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  • University of California, Davis

    EME 185

    Mechanical Engineering Systems Design Project

    Formula Electric DrivetrainFinal Design Report

    Michael BrownNicholas HoriJon HromalikZac MarchBryce Yee

    March 21, 2014

  • Contents

    1 Introduction 2

    2 Layout Drawings 3

    3 Bill of Materials 13

    4 Calculation Notebook 154.1 Motor Brackets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

    4.1.1 Scenario 1: Steady State Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154.1.2 Scenario 2: Lateral Forces During Turning . . . . . . . . . . . . . . . . . . . . . . . . . 154.1.3 Scenario 3: 10g Bump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154.1.4 Worst Case Scenario: Scenario 3 - 10g Bump . . . . . . . . . . . . . . . . . . . . . . . 15

    4.2 Center Axle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.3 Spindles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    4.3.1 Spindle 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164.3.2 Spindle 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

    4.4 Axle Supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174.5 Sprockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.6 Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    4.6.1 Sprocket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.6.2 Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

    5 Summary Report 225.1 Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225.2 System Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

    5.2.1 Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235.2.2 Weaknesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235.2.3 Incomplete Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245.2.4 Possible Redesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

    6 Part Description 246.1 Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246.2 Axle Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246.3 Axle Supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256.4 Spindles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256.5 Center Axle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256.6 Center Axle Spacer and Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266.7 Sprockets: 13 & 59 teeth ANSI 40 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266.8 Eccentrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266.9 Taylor Race Engineering Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

    6.9.1 Tulip stub axles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266.9.2 Wheel drive flanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276.9.3 Half Shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276.9.4 Tripod Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

    6.10 Motor Mounting Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276.11 Chain Guard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

    7 Assembly Procedures 28

    8 Material Choice and Manufacturing 29

    9 List of manufacturing processes and Associated Parts 30

    1

  • 1 Introduction

    Formula Racing at UC Davis is a student design team challenged to design, build, and race a formula styleelectric vehicle for the 2013-2014 FSAE competition. Students are tasked with designing and fabricating avehicle that can be sold to a manufacturing firm for mass production and targets the weekend autocrossracer. The competition provides team members with the vital hand-on experience and skills necessary tosucceed as engineers.

    This project focused on the electric drivetrain of the vehicle consisting of a dual motor setup and a customrear axle system that incorporated a student-developed torque vectoring system. It also integrated withthe rest of the car including a sensor array network. All designs were made to meet SAE Formula Electricspecifications described in the 2014 rulebook.

    2

  • 2 Layout Drawings

    Figure 1: Motor Assembly

    Figure 2: Axle Assembly

    3

  • Figure 3: Exploded View: Axle

    Figure 4: Exploded View: Half Axle

    4

  • Figure 5: Exploded View: Motor Assembly

    Figure 6: Assembly with Brackets

    5

  • Figure 7: Exploded View: Whole Axle Supports

    Figure 8: Center Axle

    6

  • Figure 9: Sprocket

    Figure 10: Spindle 1

    7

  • Figure 11: Center Axle

    Figure 12: Eccentrics

    8

  • Figure 13: Bearing Spacer

    Figure 14: Axle Support Bottom

    9

  • Figure 15: Axle Support Cap

    Figure 16: Motor Mounting Bracker

    10

  • Figure 17: Motor Spacer 3

    Figure 18: Chain Guard

    11

  • Figure 19: Chain Guard Bracket

    12

  • 3 Bill of Materials

    The financial goals were to keep overall costs as low as possible, preferably below $500, throughsponsorship and donations. $2,100 was budgeted for new axles from Taylor Race Engineering and $500 forthe remainder of the project. Included in the bill of materials are retail prices of all materials that werenecessary for the project. Costs for machine time in the Engineering Fabrication Laboratory and CNCmachining were excluded from this report. Manufacturing time, labor, and consumables will need to betaken into account for volume production.

    A copy of the bill of materials is included on the following page. The first value in the Overall TotalPrice column is the amount needed to build an additional drivetrain assembly. The value below, TotalWithout Taylor, is the price for all materials excluding Taylor Race Engineering parts. The third value,Cost to the Team, is the amount spent to build the powertrain for this years vehicle. This value reflectsover $300 in donated parts and materials.The team went a little over budget with this system. Costs may be reduced by purchasing smallerquantities of some components, such as bolts, as the minimum stock quantities were more than necessaryto build a single drivetrain. For mass production, these changes would keep the project under budget.

    13

  • Figure 20: Bill of Materials

    14

  • 4 Calculation Notebook

    4.1 Motor Brackets

    Material: 6061-T6 Aluminum

    4.1.1 Scenario 1: Steady State Operation

    Forces: Weight of Motor ( 80 lbs)Torque: Moment on each motor sprocket (70 ft-lb)Fixed Points: The three mounting points of the motor brackets. The bolts in the brackets.Assumptions: Chassis brackets are rigid

    4.1.2 Scenario 2: Lateral Forces During Turning

    Forces: 1.5g Side Loading ( 120 lbs)Fixed Points: The three mounting points of the motor brackets. The bolts in the brackets.Assumptions: Chassis brackets are rigid.

    4.1.3 Scenario 3: 10g Bump

    Forces: 10g vertical load ( 800 lbs) Fixed Points: The three mounting points of the motor brackets. Thebolts in the brackets Assumptions: Chassis brackets are rigid.

    4.1.4 Worst Case Scenario: Scenario 3 - 10g Bump

    Figure 21: FEA Results: Scenario 3 - 10g Bump

    15

  • 4.2 Center Axle

    Forces: 763 lbf spread over over the contact area with bearings. 763 lbf spread over over the area on oppositeend of bearings that sits on spindle.Fixed Points: The outside flat ends of the smaller cylinder.Assumptions: Both motors outputting torque in opposite directions. Bearings have seized and all of thetorque is converted into normal forces on the partMaterial: Plain Carbon Steel

    Figure 22: FEA Results: Center Axle

    4.3 Spindles

    Material: 6061-T6 Aluminum

    4.3.1 Spindle 1

    Forces: 763 lbf spread over the four bolt connectionsFixed Points: The bolt holes at the sprocket connection on the opposite side of where the torque is appliedAssumptions: Full torque from motor applied to spindles. Opposite connections lock up. Whole componentunder torsion.

    16

  • Figure 23: FEA Results: Spindle 1

    4.3.2 Spindle 2

    Spindle 2 is larger than Spindle 1 in all respects and experiences the same forces, therefore it is reasonableto assume Spindle 2 is sufficiently strong for this application.

    4.4 Axle Supports

    Material: 6061-T6 AluminumForces: Lateral forces during full throttle ( 750 lbs) and 10g vertical bump ( 200 lbs)Fixed Points: The three legs of the bracket were fixed to simulate a bolt-through-tab connection. The capwas secured to the bottom bracket with three SAE grade 5 14 -20 bolts.Assumptions: Brackets is rigid.Minimum Factor of Safety: 3.4

    17

  • Figure 24: FEA Results: Axle Supports

    4.5 Sprockets

    Material: 6061-T6 AluminumForces: Full throttle force along the chain ( 720 lbs) a