Engineering Analysis Presentation
ME 4182Team: 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 AnalysisWeight Density [lb/ft3]
Mass Density
[slugs/ft3]
Yield Stress [ksi]
Ultimate Stress [ksi]
Modulus of
Elasticity E
[ksi]
Approximate Deflection
[in]
Aluminum 170 5.3 40 45 10000 0.0032
High Strength
Steel490 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
D L3 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 lbRack & Pinion ≈ 1 lbExtras ≈ 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
MB 0 (Ax 5 ft) (Nx 1.5 ft) (W 3.85
12ft)
Fx 0 Nx Ax Bx
Fy 0 Ay By W
Reaction Value (lbs)
Ax 2.03
Bx 3.47
Ay 2.95
By 2.95
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
Reaction Value (lbs)
Ax 4.23
Bx 1.27
Ay 2.95
By 2.95
Fy 0 Ay By W
Fx 0 Nx Ax Bx
MB 0 (Ax 5 ft) (Nx 1.5 ft) (W 3.85
12ft)
Possible points of failure
Shear Analysis on the wheels
Wheels
Track
Top View
Front View Side View
Wheel SupportSupport Attachment
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
Area of the wheels under shear
Fs,N = 2.950 lb
Area of the wheels under shear
Fs,N = 4.229 lb
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
Horizontal Torque Requirements
• 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 minimumFmax, tension = 7 lbs.
Treq = 2.6 lb-ft
Motor
4.5” ID Pulley
Vertical Torque Requirements
• Required Torque calculation:
T = Fmax(friction+weight)·rgear
= (12 lbs.)(1.875 in.)
= 22.5 lb-in
= 1.875 lb-ft
Treq = 1.875 lb-ft minimum
Fweight = 5 lbs.
Ffriction = 7 lbs.
Fweight = Weight of Motor Assembly (3 lb est.) plus Eraser Backing (2 lb est.)
Motor3.75” ID Gear
SupplierMotor
Number Motor Name Description
Ref. Voltage
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
74550-0642
Power Wheels
Motor only 12 0.477 24000 2513 0.209 1100
CIM FR801-001 (Chiaphua, Atwood)
Keyed output shaft, ccw 12 1.81 5342 559 0.789 244
Fisher-Price
74550-0642
Power Wheels
Motor and gearbox 12 181 56.8 133 13.9 25.1 6.1
Globe 409A586 2WD/4WD transfer mtr.
Motor only 12 0.182 9390 983 0.0811 429
Taigene 16638628 Sliding (van) door
Worm Gearmotor 10.5 22.1 75 7.9 9.59 3.4
Globe 409A587 2WD/4WD transfer mtr.
Planetary Gearmotor 12 117 9.59 80 8.4 4.79 3.7
Nippon-Denso
E6DF-14A365-BB
Window Lift Worm Gearmotor 12.6 6.79 92 9.6 2.95 4.1
Motor Analysis
Minimum Torque Requirements:
Horizontal Sliding = 1.3 lb-ft
Vertical Sliding = 1.875 lb-ft
SupplierMotor
Number Motor Name Description
Ref. Voltage
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
74550-0642
Power Wheels
Motor only 12 0.477 24000 2513 0.209 1100
CIM FR801-001 (Chiaphua, Atwood)
Keyed output shaft, ccw 12 1.81 5342 559 0.789 244
Fisher-Price
74550-0642
Power Wheels
Motor and gearbox 12 181 56.8 133 13.9 25.1 6.1
Globe 409A586 2WD/4WD transfer mtr.
Motor only 12 0.182 9390 983 0.0811 429
Taigene 16638628 Sliding (van) door
Worm Gearmotor 10.5 22.1 75 7.9 9.59 3.4
Globe 409A587 2WD/4WD transfer mtr.
Planetary Gearmotor 12 117 9.59 80 8.4 4.79 3.7
Nippon-Denso
E6DF-14A365-BB
Window Lift Worm Gearmotor 12.6 6.79 92 9.6 2.95 4.1
Horizontal Sliding: speed, high torque
Vertical Sliding: small, light weight
Motor Analysis
Minimum Torque Requirements:
Horizontal Sliding = 1.3 lb-ft
Vertical Sliding = 1.875 lb-ft
BULKY COMPARED TO GLOBE MOTOR
FACTOR OF SAFETY TOO SMALL
MINIMUM TORQUE NOT MET
MINIMUM TORQUE NOT MET
MINIMUM TORQUE NOT MET
sec
in.7.13
rev1
in.5.4
rad2
rev1
sec
rad1.6
SupplierMotor
Number Motor Name Description
Ref. Voltage
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
74550-0642 Power Wheels Motor and gearbox 12 181 56.8 133 13.9 25.1 6.1
Globe 409A587 2WD/4WD transfer mtr.
Planetary Gearmotor 12 117 9.59 80 8.4 4.79 3.7
Motor Analysis
sec
in.9.6
rev1
in.75.3
rad2
rev1
sec
rad7.3
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 = 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.
lb 7
022
0
fm
fmm
x
FF
FFF
F
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