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 – Governed at 3800 RPM – 50 lb (dry)

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

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

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

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

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

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

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

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

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

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)

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: ” clearance from min bearing ID – Output shaft: ” clearance from min bearing ID – Gear internal splines given 0.003” clearance for slip fit

Gearbox Assembly

Drivetrain Assembly

Weight Summary ComponentWeight (lb) Engine50 CVT11.8 Gearbox Case7.6 Gears & Pinions9.0 8 Ball Bearings Shafts3.1 Sprocket (22t)0.4 Freewheel + Adapter (22t)0.9 Chain (18" #410)0.5 CVT Guard Metal (.120 aluminum)2.75 CVT Guard Fiberglass/Plastic0.25 Fasteners0.75 Throttle Cable0.15 Adjustable Throttle Stop0.25 Total88.51