1. Sarah-Rose Lancaster
Mechanical Engineering Portfolio
• Will receive BS of Mechanical Engineering in June 2017,
seeking full-time employment starting afterwards
• Completed 3 internships at Apple, 1 at Tesla
and 1 at Pebble Technologies
• Experience working with tight packaging,
cosmetic constrains and extensive reliability specifications
3. Stress Monitoring Wearable
The Technology Key Contributions
Skin
resistance
across
electrodes
+
-
Voltage Measured
At Pebble I was tasked with implementing a psychological
stress sensor on a future product. The selected sensor,
known as an electrodermal activity (EDA) sensor, measured
the conductance of the user’s skin. Since sweating is a
reaction of the body’s sympathetic nervous system,
increases in the skin’s conductance could be related to an
increase in stress through algorithmic analysis.
Electrodes
Empatica’s Embrace
with EDA sensor
Voltage Applied
Known
Impedance
Basic schematic diagram of
an EDA sensor
EDA sensors apply a small voltage across electrodes in
series with resistive elements of known impedance. The
resultant voltage across the electrodes (which touch the
skin) is then measured to determine the skin’s resistance,
and thus its conductance. As such, one of the most
important factors in the design of an EDA sensor is the form
factor of the electrodes.
Jump Scares Walk
Lying
Down
Ru
n
Prototype 2
(Back)
Prototype 1
(Back)
I researched state of the art
EDA sensors and connected
Pebble with several experts in
the field. I prototyped initial
form factors of sensors and ran
preliminary tests on the
reliability of their
measurements.
The above graph shows skin conductance vs time for the
“Prototype 2” device. The test involved the user remaining
still for 5 minutes and then watching a series of “jump-
scare” videos. Certain peaks in the graph correspond to the
user being scared. The user then walked, lied down, and
ran on a treadmill. Although preliminary data contained
motion artifacts, it confirmed that ”Prototype 2” was
adequate for accurate conductance measurement.
Electrodes
4. Pebble Time Steel Microphone Module
The Product Key Contributions
Pebble Time Steel makes uses of a microphone for text
reply and voice commands in certain apps.
Microphone
Module
Hole Insert
(Welded)
Drilled Holes
Microphone
Bracket
The microphone module is held snugly against the housing’s
mic opening through the use of a U-shaped bracket. The
bracket is secured to the housing with screws, one of which
is placed in a welded hole insert that adds significant
manufacturing costs.
Original
I re-designed the mic bracket to
eliminate use of the welded hole
insert, reducing manufacturing
costs. I explored two designs.
New One Screw Design
New Two Screw Design
The one screw design eliminated the use of one of the
drilled holes as its right side was secured by ”digging” into
a wall of the housing.
After drop testing, the two screw design outperformed the
one screw design, which came loose after ~7 1m drops
on concrete. The two screw design was used.
5. Model S and Model X Sun Visor
The Products Key Contributions
Model X Visor Reliability Testing
The Model X sun visor is unique in that it attaches to the
A-pillar of the car instead of the headliner (due to the X’s
panoramic windshield). It features a secondary blade that
flips down for extra coverage, as well as a sleek mirror
and vanity lights, concealed by a smart cover.
The Model S Sun Visor attaches to the headliner and has
a plastic cover that conceals a mirror. The visor is
currently without vanity lights.
Model S Visor Vanity Lights
Since the visor is a long, slim, cantilevered beam, it
required extensive testing to ensure it would not fail in the
field. I developed several test fixtures and procedures
which tested both the haptic and strength performances
of the visor. Of note were novel tests co-relating what a
user “feels” while using the visor to quantitative data. The
test results I obtained were used to improve the visor
manufacturing processes and obtain a better quality
product.
I developed the initial CAD and prototype for a Model S
Sun Visor that uses a smart-cover to conceal a mirror and
vanity lights. The design had to fit within the existing sun
visor shape and packaging. I gained valuable skills
working with surfacing in CATIA during the project.
I was given a timeline of only 2 weeks and managed to
impress my manager with my progress despite also
working on other projects simultaneously.
6. Model S Air Vent
The Product
The Model S air vent features a design that uses the air-
vent control knob, instead of a scroll wheel, to shut off air
flow.
Key Contribution
Improving Haptic Feeling of Control Knob Movement
The vent uses a mechanism to open and close a door at its
rear that controls air flow.
Due to the engagement of two gears at the mid-point of
the knob’s sideways movement, adjusting the air flow
direction lacked a feeling of smoothness. The
engagement of the gears would cause the amount of
force required to be higher than when the gears weren’t
engaged. I was tasked with improving the smoothness
without changing the overall design of the vent.
To achieve a smooth feeling I focused on making the
amount of effort required to move the control knob itself
higher. I broke the knob down into its individual
components and modified each until the perfect “feeling”
was found. I then worked with the air vent supplier to
translate these modifications into injection molding tool
changes to create a new air vent.
Control knob
Gears
7. iPad Pro Smart Keyboard Connectors
The Product
Apple’s iPad Pro has a Smart Keyboard accessory which
attaches magnetically through a 3-pin connector.
The 3-pin connectors on both the iPad Pro and Smart
Keyboard feature a sleek design. Working on Apple’s
Interconnect Design group I was able to contribute to both
connectors.
Key Contributions
Smart Keyboard Flex Cable
I designed the section of the keyboard’s flex cable which
sends the keyboard signals to the keyboard’s connector. A
challenging project due to tight space constraints and the
need to meet electrical engineering requirements.
Connector Reliability Testing
I developed several reliability tests for the connectors,
determining performance parameters such as corrosion
resistance and average connector contact force. The results
I provided drove design changes which led to improved
connector performance.
9. Echo – Technical Art Project
Echo is a project I completed with a partner for
Waterloo’s Technical Arts course. Echo re-
creates the sound of a heart ultrasound using a
combination of sounds from found objects.
Sheet metal in struck (bent)
position
Echo uses a combination of four actuated objects to re-create the
sound of a heart beat. A piece of sheet metal is struck to create a
whooshing sound as it bends. The glove rotates 180º and strikes the
balloons, creating a thumping noise. The box opens and closes using a
circular cam mechanism, creating a beating noise. Finally, the broom is
moved back and forth along a wooden surface using a belt and pulley,
creating a brushing noise.
Each mechanism is actuated with 180º servos that are controlled by an
Arduino Uno. The entire system begins movement once a proximity
sensor senses movement within 4ft of the piece.
Sheet Metal
Glove + Balloons
BoxBroom Proximity
Sensor
Sheet metal actuator
10. Elevator Installation Hoist System
Cambridge Elevating, located in Cambridge,
Canada, designed an electric elevator system
that uses a motor and winch assembly to lift an
elevator cab up and down a rail system. The
motor and winch assembly, which is fixed to the
top of the elevator shaft, weighs approximately
350 lbs. and the elevating company lacked a
safe method of installing it.
Working with three other students I conceived,
designed and performed detailed analysis on
an installation system for the motor and winch
assembly. The motor and winch assembly are
fixed to a small shelf that is pulled up the
existing elevator rails by a cable actuated with a
small winch and pulley. Once at the top, the
assembly is pushed onto a holding bracket and
secured.
Motor and Winch
Assembly
Shelf used
to lift
winch
assembly
Motor and Winch
Holding Bracket
Small Lifting Winch
Pulley
Attachment
for cable
connected to
pulley
Lifting
Cable
11. Elevator Installation Hoist System
The most challenging aspect of designing the hoist
system was the conceptual design phase, as the system
had several space and safety constraints to adhere to.
The system had to fit inside of a ~40 in wide elevator
shaft, of which only the back wall could bear any load.
The system also had to have a high factor of safety (>5
for any load bearing component) as well as at least 3
redundant safety features.
My major contributions to the project were developing
the idea to use a rail riding shelf to lift the winch
assembly and the detailed structural analysis of the shelf
itself. The structural analysis involved finding the
weakest points in the shelf assembly and performing
extensive calculations to determine at what loads they
would yield.
Rail Riding Shelf,
“Elbow” circled
Two of the most important considerations in the shelf’s structural analysis were the stresses in the bolted connections at the
shelf’s elbow (left), and the torsional load applied to the shelf due to eccentric loading of the shelf’s arms (FBD on right).
Extensive calculations were performed in excel which fed into an iterative design process that allowed the shelf to meet a
factor of safety of at least 5 at all critical stress points.
Second Bolt Added
12. Racecar Drag Reduction System
Working with a team of four other students I conceived,
designed and built a model of a drag reduction system for
Waterloo’s formula car. The goal of the system was to
adjust the angle of the racecars’ wings to either increase
down force or decrease drag depending on if the car was
cornering or in a straight-away.
I performed linkage synthesis
calculations to determine the
appropriate linkage dimensions. I also
performed fatigue calculations to
ensure the system would not fail.
Along with another team member I completed the
CAD for the drag reduction system. The final product, in both
the “up” and “down”
positions.
