make a high quality product at a competitive price. Below is a list of market prices:Major Parts to PurchasesApproximate Market PricingBattery$600Motor$90 - $130Wiring$20Speed control$20Snap action switches$15 - $20Weatherproof housing for fuse & fuse$8Support Clamps$10 per pairSupport Rods$10 - $20 per pair Total $880This cost is much higher than initially anticipated and may go up even further. The reasons our costs are so high is because we are designing an outstanding all around system. In addition, by opting for a lithium-ion battery, we make significant reductions to weight and increase drivability.Spring Semester 2018 Tentative ScheduleOur schedule below is a projected view of our tasks to complete in the upcoming semester, Spring 2018. A goal for next year is to finalize our force analysis on any additional components for our mechanism. A possible addition could be a type of dampener to prevent the motor from experiencing damaging jolts from uneven surfaces. We also plan to improve our circuit and determine the most efficient location for our battery. Other tasks include improving our mount designs and determining dimension specifics. The team will work together in researching and ordering efficient and cost effective parts. We will also assemble our mechanism onto a bike and do some field-testing. Our team will then make adjustments accordingly. We will then be able to present the total cost for our mechanism.ConclusionIn conclusion, this semester has brought many challenges to the team, but through each team member doing their part it has come together better than we could have ever anticipated. Next semester should go a little more smoothly now that we know each other’s strengths and weaknesses. We set out to come up with a bicycle power aid readily available to everyone without having to spend a fortune and we believe our design will price match any design out there. Thomas’s force analysis and research into design problems has kept the stress level of the group down significantly. Jeremy’s input on design ideas and handling all electrical problems for the group helped by allowing more options and last-minute changes. Evan’s push to keep everything on schedule and his Inventor designs made the group keep a high pace all semester along with bringing ideas to reality. Samuel’s diligence with keeping everyone on kept the group within reason when some farfetched ideas came to the table, as well as producing Solid Work mount designs that allowed us the freedom to pick several different battery and motor options with his universal designs. We look forward to continuing our research and improving on what we have already done for next semester.AppendixAverage Bicycle Weight in lbAh Ratings Without Safety FactorAh Ratings Using 80% of Ah RatingTable Used To Calculate Air ResistanceImage 1: C-ClampImage 2: Connecting RodImage 3: Loop End Piece on Connecting RodImage 4: Mount DesignImage 5: Axle Mount DesignList Of , Robert L.(2010) Statics and Strengh of Materials.Upper Saddle River, New Jersey: Pearson Education, Inc. ................
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