Senior Design Project Data Sheet
Project #
Project Name
Project Track
Project Family
P13203
TigerBot Extension
Humanoid Platform
TigerBot
Start Term
Team Guide
Project Sponsor
Doc. Revision
Winter
2012
Prof. Slack
Dr. Sahin
1
Project Description
Project Background:
The purpose of this project is to design a humanoid robot
with various features. This project is the fourth iteration of
its kind, with two previous iterations already completed and
one currently in progress. The first two iterations were not
capable of continuous walking, so the main goal of this
iteration is to create an autonomous robot that can walk.
Problem Statement:
The main objective of this project is to design a humanoid
robot that is capable of balancing on its legs, and is able to
walk. The robot should also be able to respond to voice
commands, avoid obstacles, and pick itself up from a fall.
Objectives/Scope:
1.
2.
3.
4.
Robot is able to walk on its own
Robot is able to maintain balance while walking
Robot responds to voice commands
Robot will be able to pick itself up from a fall
Deliverables:




A functional robot meeting the project needs
Concepts and sketches of robot design
Electrical diagrams of robot electronics
Software for robot functionality
Expected Project Benefits:


Gather interest from potential students
Basis for expansion and future iterations
Core Team Members:








Mohammad Arefin
Geoffrey Herman
Michael Lew
Sean Lillis - Project Manager
James O'Donoghue
Brian Stevenson
Thomas Whitmore
Daniel Wiatroski
Strategy & Approach
Assumptions & Constraints:
1.
2.
3.
4.
The team must have an understanding of robotics and
what makes a humanoid robot
The robot must not be too heavy to move properly
The amount and type of electronics used must not be
too heavy to interfere with the robot's ability to walk
The budget of $2500 limits the choices of equipment,
potentially causing less efficient equipment to be used
Issues & Risks:



Servos do not have enough torque to move limbs
as needed
Difficult to fabricate joint brackets and 2DOF
housing boxes
Potential issues with press fit joint assemblies
KGCOE MSD
Detailed Design Review Agenda
P13203: TigerBot Extension
Meeting Purpose
1.
2.
3.
4.
Present execution of design concepts
Confirm feasibility of design
Discuss build strategies moving forward with project
Get design approval to go ahead into MSDII build
Materials to be Reviewed
1.
2.
3.
4.
5.
6.
7.
Complete CAD Design
Joint Assembly
Structural and Stress Analyses
Joint Torque Requirements/ WeBot Simulations
Shell Design and Integration
Bill of Materials
Risk Assessment
Team Members: Mohammad Arefin (EE), Geoffrey Herman (ME), Michael Lew (ISE), Sean Lillis (CE),
James O'Donoghue (CE), Brian Stevenson (EE), Thomas Whitmore (ME), Daniel Wiatroski (ME)
Meeting Date: February 15, 2013
Meeting Location: Room 17-2510
Meeting time 2:00 – 4:00 pm
Timeline
Meeting Timeline
Start
time
2:00
2:05
2:10
2:30
2:40
3:10
3:35
3:40
3:45
Topic of Review
Project Introduction
Complete CAD Overview
CAD Detail on Joint Assembly
Shell Design and Integration
Structural And Stress Analysis
Joint Torque Requirements / WeBot Simulation Results
Bill of Materials
Risk Assessment
Q&A
Required Attendees
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Dr. Sahin, Prof. Slack
Overall Design_______________________________________________________________
Exploded View - Typical Radial Loaded Joint (Knee shown)
Upper Knee Bracket
1/16” Spring Pin
Servo Output Shaft
Plastic Spacers
M5 Fasteners
XQ Servo
M4 Fasteners
Radial Ball Bearing
Servo Horn
Bronze Thrust Washer
Bronze Flanged Bushing
Lower Knee Bracket
Exploded View - Typical Thrust Loaded Joint (Pelvis/Hip Twist shown)
RoBoard Servo
Pelvis Plate
Plastic Spacers
½” Hex Nut
#1 Machine Screws
½” OD Threaded
Hollow Tube
Thrust Ball Bearing
1/16” Spring Pin
Hip Bracket
Servo Horn
Servo Output Shaft
M5 Fasteners
Close up View - Shoulder Joint
Close up View – Upper Arm/Elbow Joint
Close up View – Ankle Joint /Foot
2DOF Housing Box Internals (Hip Joint shown)
Close up View – Upper Leg
Industrial Engineering Shell Design
Stress Analyses______________________________________________________________
Overall Assumptions:




All limb masses calculated assuming solid aluminum rod of OD 0.5" (conservative over-estimate)
Foot has mass of Joint Bracket
2D Housing Box has mass of Joint Bracket
Joint bracket mass from 6" X 2" X .125" sheet Al
System Parameters:
Limb Linear Density (high estimate)
OD
ρ (Aluminum)
Linear Density (mass/length)
Assumed Component Masses
Torso Enclosure (from Mike)
Torso Internal Components
Head Shell
Arm Shell (for each segment)
Leg Shell (for each segment)
XQ Servo (pelvis and below)
RoBoard Servo (arms)
Joint Bracket (2 per joint)
Pelvis Bar (2X Joint Bracket)
Bearings
Bearings per Joint
Shoulder
Elbow
Pelvis
Hip
Knee
Ankle
Limb Rod Lengths
Upper Arm
Lower Arm
Thigh
Shin
0.5
0.0127
2.7
2700
0.34202755
1.315
1.5205
0.113
0.057
0.091
0.177
0.07
0.064
0.128
0.005
in
m
g/cm
kg/m
kg/m
kg
kg
kg
kg
kg
kg
kg
kg
kg
kg
4
2
3
4
2
4
5.83
0.148082
4.48
0.113792
8.07
0.204978
7.17
0.182118
in
m
in
m
in
m
in
m
*NOTE: Limb rod lengths are pivot to pivot lengths, which are accurate representations of lever arms, but
conservative over-estimates of mass.
Projected Total Mass of Robot (from stress analysis assumptions) = 8.45 kg [18.63 lbs]
Actual Total Mass of Robot (from CAD) = 8.09 kg [17.83 lbs]
Arm stress analyses (include forces at key points)
Assumptions



Worst case compression is in high point in pushup
Worst case bending is low point in pushup
Weight of torso, head, and legs is near center of height
Buckling Calculations
Figure 1: FBD of arm
Bending Stress for upper arm
𝐵𝑒𝑛𝑑𝑖𝑛𝑔 𝑠𝑡𝑟𝑒𝑠𝑠 =
Moment ∗ 𝑂𝐷/2
(𝑂𝐷4 − 𝐼𝐷4 )
𝜋∗
64
𝑉𝑚𝑎𝑥 = 𝑠ℎ𝑒𝑎𝑟 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ ∗ 𝐴𝑟𝑒𝑎
Results
Pelvis Stress Analysis
Assumptions:
 Rigid Body
 All weight above pelvis is considered to be applied at the center of the pelvis
 Worst case for bending and deflection is when robot is standing on one leg
Shear Stress:
Figure 2: Free Body Diagram for shear stress
Pelvis
Masses
Torso
Arm
Servo
Mtot
Wtot
Shear Stress
F/A
3.1255
0.7696
0.177
5.0186
49.1826
185526.8689
0.185526869
kg
kg
kg
N
Pa
MPa
Note: Thrust bearing (6655K190) (turntable) is rated to 52 lbs, ~230 N. The load going through the
bearing will be minimal; maximum would be 49N.
Deflection:
a
Figure 3: FBD for deflection and bending
Deflection Calculations
Masses
M-leg
W-leg
1.643397496
16.10529546
kg
N
M-pelvis
W-pelvis
0.177652816
1.7409976
kg
N
Moment of
Intertia
2.42869E-10
m^4
-0.003852584
7.570119277
m
Nm
Deflection
M
𝜹=
𝑭𝟏 𝒂𝟐 (𝒂 − 𝟑𝒍) 𝑭𝟐 𝒍𝟑
−
𝟔𝑬𝑰
𝟔𝑬𝑰
Bending Stress:
Shear Moment Diagrams
13.6737
70
14
Shear
67.0289
Shear Force (N)
16
15.1402
60
12
Moment
50
10
40
8
7.5701
30
6
20
4
16.1053
10
2
0
0
0
0.05
0.1
0.15
0.2
Distance along the Pelvis (m)
Figure 4: Shear and Moment Diagram
Bending
I
y
M (internal)
Bending Stress
Max
Factor of Safety
𝝈𝒃 =
𝑴𝒚
𝑰
4.85739E-10
0.0015875
15.14023855
49481588.92
49.48158892
m^4
m
Nm
Pa
MPa
276
5.58
MPa
Internal Moment (N*m)
80
Thigh Limb Stress Analysis
Assumptions:

Worst case for axial stress in legs is when leg is straight and robot is balancing on one leg

All weight above hip joints (pelvis, torso, arms, etc...) considered to be applied at the hip joint

Weight of other leg also considered to be acting on top of balancing leg for worst case

Smallest Aluminum rod from McMaster used for axial stress calculations (1/4” OD, 0.035” wall thk.)

Worst case for bending is with thigh and shin parallel to the ground, on one leg
Axial Stress Calculations:
M-tot
7.30703374 kg
W-tot
71.60893065 N
OD
ID
A
0.00635 m
0.004572 m
1.52519E-05 m2
Stress (σ)
MaxStress
4695084.125 Pa
4.70 MPa
276 MPa
Deflection (δ)
1.39679E-05 m
Buck ling
C
E
Sy
I
k
l/k
(l/k)1
Pcr/A (Euler)
Ratio to S y
Pcr/A (Johnson)
ratio to Sy
1
68900000000 Pa
276000000 Pa
5.8363E-11 m4
0.001956171 m4
104.7853142
70.1972244
61932431.02 Pa
0.224392866 should be <.5
-31496406.74 Pa
-0.114117416 should be <.5
Bending Stress Calculations:
OD (in) Wall Thk (in)
0.25
0.035
0.375
0.035
0.875
0.035
0.25
0.049
0.375
0.049
0.5
0.049
0.75
0.049
1
0.049
0.625
0.058
0.5
0.065
0.625
0.065
0.75
0.065
0.875
0.065
1
0.065
ID (in)
0.18
0.305
0.805
0.152
0.277
0.402
0.652
0.902
0.509
0.37
0.495
0.62
0.745
0.87
*NOTE: Shear stress is
negligible, resulting in a
value of only 1.6 MPa for
the selected rod geometry
(due to the relatively low
shear force in the beam).
*NOTE: Maximum
deflection due to bending
occurs at the hip end of the
thigh, and has a magnitude
of 4mm from this analysis.
Rknee = 72.3 N
OD (m)
0.00635
0.009525
0.022225
0.00635
0.009525
0.0127
0.01905
0.0254
0.015875
0.0127
0.015875
0.01905
0.022225
0.0254
ID (m)
0.004572
0.007747
0.020447
0.003861
0.007036
0.010211
0.016561
0.022911
0.012929
0.009398
0.012573
0.015748
0.018923
0.022098
A (m2)
1.52519E-05
2.41193E-05
5.95888E-05
1.99622E-05
3.23766E-05
4.47909E-05
6.96196E-05
9.44482E-05
6.66543E-05
5.73086E-05
7.37766E-05
9.02446E-05
0.000106713
0.000123181
c (m)
0.003175
0.004763
0.011113
0.003175
0.004763
0.00635
0.009525
0.0127
0.007938
0.00635
0.007938
0.009525
0.011113
0.0127
I
5.8363E-11
2.2724E-10
3.3967E-09
6.8905E-11
2.8376E-10
7.4339E-10
2.7724E-09
6.9069E-09
1.7462E-09
8.9406E-10
1.891E-09
3.4457E-09
5.6826E-09
8.7264E-09
σmax (Mpa)
802.34132
309.1081
48.251486
679.58796
247.53796
125.98234
50.670617
27.118946
67.041535
104.75157
61.908809
40.77041
28.841232
21.464454
Shin Limb Stress Analyses
Axial Stress Calculations:
M-tot
W-tot
7.692141863 kg
75.38299026 N
OD
ID
A
0.00635 m
0.004572 m
1.52519E-05 m2
Stress (σ)
MaxStress
4942532.693 Pa
4.942532693 MPa
276 MPa
Deflection (δ)
1.30642E-05 m
Buck ling
C
E
Sy
1
68900000000 Pa
276000000 Pa
I
k
l/k
(l/k)1
5.8363E-11 m4
0.001956171 m4
93.09921965
70.1972244
Pcr/A (Euler)
78456130.69 Pa
Ratio to S y
Pcr/A (Johnson)
ratio to Sy
0.284261343 should be <.5
33265623.06 Pa
0.12052762 should be <.5
Bending Stress Calculations:
OD (in) Wall Thk (in)
0.25
0.035
0.375
0.035
0.875
0.035
0.25
0.049
0.375
0.049
0.5
0.049
0.75
0.049
1
0.049
0.625
0.058
0.5
0.065
0.625
0.065
0.75
0.065
0.875
0.065
1
0.065
ID (in)
0.18
0.305
0.805
0.152
0.277
0.402
0.652
0.902
0.509
0.37
0.495
0.62
0.745
0.87
*NOTE: Shear stress is
negligible, resulting in a
value of only 1.7 MPa for
the selected rod geometry
(due to the relatively low
shear force in the beam).
*NOTE: Maximum
deflection due to bending
occurs at the knee end of
the shin, and has a
magnitude of 3mm from this
analysis.
Rankle = 76.0 N
OD (m)
0.00635
0.009525
0.022225
0.00635
0.009525
0.0127
0.01905
0.0254
0.015875
0.0127
0.015875
0.01905
0.022225
0.0254
ID (m)
0.004572
0.007747
0.020447
0.003861
0.007036
0.010211
0.016561
0.022911
0.012929
0.009398
0.012573
0.015748
0.018923
0.022098
A (m2)
1.52519E-05
2.41193E-05
5.95888E-05
1.99622E-05
3.23766E-05
4.47909E-05
6.96196E-05
9.44482E-05
6.66543E-05
5.73086E-05
7.37766E-05
9.02446E-05
0.000106713
0.000123181
c (m)
0.003175
0.004763
0.011113
0.003175
0.004763
0.00635
0.009525
0.0127
0.007938
0.00635
0.007938
0.009525
0.011113
0.0127
I
5.8363E-11
2.2724E-10
3.3967E-09
6.8905E-11
2.8376E-10
7.4339E-10
2.7724E-09
6.9069E-09
1.7462E-09
8.9406E-10
1.891E-09
3.4457E-09
5.6826E-09
8.7264E-09
σmax (Mpa)
749.87237
288.89404
45.09609
635.14645
231.35027
117.74375
47.357022
25.345508
62.657368
97.901359
57.860295
38.104238
26.955165
20.060791
Joint Bracket Stress Analyses
The stress in a typical joint bracket was analyzed using the FEA analysis package within SolidWorks. The
joint axis holes in the brackets were constrained, and a force of 80N (representative of the total weight of the
robot) was applied along the limb axis (representing a case where this load was transmitted through a limb in
a vertical orientation).
Von Mises Stress Plot (0.090” Thk Plate shown)
Deflection Plot (0.090” Thk Plate shown)
Plate
Thickness (in.)
σmax
(MPa)
δmax (m)
0.125
0.0625
0.090
29
92
45
2.00E-05
2.00E-04
7.00E-05
Simulation Results
Results: For all of the Plate Thickness values simulated, the corresponding stress and deflection values were
quite low and very acceptable. However, as bearings will be press fit into these brackets, and the weight
reduction from going to the 1/16” plate is minimal, we have decided to use the 1/8” aluminum plate.
Bushing Stress Analysis:
Material: SAE 841 Bronze (Oilite), σyield = 75.8 MPa
ID
OD
A
Max Shear Load
Shear Stress
Factor of Safety
0.375
0.009525
0.5
0.0127
5.5421E-05
in
m
in
m
m2
80 N
1443492.75 Pa
1.44349275 MPa
52.5115212
*NOTE: Radial bearing for this assembly is rated to 1,148 lbs [5100 N]
Joint Torque Requirements____________________________________________________
Leg Lift:
Angluar Velocity - Leg Lift
5.00E+00
Body Twist
4.00E+00
RA-up
Angular Velocity (deg/s)
3.00E+00
RA-out
2.00E+00
RA-twist
1.00E+00
RA-elbow
0.00E+00
-1.00E+00 0
1
2
3
4
5
LA-up
-2.00E+00
LA-out
-3.00E+00
LA-twist
-4.00E+00
LA-elbow
-5.00E+00
RL-twist
-6.00E+00
RL-out
Time (s)
Leg Lift - Joint Torques
2,000
Body Twist
1,500
RA-Up
Torque (oz-in)
1,000
RA-Out
500
RA-Twist
RA-Elbow
0
-500
0
2
4
6
8
10
LA-Up
LA-Out
-1,000
LA-Twist
-1,500
-2,000
LA-Elbow
Time (s)
RL-Twist
Low Crouch:
Low Crouch - Joint Torques
400
Body Twist
RA-Up
200
Torque (oz-in)
RA-Out
0
0
2
4
6
8
10
12
-200
RA-Twist
RA-Elbow
LA-Up
LA-Out
-400
LA-Twist
LA-Elbow
-600
RL-Twist
-800
RL-Out
Time (s)
Angular Velocity - Low Crouch
6.00E+00
Body Twist
RA-up
Angular Velocity (deg/s)
4.00E+00
RA-out
2.00E+00
RA-twist
RA-elbow
0.00E+00
0
2
4
6
8
LA-up
LA-out
-2.00E+00
LA-twist
LA-elbow
-4.00E+00
RL-twist
-6.00E+00
Time (s)
RL-out
Pick Up:
Get Up (Front)- Joint Torques
2,000
Torque (oz-in)
Body Twist
1,500
RA-Up
1,000
RA-Out
RA-Twist
500
RA-Elbow
0
-5
-500
5
15
25
35
45
LA-Up
LA-Out
LA-Twist
-1,000
LA-Elbow
-1,500
RL-Twist
-2,000
RL-Out
Time (s)
Angular Velocity - Pick Up
3.00E+00
Body Twist
Angular Velocity (deg/s)
2.00E+00
RA-up
1.00E+00
RA-out
0.00E+00
-1.00E+00
RA-twist
0
10
20
40
RA-elbow
LA-up
-2.00E+00
LA-out
-3.00E+00
LA-twist
-4.00E+00
LA-elbow
-5.00E+00
-6.00E+00
30
RL-twist
Time (s)
RL-out
Currently the third iteration of the TigerBot does not have any gear reduction. Because our design is smaller
and lighter, if their robot works, then there is no need for us to have a gear reduction.
Bill of Materials
_________________________________________________
Risk Assessment
ID Risk Item
_________________________________________________
Effect
Cause
1
Budget is too low
Unable to purchase all the parts
we would like for the project
2
Stress in limbs
Excessive deflection of limbs
3
4
5
Servos will not have Robot will be unable to complete
enough torque
task
Battery life is too
short
Robot cannot operate for a long
period of time
Parts not arriving on Pushes timeline back making late
time
deliverables
Likelihood Severity Importance Action to Minimize Risk
Certain parts required for robot cost
more than budget allowed
3
3
Limbs can not handle load
2
2
Owner
9
Prove that we need an
increase in budget
Team
4
Thorough structural load
analysis
ME
Incorrect measurements were made /
wrong servos purchased
2
3
6
Accurately measure the
torque in servos / Webot
simulation
Consult with advisor /
customer
ME
Robot draws too much power
2
2
4
Poor planning / reordering parts that
were damaged or not in taken into
account / Lead time not taken into
account
EE
2
2
4
Research parts and know the
actual lead time per part
Team
6
Machining of parts
Pushes timeline back making late
deliverables
Unable to machine parts correctly
1
2
2
Design for simple
manufacturing
ME
7
Roboard has enough
power to process
information
The time to compute commands
will take too long
Unable to estimate the computing
power needed
1
1
1
Research capabilities of
Roboard
CE
8
Interfacing old code
and code structure
for Tigerbot v4
Increase time of coding
Unable to contact previous teams about
their code
2
2
4
Make early effort to get in
touch with last year's team
and start using the new
interface with the old code
CE
9
Circuitry
Burning chips
Servos drawing to much current
2
2
4
Test circuit
EE
10
Team
Communication
Cause unnecessary delays
Poor meeting structure / agenda
3
2
6
Have a set plan for each
meeting to know what needs
to be covered
Team
11
Time for Software
Calibration
Robot performance (walking,
balancing, etc.) would not be
ideal
Not enough time to test/debug code
2
2
4
12
Not Completing
WeBot Simulation
2
3
6
13
Walking Scheme
Misinterpreting what customer wanted
2
3
6
14
Voice Recognition
Not enough time to test/debug code
and sensor
2
2
4
Adaptor too expensive for our budget
2
3
6
Look for cheaper alternatives
ME
Robot will be unable to move
Fasterner design was not correct
1
3
3
Weld joints instead
ME
CNC capabilities too expensive for our
budget
Using correct press fit tolerance and
interference. Working within
constraints of joint brackets
2
3
6
Look for cheaper alternatives
ME
2
2
4
Test Assembly
ME
15
16
Output Shaft
Connection
Fasteners Will Not
hold the joints
Pushes timeline back making late Unable to understand WeBot Software
deliverables
and not asking for help
Unable to complete major
deliverable
Unable to complete major
deliverable
Unable to attach servos to move
joints
17
Make Housing Box
Unble to have the degrees of
freedom needed
18
Press Fit Assembly
Output shaft will take loading
Start debugging early, ensure
physical portion is completed
CE
on time
Asking for help to understand
how to use WeBot Software to Team
simulate robot
Understand how humanoid
does the walking scheme have Team
to be for the robot
Adjusting and testing voice
CE/EE
recognition system