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Drive Train

Drive Train. Ryan Barba Patrick Hickey Andrew Hill. Goals. 90 lb weight goal Excluding engine and CVT: ~29 lb to work with 25 mph top speed Easy integration with rear suspension, frame, and brakes. Engine. Briggs & Stratton Model 20 Designed for Baja SAE 10 HP 14 ft-lb torque

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Drive Train

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  1. Drive Train Ryan Barba Patrick Hickey Andrew Hill

  2. Goals • 90 lb weight goal • Excluding engine and CVT: ~29 lb to work with • 25 mph top speed • Easy integration with rear suspension, frame, and brakes

  3. Engine • Briggs & Stratton Model 20 • Designed for Baja SAE • 10 HP • 14 ft-lb torque • Governed at 3800 RPM • 50 lb (dry)

  4. Transmission Types • CVT • Optimizes ratio for application • Lightweight • Experience from previous years • Very adjustable • Manual • Heavier • Ease-of-use issues • Shifting while driving

  5. Ratio • Require approximately 10:1 ratio with 23” tire • Provides realistic top speed while maintaining efficient hill-climb ability • CVT Ratio • Low: 3.9 • High: 0.9 • Top speed: 25 mph • Max torque: 585 ft-lb

  6. Reduction • Gearbox • Efficiency • Possibility of reuse • Robustness • More expensive • Easier to mount • Chains and Sprockets • Easily adjustable • Cheaper • Requires tensioner and external guarding

  7. Gearbox Design • Commercial Options • Cheaper • Proven reliability • Not purpose-built • Heavy • Custom Design • Lighter weight • Customization of packaging • Narrow • Ability to design for exact ratio • More expensive

  8. Gearbox Design • Double Reduction • Spur gears with 20° pressure angle • First: 75/19 = 3.95:1 ratio • 10 diametral pitch • Face width = 0.50” • Second: 58/23 = 2.52:1 ratio • 8 diametral pitch • Face width = 1.00” • Overall 9.96:1 ratio • 4340 alloy steel

  9. Gearbox Design • Case • Billet 7075-T651 Aluminum • CNC machined • Bearings • Timken Extra Small ball bearings • Small width and low weight • Freewheel • White Industries Trials • Allows wheels to overrun engine

  10. Gearbox Design • Shafts • 4140 steel • Grooves with retaining rings for gear location • Hollow for less weight • Splines on final two shafts • CVT secondary and Freewheel are already keyed • Internal splines on output for CV joint integration

  11. Gear Design • Face widths calculated from AGMA standards • Material removed from the webbing to reduce weight using FEA in Creo 2.0 • All loading modeled at maximum output torque Gear 1 (left) SF: 6 Gear 2 (right) SF: 4.1

  12. Case • FEA modeled with maximum bearing and brake caliper loads, CVT load of 200 lb • Safety Factor: 6.5

  13. Case • Brake caliper mounted to case for easier integration • Metal-rubber shaft seals • 0.375” flange for sealing • Permatex Black RTV Gasket Maker • Bearing/Case interface given 0.001” interference for pressfit (from min bearing OD)

  14. Shafts • Splined shafts from Grob Inc. • Steps for bearing location • First three shafts have 0.75” ID bearings • Final shaft has 1.25” ID bearings • Clearance (tight slip) • First three shafts: 0.0003” clearance from min bearing ID • Output shaft: 0.0004” clearance from min bearing ID • Gear internal splines given 0.003” clearance for slip fit

  15. Gearbox Assembly

  16. Gearbox Assembly

  17. Gearbox Assembly

  18. Drivetrain Assembly

  19. Weight Summary

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