Trebuchet From Laser Cut Wood and 3D Prints.

This is my entry for the Digital Fabrication Student Design Challenge. I'm an undergraduate student at The University of Texas at Arlington.

For my freshmen design class, we were tasked with designing a Trebuchet that can launch a penny using 10 quarters. It was supposed to be made from Laser cut wood and 3D Printed parts, as well as at least one 'COTS' component (Commercial Off The Shelf).

3D Printer

Laser Cutter

Metal rod/ bolts

Nuts

Glue (optional)

When designing any project, you have to define what your requirements and objectives are. For example, my trebuchet was supposed to have a Max footprint of 18" * 18". It needed to launch a US Penny using 10 US Quarters. Keeping these steps in mind, I started by design process.

When designing something, it helps to looks at what other design exists, and what are the commons mistakes to avoid. After my research, I decided to create a trebuchet with Laser Cut and 3D printed parts. It would have a Hanging counter-weight, as it increases the amount of free fall for the counterweight.

Designing for Laser Cutting:

When designing parts for laser cutting, it is important to understand the properties of your stock material, such as its thickness. I will be using 6 mm thick Russian Birch. I wanted this design to assemble without the help of any adhesives. Hence, I designed interlocking, friction-fit notches in the body of the trebuchet. Make sure that you test print these notches before finalizing the dimensions, as most laser cutters take a 0.5 mm (millimeter) from each side of the cut.

Designing for 3D Printing

When designing parts for 3D printing, it is essential for you to minimize the amount of support material required. This is not only decrease print time but also print cost. Try to design the part with this concept in mind. Of course, sometimes this is not avoidable, so then try to make sure that the support material is in a easy to remove spot and that the surface flatness is not paramount to the functioning of the trebuchet. I've designed the part that hold the penny and the counterweight to be 3D printed.

Most laser cutting machines use a vector file to cut materials. In most CAD programs, you can export a surface profile into a vector drawing file. Use the attached YouTube video to understand how to export a .DXF file (vector file) from a drawing/model.

Once you load up the drawing onto the laser cutter's software, ensure that:

1. Your material is flat.
2. The laser is focused & the correct strength is selected.
3. The stock material is big enough for the cut.

If all the pieces aren't cut out on the first pass, feel free to do another pass.

This step is straight forward if you have previous experience in 3D printing. Make sure that you print a test piece so that you can check measures the actual sizes of the features, especially when you have tight tolerances.

You just have to export your part as a .SDL file and send it to your 3D printer. Alternatively, you could send it directly to your 3D printer using the 'send to 3D printer' option.

I used ABS plastic for both of my 3D prints.

After printing out everything, you will notice that some parts of the Trebuchet don't join as expected. This is where you have to go back to the sketches and edit the dimensions. Try to only change one part every iteration so that you can measure the impact of the changes.

Just a heads-up, add the nut and bolts (COTS) in the 3D design is out of the scope of this tutorial.

Alas, you have your completed trebuchet, feel free to knock down a tower of paper cups. If you'd like to do something more, try changing your design, again, once part at a time. Find out the best parameters for the furthest launch. What about placing the whole trebuchet on wheels? Would that impact the range?

Feel free to comment any questions you might have.