Respecting Coffee Cans & Legos
Building Early Mockups and Prototypes to Answer Engineering Questions
I had just succeeded in building a tiny in-house prototyping space to house hot glue, foam board, balsa wood, Legos, etc. for engineers in the mechanical engineering department to build mockups and tinker with ideas. I was working on the early proposal phase of the Insight Lander mission to Mars, and was tasked with developing a workable concept for a seismometer windshield. The Mars Lander would use a robotic arm to place the seismometer on the Martian surface. The windshield would be a cover, placed over the seismometer, and conform to the rough Martian surface to seal against wind noise. Had the experiment been run on Earth, there would have been an array of seismometers buried deep in the ground, where it could measure earthquakes and not wind noise. However, with the current robotic limitations and power challenges of digging a big hole on Mars, we had to deal with non-ideal potentially rocky and uneven surface location of the seismometer and just try to keep the environment as quiet as possible.
I consulted our softgoods guru, and snagged samples of space rated and potentially space rate-able blanket materials. Then I needed to see how they would drape over rocks and a generally irregular ground surface. To run the test I snagged an empty coffee tin, and threw together a functional mockup with hot glue, fabrics, weights, and Styrofoam balls as stand-ins for rocks, and took some photos. Conclusion? We’d likely need added weights in the bottom of the textiles, and we might need to certify a new, more flexible fiberglass textile, rather than our usual MLI (space blanket) materials which were too stiff. Total material cost? Something under $30.
Early mockup used to determine fabric draping and flexibility on spherical and flat shapes.
But it’s a coffee tin! It looks like a craft project!
Yes. Someone could have spent $3000 developing a fancy shiny rig (sans coffee tin) to do the same thing, but why? The test drove the need, and the need could be satisfied with the available inexpensive materials.
We later did spend a more significant amount of money to build a properly scaled, very nice looking Mars-mass simulation of the full windshield design to determine the dynamics of the robot arm lifting the cover and functionality of a custom magnetic latch in a Mars sandbox testbed. At this point, it should be noted, the design was mature enough to build a scaled functional model. The model utilized composites and other flight-like materials in order to match scaled mass and CG (center of gravity). The test drove the need for the fidelity of the model.
Mass-model functional prototype of early windshield concept.
Often, but not always, the best tools for trying out a concept are inexpensive and readily accessible. I keep a large kneaded eraser and a tub of PlayDoh in my desk at most times to quickly build up and explain a form. Sometimes hotglue foam board and poster board are better tools. When figuring out and communicating mechanisms (which are best seen and felt while in motion), I prefer Lego Technic mechanisms sets and K’nex (which work fantastic for modeling gantry operation). My favorite Lego mechanism set is the Lego Educational Simple Machines and Mechanism set, which is mostly gears, gearboxes, and linkages (see photo below). I’ve taken apart an old CD ROM drives or printers to pull out an existing mechanisms to play with, and reverse engineer. When a design is really straightforward, I’ll go direct to a process known as “McMaster engineering”, where engineers build an entire assembly using off-the-shelf parts from a hardware store.
Fail Early, Fail Often.
Again, the goal is to quickly brainstorm, evaluate, share, or conceptualize an idea, without spending more money than the idea is worth. Failing early (finding out an idea won’t work early on) means cost and time savings down the road. Whether you like using toys, craft materials, Erector sets, wood, or bits from the store, that’s the end goal. You’ll find stories of the “Grey Beards” in the good old days doing the same thing, building parts of Mars Rovers and rockets in their garages.
Do the ideas developed in Legos always work? Nope. That’s where the real engineering comes in. Loads, clearances, bearing design, tolerances, environments, materials, physics, manufacturability, etc. need to be considered in a solid design. The depth of which those are considered depends on the application and what the customer’s engineering needs are.
In summary, don’t mock low fidelity prototypes. And go buy yourself some toys. You can pretend it’s for your/someone else’s kids if it makes you feel better. They’ll make you a better designer, engineer, and communicator.
