Design of an Electric Drivetrain in aSpoke-Less Bicycle WheelRajdeep Mukherjee1,Nayan Arora21, 2 Departmentof Mechanical Engineering, University of Petroleum & Energy Studies Abstract:The most interesting and exciting thing about electric bikes is that, theybridge gap between human-powered bicycles and motor-powered vehicles.
Theredesigning of the electric bicycle could be effectively done by changing theposition of the drivetrain considering the dynamics, the feasibility and theaesthetic values of the present design. With the aim of modifying the existingtrend in the electric bicycles and to improve its ergonomics and aesthetics, anew model needs to be fabricated. Since the front wheel is not an active memberof the drivetrain of a bicycle, hence it can be used to implement a newelectric drivetrain. This study focuses on front spoke-less wheel that willhouse a motor and two idler pulleys in a triangular formation. The idlers willfulfill the purpose of force balancing and stability of the friction drive. The rear transmission will be left unchangedleaving the option of changing the front wheel to the user.
Friction-drive willbe chosen as the means of transmission, due to fewer parts and sufficient powertransmission capabilities. The front wheel will house a motor and two idlerpulleys with an angle of 120° between them to counter balance the forces. Theidea of this setup is primarily to provide the rider with the buffer power thatcan take him along difficult terrains and inclinesKeywords:Spoke-less, Idler pulleys, Triangular formation, Friction drive, ElectricDrivetrainI.INTRODUCTIONAnelectric bicycle uses the same designs and components as any other bicycle, butalso includes an electric motor that supplements the power available to therider. The motor is powered by a rechargeable battery which provides aconvenient, and less strenuous cycling experience, making electric bicycles theworld’s most accessible way to travel.Theelectric bicycles in market today have their drivetrain installed in thebicycle frame itself. Also, the cost of an electric bicycle poses a majordrawback. But, this gap in the present electric bicycle can be sorted out by amechanism that would allow the rider to convert any traditional bicycle into anelectric one.
With this aim a new model needs to be fabricated. This projectaspires to modify the existing trend in the electric bicycles, to improve theergonomics and aesthetics of the bicycle by modifying the front wheel of thebicycle. Sincethe front wheel is not an active member of the drivetrain of a bicycle, henceit can be used to implement a new electric drivetrain. The front wheel willhouse a motor and two idler pulleys in a triangular formation. The idlers willfulfill the purpose of force balancing and stability of the frictiondrive.
The rear transmission has beenleft unchanged leaving the option of changing the front wheel to the end user.Frictiondrive was chosen as the means of transmission as it has less number of partsand sufficient power transmission capabilities required in our drive train. Thefront wheel will house a motor and two idler pulleys with an angle of 120°between them to counter balance the forces. The power from a 250W motor will bedirectly transmitted to the inner rim of the front wheel. The speed will becontrolled by a throttle integrated in the existing handle bar of the bicycle.II.DESIGN OF FRAME RIM IDLER MOTOR 120o While designing the frame, the main aim was to make itstrong enough to withstand static loads and impact loads from the road shocks.
The other design considerations kept in mind were to make a compact drivetrain with low Centre of Gravity. Low centre of gravity ensuresbetter stability to the vehicle. Also, the entire drivetrain had to fit insidethe front wheel. A simple frame was designed by placing the motor on the lowerpart of the rim and two idlers in a triangular formation. The final frame comprisesof linkages which add rigidity to the frame and provides ample space forplacing all the drivetrain components. Further provisions were added so thatthe wheel could be attached to the front fork of the bicycle.
The design offrame and assembly of the vehicle was done on SolidWorks 2016. III.ANALYSISIV.MATERIAL SELECTIONMaterial selection ensures that thedesired weight, strength and safety of the component is achieved at minimumcost.
To make an optimal material selection extensive study of materials on thebasis of mechanical properties and availability was done. Yield strength, ultimatetensile strength, density, bending stiffness and welding requirements were thekey parameters for the final selection. Aluminium of Grade 6061 was chosen asthe material for fabrication of the frame. Tensile strength 420 MPa Yield strength 350 MPa Modulus of elasticity 205 GPa Shear modulus (typical for steel) 80 GPa Hardness, Brinell 121 V.
TORQUE CALCULATIONS FOR MOTOR SELECTIONConsider, Mass of rider = 75 kgRadius of Crank = 10 cm(Rc) Radius of Pedal = 15 cm (RP)Radius of Rear Tire = 30cm (RT)Radius of Rear Sprocket =3 cm (RS)T= Tension?= Torqueµ= Coefficient offrictionF= Force due to friction?f= Torque due tofrictionAt constant speeds, ??=0? =0 = Rc*(T) – RP*(W)T= (0.15)*(75*9.81)/(0.1)T= 1103.
61 NAt rear sprocket,? = (Rs) T= 0.03*1103.61? = 33.108 Nm (Max Torque applied byrider which is enough to make bicycle move)Now, for static friction, µ= 0.8Therefore, F= µ*(mTotal)*g (say mTotal = 100Kg)F= 0.8*100*9.81F= 784.8 N?f= 235.
44 NmFor rolling friction,µ= 0.05F= 49.05 N?f= 14.715 Nm? (Rear) = ? (Tension) –?(Friction)=18.39 Nm VI.TRANSMISSION BASED ON V-BELT DRIVEFrictiondrive was chosen as the means of transmission as it has less number of partsand sufficient power transmission capabilities required in our drive train.
Itis also easy to fabricate, hence it was the best system for this model. Therim has a V-shaped cross section which meshes with the pulleys. The surface is coatedwith rubber, which increases the contact and thus the friction between thesurfaces. VII. SPECIFIC COMPONENTS USED IN THEWHEEL ASSEMBLY· Motor: A 250 W motor producing 21 Nm oftorque · Batteries: Lithium Ion batteries.
· Wheel rim: A double walled cycle rim waspurchased. · Solid Tyre: A solid tyre made from butylrubber was purchased. Figure 9.
Solid Tyre 2.6 Fabrication ProcessThe fabrication of the model wascompleted in following phases:· Machiningof the idlers and the motor groove. Figure10. Machining on the Motor Rim and theIdlers· Weldingof the Mild Steel frame according to the wheel rim.· Devisinga mechanism for the assembly of the wheel.
Figure11. Machining on the Motor Rim and theIdlers· Assemblyof the wheel. Figure12. Structure of the Wheel· Assemblyof the wheel with the cycle.
Figure13. The completed cycle· Testingthe cycle without the electric motor, to determine the maximum resistance dueto the friction drive.VII. CONCLUSIONThe aim of this study wasto reduce the existing anomalies in the electric bicycle design including theergonomics and economics of the bicycle. Front wheel was selected to implementthe electric drivetrain because it is not the part of the manual drivetrain ofthe bicycle. The frame consisted of a 120° setup supporting the motor and twoidler pulleys. Al 6061 was selected as the material of construction to conformto the values of strength and hardness. The starting torque was calculated tobe 18 Nm thus, 250W motor used which could produce 21Nm torque.
For thetransmission of power from motor to wheel, friction drive was selected due toits optimum transmission characteristics and less number of moving partsreducing the maintenance costs. The motor was machined in V-shaped cross sectionto implement the friction-drive which increased the contact area and thus avoidedslippage.XI. REFERENCES Jobst Brandt (1981).The Bicycle Wheel 3rd Edition. California: Avocet, INC. Heinen, E., van Wee,B.
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