A Design Proposal for SPECIAL PURPOSE MOBILITY CONCEPT By M.N.PRAGADISH 3 rd year, B.E Mechanical engineering KCG college of technology Address:5/419,Mogappair east, Chennai-37 Mail id: mnpragadish@gmail.com A.SARAVANA KUMAR 3 rd year, B.E Mechanical engineering KCG college of technology Address: No.14/7,V.O.C street, Chengalpattu-603001 Mail id: saravann14@gmail.com GUIDED BY: Mr. Karthikeyan Associate Professor, Electrical and Electronics Department, KCG College of Technology Karapakkam,Chennai-97 Mail id: karthikeyan@kcgcollege.com PRINCIPAL: Mr. T. Rengaraja, Principal, KCG College of Technology, Karapakkam,Chennai-97 Mail id: principal@kcgcollege.com KCG COLLEGE OF TECHNOLOGY, Karapakkam, Chennai-97
Contents TITLE Page No. Introduction 1 Current Scenario 2 Proposed design 3 Key innovations 4 1. Hub Motors 4 2. Regenerative Shock- Absorber 7 3. Solar Panel 10 4. Torque Vectoring 11 5. Regenerative Braking 13 6. Efficient frame design 15 7. Lithium ion batteries 16 8. Superior suspension design 17 Cost estimation 19 Future improvements 19 Conclusion 20
INTRODUCTION Electric vehicle technologies have progressed extensively over the past decade. It can be attributed to the development of next generations motors, batteries and sensor technologies which are smaller in size yet robust in performance. Electric vehicles / bikes in the market are largely designed for general public use. Electric vehicle for the differently-abled has largely been a dream so far. Therefore, the objective of our project was to create a electric vehicle that can be used by everyone alike. With our unique design, we hope to use hub integrated motors to not only increase the range of the vehicle but also offer a comfortable and a safe ride for the user. Moreover, using hub motors not only eliminates the use of a transmission system, it also greatly reduces the weight of the vehicle. We also employ regenerative technologies which further increases the range. 1
CURRENT SCENARIO Currently, the bikes available for differently-abled are actually after-market fitted with two extra wheels. It generally costs an extra Rs.5000 to fit these wheels on to the bikes. But these bikes come with added disadvantages. Firstly, adding two extra wheels reduces the mileage of the bikes. Secondly, these wheels add to extra un-sprung mass. The suspension needs to be modified to take into account the extra un-sprung mass. This is normally ignored, which leads to rocky ride for the user. So, the users tend to suffer from frequent back pains and body pains. Moreover, they face difficulty in parking the vehicle as there is no provision to reverse it. Fig 1 : Current design 2
PROPOSED DESIGN Fig 2:Proposed design We have designed a special mobility vehicle which incorporates key features like Hub motors, Regenerative shock absorbers, Solar panel and Torque vectoring system. These features coupled with a ergonomic frame design, adjustable seats and independent suspension makes this vehicle more safer, economical and comfortable than any other bike available in the market today. The solar panels, regenerative shock absorbers and regenerative braking makes this vehicle more eco-friendly than a conventional electric vehicle. These renewable technologies effectively increase the range efficiency of the vehicle. 3
KEY INNOVATIONS 1. Hub Motors 2. Regenerative Shock- Absorber 3. Solar Panel 4. Torque Vectoring 5. Regenerative Braking 6. Efficient frame design 7. Lithium polymer batteries 8. Superior suspension design 1. HUB MOTORS Fig 3:Hub motor to be used The wheel hub motor is an electric motor that is incorporated into the hub of a wheel and drives it directly. In a brushed motor, energy is transferred by brushes contacting the rotating shaft of the motor. Energy is transferred in a brushless motor electronically, eliminating physical contact between stationary and moving parts. Although brushless motor technology is more expensive, most are more 4
efficient and longer-lasting than brushed motor systems. Electric motors have their greatest torque at startup, making them ideal for vehicles as they need the most torque at startup too. Their greatest torque occurs as the rotor first begins to turn, which is why electric motors do not require a transmission. Rated voltage Rated Power Rated Torque Weight Efficiency 48V 500 Watts 50 Nm 6Kg 85% Table 1:Specification of the hub motor being used Fig 3: Center of gravity using solid works Moreover, using hub motors ensures a very low center of gravity which enhances the stability of the vehicle and makes it more comfortable to ride. 5
1.1Controller for Hub motor Fig 4: Controller diagram The above diagram shows the basic wiring circuit of a brushless motor. The programmable BLDC motor controller provides efficient, smooth and quite controls for electric motorcycles, golf carts, go-carts, as well as industry motors speed or torque control. Motor speed controller uses high power MOSFET, PWM to achieve efficiency 99% in most cases. Powerful microprocessor brings in comprehensive and precise control to BLDC motor controllers. This programmable brushless motor controller also allows users to set parameters, conduct tests, and obtain diagnostic information quickly and easily. 6
2. REGENERATIVE SHOCK- ABSORBER During the everyday usage of an automobile, only 10 16% of the fuel energy is used to drive the car to overcome the resistance from road friction and air drag. One important loss is the dissipation of vibration energy by shock absorbers in the vehicle suspension under the excitation of road irregularity and vehicle acceleration or deceleration. In our design, we modify a existing shock absorber to efficiently recover the vibration energy economically in a compact space. The lateral movement of shock-absorber is converted to electricity by using faraday s laws. This is achieved by the use of linear electro-magnetic system. This shockabsorber s applications include bikes, cars, commercial vehicles and Electric locomotives. It has the capability to increase the fuel efficiency of hybrid-cars by up-to 6-7%. Fig 5: CAD model of the shock absorber designed in CATIA V5R20 7
2.1 Materials used A Indica V2 rear gas charged mcpherson strut with a spring stiffness of about 60 N/mm. A magnet with magnetic flux density of 1.03T. Insulated copper coil of 33 SWG. Rectifier, battery, transformer and multimeter. 2.2 Circuit design Fig 6: Basic Circuit Design Fig 7: Rectifier coupled with a booster circuit 2.3 Working According to faraday s law, any change in the magnetic environment of a coil of wire will cause a voltage (EMF) to be induced in the coil. When the shockabsorber undergoes a deflection, the coil assembly undergoes relative movement with respect to the magnet assembly. Due to this, the flux lines of the magnet are disturbed which produces a EMF in the copper coil. The shock absorber generates about 10 Watts of electricity which is dependent upon the frequency of the vibration. 8
Output voltage 2.4 Testing The magnet and coil assembly was tested in the laboratory. The ends of the copper coil were connected to 700Ω rheostat and output was measured across a 50Ma AC ammeter and a 50V AC voltmeter. The output was tested for normal road conditions. Fig 8: Circuit used for testing 40 30 Number of turns 20 10 0 3000 turns(25swg) 4500 with 3 stacks(25swg) 6000 with 4 stacks(25swg) 17300 with 5 stacks(33swg) Voltage 3 5 9 30 Fig 9: Experimental result 9
2.5 Design Comparison Actual patented design Our design By Lei Zuo of Stony Brooks University Uses radial magnets Uses axial magnets Number of magnets used =12 Number of magnets used =3 Weight =28Kg Price=Rs.15000-20000 Weight=Original weight+1.5kg Price=Rs.3000 3. SOLAR PANEL The solar panel is to be used as a roof top as well as for generating electricity for recharging the battery. The solar panel we propose to use is of 100 Wp capacity which continually replenishes the battery thereby enhancing its range further. 10
4. TORQUE VECTORING: The idea and implementation of torque vectoring are both very complex. The main goal of torque vectoring is to independently vary the torque being sent to each wheel. Differentials are generally consisting of only mechanical components. This ability improves a vehicle s capability to maintain traction in poor weather conditions. When one wheel begins slipping, the controller can reduce the torque being sent to that wheel, effectively braking the wheel. The basic idea of torque vectoring is that given requests from the driver (steering angle, brake and acceleration signals) will be processed and distributed as torque commands to the wheels of the vehicle. With the individual torque distribution the vehicle performance, agility and safety can be improved. For any steer angle and forward velocity, an ideal yaw rate can be calculated by assuming no tire slip, and using the wheel geometry to approximate the turn radius. The measured yaw rate is then used as feedback, giving a yaw error. A differential term (yaw acceleration) is included for damping. The output is used to control the rear steer. For torque vectoring, the same signal can be used to control the distribution of drive torque; i.e. for a left turn, an additional torque is applied to the right, with an equal braking torque applied to the left. These torques are in addition to the normal drive torque that maintains the vehicle forward velocity. It is done with the help of ADXL330 three-axis accelerometer and a wheel speed sensor coupled with a ARDUINO board and the output is finally fed to the hub motor controller for effective torque distribution. 11
Fig 10:Torque vectoring algorithm Fig 11: Accelerometer sensor used Fig 12: ARDUINO Board 12
5. REGENERATIVE BRAKING Fig 13:Hub motor cut section In dynamic braking, power is being wasted in resistance making the system an inefficient one, thus regenerative braking is developed. Normally energy is dissipated in any braking procedure and in most cases, energy is lost as heat. By recovering the mechanical energy stored in the rotating parts and pumping it into the supply lines the overall energy efficiency is improved. This is called regeneration. A regenerative brake is an energy recovery mechanism which slows a vehicle or object down by converting its kinetic energy into electrical energy, which can be either used immediately or stored until needed. 13
In a machine, for the generated energy to be supplied to the source two conditions should be satisfied i) back emf should be greater than supply voltage (E > V) for all speeds ii) Current has to reverse its direction For the above two conditions to be satisfied, we have to increase the back emf so that it is greater than the supply voltage. In order to increase the back emf, increase the speed. The speed increases when the vehicle is moving down the gradient or by increasing the field flux. But increasing the field flux beyond rated is not possible as the permanent magnets are used in field system. So, for a source of fixed voltage of rated value regenerative braking is possible only for speeds higher than rated value and for a variable voltage source it is possible for below rated speeds also. During regeneration if the generated power is not absorbed by the load, it will be supplied to the line and the line voltage will rise to dangerous values leading to insulation break down. Hence regenerative braking should be used only when there are loads connected to absorb regenerated power. Therefore a battery source is used which enables power flow from load to source. 14
6. EFFICIENT FRAME DESIGN ASI 1018 Mild/Low Carbon steel was chosen because of its low cost, weldability, ease of availability and machinability. The welding method that would be used is MIG with copper filler rods. The outer diameter of the Roll-cage is 1 and the thickness is 3 mm. The weight of the roll cage is 28.8 kg. The Roll cage was designed in ergonomic way so that it is more user-friendly and also provides a good ground clearance. S.No. Material Tensile Strength MPa Density lb/in 3 Cost(Rs.) Per meter 1 ASI 1018 Mild/Low Carbon steel 370 0.284 184 Fig 14:Roll cage 15
7. LITHIUM ION BATTERIES We would be using two 48V 15Ah Li-ion batteries due to its low weight and high efficiency. Each battery unit costs Rs.7000 and weighs around 7 Kg. The charging time for the batteries is about 6 hours. E-bike 48V 15Ah battery Advantage 1. Extremely safe and stable chemistry 2. Long life-cycle: Can be circularly used, more than 1000 times recycles, 4 times that of a Lead acid battery. 3. Lighter weight, with best power-to-weight ratio: 1/3 of Lead acid battery weight. 4. Good performance at high temperature and high temperature resistance 5. Low self-discharge rate, less than 3% monthly. 6. Environment friendly: Clean and Green energy poses no pollution threat. Fig 15: Description of battery to be used 16
Technical Specification of battery 8. SUPERIOR SUSPENSION DESIGN Fig 16:Macpherson strut design 17
Fig 17: Suspension design We have designed a Macpherson strut type independent suspension. The advantages of McPherson suspension are low un-sprung masses, a large support base, low forces and a more compact design. The suspension has been designed keeping in view the high un-sprung masses due to the hub motors. Specification for suspension: 1. Lower A Arm Length = 12.50 inches 2. Stiffness = 60 N/mm 3. Wire diameter (d) = 13mm 4. Coil diameter (D) = 100mm Fig 18: Knuckle design 18
COST ESTIMATION ITEM PRICE 2 Hub motors Rs. 12000 2 Regenerative shock absorber Rs. 6000 Roll cage cost Rs. 5000 Front bike assembly Rs. 6000 Solar panel Rs. 7000 E-bike kit(motor controller,throttle etc) Rs. 5000 Seat Rs. 6000 Labor cost(welding, machining) Rs. 2000 2 batteries Rs. 14000 Arduino board with sensors Rs. 1200 12inch wheels Rs. 3000 M12 nuts and bolts Rs. 500 Tail light Rs. 300 Total cost Rs68000 (approximately) FUTURE IMPROVEMENTS We are planning to design a steering system that can be easily operated by using the foot for people with hand disabilities. We also intend to install a Antilock Braking System (ABS) for an extra cost, which will greatly enhance the safety of the vehicle. 19
CONCLUSION: Making technology more affordable and eco friendly for the masses has been the greatest challenge of any engineer. With our superior ergonomic and aesthetic design, we hope to have a range of 60Km on a single range. With solar panels, and regenerative shock absorber, we hope to reduce the effective charging time to less than 4 hours compared to the conventional charging time that is more than 6 hours. Moreover, hub motors will be at the heart of automotive revolution in the future paving way for more efficient and greener commuting. Hence, we expect our vehicle to revolutionize the way people with disabilities commute. We hope this vehicle will make their commuting safer, more comfortable without causing any pollution to the environment. This vehicle will also instill a sense of self confidence, respect, satisfaction and a better value for their money. Fig 19: Side view 20
Fig 20: Prototype of our shock absorber Fig 21: Shock absorber cut section 21