Orbit Engineering Moonbuggy Wheels James Roland Jacob Lloyd Ian Henry Kevin Beckman

Presentation Outline This presentation will cover: Problem Overview Wheel Design Prototype Fabrication Compliance Testing Final Wheel Fabrication Conclusions 2

Problem Overview

Design Goals Win 2013 NASA Great Moonbuggy Race Improve performance over bicycle wheels Increase suspension Increase axial load capability Reduce rolling resistance 4 Figure 1. Tire inflation vs rolling resistance Source:

Initial Design Specifications Radius 13.0 in Maximum width 2.5 in Maximum weight 5.75 lbm Maximum radial force 1,100 lbf Maximum axial force 300 lbf Spring constant 300 lbf/in Project budget $2,000 5 Source: Adam Karges, 2012

Wheel Design Methodology SolidWorks® Finite Element Analysis (FEA) Compare wheel geometries Analyze single spokes Arc angle, thickness, width Analyze entire wheels No. of spokes, rim thickness 6 Figure 2. Wheel being modeled under radial load in SolidWorks®

Final Wheel Design Non-pneumatic composite wheel Kevlar® rim and spokes, aluminum hub, rubber tread SolidWorks® analysis Radius 13.0 in Rim width 2.0 in Spoke width 1.5 in Weight 5.65 lbm Axial force 300 lbf Radial force 1,100 lbf Non-linear spring constant 400 lbf/in at 100 lbf 190 lbf/in at 500 lbf Built test spoke and compared to SolidWorks® model 7 Figure 3. Isometric view of final wheel design modeled in SolidWorks®

Prototype Fabrication Manufacturing tools Spoke mold Rim mandrel 8 Figure 4. Spoke moldFigure 5. Rim mandrel

Hub Fabrication Machining tools Abrasive water jet Lathe Mill 9 Figure 6. Disk brake attachment on lathe Figure 7. Spoke holder after being machined on water jet

Hub Assembly 10 Figure 8. Hub assembly in SolidWorks® Figure 9. Actual hub assembly

Spoke Layup Technique 11 Prepare mold with release agent 12 layers of Kevlar® 13.5 x 30 in strips Resin Fibre Glast 2000 Epoxy Resin 2060 Hardener Hand layup Figure 10. Spoke layup

Spoke Cure Process Vacuum bag technique Peel ply Bleeder cloth Bag Vacuum pump Cure pressure of 5-6 psi for 36 hours Spokes cut with band saw 12 Figure 11. Vacuum bagging

Rim Layup/Cure Technique Kevlar® Plain Weave Tape 50 yard roll, 2 in wide 13 Figure 12. Rim on mandrel after layup

Prototype Wheel Assembly Spoke spacing template Clamps Fibre Glast 1101 Epoxy Paste Bonding Adhesive 14 Figure 13. Spokes clamped to rim after bonding

Compliance Testing Axial strength test Adhesive failure at hub - 95 lbf Radial strength test Instron™ Compression Machine Test 1: Adhesive failure at hub lbf Test 2: Adhesive failure at rim lbf Design changes Longer spokes Stronger adhesive 15 Figure 14. Radial compression test

Compliance Testing Results 16 Figure 15. Force-deflection curve of 2 nd radial compression test

Compliance Testing Results 17 Figure 16. Force-deflection curve of 2 nd radial compression test vs SolidWorks® analysis

Final Production Decision Design specifications not met Axial strength, radial strength Decision made to continue to final production Time and money limitations Design flaws were corrected 18 Figure 17. Failure in first radial test

Final Wheel Fabrication Changes Kevlar® Plain Weave Fabric 5.0 oz/sq yd 12 layers of Kevlar® for back wheels, 14 layers for front in pre-compression Less tension in spokes Decrease rolling resistance without changing spring constant 19

Final Wheel Fabrication Same technique Bicycle tire tread Removed side walls Flexible adhesive Weldwood® Contact Cement Ratchet strap Weight specification Front wheel – 7.90 lbm Rear wheel – 7.20 lbm 9 lbm suspension system 20 Figure 18. Final wheel

Moonbuggy Implementation 21 Figure 19. Wheels installed on moonbuggy Figure 20. Moonbuggy in folded position

Final Design Changes During moonbuggy testing, adhesive failure occurred Axial stress Mechanical joining necessary Epoxy too brittle 3480 psi shear stress Aluminum rivets 310 lbf shear force 22 Figure 21. Wheel after adhesive failure

Final Result 23 Figure 22. Substrate failure Figure 23. Close up view of substrate failure

Project Cost Item DescriptionCost Kevlar ® Twill Weave Fabric, Cut To Length$615 Kevlar ® Tape, 2" - 50 yd roll$780 System 2000 Epoxy Resin$ Epoxy Hardener$135 Epoxy Paste Bonding Adhesive$105 Medium Density Fibreboard, 4ft x 8ft x 3/4in$33 Tee Nuts, 3/8 - 16$8 18 GA Cold Rolled Steel Sheet, 4ft x 4ft$29 Shipping$240 Discounts($170) Total Cost$1, Table 1. Final Bill of Materials Cost per wheel - $450

Conclusions and Recommendations 25 Specifications met Wheel dimensions, spring constant, project cost Specifications not met Wheel weight, maximum radial/axial load capacity Future recommendations Test for actual moonbuggy forces Test maximum load capacity of pneumatic wheel Design better joints Use exact same material for prototype and final wheels

26 Figure 24. Completed moonbuggy and wheels

Questions and Comments Special thank you to Dr. David Walrath, Mr. Scott Morton, and Dr. Dennis Coon for all your help and advice this year Thank you to Dr. Shawna McBride and the NASA Space Grant Consortium for providing the funding to make this project possible Finally, thank you to shop technicians Mr. Vince Dauer and Mr. Mike Schilt for all your guidance during our work in the UW machine shop 27