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Blocks & Sketches: Prototyping in CAD

We are visual creatures. And in the world of engineering, that’s where prototypes come in.

Prototypes are, undoubtedly, one of the most useful things an engineer can use to begin the design phase of an engineering process.

A prototype is anything that allows a designer to capture more information on a potential solution to the problem they’re trying to solve. These can range from physical mockups, made crudely of wood and plastic, to more advanced models, constructed with 3D printed parts and laser cut parts. However, in recent years designers use powerful CAD (Computer-Aided Design) software to lock down important geometries and help begin performing systems integration.


Crayola CAD vs. Layout Sketches

Crayola CAD is the first form of crude 3D parts created in the 3D modeling world to illustrate what will later evolve into complex assemblies and linkages. The purpose is to simulate how different parts of a system will interact with each other, i.e., how they’ll move, slide, or pivot. A designer can easily see how those assemblies will “fit” with other objects outside the system or how they’ll interact with their surroundings.

Crayola CAD simulating interaction

For instance, if one had to design a drivetrain capable of traversing rocky, hilly terrain, the Rocker-Bogie system may work. In use since 1988 by NASA for their Mars Rovers, a quick sketch and prototype of the design in a piece of CAD software would show that it’s an elegant solution to a seemingly difficult problem.

Rocker Bogie Suspension Design GIF
Rocker Bogie Suspension Design

On the other hand, 2D Layout Sketches serve to visualize specific geometries and interactions between objects in the surroundings. If a designer was unsure of certain geometries, for example the angle an intake mechanism approaches an object,

2D sketches illustrated dimensions

2D sketches are one way of visualizing them. Whilst it may not be as fancy or colorful, they can make for extremely intuitive screenshots and explanations that communicate the required dimensions for a mechanism or system.

An Organic Evolution

As with most engineers, projects are all about iteration. CAD designs go through much iteration, evolving from solid-colored boxes to fully assemble-able designs complete with wiring and tubing. After measurements and design decisions are made, designers will often draw upon these often crude prototypes to better form their designs.

Among the many challenges engineers face, systems integration and layout is among the most difficult: getting your mechanism to work well in sync with others’. When working with a full engineering design team, it might sometimes seem like a game of Monopoly, trying to snatch up valuable real estate before other designers claim them for their designs. To more easily resolve, or better yet, avoid entirely, these issues, teams will rely on early prototypical Crayola CADs.

A very early prototype, contrasted with the final design

This isn’t to say, of course, that napkin sketches won’t ever see the light of day. Many a fine design was conceived on the back of an old test or on the whiteboard, and have been developed into much more fleshed out versions, going on to fabrication and assembly.


In Summary

An oft-shared adage among budding designers is “start with what you KNOW, then draw a guess of what you WANT, then refine things slowly based on what’s most important to you”.

Maybe in the beginning you only know the end goal, and draw a big block to represent that. But if all goes well, that solid colored block will evolve into something beautiful and complex before you know it.

CAD images courtesy of FRC Team 2637 Phantom Catz & FRC Team 148 Robowranglers

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