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 5” 2” 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 Weight Density [lb/ft 3 ] Mass Density [slugs/ft 3 ] Yield Stress [ksi] Ultimate Stress [ksi] Modulus of Elasticity E [ksi] Approximate Deflection [in] Aluminum High Strength Steel Stainless Steel Polyethylene752.35N/A 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 = 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 · 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, N x 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 ReactionValue (lbs) AxAx 2.03 BxBx 3.47 AyAy 2.95 ByBy

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, N x 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 ReactionValue (lbs) AxAx 4.23 BxBx 1.27 AyAy 2.95 ByBy

Possible points of failure

Shear Analysis on the wheels Wheels Track Top View Front View Side View Wheel Support Support Attachment Area of the wheels under shear

Shear stress on the wheels due to weight Area of one wheel under shear, A w = in 2 Total Area under shear, A T,w = in 2 Shear stress due to Normal force, τ N = F s,W / A T,w = psi Shear strength of Nylatron, S y = 10,500 psi Factor of safety for the wheels, n = 1803 Area of the wheels under shear F s,N = lb

Area of the wheels under shear F s,N = lb Shear stress on the wheels due to Normal Force Area of one wheel under shear, A s = in 2 Total Area under shear, A T,s = in 2 Shear stress due to Normal force, τ N = F s,N / A T,s = psi Shear strength of Nylatron, S y = 10,500 psi Factor of safety for the wheels, n = 760

Horizontal Torque Requirements Required Torque calculation: T = F max tension due to friction ·r pulley = (7 lbs.)(2.25 in.) = lb-in = 1.3 lb-ft T req = 1.3 lb-ft minimum F max, tension = 7 lbs. T req = 2.6 lb-ft Motor 4.5” ID Pulley

Vertical Torque Requirements Required Torque calculation: T = F max(friction+weight) ·r gear = (12 lbs.)(1.875 in.) = 22.5 lb-in = lb-ft T req = lb-ft minimum F weight = 5 lbs. F friction = 7 lbs. F weight = Weight of Motor Assembly (3 lb est.) plus Eraser Backing (2 lb est.) Motor 3.75” ID Gear

Supplier Motor NumberMotor NameDescription Ref. Volt age 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) Fisher- Price Power Wheels Motor only CIMFR (Chiaphua, Atwood) Keyed output shaft, ccw Fisher- Price Power Wheels Motor and gearbox Globe409A5862WD/4WD transfer mtr. Motor only Taigene Sliding (van) door Worm Gearmotor Globe409A5872WD/4WD transfer mtr. Planetary Gearmotor Nippon- Denso E6DF- 14A365-BB Window LiftWorm Gearmotor Motor Analysis Minimum Torque Requirements: Horizontal Sliding = 1.3 lb-ft Vertical Sliding = lb-ft

Supplier Motor NumberMotor NameDescription Ref. Volt age 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) Fisher- Price Power Wheels Motor only CIMFR (Chiaphua, Atwood) Keyed output shaft, ccw Fisher- Price Power Wheels Motor and gearbox Globe409A5862WD/4WD transfer mtr. Motor only Taigene Sliding (van) door Worm Gearmotor Globe409A5872WD/4WD transfer mtr. Planetary Gearmotor Nippon- Denso E6DF- 14A365-BB Window LiftWorm Gearmotor Horizontal Sliding: speed, high torque Vertical Sliding: small, light weight Motor Analysis Minimum Torque Requirements: Horizontal Sliding = 1.3 lb-ft Vertical Sliding = lb-ft BULKY COMPARED TO GLOBE MOTOR FACTOR OF SAFETY TOO SMALL MINIMUM TORQUE NOT MET

Supplier Motor NumberMotor NameDescription Ref. Volt age 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) Fisher- Price Power WheelsMotor and gearbox Globe409A5872WD/4WD transfer mtr. Planetary Gearmotor Motor Analysis Free Speed Calculations: Fisher-Price: Globe: Across the board Up/down board

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. With the chosen motor (maximum torque of 34 N-m = 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