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Engineering Analysis Presentation ME 4182 Team: 5 Guys Engineering + 1 Nathan Bessette, Rahul Bhatia, Andrew Cass, Zeeshan Saiyed, Glen Stewart YJ Chok Automatic Whiteboard Wiper • Last Time – Layout Drawings • Layout or assembly drawings – How individual parts or subsystems fit together as a whole • Encouraged to use computer modeling software • Drawings for actual design, not prototype • This Time – Present a critical analysis of the design – Determine the areas that are most likely to fail – Potential engineering and/or manufacturing problems Calculations Using the situation with the heavy writing 2” 5” For 9.6 erasers to span the height of the board For 4.8 erasers to span half the height of the board Material Analysis Modulus Weight Mass Yield Ultimate of Approximate Density Density Stress Stress Elasticity Deflection [lb/ft3] [slugs/ft3] [ksi] [ksi] E [in] [ksi] Aluminum 170 5.3 40 45 10000 0.0032 High Strength Steel 490 15.2 100 130 29000 0.0011 Stainless Steel 490 15.2 70 105 29000 0.0011 Polyethylene 75 2.35 N/A 2.5 150 0.2101 3 D L W 48 E I Deflection Analysis For Vertical Slider Bar -Assume Circular cross section -5 ft. long -Half the normal force from the board acts at the center of the rod (5.5 lbs) Eraser sub-assembly Weight Calculation Eraser Subassembly Weight Calculation • Density: ρ = 0.5097 lbs. / Ft. of bar • Quantity of bar 2 x 60” bars = 120” 4 x 5” supports = 20” 1 x (2” x 24”) eraser backing = 48” TOTAL = 15⅔ ft • Aluminum Weight = 15⅔ ft · 0.5097 lbs. / Ft. ≈ 8 lbs. • Motor Assembly Motor ≈ 2.3 lb Rack & Pinion ≈ 1 lb Extras ≈ 0.5 lb • Motor Assembly Weight ≈ 3.8 lbs. • TOTAL WEIGHT, W ≈ 11.8 lbs. Statics Analysis (Eraser at bottom) • Forces on A and B are reactions on Sliding Assembly from sliding rails. – Total of two sliding rails attached together • • • Weight acts at the center of gravity (3.85 inches from the wall, 2.75 feet from the bottom of the assembly) Normal force from board, Nx is 11 lbs and acts at the center of the eraser (1.5 feet from the bottom of the assembly) Reactions calculated by summing forces and summing moments about a fixed point Fy 0 A y B y W Fx 0 N x A x B x M B 0 ( A x 5 ft ) ( N x 1.5 ft ) (W 3.85 12 Reaction Value (lbs) Ax 2.03 Bx 3.47 Ay 2.95 By 2.95 ft ) Statics Analysis (Eraser at Top) • Forces on A and B are reactions on Sliding Assembly from sliding rails. – Total of two sliding rails attached together • • • Weight acts at the center of gravity (3.85 inches from the wall, 1.90 feet from the bottom of the assembly) Normal force from board, Nx is 11 lbs and acts at the center of the eraser (3.5 feet from the bottom of the assembly) Reactions calculated by summing forces and summing moments about a fixed point Fy 0 A y B y W Fx 0 N x A x B x M B 0 ( A x 5 ft ) ( N x 1.5 ft ) (W 3.85 12 ft ) Reaction Value (lbs) Ax 4.23 Bx 1.27 Ay 2.95 By 2.95 Possible points of failure Shear Analysis on the wheels Side View Front View Track Wheels Support Attachment Top View Wheel Support Area of the wheels under shear Shear stress on the wheels due to weight Area of one wheel under shear, Aw = 0.1266 in2 Total Area under shear, A T,w = 0.5063 in2 Shear stress due to Normal force, τN = Fs,W / A T,w = 5.825 psi Shear strength of Nylatron, Sy = 10,500 psi Factor of safety for the wheels, n = 1803 Fs,N = 2.950 lb Area of the wheels under shear Shear stress on the wheels due to Normal Force Area of one wheel under shear, As = 0.0765 in2 Total Area under shear, A T,s = 0.3061 in2 Shear stress due to Normal force, τN = Fs,N/ A T,s = 13.816 psi Shear strength of Nylatron, Sy = 10,500 psi Factor of safety for the wheels, n = 760 Fs,N = 4.229 lb Area of the wheels under shear Horizontal Torque Requirements 4.5” ID Pulley Treq = 2.6 lb-ft Motor Fmax, tension = 7 lbs. • Required Torque calculation: T = Fmax tension due to friction·rpulley = (7 lbs.)(2.25 in.) = 15.75 lb-in = 1.3 lb-ft Treq = 1.3 lb-ft minimum Vertical Torque Requirements • Required Torque calculation: T = Fmax(friction+weight)·rgear = (12 lbs.)(1.875 in.) F = 7 lbs. = 22.5 lb-in Motor = 1.875 lb-ft friction 3.75” ID Gear Fweight = 5 lbs. Fweight = Weight of Motor Assembly (3 lb est.) plus Eraser Backing (2 lb est.) Treq = 1.875 lb-ft minimum Motor Analysis Supplier Motor Number Motor Name Description Stall Torque (lb-ft) Free Speed (rpm) Free Speed (rad/s) Torque at Peak Power, 10.5 V Supply (lb-ft) 12 0.477 24000 2513 0.209 1100 1.81 5342 559 0.789 244 56.8 133 13.9 25.1 6.1 0.182 9390 983 0.0811 429 9.59 3.4 Ref. Volt age FisherPrice 745500642 Power Wheels Motor only CIM FR801-001 (Chiaphua, Atwood) Keyed output shaft, ccw 12 12 FisherPrice 745500642 Power Wheels Motor and gearbox Globe 409A586 2WD/4WD transfer mtr. Motor only Sliding (van) door Worm Gearmotor 10.5 2WD/4WD transfer mtr. Planetary Gearmotor 12 Window Lift Worm Gearmotor 12.6 Taigene Globe NipponDenso 16638628 409A587 E6DF14A365-BB Gear Ratio 181 12 Minimum Torque Requirements: Horizontal Sliding = 1.3 lb-ft Vertical Sliding = 1.875 lb-ft 22.1 117 75 7.9 Speed at Peak Power, 10.5 V Supply (rad/s) 9.59 80 8.4 4.79 3.7 6.79 92 9.6 2.95 4.1 Motor Analysis Supplier Motor Number Motor Name Description FisherPrice 745500642 Power Wheels Motor only CIM FR801-001 (Chiaphua, Atwood) Keyed output shaft, ccw Power Wheels Motor and gearbox Globe 409A586 2WD/4WD transfer mtr. Motor only Sliding (van) door Worm 2WD/4WD transfer mtr. Planetary Gearmotor Window Lift Worm Gearmotor Globe NipponDenso 409A587 E6DF14A365-BB Free Speed (rpm) Free Speed (rad/s) MINIMUM TORQUE NOT 12 1.81 5342 MET 559 745500642 16638628 Gear Ratio Stall Torque (lb-ft) MINIMUM TORQUE NOT 12 0.477 24000 MET 2513 FisherPrice Taigene Ref. Volt age 12 181 56.8 133 13.9 MINIMUM TORQUE NOT 12 0.182 9390 MET 983 BULKY COMPARED TO GLOBE Gearmotor 10.5 22.1 75 MOTOR 7.9 12 117 9.59 80 8.4 FACTOR 12.6 OF SAFETY 6.79TOO92SMALL 9.6 Minimum Torque Requirements: Horizontal Sliding = 1.3 lb-ft Vertical Sliding = 1.875 lb-ft Torque at Peak Power, 10.5 V Supply (lb-ft) Speed at Peak Power, 10.5 V Supply (rad/s) 0.209 1100 0.789 244 25.1 6.1 0.0811 429 9.59 3.4 4.79 3.7 2.95 4.1 Horizontal Sliding: speed, high torque Vertical Sliding: small, light weight Motor Analysis Motor Number Motor Name FisherPrice 74550-0642 Power Wheels Globe 409A587 Supplier 2WD/4WD transfer mtr. Gear Ratio Stall Torque (lb-ft) Free Speed (rpm) Free Speed (rad/s) Torque at Peak Power, 10.5 V Supply (lb-ft) Speed at Peak Power, 10.5 V Supply (rad/s) 12 181 56.8 133 13.9 25.1 6.1 12 117 9.59 80 8.4 4.79 3.7 Ref. Volt age Motor and gearbox Planetary Gearmotor Description Free Speed Calculations: Across the board Fisher-Price: 6 . 1 rad 1 rev 4 . 5 in. in. 13 . 7 sec 2 rad 1 revsec Globe: Up/down board 3 . 7 rad 1 rev 3 . 75 in. in. 6 . 9 sec 2 rad 1 rev sec Can the cable subassembly overcome frictional forces without breaking? Proposed materials: Bicycle brake cable (steel) Rubberized Nylon cable Here, we will analyze the 5 mm cable with the lowest tensile strength to ensure a sufficiently high factor of safety for the stationary board. Weight considerations are largely ignored for this analysis as they not pertinent to the direction of motion. A distributed load of 7 lbf is applied against the direction of motion of the cable due to the board friction present. Thus the motor force must overcome the friction force. Since there are 2 pulleys (top and bottom) aiding the path of motion of the eraser, the stress on the cables is halved indicating that the cable tension in summation must overcome eraser assembly friction, pulley/bearing friction, and applied motor stress. Fx 0 Fm F m F f 7 lb 2 Fm 2 Ff 0 With the chosen motor (maximum torque of 34 N-m = 25.077 ft-lb.) at a distance of 2 ft, the cable has a F of S of at least 20 which is ample to ensure that the cable, even with the smallest tensile strength, will not stretch or deform and will definitely not snap. This means that cost can largely dictate the cable material that is chosen. Automatic Whiteboard Wiper • Next Time – Part Drawings • Prepare a complete set of part drawings – Must contain enough information so the part can be fabricated • Drawings are for the actual design, not for the prototype