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It started simply enough. I posted a quick message on the Type A Machines Forum to see if anyone was interested in setting up a 3D printing contest. It had been just under a year since I purchased my first 3D printer, a Series 1, and I was looking at improving my skills. What better way to push myself than a friendly competition?

After much forum deliberation and about 10 different opinions, Espen Sivertsen (CEO of Type A Machines) stepped in and launched the Desktop Warfare contest. The mission: “to build a catapult, ballista, trebuchet, or other mini weapon of mass desktop destruction.”

catapult 2

Jonas’ winning catapult.

It is said that necessity is the mother of invention and one could argue that no one has really needed to design a catapult since the 9th Century. But throw in a contest with prizes and the need arises. While I do have a background in aerospace engineering, catapults were never on my radar and I somehow went through 16 years of schooling without ever building one. Until now that is. I started by jumping on Thingiverse and looking at what was out there. There were a few respectable models, but most required frame assembly and rubber bands. I wanted something different. So, my goal was to design a catapult that had a one-piece frame, was easy to assemble, and fully 3D printed.

I designed the catapult using SolidWorks, a professional CAD tool great for designing engineering type structures (if you want to design sculptures or more artistic things, programs like Blender or Zbrush  are more appropriate). Going 100 percent 3D printed meant no rubber bands, leaving me with the only thing I could think of for propulsion: some torsion springs. However, I print with PLA, which is stiff and inelastic, so I wasn’t sure if it would even work as a spring. I played with a few designs and tweaked the thickness and number of ‘loops’. Eventually, after four prototypes, I got something that had a surprising amount of power and didn’t seem to stress the material much at all.

catapult 1

The springs give the catapult its pop.

When the design was finalized, I exported the model as an STL and then imported into my slicing software. In this case I used Simplify3D Creator software for slicing. Opting for strength over speed, I printed it with six perimeter loops and 20 percent fill giving the frame enough strength that I could stand on it. After eight hours of printing on my Type A Machines Series 1, the catapult was real. While the print came out clean, I’m not a fan of the ‘layered’ look and decided to give it some light sanding followed by several coats of white Plasti-Dip. With my showroom ready catapult I created a quick video showing it in action with Dillon Baldassero’s rendition of the Inception theme for the soundtrack. Nothing artificially heightens drama like a low-pitched ‘BWAAAH.’ I guess it worked as I scored 1st place amidst some very good competing designs.

While the life-cycle of an idea usually ends after it has transformed into a tangible creation, I had in mind one more task for the catapult. Show me the money! After all, I did spend countless hours designing and printing it, so why not try to make some return on investment? Enter the 3d printing marketplace. Sites are popping up left and right in an attempt to become the next iTunes of 3d printing. The concept is simple, people upload great quality models to these sites and set a price, when someone buys it the website takes a cut and gives the designer the majority of the profit. But will anyone pay for a design (really just an STL file) when there is so much free stuff on Thingiverse and other sites like GrabCAD?

To put it to the test, I uploaded the catapult to five marketplace websites (see the full details here). I priced it at a very reasonable $2.99 and tracked sales for 30 days. Fast forward a month and I ended up with 6 sales totaling about $18. The full breakdown on the sales is available here, but long story short is they all came from Ponoko. The Ponoko folks are nice enough to not even take a commission on the sales so if you are interested in purchasing my beloved catapult please buy from Ponoko so I get my full two dollars and ninety nine cents. Certainly, $18 is not worth all the time spent designing the model, but only time will tell how many sales it will get in six months, a year, and beyond. For now I’ll just enjoy being a maker. After all, if you don’t enjoy what you do, you should probably stop doing it.


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