Every other week, MAKE’s awesome interns tell about the projects they’re building in the Make: Labs, the trouble they’ve gotten into, and what they’ll make next.
By Kris Magri, engineering intern
Part I: The First Design
This summer I was given a once-in-a-lifetime opportunity to make a robot for the pages of MAKE Magazine (Volume 19, “My Robot, Makey”). As an intern, I had the inside scoop that an upcoming issue would focus on robotics. I talked with one of the editors, Goli Mohammadi, about including a step-by-step article showing people how to make their own autonomous robot from scratch, using an Arduino microcontroller. She took the idea to the rest of the crew, and they gave me a chance, asking for a draft article about the robot. I went into hyper-drive that weekend, designing and building a robot prototype in 44 hours over three days. This is a behind-the-scenes look at designing Makey.
The first thing I did was sketch ideas on paper. I based Makey on WALL-E, the little yellow robot hero from the movies. I quickly noticed that WALL-E’s eyes are huge in contrast to his body. I knew the dimensions of the Parallax Ping sensor, which I planned to use for Makey’s ‘eyes,’ so I realized I’d need to keep Makey’s body as small as possible, to make the eyes look as big as possible.
I used Autodesk Inventor to design Makey. I can’t say enough good things about this software. I’ve been using PCs for a good long while, and compared to big Unix workstations, I’ve never been impressed with what PCs can do for you. Inventor changed that. Inventor is the single best reason to own a PC, IMHO. I learned Inventor at school as part of my engineering curriculum, and this software is the “missing link” that has finally allowed me to design robots like I want to. Makey is the fifth robot I’ve built from scratch, and the first one I’ve designed on the computer, and the difference is like night and day.
From MAKE magazine:
In MAKE, Volume 19: Robots, Rovers, and Drones, learn how to make a model plane with an autopilot and a built-in robot brain. We’ll also show you how to make a comfortable chair and footstool out of a single sheet of plywood, a bicyclist’s vest that shows how fast you’re going, and projects that introduce you to servomotors. All this, and lots more, in MAKE, Volume 19! Subscribe here. Buy the issue in the Maker Shed.
Fig. 1: The first models of Makey’s tires, wheels, and motors, created in Autodesk’s Inventor software.
Fig. 2: Playing with ideas for fitting all the parts into a 3″ square body.
So I fired up Inventor and started drawing, or modeling, the parts that would go into the body. I needed to know how much space each would take up, and how best to arrange them inside the overall space. In Figure 1 you can see the models I made of the wheels, tires, and motors. Fitting everything in was a major challenge. This is where Inventor really paid off, because I was able to try out many different configurations, such as mounting the motors vertically as shown in Figure 2. I believe the key benefit to using a computer, instead of cardboard and tape, concerns gravity. In the computer, gravity doesn’t exist, so you can stick the motors wherever you want, and they stay. Then you can fit things in around them. In the real world, gravity works against you. It’s just not easy to secure parts where you want them.
Fig. 3: The first overall design of Makey. It’ll change a lot.
I spent many hours trying to cram everything into a 2.8″ cube, but just couldn’t do it. In the end, I reluctantly gave up two-tenths of an inch and settled for a 3.0″ cube, though it sure hurt to do so. In Figure 3 you can see the results of the modeling in the form of a first design. It’s quite a bit different from the final version of Makey. For instance, it uses 4 AA batteries, instead of two 9Vs, and the Arduino’s PC board is positioned sideways, with the USB connector poking through one side above the tire.
Fig. 4: My model of the prototype body.
Fig. 5: The prototype body in sheet metal, cut and bent with the help of Steamboat Ed and Bruce the Elder.
The next step was to make a prototype. Off I went to the house of my friend Steamboat Ed, who has sheet metal equipment. A Dorkbot member, Bruce the Elder, had taught us how to cut and build a box using Ed’s finger brake just a few days before. In Figures 4 and 5 you can see the model of the body and the actual body that we constructed that weekend. We also fabricated a simple folded piece of metal to cover the body. To bolt the wheels on, Steamboat Ed measured the motors and roughly laid out where the mounting holes should be drilled into the box. After drilling, I had to file the holes into slots to actually get the motors to fit.
Fig. 6: The first prototype of Makey, good-looking but still brainless.
I made some wheels, bolted everything together and took a photo for the draft article. Figure 6 shows the first prototype, just a metal box, 2 motors, and 2 wheels. No brains or electronics were inside at this point, and I simply perched the Ping sensor on top for effect. Based on this photo, a few screenshots from Inventor, and a draft article, Makey was approved. I was in business.
After the concept was approved, discussion among the editors focused on the audience for the article. The consensus was that people should be able to fabricate the robot without a lot of specialized equipment. That meant that using a finger brake was out, as was using CNC to cut the parts. For me, this meant major redesign. I had to simplify the body so it could be made on a very simple, rudimentary, inexpensive bending brake.
There are specific sheet metal modules and actions built into the Inventor software. To design a sheet metal part, you model it in 3D, with all the bends you need, and when done, Inventor flattens it out into a 2D template for you.
However, when you bend sheet metal, you lose a little bit of the length of the part to the bend, that is, the bend uses up some material. So, even if you know what width you’re shooting for, you don’t know exactly the length of the material needed, before bending, to get that width. It varies based on the degree of the bend and the thickness of the metal. In designing the metal body for Makey, a major challenge for me was to design it in such a way that it could “stretch” to match whatever width I needed. My goal was to cram the many parts into the interior, and then “stretch” the metal skin around that to fit perfectly. Then I could locate all the mounting holes for the motors, sensors, switches, batteries, and so on by “adaptively” cutting holes in the body at the exact spots the model predicted they needed to be.
It took me a while to figure this out, and in Part 2, I’ll tell you the key to setting things up in Inventor to get this result.
Up Next:
Part 2: Creating the “Stretchy” Robot Body
Part 3: Fitting the Electronics in TIme for Maker Faire
Part 4: Design, Cut, Shoot — Going Horizontal with the Arduino
Part 5: Wrapping Up — Finalizing the Templates
From MAKE magazine:
In MAKE, Volume 19: Robots, Rovers, and Drones, learn how to make a model plane with an autopilot and a built-in robot brain. We’ll also show you how to make a comfortable chair and footstool out of a single sheet of plywood, a bicyclist’s vest that shows how fast you’re going, and projects that introduce you to servomotors. All this, and lots more, in MAKE, Volume 19! Subscribe here. Buy the issue in the Maker Shed.
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