Onager Catapult: Reverse Engineering Project
Intro: Onager Catapult: Reverse Engineering Project
I have always wanted to design a mini-catapult that works and I thought, what's the fastest way to learn than to learn from others. In this Instructable, I will walk through on my reverse engineering process to break down a mini-catapult design that I have gotten online and have an attempt to reverse engineer the parts and explain how each component works. Additionally, I will show a successful replication of the design that works!
Who knows, maybe I should create a series of such "reverse engineering" pieces! There's so much to learn!
*Disclaimer: Just to be precise, the onager was a Roman torsion powered siege engine. It is commonly depicted as a catapult with a bowl, bucket, or sling at the end of its throwing arm. Thank you one of the members for clarifications!
STEP 1: Getting a Reference Image
One of the key steps of reverse engineering is to figure out the components of the catapult. For my case, I broke down off-the-shelf catapult schematics from an online image of a figurine and laid them out for visualization. Using a top-down image basically shows the entire blueprints of the design.
Next, open up illustrator or Rhino 5.0, and make traces of the image using vector lines and curves. A tip is that I had to size a relative dimension of the size of the design which I want and scale the design accordingly.
A few pointers to note:
- Interfacing elements (e.g. slots) has to match the thickness of the material sheet
- Tolerances for certain snap-fits have to be fine-tuned as well
- Fortunately, with a lasercutter, iterative prototyping is extremely fast
STEP 2: Understanding the Mechanics
From tracing and iterative process of prototyping, I managed to understand how each component interacts with the other. The concept of interlocking joints, laser-cut collar shafts and bearings are really interesting concepts to take note of. This will definitely bring me to the next level to create new toys from these learnings.
A few pointers to take note of:
- Wooden materials are isotropic, making sure that you cut along/across grain depends on the mechanical load that the component is to take.
- Compliant snaps should not have thicknesses that are less than 1.5mm else the beam will have a high risk of breakage (have to negotiate the clearances and tolerances)
- The catapult slots have to be a tight fit to snug in place else it will be loose and glue is required (undesirable)
- Once your blueprints are sorted you may scale it to other materials too!
As some of you have noticed, I have quite a few failure pieces. The point about reverse engineering is not about the outcome but the process of learning from it.
For convenience, I have attached a graphic on the different components of an Onager Catapult. (By Rpanjwani3 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1...)
STEP 3: Final Demo
With all that effort, here's the final video of the success of the design process! The current design dimensions are about 75mm x 75mm in footprint. A cute palm-sized design for any portable fun! Check out the video to enjoy the assembly process!
STEP 4: Further Explorations
Feel free to drop down a comment, if you think I should scale this bigger or bring this further! Drawing inspiration from online material, I have some plans to design target boards as well as creating projectile balls (which is already proven to be doable) and possibly make this a carnival game for my future kids? What do you think?
And with that, we have completed a basic introduction on how to reverse engineer some of the available 2D designs. I am very satisfied with how it turned out. If you find this Instructable useful, do LIKE and SHARE this post and I will be submitting it to the Make It Fly design challenge!
4 Comments
saadatmuhammad198 1 year ago
einar.mikkelsen 2 years ago
pieniondz 2 years ago
This comment was written by the trebuchet gang.
P.S. I'm not saying you're wrong, just not precise
dexterch 2 years ago