SAE Mini Baja: Powertrain By: Chris Gilson & Spencer Suggs Advisor: Ho-hoon Lee Instructor: Cris Koutsougeras ET493

What is Mini-baja? The SAE mini-baja is an international collegiate engineering challenge to design and build an off-road vehicle This vehicle will go through various stress tests: Acceleration Off-road terrain Steep incline Endurance

powertrain The Powertrain is the mechanisms that transmit the driving force from the engine of a vehicle to its axles Includes: Engine Continuously Variable Transmission (CVT) Differential

Engine Model: Briggs & Stratton 10HP OHV Intek Cost: $250.00 Max Power Output: 10HP Max Torque Output: 14.5 ft.lbs.

Engine Mount design Designed for easy removal & maintenance Material: T6 6061 Aluminum Dimensions: 9” Length 8.37” Frame Rail Span 1” Thickness

Engine mount stress analysis Σ 𝑀 𝐴 =−wa−Fb+2a 𝑅 𝐵 =0 𝑅 𝐵 = 𝐹 𝐵 +𝑤𝑎 2𝑎 = 𝐹 𝐵 2𝑎 + 𝑤 2 𝑅 𝐵 = 21.2 2∗.0975 + 275.6 2 𝑅 𝐵 =108.718+137.8 𝑅 𝐵 =246.52 𝑁 Σ 𝑀 𝐵 =𝑤𝑎−𝐹𝑏+2𝑎 𝑅 𝐴 =0 𝑅 𝐴 = 𝐹 𝐵 −𝑤𝑎 2𝑎 = 𝐹 𝐵 2𝑎 − 𝑤 2 𝑅 𝐴 = 21.2 2∗.0975 − 275.6 2 𝑅 𝐴 =108.718−137.8 𝑅 𝐴 = −29.1 𝑁 Max Torque from engine is 14.5 ft. lbs. = 19.7 Nm Torque = F * distance F = 107.1 N W = m * g W = 275.6 N

Force equilibrium +↑ΣFy=0 RA+RB+29.1−246.5=0 RA+RB +29.1−246.5=0 RA+RB =217.4N   +↺ΣMA=0 RB (0.225)+(29.1)(0.015)-(246.5)(0.21)=0 RB (0.225)+(29.1)(0.015)-( 246.5)(0.21)=0 RB=228.127N RA+RB=217.4 RA +228.127=217.4 RA =−10.727N

Shear force diagram 0≤x≤0.015: +↑ΣFy=0 −10.727−V1=0 V=−10.727 N   0.015≤x≤0.21:  +↑ΣFy=0 −10.727+29.1−V=0 V=18.373 N 0.21≤x≤0.225: −10.727+29.1−246.5−V=0 V=−228.127 N

Bending moment diagram 0≤x≤0.015:  +↺ΣMb=0 −10.727x−Mb=0 Mb=−10.727x Nm   0.015≤x≤0.21:  −10.727x+(29.1)(x−0.015) −Mb=0 Mb=18.373x−0.436 Nm 0.21≤x≤0.225:  +↺ΣMx=0 −10.727x+(29.1)(x−0.015)+(−246.5)(x−0.21)−Mb=0 Mb=−228.127x+51.328 Nm

Solidworks stress simulation T6 6061 Aluminum yield strength = 2.75e8 N/m2 Largest concentration of stress = 1.102e5 N/m2 Material will not fail under load

CVT Transmission The continuously variable transmission is an automatic transmission that can change seamlessly through a range of speed ratios Commonly used in ATV / off-road utility vehicles

CVT Model: COMET 780 Price: $250.00 Specs: High Speed Ratio ( 𝑅 𝐻 ) = 3.71 : 1 Low Speed Ratio ( 𝑅 𝐿 ) = .69 : 1 CVT Efficiency (NCVT) = 88% Gear Reduction Ratio (RG) = 12.58 : 1 RPM-Engage : The RPM at which the CVT first engages = 800 rpm RPM-Range : Highest rpm – idle rpm = 2800 rpm

Differential Selection Independent Rear Suspension (IRS) PROS: Greater suspension travel Better ride quality Greater cornering performance Higher ground clearance CONS: Less power transfer Higher cost Higher chance of mechanical failure

Differential Model: Dana Spicer H-12 FNR Price: $400 Specs: Load Rating: 1500 lbs. Input Torque Rating: 24 ft. lbs. continuous Max Torque Rating: 96 ft. lbs. intermittent Gear Ratio: 12.58 : 1

Differential mount Designed for easy removal & maintenance Material: T6 6061 Aluminum Dimensions: 12” height 10” length .25” thickness 4” axle hole

Mounting bracket material selection Material: T6 6061 Aluminum Tensile Strength: 290 Mpa (42,000 psi) Yield Strength: 240 Mpa (35,000 psi) Weight: .098 lb./c.u. in.

Bolt grade selection Engine bolt size = .375 m Max Concentration Force Doubled for Safety Factor = 500 N Max Shear Force = 228 N = 480 N Selection using graph: SAE Grade 5 Tension Cap. = 43985 N Shear Cap. = 36831 N

Torque transferred to wheels RPM CVT Ratio (RCVT) Complete Ratio (RC) Engine Output Torque (ft. lbs) Torque at the Wheels (ft. lbs) 1800 2.63 : 1 29.11 : 1 13 336 2800 1.66 : 1 18.37 : 1 14.5 235 3600 .69 : 1 7.64 : 1 13.8 98

Powertrain Positioning Simplistic Design Easy Installation Painless Maintenance 45 Degree belt angle Decreases belt length Smaller wheel base length

Going forwrd Begin to order parts needed Machine parts to spec Begin Assembly Test

Needed PArts

Team member responsibilities Engine Components Acquisition – Spencer Differential Components Acquisition – Chris Machining quote – Spencer Engine Mount Fabrication – Spencer Differential Mount Fabrication – Chris Engine Components Assembly – Spencer Differential Components Assembly – Chris Testing – Chris/Spencer

Timeline Week 1 Week 2 Week 3-5 Week 6 Research and compare pricing for Engine & Differential components Get quote for mount material and machining Week 2 Purchase necessary components Order materials for mount and machine to spec Week 3-5 Assist frame and suspension team on fabrication Week 6 Test-fit power-train on completed frame with mounts Modify is needed

Timeline Week 7 Week 8 Week 9 Week 10 Test-fit and modify components Modify if needed Week 8 Final installation of all power-train components Week 9 Break-in & stress test power-train system Week 10 Test drive & complete build