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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
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