Speed Cam Enclosure
3D Printing Autodesk Fusion 360
Designing Manufacturable Containment for Embedded Electronics
In this project I leveraged my technical CAD design skills and my materials and manufacturing knowledge to create a secure enclosure for a raspberry pi doppler radar system and pi camera. Several iterations of the case were designed, with a final design for low-quantity production via 3D printing and a design for injection molding.
The impetus for this project was from a friend's alumni connection. This alumni, our “customer” , requested a method to monitor the speed of cars driving down his busy New York side street. Our customer suspected that a recent increase in car speeds was causing more bike accidents in what should have been a slower residential area of the city and wanted to be able to report speeding cars, especially delivery vehicles, to the police. Working closely with my classmate we devised a doppler radar system paired with a camera which would record footage only of cars going above a set speed. For this partnership I was tasked with creating a sealable, ergonomic, and secure housing for the embedded electronics (the raspberry pi pcb, short-range doppler radar board, miniature pi-camera, and battery pack).
I intentionally expanded this project past the single product necessary, using this project as an opportunity to expand my knowledge of manufacturing processes through designing a real-world feasible product.
The challenge of translating product and hardware requirements into robust mechanical designs that suitably and safely integrate electronic subsystems, straddles the line between product design and mechanical engineering. One must consider materials and manufacturing on one hand without neglecting the importance of human factors and use-case scenarios for the product (ergonomics, aesthetic, human interactions etc.). My approach to the product design process was inspired by The Mechanical Design Process by Ulman.
This phase of the design process involves determining the functions the product is meant to fulfil, based on the customer's problem statement, and the constraints (material, cost, etc.) on the products' design. The main functionality of the product can be determined fromthe customers problem statement
In defining the problem I also considered factors such as the target “market” and corresponding demand: in this case an eccentric man living in a busy city, but this product may have potential for broader applications and a broader market so I designed with mass-manufacturability in mind as well. Factors such as “lifespan” are also important when choosing materials and considering environmental impact (something only of hypothetical interest for this project, as I have no plans to actually mass-produced this product). To gain a more in-depth understanding of the key factors of this project I also performed a “pre-study” – researching and assessing what I determined to be the most impactful factors to be considered in this products design, namely seal design, materials and manufacturing, and the best practices for enclosing sensitive electronic components.
Seal design
For the purposes of this box, I investigated static seals; seals used between two stationary surfaces. The primary designs of static seals are either radial or axial. Axial seals are used in open-face type applications, while axial seals are common for cap and plug designs.
The main differentiating factor between these sealing mechanisms is the customization and cost of production. While gaskets come in myriad shapes and sizes, their production cost for custom die-cutting is higher. Although the O-ring’s simple circular design is a bit limiting, it was selected for this product because it is one of the cheapest methods of sealing a container for low-volume production.
Seal thickness should be seventy percent of the groove's thickness. More groove dimensioning.
Important to also consider rigidity or compression from deflection (CFD) of the material, especially in relation to the flexibility of the O-ring or gasket. More rigid materials should have proportionally strong rubber gaskets to create the proper seal.
Manufacturing Processes
Process and material must be factored into the design decisions following design for manufacture (DFM) guidelines; design simplification and design standardization are the two main principles to consider when designing a product to be manufacturable. The main criteria for selecting a manufacturing process relate to material, quantity of production, and cost. Plastic is suitably durable, and cheaper than most metal manufacturing processes so I compared the pros and cons of some of the more common plastic forming methods:
More on manufacturing processes: Formlabs Guide
I decided 3D printing best suited my production quantity and was also the most expedient and cost-efficient method for this project. Design for 3d printing also provides a lot of flexibility; undercuts and draft angles are of little concern, although as a result of this choice I did have to consider different finishing techniques to ensure a high quality and water-tight final product. For fun, I did design my part with appropriate draft angles and other DFM considerations that would be necessary if I were instead to mass-produce the product with injection-molding, although I only intend to 3d print the final product.
Materials
Factors to consider:
Design for sensitive embedded electronics:
Protecting and insulating electronics is the main goal when designing for electronics. Offsetting sensitive electronics with bosses is a basic practice when working with pc boards.
As previously discussed, a good seal is essential to this design. Water and condensation inside the enclosure can cause device malfunctions and damage components, and wind-blown dust and debris can penetrate devices and cause damage.
Additionally, making sure the case is well ventilated is especially important if your application includes rapid temperature swings: from environmental temperature changes or even internal temperature swings based on the electronics. These fluctuations can cause pressure build-up inside the enclosure and continuous stress to the seal. Over time, this allows ingress of water or other particles into the enclosure. Thus, venting prevents both condensation and pressure fluctuations and protect the sensitive electronics. For this factor I researched common industry practices and found a Gore-Tex valve used in a product with similar intended use conditions; Gore-Tex is a liquid repelling yet breathable membrane that would allow for air to permeate the enclosure but not moisture.
Design for embedded electronic systems is also dependent on the simultaneous development and testing of the electronic components themselves, so design that incorporates modularity makes for easier prototyping and more flexibility for embedded system development.
EVALUATE
Evaluation of either a prototype or a finished product must consider both consumer use-cases and industry standards. The design process is iterative, so the product may be redesigned and retested multiple times.
The more rigorous tests outlined below are the tests I ran on my product once I'd settled on a design that fulfilled all the basic use-case criteria:
National Electronics Manufacturers Association (NEMA) testing is a set of standards with a focus on protecting personnel and equipment and is commonly used for large industrial automation enclosures. The NEMA standards have multiple stages of classification. The most appropriate for this enclosure is type T4:
T4 comes with a set of material and design recommendations to help products meet this standard. For example, to make a container suitably water and weatherproof, strategic placement of fasteners, use of sealing screws, and/or latch-hinge combinations are recommended. Additionally, minimizing seams created during for the manufacturing process and use of non-corrodible but durable materials like aluminum. These standards were considered in the design of this product, though not strictly adhered to.
Ingress Protection (IP) is another common set of testing standards for product development. These standards hinge on quantifying dust, dirt, and liquid protection. There are two separate categories of protection for this standard; solids and water, whose ratings are combined into a two-digit number that represents the products overall resilience. For this project I targeted an IP55 rating; limited dust protection (type 5 solids) and limited splash and precipitation protection (type 5 water).
To meet IP and NEMA standards, products can be sent to get rigorously tested at testing facilities, but for this product I tested the prototypes at home with some variations on standard ingress tests.
The enclosure was placed under a running faucet with a flow rate of 1.0 GPM for 30 minutes. Tissue paper inside the box was used as a sensitive indicator of moisture ingress. This test was repeated for each side of the enclosure. Based on visually inspecting the test paper, no water permeated the boxes seal.
SELECT
During the process of selection one attempts to narrow down the concepts from the ideation phase, so that just a few may be explored in more depth. Decisions are made by weighing a variety of practical considerations.
BUILD
The build phase includes several sub-phases; depending on the complexity of the product, fabrication may require more than one prototyping phase and redesign for manufacturability. The end result is a useable product.
Prototype I: Rectangular Box with Snap Lid
Initial phases of design were focused around creating a quick housing to accelerate embedded system and software testing. I designed and 3d printed a simple rectangular box design that would securely house the electronic units during the early phases of indoor testing, with the radar and camera aimed out a window.
Prototype II: Rectangular Box with Hinge & Clamp
Tried to correct for difficult snap tolerancing and fit by adding a more adjustable clamp closure. Also tried to reduce tension on wires and connections when the box is open by attaching the lid to the box. To solve the O-ring issue I also tested gel-glue as an O-ring alternative: I lined the seal-groove with a thin bead of jelly-like water-proof caulking glue that I hoped would form a seal with the lid like a regular gasket.
Prototype III: Cylinder Design
Tried to embrace the DFM principles of simplicity: this design prioritized the reduction of parting lines and moving parts.
• Opted for axial design·
• Rethought the ease-of access element of the design
IDEATE
The focus of the ideation phase is creativity. An emphasis is placed on quantity and variety of ideas one can produce in order to explore all the possibilities that fit into the previously defined constraints/objectives framework. Took all of the above factors, and designed with the user in mind; with an eye for ergonomics and aesthetics as well as the factors previously discussed
The final printed product and the final product design are documented and diagramed below.
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This diagram showcases the real-world deployment of this unit. The design is intentionally somewhat bland, so it does not attract attention, however, as a precaution against meddling, it also has a hole suitable for a traditional combination lock. A lock can be employed to secure the main unit to the mounting housing which can be secured to a post with metal zip-ties.
Of course, because it is only made of plastic, it could still easily be smashed and stolen with a baseball bat or pair of metal pliers, but I think that is also true of most otherwise secure structures such as mailboxes and cars.
This view of the electronics unit highlights the stackable and modular nature of the design; each piece of the embedded system is screwed into bossed holes set into a separate shelf. There is ample room between the shelves and the walls of the containment for cables and wires connecting these units, but each shelf can also be separated from the others to make the system more accessible. Additionally, should the configuration or parts in the system change, a new shelf can be custom designed and integrated without redesigning and reprinting the entire enclosure.
