Sarah-Rose LancasterMechanical 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

Internship Projects

Stress Monitoring WearableThe

TechnologyKey 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 Impedanc

e

Basic schematic diagram of an EDA

sensorEDA 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

Pebble Time Steel Microphone ModuleThe 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.

Model S and Model X Sun VisorThe 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.

Model S Air VentThe 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

iPad Pro Smart Keyboard ConnectorsThe 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 ContributionsSmart 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 TestingI 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.

School Projects

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

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

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

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.