Detailed Design Review
MSD P14045 12/5/13
Emily Courtney, John Daley, Alex Hebert,
Greg Roeth, Martha Vargas
Agenda
1. Addressing Previous Concerns
2. Engineering Requirements
3. Feasibility of Critical Areas
a. Wheel Adapter
b. Tray
c. Packaging
d. Electrical Systems
4. Bill Of Materials
a. Electrical
b. Mechanical
c. Totals
14045 Detailed Design Review – 12/5/13
7.
8.
9.
Risk Assessment
Test Plan
MSD II Plan
2
Addressing Previous Concerns
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LEGO Tray
o Contacted LEGO, ok to use as long as we do not profit.
iPad
o Dropped due to complexity/time constraints.
o May include a recommendation for future generations.
Actuator
o Cost too high
o Could not determine a viable solution within allotted time
 Changed to a Manually operated tray folding mechanism.
Acceleration/Deceleration
o Ramp-up mechanism included in software.
Straight Travel (tires/wheel similarity)
o Added encoder functionality to motorized wheels in order to create a
feedback system.
o Sensitivity tests added to the test plan.
14045 Detailed Design Review – 12/5/13
3
Engineering Requirements
Go to the Document!
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4
Feasibility of Critical Areas
1. Wheel Adapter
2. Demonstration of Tray
3. Demonstration of
Battery Box
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Wheel Adapter
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Critical areas turned out to be the top and
bottom of the fillet near the step.
Stress on critical locations converged to
within 6% of calculated values.
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ANSYS Results - in Detail
Maximum Stresses:
Blue Stander: 12,905 psi
Red Stander: 12,374 psi
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Issues:
If we 3D print these parts, this stress exceeds the maximum tensile stress
of ABS Plus (5300 psi)
Impact force greatly varies with impact time. These values based off an
impact lasting 0.05 sec.
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Impact Analysis
I will need to determine the
actual impact time for
dropping the stander to
properly estimate stress.
However, this is all academic
because...
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Cost Analysis
The Cost of creating the four required parts makes manufacturing infeasible.
3D printing all parts @ $15/in3 = $457.50
CNC is $95/hr
o Rate is for both programming and machine run time
o Does NOT include material cost
o Time for 4 parts and the necessary programming would easily make
the cost meet or exceed the break-even point with 3D printing.
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•
Best option:
Contact R82 (stander manufacturer) and get replacement adapters.
Do a better job machining the parts to fit the current setup.
Keep this design as a theory for the kit we would make.
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Tipping Analysis
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Updated 13045 Results
2 Dimensional Analysis
Assumptions:
no slipping
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Case 1
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Case 2
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Demonstration of Tray
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Demonstration of Tray
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Tray Mounting System
Current attachment:
New attachment piece:
* Fits snuggly inside the
slot for greater stability
and adjustability
top view
14045 Detailed Design Review – 12/5/13
side view
* Thumb screws will
anchor outer bracket
through this piece to
center
16
Tray Bracket
side view
front view
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http://www.adjustablelockingtech.com/products_variloc_stainless_mounting-flange_dimensions.php
Tray Deflection
Analyzing the tray as a beam in
bending, we calculated a
maximum expected
deflection for the end of the
tray.
The maximum expected
deflection is 0.044 inches if
the tray is pushed down by a
force of 110 lbf.
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Demonstration of Battery Box
Total Area = 252.75 in2
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Battery Box
We are still working to determine the material for the box
Most likely a plastic
•
We are also unsure on manufacturing
Make it ourselves?
Outsource?
o Need to analyze cost & labor
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•
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Electrical System
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Schematic
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Power
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12V battery
Launchpad takes +5v through USB micro B
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o Gives output of 3.3V
Each Launchpad takes .9A
Each HB-25 can take 25A continuous
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3.3 V - Quadrature Encoders, HB-25, Temperature Switch, Bump Sensor
5V - Launchpad
12V - HB-25 (motor voltage)
Worst Case Power: 325W
o
(With a current draw of 12A in each motor)
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Processors
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Original Project used Stellaris Development board
o turned into the stellaris launchpad
o turned into the Tiva C launchpad
Same RAM and Flash memory
Has plenty of GPIO channels, 2 QEI modules,
2+ UART, 3+ GP timers,
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Software
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Written in C
Monolithic loop
Uses Tivaware extensively
o Will require rewriting portions of the code

syntax not algorithm
o Codebase was cluttered
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Software Flowchart
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Controls
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Addition of Quadrature Encoders
o Position capture
o Enabled by Tivaware
Master Wheel Speed
o Incremented or Decremented each update by a standard
acceleration
Set Slave wheel speed
o Straight:
 SlaveSpeedOffset= k(Pm-Ps)
o Turning:
 SSO= k(Pm-(Ps-Of)
 Of=Of-1+tr
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Motor Drivers
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Kit from Parallax
HB-25 takes servo motor controls
o Pulse width determines position
Uses PWM6 and PWM7
o 100ms period
Digital power off 3.3V from launchpad
*image from www.parallax.com
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Communication
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Considered
o Bluetooth - Bluegig wt12
 dropped due to complexity and cost, and drop of iPad
functionality, requires a breakout board
o Electric Imp
 dropped because overkill and dependance on wifi
o Xbee
 dropped requires a breakout board
RC transmitter and receiver
o separate module, stands alone, does some self sanitising inputs
o requires interpretation
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B.O.M. for Electrical
Description
Price
Stellaris Launchpad
$7.99
0
$0.00
Touchscreen Overlay
$81.51
1
$81.51
RC Transmitter
$64.99
1
$64.99
Controller for Touch Screen Overlay
$78.66
1
$78.66
RC Receiver
$5.89
1
$5.89
36-Position Quadrature Encoder Set
$39.95
0
$0.00
Project Boxes
$3
1
$3.00
HB-25 Motor Controller
$49.95
0
$0.00
Potentiometer
$1.02
1
$1.02
Wheel Mount Kit
$299.00
0
$0.00
Potentiometer Knob
$1.73
1
$1.73
12V 20AH Lithium Ion Battery
$70.00
1
$70.00
USB cable - Micro B(m) to A-female
$4.1
1
$4.10
Temperature Switch
$1.00
1
$1.00
USB cable - Micro B(m) to A male
$3.66
1
$3.66
Keypad Membrane Switches (Stander)
$41.00
0
$0.00
12V to 5V regulator
14045 Detailed Design Review – 12/5/13
$2.83
Qty. Total Cost
1
Total:
$318.39
$2.83
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B.O.M. for Mechanical
14045 Detailed Design Review – 12/5/13
Description
Price
Qty.
Total Cost
Brace
$115.00
1
$115.00
Caulk
$12.00
1
$12.00
Spacing stud
$1.73
1
$1.73
Material for Battery box
$100.00
1
$100.00
Epoxy
$5.48
1
$5.48
Hinges
$6.00
4
$24.00
Latches for box (4pc)
$4.40
1
$4.40
Flat bellows (pinch point cover)
$25.64
1
$25.64
Total:
$288.25
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B.O.M. Totals
14045 Detailed Design Review – 12/5/13
Already Spent
$496.00
ME To-purchase
$288.25
EE to-purchase
$318.39
TOTAL:
$1,102.64
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Risk Assessment
Go to the Document!
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Test Plan
Go to the Document!
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MSD II Plan
Go to the Document!
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Questions?
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