Eagle Pullers. Biosystems Engineering Department. 200 Tom Corley Building. Auburn, AL Dear Eagle Pullers,

Transcription

1 Eagle Pullers Biosystems Engineering Department 200 Tom Corley Building Auburn, AL Dear Eagle Pullers, Thank you for the opportunity for Quarter Power to provide designs for the Screaming Eagle 16 tractor, and your cooperation during the design process. We hope that you will find that our design recommendations exceed adequacy requirements. The suggested incorporation of the continuously variable transmission meets the requirement for rapid and reliable removal and installation to and from the engine for inspection and maintenance. As requested, gear ratios have been specified that meet the requirements of the low speed competitions, the pulling competition, and tractor relocation. It has been a pleasure working with you and we wish you the best during the competition. Respectfully, Quarter Power Biosystems Engineering Department 200 Tom Corley Building Auburn, AL Bud Bliss Sam Dunbar John Llorens 1

2 Quarter-Scale Tractor Drivetrain Design Report Auburn University APRIL 12, 2016 Client: Dr. Tim McDonald, Dr. Jeremiah Davis, and the Eagle Pullers BUD BLISS SAM DUNBAR JOHN LLORENS Provided by: Quarter Power 2

3 Quarter-Scale Tractor Drivetrain Table of Contents 1. Executive Summary 2. Background and Introduction 2.1 ASABE Quarter-Scale Tractor Competition ASABE Constraints 2.2 Auburn University Quarter-Scale Team Eagle Puller s Constraints 2.3 Problem Statement 2.4 Objectives 3. Design Methodology 3.1 Continuously Variable Transmission Primary Clutch Adapter Removal and Replacement of Primary Clutch Adapter Justification for Omission of Additional Primary Clutch Support Justification for a Tapered Primary Adapter Shaft Design Secondary Clutch Adapter Secondary Shaft with Support Brackets 3.2 Gear Ratios First Gear - 4 MPH exhaust test Second Gear - Optimal Pulling Ratio Third Gear - Optimal Cruising Speed 3.3 Driveshaft Specification Universal Joints 4. Cost Analysis 5. Final Design Recommendations 6. References 7. Appendices 3

4 1. Executive Summary Quarter Power was tasked with the design of a drivetrain suitable for use in a tractor to compete in the ASABE International Quarter-Scale Tractor Competition, and has been provided to the Auburn University tractor team, Eagle Pullers. This drivetrain was designed to make use of a continuously variable transmission (CVT) and a Cub Cadet transaxle. Additionally, this drivetrain has been designed to utilize the tractor frame design developed by Eagle Pullers with minimal modifications. The total cost of the drivetrain is estimated to be $6,084.93, which constitutes 80.83% of the entire $ cost of the Eagle Pullers Screaming Eagle 16 tractor. The mounting adapter designed by Quarter Power will mate the keyed output shaft of the engine with the splined interior of the primary clutch of the aforementioned CVT and has been designed to permit rapid removal through use of a grease gun to separate the adapter from the engine output shaft. A second adapter allows the secondary clutch of the CVT to be held in place via a frontal extension of the 16 gauge, cold rolled, sheet-metal tractor frame. Roller bearings will allow the secondary adapter to rotate freely within this frame, and a portion of the frame will be removable to allow replacement of the belt. The secondary adapter shaft will transmit power to a yoke and u-joint connected to a driveshaft. This driveshaft will transmit power through an additional yoke and u-joint of the same type to the transaxle. Gear ratios were also determined and selected for the transaxle based on the specifications of the Titan tires and 31hp Briggs and Stratton engine. For first gear, a ratio of 50:1 was selected which will propel the tractor at 5.8 mph while the engine operates at its maximum of 3600rpm for the exhaust test. The ratio 29.5:1 was determined to be optimal for second gear, which is designated as the pulling gear for the progressive weight sled pulling competition. This ratio will yield a top speed of 9.8 mph. Third gear was designated as the travel gear and a ratio of 17:1 was selected to yield a higher speed of over 15 mph with less regard to tractor load and torque. 4

5 2. Background and Introduction 2.1 ASABE Quarter-Scale Tractor Competition The American Society of Agricultural and Biological Engineers hosts an annual Quarter-Scale Tractor competition. Each participating team builds a quarter-scale size tractor from the ground up to compete against each other in a series of events to demonstrate the best tractor based on criteria of power, manufacturability, serviceability, and safety. The winner of the competition is determined by judges from the agricultural machinery industry. To coincide with the competitive events, each team presents a design report and presentation directly to the judging committee. The event is held in Peoria, IL during the summer semester where teams from across the country come together to see who has built the best tractor based on the aforementioned criteria. To further explain how the rules and regulations will influence each team s design, The Quarter- Scale Tractor Competition Committee has published a handbook. In this handbook teams are given all of the details of the competition events and the scoring criteria ASABE Constraints ASABE has developed a list of rules and regulations that restricts the designs of competing teams in certain aspects (Wonderlich and Corban, 2015). Quarter Power, along with the Eagle Pullers, have read through the rules and regulations to determine what constraints apply to the drivetrain. The pertinent constraints as outlined in the ASABE Quarter-Scale Competition rules and regulations handbook are as follows: 1. The overall weight of the tractor may not exceed 800 lbs for the competition. As such, the components of the drivetrain must be as light as possible without sacrificing durability. 2. For technical inspection, the engine must be disconnected from drivetrain in less than two minutes. The design of the adapter for the primary clutch must facilitate this by allowing quick and easy removal from the engine. 3. All moving parts must be shielded by 1/8 in steel or 1/4 in aluminum. This includes clutches, belts, or shafts. This additional shielding must also be designed such that minimal material is used to eliminate excess weight and must also allow disconnection/connection of the engine to the drivetrain in less than two minutes. 4. For sound test, the engine must operate at full power and speed (3600 rpm) and the speed of the tractor must not exceed 4 (+/- 2) mph. The gear ratios within the transaxle must include a ratio to limit the tractor speed to 4 mph for this competition event. 5. For durability test, the same speed limitations apply as those in the sound test, further highlighting the importance of selecting a proper gear ratio for these tests to maintain 4 (+/- 2) mph. 6. The tractor will be scored based on its manufacturability and simplicity of design, and as such, the use of easily manufactured parts such as folded sheet metal should be selected over more complex structures or welded designs. 5

6 2.2 Auburn University Quarter-Scale Team For the last eight years Auburn University has not fielded a quarter-scale tractor team. In 2015 The Eagle Pullers started the process of rebuilding the team, however they were not able to get a tractor built in time to compete in the 2015 competition. Despite this, they attended the competition to gather information to prepare for the competition during the following year. Beginning in the fall of 2015, Eagle Pullers began designing their tractor under the advisement of Dr. Tim McDonald (Faculty Advisor), and are now in the assembly phase Eagle Puller's Constraints Figure 1: Tractor Frame with Frontal Modification Eagle Pullers has already designed and developed portions of the quarter scale tractor and selected several components for use. Eagle Pullers intends to use a continuously variable transmission (CVT) to maintain an appropriate gear ratio during the pulling competition without losing momentum, and a transaxle to select from separate ranges of speeds appropriate for each event. A pre-existing CVT and transaxle have been selected for use. The tractor frame has already been manufactured, shown in Figure 1 with Quarter Power s frontal modifications to accommodate the CVT. As such, Quarter Power s drivetrain design must make use of these preexisting components. 1) Quarter Power will use the frame designed by Quarter Power and mount extensions wherever necessary as part of the drivetrain supports. The frame was built of 16 gauge sheet metal and formed into C -channel. The drivetrain must fit within the confines of this frame and make use of this frame for support. 2) Eagle Pullers intends to utilize a CVT from a Kawasaki Mule to provide seamless transition between high speed to high torque in their tractor. Quarter Power s drivetrain must make use of this CVT in its design, and account for the range of gear ratios that it provides when selecting gear ratios for the transaxle. 6

7 3) Eagle Pullers have selected a Cub Cadet transaxle for use in the tractor to allow the range of gear ratios that the CVT will operate within to be selected for each competition event independently. Quarter Power must therefore select optimal gear ratios for this transaxle to maximize torque while limiting speed for various competition events. 2.3 Problem Statement The American Society of Agricultural and Biological Engineers (ASABE) hosts an annual quarterscale tractor design competition, during which each contending team s tractor enters into several competitive events. Eagle Pullers intends to utilize a CVT and transaxle in their tractor design. The CVT allows the tractor to seamlessly shift through a continuous range of gear ratios by varying the engine speed. This minimizes loss of momentum while maintaining optimal torque. The transaxle will transmit power from the output pulley of the CVT to the rear tires and will allow the tractor operator to select the range of speeds that the CVT will operate within. The gear ratios for the transaxle must be selected to provide optimal speed and torque ranges for the various competition events. Quarter Power must provide designs for a suitable drivetrain for a competition tractor that makes use of the CVT and transaxle selected by Eagle Pullers. This drivetrain must also meet the requirements imposed by ASABE Quarter Scale Tractor Competition regulations. 2.4 Objectives 1. Design an adapter to mate the splined interior of the primary clutch of the CVT to the keyed output shaft of the engine. This shaft must facilitate removal of the primary clutch assembly from the engine within 2 minutes by a single individual. 2. Design an adapter and necessary support for the secondary clutch of the CVT to secure it to the tractor. This adapter and associated supports must permit convenient removal and installation of the CVT belt. 3. Select all necessary components for transmission of power between the components, including the CVT belt, driveshaft, and u-joints. These components must be rated for the maximum forces that they may experience during operation of the tractor. 4. Analyze the necessary gear ratios for the transaxle that will provide for the required optimal or maximum speeds for the various competition events. These gear ratios selected must provide optimal torque at 4 mph for two competition events, 10 mph for the pulling competition, and a travel speed in excess of 10 mph for transport of the tractor. 5. Design all additional components, including shielding and safety loops, to ensure that the drivetrain meets ASABE safety standards and competition regulations. 6. Provide engineering schematics for the entire assembled drivetrain and its configuration within the tractor so that Eagle Pullers may assemble the tractor and fabricate or purchase the necessary components. 7

8 3. Design Methodology 3.1 Continuously Variable Transmission The transmission is an important component in the drivetrain that reduces the high rotational speed of the engine output shaft while increasing torque, or vice versa. Eagle Pullers has chosen to utilize a CVT in its tractor design. In contrast to the more common multi-ratio automatic transmission, a CVT offers the advantage of allowing seamless transitions between optimal gear ratios. This is advantageous as minimal loss of momentum occurs when transitioning between gear ratios. The CVT selected by Eagle Pullers has been taken from a Kawasaki Mule, and has a splined interior that will not readily mate with the keyed output shaft of the engine. This CVT is a variablediameter pulley type which utilizes two pulleys that contract or expand to vary the ratio of a friction driven belt that transfers power between the two. A flyweight system within the pulleys controls the expansion and contraction based on the rotational speed of the pulley. This mechanism offers the advantage of simplifying the transmission such that it does not require hydraulics to shift through various gear ratios, and the process will occur automatically. A primary design objective that Quarter Power was tasked with is the utilization of the CVT selected by Eagle Pullers in the drivetrain. Utilization of this CVT mandates that the design facilitate the connection of the primary clutch of the CVT, with its splined interior, to the keyed engine output shaft. In addition, this primary adapter must be designed to facilitate rapid removal and installation of the primary clutch to the engine in under 2 minutes. The secondary clutch of the CVT also has a splined interior and therefore requires a secondary adapter, and must also be supported by the tractor frame. The entire assembly must be shielded as most components of the CVT rotate during operation. Quarter Power s design for the adapters and frames to support the CVT meet these requirements Primary Clutch Adapter Figure 2: Primary Clutch Adapter The primary clutch adapter shown in Figure 2 is a solid machined part that will link the primary clutch to the engine output shaft. This adapter has a in diameter bored hole with an extruded keyway running longitudinally that will interlock with the keyed slot on the output shaft of the 8

9 motor. This hole is seen in the bottom right of the figure above. A 1 4 in threaded hole bored into the side of this half of the shaft allows for a grease fitting to be inserted, which can be seen near the center of the shaft. This grease fitting allows grease to be pressed into the adapter to generate pressure to remove the adapter from the engine output shaft. When replacing the adapter, the grease fitting is removed so that excess grease may be expelled as the adapter is placed on the shaft prior to securing it with a bolt, and the grease fitting replaced once the adapter is secured. On the opposite end of the adapter will be a splined shaft with 26 total splines that will slide into the primary clutch mating with the splined hole in the clutch. A 3 8 in diameter hole runes through this section of the adapter shaft so that a bolt may pass through to secure the shaft and primary clutch to the engine output shaft. The entire adapter shaft is in long, and is 7 16 or 1 2 in thick in most locations to provide durability while subjected to the maximum torque of 66 ft lb that may be provided by the engine. The schematics for the final design of this adapter are provided in Appendix 1. The arrangement of the primary clutch, adapter shaft, engine, and the securing bolt can be seen below in Figure 3. Figure 3: Primary Clutch Assembly The bolt running longitudinally through the entire adapter shaft serves two purposes, holding the clutch onto the adapter and holding the adapter onto the engine output shaft. The bolt must be in long, 3 8 in diameter, and threaded to 2 in. The only forces acting on this bolt would be lateral reactionary forces due to the spring in the flyweight system inside of the primary clutch. 9

10 Removal and Replacement of the Primary Clutch Adapter Figure 4: Removal of the Primary Clutch Assembly This design facilitates rapid removal and installation of the primary clutch assembly for inspection of the engine. As shown above in Figure 4, removal begins in step 1 with the entire primary clutch assembly in place on the engine. In step 2, the securing bolt is loosened such that it is still secured in the engine output shaft, but the primary adapter and clutch may still slide off of the engine output shaft. In step 3, grease is pumped into the adapter via the grease fitting to generate pressure and push the adapter off of the engine output shaft. In Figure 4, the securing bolt is unscrewed completely and the entire assembly is removed. Replacement of the primary adapter and clutch assembly is a much simpler process. The grease fitting is removed to allow excess grease to be expelled through the hole that the grease fitting was removed from. The adapter and primary clutch is placed over the engine output shaft and then secured in place with the bolt. Once secure, the grease fitting is replaced Justification for Omission of Additional Primary Clutch Support The primary adapter assembly design by Quarter Power lacks additional support frames to conserve weight and facilitate rapid removal of the assembly from the engine for inspection. To justify the viability of this choice, Quarter Power analyzed the stresses that this design may place 10

11 upon the engine crank case, the following force/moment analysis was applied to determine if the moment acting on the engine output shaft would cause damage to the oil seal on the engine case or the crankshaft. The following assumptions were made to relate the forces acting on the oil seal on the engine case to the maximum torque that the engine is capable of outputting. The belt will not slip or break. The belt is completely slack on return side of the pulley, and is therefore ignored. The primary clutch is constricted to force the belt out to its maximum radius. The secondary clutch is rigid and may not rotate. Figure 5: Primary Clutch Free Body Diagram Side View Figure 6: Primary Clutch Free Body Diagram Frontal View Fb represents the tension in the belt pulling down on the primary clutch. L represents the horizontal distance from the oil seal of the engine to the center-point around which the belt acts on the primary clutch. The moment Mr is produced in reaction to Fb, and provides some measure of stress on the engine due to a lack of support for the primary clutch assembly. Mr may therefore be expressed in terms of Fb. MM rr = FF bb LL. Equation 1: Moment Acting on Engine Output Shaft 11

12 T represents the maximum torque that can be supplied by the 31hp Briggs and Stratton Engine. X represents the radius from the center of the primary clutch to the belt in its outermost position when the clutch is fully closed. Fb represents the tension in the belt. Fb may therefore be expressed in terms of T. FF bb = TT xx Recalling that MM rr = FF bb LL, Mr may be expressed in terms of T. Equation 2: Belt Tension in Relation to Engine Torque MM rr = TT LL xx Equation 3: Moment with Respect to Engine Torque Taking L to be 6 in, X to be 3 in, and T to be the rated maximum torque of the engine, 66 ft lb, we find that the moment applied to the oil seal at Mr is roughly 132 ft lb. Although the manufacturer specifications for the engine were not available, comparison of this value to the specifications for engines of similar size and construction made by competitors suggest that this moment is tolerable and within the limitations of the engine Justification for a Tapered Primary Adapter Shaft Design Figure 7: Stress Analysis of Tapered and Non-Tapered Primary Adapter Shafts Although the tapering seen at the center of the primary adapter shaft adds additional weight compared to an untapered design, the additional strength and deformation resistance that the taper allows was deemed beneficial. A comparison of the tapered and non-tapered shafts can be seen above in Figure 7. This comparison assumes a maximum torque of 66 ft lb as specified by the engine manufacturer, as well as a load of 500 lb. The 500 lb is well above the maximum load applied by the belt, determined from the calculations in section to be 22 lb. Despite this, adding the tapered section to the primary adapter shaft increases the factor of safety with these applied loads by 2.52, a significant increase. It was therefore elected that the tapered shaft be utilized. 12

13 3.1.2 Secondary Clutch Adapter Figure 8: Secondary Adapter Shaft For the adaption of the secondary clutch to the drivetrain, a 1 in diameter shaft has been designed (Figure 8). This shaft will slide through the secondary clutch leaving protrusions on either end that will be supported by bearings mounted within a support bracket. This shaft, similar to the primary clutch adapter, will be splined on the end that runs through the front of the secondary clutch. One addition that this shaft will incorporate approximately 1 in of threading on the outside of the shaft to allow for a locking nut to be threaded to prevent the clutch from sliding off of the adapter shaft. The shaft will have a inch long and 3 4 inch diameter hole running through it to conserve weight and materials. The schematic for this adapter is available in Appendix Secondary Shaft Support Frame Figure 9: Secondary Adapter Shaft and Support Frame The secondary shaft and clutch have been designed to be supported by an extension of the tractor frame rails. Quarter Power suggests that this frame be machined from the same piece of sheet metal that comprises the tractor frame. This frame will provide a rigid mount for the secondary clutch and shaft to rotate within. The entire tractor frame, including the secondary clutch support, will be made of 16 gauge sheet metal and will have two McMaster Carr flange 13

14 bearings, rated for 5000 rpm, to minimize frictional forces. This frame and adapter can be seen in Figure 9. Figure 10: Secondary Clutch Adapter and Support Frame Stress Analysis Figure 10 illustrates the stress analysis performed on the adapter shaft and support frame for the secondary clutch. This analysis was conducted assuming 200 lb weights mounted to the front of the frame and an upward force of 500 lbs, in excess of the calculated maximum 22 lb. The maximum estimated displacement for any part of the assembly was determined to be under one one-thousandth of an inch. This analysis reveals that the secondary adapter shaft may be hollowed during the manufacturing process as an additional step to reclaim steel for resale during production. 3.2 Gear Ratios Within most transmissions there are multiple sets of gears. Each set of gears is driven by the engine and produces a set range of speed and power. The range is determine by two factors, the rotational speed of the engine output shaft and the gear ratio. The gear ratio of a certain gear can be determined by dividing the number of teeth of the driven gear by the number of teeth of the drive gear. The result will be a ratio of engine speed to ground speed. By altering the combination of gears and the number of teeth of each gear, the gear ratio can be increased or decreased to produce a desired speed or power requirement. For the Quarter-Scale Tractor Competition there are four different events: sled pulling, maneuverability, durability, and sound test. For each of these disciplines there are a number of parameters confining the tractor, however with the proper gear ratios each of these events can be conquered. Speed is achieved at the cost of torque with high gear ratios, while torque is gained at the cost of speed with low gear ratios. For the events, the ability to select for speed or torque will allow the operator to gain momentum before transitioning to a higher torque gear ratio by 14

15 varying engine speed. Prior to the events, the range of ratios may be selected with the transaxle. Through the help of already published Excel documents, and Equation 4, we were able to determine the proper ratios (Midwest Supercub). OOOOOOOOOOOOOOOOOO GGGGGGGG GGGGGGGG RRRRRRRRRR = 4.6 PPPPPPPPPPPP GGGGGGGG BBRRRRRRRRBB SShaaaaaa TTTTTTTTh NNNNNNNNNNNN TTTTTT SShaaaaaa TTTTTTTTh NNNNNNNNNNNN Equation 4: Gear Ratios Quarter Power determined that instead of replacing the gear sets for all three forward gear, one 43% overdrive gear would accomplish the same end goal while minimizing expense and labor to swap gears. An overdrive gear takes the turns of the motor and adds turns, in this case 6 1 2, to each gear that turns the tires. However, for full-scale production of the tractor, Quarter Power recommends the following gear ratios for gears 1 through 3. These recommendations are outlined in sections through First Gear: 4 MPH Exhaust Test The speed limitation of the durability course and sound test impose a strict requirement on at least one gear ratio that must be incorporated in the transaxle. For the sound test, the decibel level of the exhaust system is measured and must be less than a set level. During this test the motor must be run at full engine rpm (3600) and the ground speed must be 4 mph, plus or minus 2 mph. It is therefore mandatory that the gear ratios specified by Quarter Power meet this requirement, allowing at least one gear to operate the Tractor at full engine speed while the tractor itself maintains a specific ground speed. A similar requirement is placed on the durability course, requiring the same 4 mph ground speed. To achieve these requirements it was determined to use the lowest gear, first gear, and that the gear ratio of first gear should be 50:1. To attain this specific ratio, the top shaft gear should have 14 teeth and the bottom shaft gear should have 38 teeth. This combination results in a speed of 5.8 mph. This was determined using Equation 4 and the spreadsheet provided by Midwest Supercub Second Gear: Optimal Pulling Ratio With the current transaxle that the Eagle Pullers have selected to use, there are three forward gears and one reverse gear. Quarter Power determined that second gear would be the optimal pulling gear. For pulling the progressive weight sled, momentum plays a key part in the distance traveled. The ideal setup would consist of initial high speed to build momentum, then transition into a higher torque/power gear to finish the pull. One of the main reasons that a CVT will be used is for this seamless transition from high speed to high torque. Keeping that in mind, Quarter Power specified a gear ratio that produced a speed high enough to build momentum, but low 15

16 enough to yield plenty of torque. The resulting gear ratio became 29.5:1 with the top tooth count being 20 and the bottom tooth count being 32. This combination should produce a top speed of 9.8 mph and provide plenty of power once the initial momentum has been slowed down. This was determined using Equation 4 and the spreadsheet provided by Midwest Supercub Third Gear: Optimal cruising speed For third gear, members of the tractor team wanted to be able to relocate the tractor without use of a larger vehicle to tow or carry the tractor. Quarter Power suggested a gear that would function as a highway gear for quick travel from place to place with minimal towing load. To accomplish this highway gear, designs were analyzed to achieve a minimum speed of 10 mph. After close examination and calculation, Quarter Power specified a gear ratio of 17:1 which will produce a top speed of 16.9 mph. This was determined using Equation 4 and the spreadsheet provided by Midwest Supercub. 3.3 Drive Shaft Sizing and Specification The driveshaft transmits power from the output of the CVT to the transaxle. As these two components are typically not aligned to conserve volume within the tractor, universal joints are used to angle the drive shaft. The drive shaft and universal joints must be able to withstand the maximum torque that may be applied by the engine and CVT. Figure 11: CVT Free Body Diagram Frontal View Figure 11 illustrates the relationship between the maximum torque of the engine and the output torque of the CVT. The variables in this diagram are identical to those outlined in section , with the inclusion of I which represents the maximum output torque from the CVT and y which represents the maximum diameter of the secondary clutch. From this diagram, it can be gleaned that the maximum theoretical torque at the output of the CVT is related to the input torque from the engine if the assumptions are made that the engine is operating at 16

17 maximum torque, the belt does not slip, and the primary clutch is operating at its minimum diameter while the secondary clutch operates at its maximum. These conditions will produce the highest torque at the output of the CVT. The following relationship defines this maximum theoretical torque. I = T yy xx Equation 5: Maximum Torque Output of CVT Taking T to be 800 in lbs, Y to be 3.5 in, and x to be 1 in, the resulting maximum torque at the output is 2800 in lbs. The driveshaft chosen for this tractor will be composed of a single piece of Drawn Over Mandel (DOM) stock. It will have a 1 in diameter with 1 8 in thick walls. The ASABE rules and regulations, the driveshaft will need to contain driveshaft loops no more than 18 in apart. The driveshaft is approximately 25 in long, requiring a single loop at the midsection of the driveshaft Universal Joints Figure 12: Universal Joint The output of the CVT is not in-line with the input of the transaxle, the driveshaft that transmits power from the CVT to the transaxle must be angled. Universal joints allow the driveshaft to be angled while still rotating freely. A universal joint is pictured in Figure 12. Quarter Power has specified and purchased the necessary universal joints for the Eagle Pullers. Quarter Power ordered a McMaster-Carr high speed rated universal joint. This universal joint has a 1 in bore to fit the specified driveshaft, it is rated for a speed of 6,000 rpm, which exceeds the maximum output speed of 3600 rpm coming from the CVT when it is operating at a 1:1 ratio, and has a maximum torque rating of 4,300 in lb which exceeds the maximum torque of 2800 in lb coming from the CVT. The universal joints will be welded onto the driveshaft. 17

18 4. Cost Analysis Part Unit Cost Quantity Total Cost Primary Clutch $ $ Secondary Clutch $ $ Drive Belt $ $99.80 Universal Joint $ $ Drive Shaft $ $5.00 cut 1 $17.74 Primary Adapter $70.00/hr 5 $ Primary Bolt $6.99/each 1 $6.99 Secondary Adapter $70.00/hr 5 $ Support Bracket Sheet Metal $45.76/sheet 1 $45.76 Sheet Metal Bends $0.05/bend 8 $0.40 Sheet Metal Shearing $0.20/cut 4 $0.80 Roller Bearing $14.14/each 2 $28.28 Transaxle Gears (3 Gear Package) $492.66/gear pkg. 3 $1, Transaxle Gasket Kit $37.53/kit 1 $ hp Briggs and Stratton Motor $1, $1, Labor $45.00/hr 10 $ Total Cost $6, Table 1: Cost Analysis for Tractor Drivetrain The cost analysis conducted by Quarter Power suggests that the total cost of the drivetrain alone is $6,084.93, utilizing ASABE Quarterscale Standards for part cost and labor reference. Eagle Pullers has declared the total cost of the entire tractor to be $ As such, the cost of the drivetrain represents 80.83% of the total cost of the tractor. 18

19 5. Final Design Recommendations Figure 11: Drivetrain Overview. Quarter Power recommends the primary adapter shaft outlined in this report to facilitate rapid removal of the primary clutch from the engine. This design provides a rapid method of removing the CVT from the engine for inspection during competition events or for servicing. It can easily and quickly be removed from the output shaft of the motor by a single person with nothing more than a ratchet and a grease gun. It is also recommended that the secondary clutch of the CVT be mounted to the tractor via an extension of the frame rails, machined from the same sheet metal that comprises the rails. This eliminates failure points and increases manufacturability. The adapter shaft that transmits power from the secondary clutch of the CVT should be hollow to conserve weight and material cost and be supported by the McMaster Carr Flange Bearings. 19

20 To meet the requirements of the design competition, gear ratios for the transaxle have been specified. For the low speed, 4 mph competitions, a first gear with a ratio of 50:1 is recommended to maintain the speed limit even when the engine is operating at 3600 rpm. For the progressive weight sled competition, a second gear with a ratio of 29.5:1 is recommended to build a speed of 9.8 mph for momentum during the beginning of the pull before lowering the throttle to gain torque. The third and final gear is recommended to have a ratio of 17:1 to provide a maximum speed of 16.9 mph. These three gear ratios may be attained by using single 43% overdrive gear for the pre-production model competition tractor. 20

21 6. References Midwest Supercub. (n.d.). Cub Cadet Gear Ration Chart [XLS]. Welton, IA: Midwest Supercub Wonderlich, G., & Corban, S. (2015, October 14). ASABE International Quarter-Scale Tractor Student Design Competition 2016 A-Team Rules and Regulations [PDF]. Peoria: ASABE. 21

22 in B in 1 2 in 0.5 in 1 4 in 0.5 in 3 in 2 in C 3 8 in 1 in 1 8 in D B 2 in R 1 2 in VIEW B-B SCALE 0.75 : in B 0.46 in in in in C VIEW C-C SCALE 0.75 : 1 B VIEW A SCALE 0.75 : in in DETAIL D SCALE 12 : R0.54 in R 1 2 in A A DRAWN BY: VIEW E SCALE 0.75 : 1 John Llorens Sam Dunbar Bud Bliss Appendix 1 Primary Adaptor Shaft

23 in B in in 3 in in C D R 1 2 in B VIEW B-B SCALE 0.75:1 B 10 in 13 in VIEW A SCALE 0.75 : 1 1 in C VIEW C-C SCALE 0.75:1 B.101 in.075 in R.375 in DETAIL D SCALE 10 : 1 R 1 2 in A A VIEW E SCALE 0.75 : 1 DRAWN BY: John Llorens Sam Dunbar Bud Bliss Appendix 2 Secondary Adaptor Shaft