Background

I was assigned this project during my role as Prototyping Engineer at ThirdEye Gen Inc. Any proprietary information has been omitted. The main goal of this project was to design and create prototypes for the first and second phases of a defense proposal. The requirements of the proposal were to make a scope that could detect vehicles using a rgb camera, and overlay the scope view with given information using an augmented reality display. I successfully delivered the phase 1 and phase 2 prototypes, resulting in a $1.5 million contract being awarded to my company. The project had a tight timeline (10 days) and budget ($1500), which I met without compromising quality by working late nights (4am) every night, working 72 hours straight over the weekend, and even sleeping in the office at times.

Design

At a high level, the design consists of many of the internal electronics from the X2 augmented reality glasses, combined with simple optics into a rugged CNC'd Aluminum housing.

I was the lead engineer for this project and managed a team of two other engineers who developed the software and firmware. I was responsible for the electrical and mechanical aspects of the design, the fabrication of prototypes, as well as the assembly and testing of the final deliverable. I have outlined some of the key technical tasks below.

Electrical Component Placement and Mounting

• After disassembling several AR headsets, I realized the wiring harnesses would be a considerable constraint on the placement of components as many of the connections were extremely small and delicate and couldn't be altered, soldered, or otherwise modified by hand.

• Next, I modeled all electrical components and connections accurately in CAD.

• I designed and evaluated several possible component layouts. I rapidly tested the layouts using prototypes of varying fidelity - ranging from cardboard and ductape to high resolution FDM 3D prints.

• I evaluated the promising options and selected the optimal one by considering factors such as thermal management, impact resistance, strain relief, ease of assembly, and ease of repair.

Thermal Analysis

• In the AR headsets, the thermal management of the heat produced by the processors was already a known challenge that was compounded by the small form factor and ergonomic considerations required by the proposal.

• The initial idea was to mount the processor to the aluminum body of the scope and use the entire enclosure to aid in heat dissipation.

• Running a variety of thermal simulations indicated that the temperature increase inside the enclosure would exceed ideal operating temperatures and the processor would be throttled.

• Anticipating the need for a more powerful processor and longer battery life in the future iterations of the design, as well as potential high temperature operating environments, I created a low-power active cooling system.

• This system was put on a separate circuit to maintain timeline. The circuit featured a small low voltage fan, a LI-Ion battery, a battery charging/protection circuitry, a thermistor, and a simple proportional controller.

Heat Sink and Thermal Interface Design

• In order to improve thermal management, I designed a heat sink and thermal interface.

• The heat sink was optimized for the size, shape, and convective environment the processor was mounted in.

• The thermal interface was designed to mate the complicated surface geometry of the processor flush against the aluminum body.

3D Printed Prototypes

• In order to test a wide variety of designs, design elements, fit/tolerances, aesthetics, and mechanism, a large number of designs were 3D printed.

• The 3D printer setup included an Ultimaker S5+ with dual extrusion, an Ultimaker S3, and to increase the speed of iterations I brought in two of my personal 3D printers (Creatility Ender 3).

• The 4 printers were running nearly constantly for the 10 days of the project using materials such as PLA, PETG, Nylon, and TPU.

• In addition to 3D printing prototypes, the final assembly featured many 3D printed parts, such as mounts for optics, interface for buttons and data ports, and mount for AR display.

Silicon Molding

• To protect the user against eye damage caused by recoil, a squishy eyepiece was required

• The limited budget could not cover any custom rubber components and no off the shelf components could match the shape and size required

• I 3D printed a mold and cast a squishy eyepiece out of silicon (total cost = $15)

CNC Aluminum Body

• The material for the main body of the scope was chosen to be AL 6061

• The finalized design was modified to be manufacturable on a 4 axis mill to meet budget requirements

• I used CAM software from AutoDesk Fusion360 to program the CNC toolpaths

• I worked with a local machine shop, Draftek Designs, to minimize cost and mitigate potential shipping delays