This is a simple catapult that I designed for a class project. Disclaimer: It has not been optimized.

You will need four(4) M4X20 bolts, four(4) M4 nuts, two(2) bearings, one(1) 100MM metal rod, one(1) rubber band, and one(1) 20MM spring(optional).

Metal Rod [https://www.amazon.com/gp/product/B082ZP5CLB/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1](https://www.amazon.com/gp/product/B082ZP5CLB/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1)

Bearings [https://www.amazon.com/gp/product/B07C6FL8TW/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1](https://www.amazon.com/gp/product/B07C6FL8TW/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1)

Bolts and Nuts [https://www.amazon.com/gp/product/B073SWXPYR/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&th=1](https://www.amazon.com/gp/product/B073SWXPYR/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&th=1)

Spring(Used spring from Ender 3)

These are what I used.

1. Place the BEARINGS inside the slots in the LEFT FRAME and RIGHT FRAME.(Place a towel over them and gently hammer them until they are flush)
2. Press the ROD the hole on the ARM.(Center the ARM on the ROD)
3. Place the ends of the ROD through the BEARINGS inside the FRAME.
4. Press one(1) NUT into each slot in the CROSS BEAM until they reach the bottom.
5. Line up the hole of the CROSS BEAM with the LEFT FRAME and the RIGHT FRAME and insert the BOLTS.(They will screw into the NUTS in the CROSS BEAM)
6. Repeat steps four(4) and five(5) for the REAR FRAME.
7. Insert the SPRING into the hole in the REAR FRAME.
8. Depress the SPRING and slide the ARM CATCH into the slot in the REAR FRAME.
9. Wrap one end of the rubber band around the ARM and loop it over the CROSS BEAM and wrap it back around the ARM.
10. Pull ARM back until the ARM CATCH latches.
11. Load ammunition of choice.
12. Depress ARM CATCH to fire.