DESIGN OF A POWER AUTONOMOUS SOLAR POWERED LAWN MOWER

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 5, May 2017, pp , Article ID: IJMET_08_05_013 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed DESIGN OF A POWER AUTONOMOUS SOLAR POWERED LAWN MOWER Sudhanshu G Chouhan, Sameer Ahmed Shaik, K Vamshi Krishna Reddy, Sai Rohith Bandaru Final Year B. Tech Student, Department of Mechanical Engineering, K L University, Vaddeswaram, Guntur, India Professor, Department of Mechanical Engineering, K L University, Vaddeswaram, Guntur, India ABSTRACT The paper presents work carried out to design a solar powered lawn mower system which renders the mowing task to be independent from external power supply. A software app has been designed which enables the lengthy design calculations to be executed quickly while attempting for future developmental activities. A prototype has been built and experiments performed which adequately indicates that the lawn mower is power autonomous i.e. it is self-dependent with regard to the power requirement for carrying out the mowing task. Solar power can be exploited to provide the required power for vehicle motion and mowing the lawn both. Simulation experiments with regard to the stability of mower, while maneuvering a turn during the task execution, has been carried out and presented. Key words: Lawn Mower, Solar power, Power autonomous Cite this Article: Sudhanshu G Chouhan, Sameer Ahmed Shaik, K Vamshi Krishna Reddy, Sai Rohith Bandaru and, Design of a Power Autonomous Solar Powered Lawn Mower. International Journal of Mechanical Engineering and Technology, 8(5), 2017, pp INTRODUCTION Lawn mowers have been in use since 1830 when the first lawn mower was invented by an English engineer Edwin Budding [1]. In year 1855, a mower called the Silens Messor was introduced by another English engineer Thomas Green[1] which used a chain drive to transmit power from the rear roller to the cutting cylinder. The first steam-powered lawn mower came in 1893.[1] In 1902, a gasoline powered lawn mower was offered by Ransomes Automaton [1]. In 1922, Ideal Power Mower Co. introduced the world's first self-propelled lawn tractor - "Triplex."[1]. In 2008, a Swedish company, Husqvarna [2], launched a solar electric hybrid robot lawn mower editor@iaeme.com

2 Design of a Power Autonomous Solar Powered Lawn Mower However all these versions were manually operated and took longer durations for mowing large lawns. The external power supply limited the flexibility of mowing operation either in terms of frequent recharges or due to the inconvenience caused by the physical wired connection. Recently solar power has been explored and exploited as an external power source for the lawn mowers. To the best of the knowledge of the authors, very few models of solar powered lawn mowers are available that too are very expensive rendering them unaffordable, especially in Indian context. The above factors have motivated the authors to investigate lawn mowing operations, various factors influencing its dynamics, and use of solar power and its implementation to design a power autonomous lawn mower. The paper essentially presents a design of power autonomous solar powered lawn mower and experimental studies on an in-house built prototype. 2. PROBLEM DESCRIPTION AND SOLUTION METHODOLOGY The work presented in this paper aims at designing a solar powered lawn mower system which can operate independent of wired external power supply. Solution to the identified problem has been attempted in the following phases: System design Experimentation on the system to prove the efficacy of the design Modelling and simulation for optimizing the behavior of the mower 3. DESIGN OF SOLAR POWERED LAWN MOWER SYSTEM Solar power lawn mower is an assembly of a vehicle, mowing cutter and solar power system. Hence design of a solar powered lawn mower requires estimation of gross power required for vehicle navigation and mower actuation Power required for the navigation of lawn mowing vehicle The section presents the assessment of power required for actuating the vehicle to navigate in the lawn. The tractive force required for the motion of the vehicle depends on following factors [3]. Fig. 1 presents the free body diagram of a lawn mower, considering the most general case of vehicle mowing on an inclined slope. Rolling Resistance (R r ) Grade Resistance (R g ) Acceleration Force (F a ) Figure 1 Free body diagram of lawn mowing vehicle [3] editor@iaeme.com

3 Sudhanshu G Chouhan, Sameer Ahmed Shaik, K Vamshi Krishna Reddy, Sai Rohith Bandaru and Table 1Coefficient of Rolling Resistance Calculations for Rolling Resistance Rolling Resistance is the force required to keep the tire rolling. R r WC rr where, R r = Rolling Resistance(N), W = Total Weight of vehicle (N), C rr = Coefficient of Rolling Resistance. Standard weight for a powered lawn mower has been considered as 105 pounds (47.62kg). Including the chassis frame, batteries, solar panel and other mountings, the weight of the mower can amount to 76.5 kg (or 750 N). Referring table 1, value of coefficient of rolling resistance (C rr ) is selected as (corresponding to grass surface & soft interaction). R WC r rr R r =56.25N (2) Calculations for Grade Resistance Grade Resistance is the force due to gravity which causes resistance to the drive of a vehicle up a slope. Rg W sin (3) where, R g = Grade Resistance (in N); θ = Inclination Angle Rg W sin 750sin(1 ), assuming slope is 1. R g = 13.08N Calculations for Acceleration Force Acceleration force is the force that supports the vehicle to attain a decided speed from zero in a definite span of time. Fa m a where, F = Acceleration Force (in N); m = Mass of Vehicle (in kg); a = Acceleration of Vehicle Required (in m/s 2 ); g = gravitational acceleration (9.81m/s 2 ). Safe mowing speed of a walk-behind mower is 3mph or 4.82kmph and of an electric lawn mower is 3.3mph or 5.31kmph [5].Considering 5.31kmph as constant velocity to be achieved in the first 5 seconds of starting the mower, the acceleration of the mower for that time period will be equal to V a 18 t 5 Contact Surface C rr Concrete (good / fair / poor).010 /.015 /.020 Snow (2 inch / 4 inch).025 /.037 Dirt (smooth / sandy).025 /.037 Mud (firm / medium / soft).037 /.090 /.150 Grass (firm / soft).055 /.075 Sand (firm / soft / dune).060 /.150 /.300 (1) (4) editor@iaeme.com

4 Acceleration, a = m/s 2 Hence, F m a 75(0.295) a F a = N Design of a Power Autonomous Solar Powered Lawn Mower Calculation of Total Tractive Force Total Tractive Force is the force needed to provide motion to the vehicle, Ft Rr Rg Fa Where, F t = Total Tractive Force (in N) Values of R r,r g, F a are computed from Eq. (2), Eq. (3) and Eq. (4) as respectively 56.25N, 13.08N, N. Hence, F F t = 91.45N t Actuator torque required at a wheel Actuator torque (τ) required for driving the wheel can be calculated as, F r (5) t W Where, F t = total tractive force; r w = radius of driving wheel. Wheel diameter has been selected as 8 inches. So the radius of driving wheel (r w ) becomes 8/2 = 4 inches or m. Therefore, F r t W τ= 9.29N-m (6) Selection of Drive Motor From eq. (6), it can be concluded that the torque required for moving the vehicle with specified velocity is 9.29N-m. Hence, we need two motors each to produce approximately 5N-m torque Selection of Mowing blade and actuator for the mowing blade The section below presents mowing blade selection considerations and computation of actuator torque required for actuating the mowing blade. Keeping in view the practical time permissible for mowing one sq. unit area of a lawn, the blade length has been selected as 12.0 in. Correspondingly the blade dimensions considered are 12.0 in. 1.0 in 0.2 in (length x width x thickness). Hence, volume of blade (V) is obtained as: 4 3 V ( ) = (1.2446)10 m Weight of cutter blade (W b ) can be calculated as: W b gv In this work, blade has been considered to be made up of mild steel having mass density equal to 7850kg/m 3. Therefore, weight of the blade W b 4 ( 7850)(9.81) ( ) N 3N Minimum Torque required (T br )to rotate the blade can be calculated as: T W r, where W b = weight of the blade (in N); r blade = blade radius (in m) br b blade Therefore, T W r 3(0.3048) / Nm br b blade editor@iaeme.com

5 Sudhanshu G Chouhan, Sameer Ahmed Shaik, K Vamshi Krishna Reddy, Sai Rohith Bandaru and Hence, power developed by the blade if rotated at N rpm can be calculated as: P T (2 N / 60) b br where, P b = Power developed by the blade (in Watt); N = Speed of the blade (rpm) Considering the blade is rotated at 3000rpm, the power generated at the blade is given by P T (2 N / 60) (6000 / 60) b br 143.6W 0.192hp 0.2hp The nearest commercially available motor which has higher rated output than required output of 0.2hp and capable of running the blade at minimum 3000rpm is selected [6] Calculation of Mowing Time The actual mowing time for different sized mower decks can be calculated by using the formula [5]. Hours to mow one acre = / (v 0.9 mower deck width in inches), where v is the mower velocity in miles per hour and 90% of the mower deck width is considered to account for the overlapping swaths for a uniform mowing job. In the work presented, the time taken to mow an acre of lawn is approximately 1 hour and 50 minutes. At this rate about 4 acres of lawn can be mowed in an 8 hour day Sizing of the Solar Power System to Vehicle Steps for sizing for a 12V system [7]. Calculating the Wattage per week: Considering two drive motors of 12V and 700mA each, Wattage = = 16.8W. Calculation of daily Watt-hour requirement: For 2 Drive Motors 16.8 (1/7) = 2.4Wh. Hence, total daily requirement = 2.4W-h. Calculation of the panel size: It can be determined by dividing the daily total Watt-hour requirement by the hours of available light expected in an average day, that is 2.4 W-h/ 9hours = 0.27W or more. Calculating the battery size Multiplying the daily Watt-hour requirement by 7 we get the weekly requirement and dividing this by 12 it is converted back to Ah in terms of which batteries are rated in. Multiplying this by 2 we get the correct battery size. The battery size needs to be = ( ) / 12 = 2.8Ah 3Ah Calculating the charge controller size Charge controller needs to be sized according to the amperes to be produced by the panel. We need a charge controller suitable for a solar input of at least 0.27 / 16.5 = A MOWCAL App An app called as MOWCAL has been evolved, on the basis of the above mentioned theoretical calculations, as shown in fig.2. It takes a few user input parameters and in one click it provides critical specifications of salient elements required to build a solar powered lawn mower editor@iaeme.com

6 Design of a Power Autonomous Solar Powered Lawn Mower Figure 2 MOWCAL App 4. SOLAR LAWN MOWER PROTOTYPE AND EXPERIMENTS Fig. 3 below shows the prototype of a solar powered lawn mower. The prototype is a scaled down model of the proposed lawn mower system which was designed in earlier sections. However, a set of experiments have been conducted to prove the concept and verify efficacy of the solar powered system to make the lawn mower independent of the external power supply. Figure 3 Experimental prototype of solar powered lawn mower Two set of experiments have been carried out, as presented below in section 4.1 & editor@iaeme.com

7 Sudhanshu G Chouhan, Sameer Ahmed Shaik, K Vamshi Krishna Reddy, Sai Rohith Bandaru and 4.1. Operation of lawn mower without solar power supply Figure 4 Lawn Mower operation without power supply (a) t = 0 min (b) t = 30 min (c) t = 60 min (d) t= 102 Table 2 Experimental data when lawn mower is operated without the solar power supply Time Voltage (Volts) (minutes) An experiment pertaining to performance of lawn mower without power supply has been carried out by periodically recording voltage supply from the battery; while keeping the lawn mower in actuated condition at a single location (mowing blade is made to rotate continuously). Fig. 4 presents the snapshots of the various stages and table 2 presents the data recorded during the execution of the experiment. From table 2, it can be noted that the battery supply voltage drops down to 4.76 volts after 102 minutes of continuous operation. After the instant, the battery is not able to produce adequate voltage supply and hence cannot rotate the mowing blade editor@iaeme.com

8 Design of a Power Autonomous Solar Powered Lawn Mower 4.2. Operation of lawn mower with solar power supply Similar experiments were carried out with solar power supply. Again voltage supply from the battery was recorded periodically. Figure 4 shows snapshots taken during the experiment done with the solar power supply. Figure 5 Lawn Mower operation without power supply (a) t = 0 min (b) t = 30 min (c) t = 60 min (d) t= 102 Table 3 Experimental data when lawn mower is operated with the solar power supply Time (minutes) Voltage (Volts) Fig. 5 shows the comparison of voltage supply from the battery under both set of system experiments viz. lawn mower operation with and without solar power supply system. It can be noted from table 3 that even after time t equal to 102 minutes, the voltage supply from the battery is 9.48 volts. It is almost double the value compared to the case of operation without power supply. Hence it is expected that the solar powered lawn mower can keep on working continuously for longer hours editor@iaeme.com

9 Sudhanshu G Chouhan, Sameer Ahmed Shaik, K Vamshi Krishna Reddy, Sai Rohith Bandaru and From the experimental results it is observed that when a solar panel is connected to the mower, it charges the mower battery continuously Voltage (V) Battery Voltage Without Solar Panel Battery Voltage With Solar Panel Time (min) Figure 6 Comparative analysis of battery voltage output with and without solar power supply It can be inferred that as long as the sunlight is available, the battery will keep on getting charged and will not discharge because the input to the battery is more than its output. This enables to run the mower for an entire day of 8 hours sunlight, plus extra 2 hours using battery alone. 5. SIMULATION Simulation performance of the system has been carried out in Solid Works 2017 Premium software. Fig. 7 presents the model of lawn & lawn mower and its operational details. The model has been used for determining optimum turning velocity for the lawn mower. Optimum turning velocity is the speed at which the mower can turn without losing its stability and without deviating from its specified path. For the purpose of computation of optimum turning velocity, work completion time and centrifugal force acting on the lawn mower, while executing a turn has been calculated. Work completion time (in seconds) and centrifugal Force (in Newton) were calculated for a range of mowing speeds. Table 4 presents the calculated values. Figure 7 Model of lawn and lawn mower: (a) Overview (b) Operation details Fig. 8 presents the plot of variation of centrifugal force and work completion time with respect to mowing speed (in m/s). The work completion time is obtained by dividing total distance travelled by the mower (for covering the entire lawn) with the mowing speed. With editor@iaeme.com

10 Design of a Power Autonomous Solar Powered Lawn Mower regard to the experimental prototype, mowing blade width is considered as 6 inches, i.e. 0.15m. Hence, total number of passes required to completely cover the entire width of a lawn (say, of one square meter area) is equal to ratio of 1m/0.15m i.e. seven. Total distance traveled in one pass is the perimeter of the rectangular path traced. Thus the total distance traveled for mowing the entire lawn is calculated. The distance values are further used for computing the work completion time. Work completion time (twc) is calculated using eq. (7). 2[(2 1) (20.85) (20.7) (20.55) (20.4) (20.25) (2 0.1)] m twc ( Speed of Mower ( m / s) 60) (7) Hence, work completion time is equal to 15.4m ( Speed of Mower ( m / s) 60). Now, centrifugal force is calculated using eq. (8). 2 mv Fc r (8) where, m = vehicle mass = 2.5kg, r = radius of curvature = 0.2m, v= vehicle velocity. Figure 8 Plot of work completion time (t WC ) and centrifugal force (Fc) with respect to mowing speed Table 4 Calculated values of work completion time and centrifugal force versus rpm Speed (m/s) Work Completion Time (sec) Centrifugal Force (N) It can be noted from fig. 8, that the value of optimum turning velocity is 0.095m/s. The optimum turning velocity is dependent on the system design. Hence it is bound to be different for different system designs editor@iaeme.com

11 Sudhanshu G Chouhan, Sameer Ahmed Shaik, K Vamshi Krishna Reddy, Sai Rohith Bandaru and 6. CONCLUSION This paper presents a detailed design of solar powered lawn mower system. The design has been verified experimentally. Experimental results prove that the integration of solar power supply system to the lawn mower makes it independent of external power supply. Simulation has been carried out to obtain optimum turning velocity for the lawn mower. Additionally, an app has been developed which incorporates the design calculations for a solar powered lawn mower. The present work emphasizes on proving that the solar panel supply system can be successfully used for making lawn mowing independent of external power supply. However, the work can be extended with respect to implementation of full scale model in real-life application. Several issues like obstacle detection avoidance, turning, lane changing, cutting different grass length and grass types can be attempted. REFERENCES [1] Wikipedia contributors. "Lawn mower." Wikipedia, The Free Encyclopedia. Wikipedia, accessed 18 Apr [2] Husqvarna reveals solar electric hybrid robot lawn mower. (n.d.). Retrieved April 18, 2017, mower/8955 [3] S. Chauhan, Motor Torque Calculations for Electric Vehicle, International Journal of Scientific & Technology Research,4(8),2015, pp [4] A. Dommenech, T. Domenech and J. Cerbiran, Introduction To The Study Of Rolling Friction, American Association of Physics Teachers, Am. J. Phys.55, 1987, pp [5] B.Klutho, Mower to Consider, SportsTURF,2001,pp [6] B. Okafor, Motor Torque Calculations for Electric Vehicle, International Journal of Engineering and Technology,3(10), 2013, pp [7] "How To: Choose A Solar Panel". Selectsolar.co.uk. (n.p.), Web. 8 May [8] Nkakini, S. O. and Vurasi, N. M.. Ergonomic Evaluation of Lawn Mower Operation for Comfort in Rivers State, Nigeria. International Journal of Advanced Research in Engineering and Technology, 6 (7), 2015, pp editor@iaeme.com