The Pocket Siege Engine | 360° Aiming + Elevation

Overview

In the context of a project at the MakerSpace of UniLaSalle Amiens, we designed, prototyped, and built a mini siege machine intended to take part in a game where the goal is to score as many points as possible by aiming at specific game elements. For more information about the Medieval Challenge: https://makerspace-amiens.fr/medieval-challenge

Key Features

• 360° rotation using a hidden gear mechanism inside the base

• Adjustable elevation (aim up/down) for controlled targeting

• Laser-cut wooden base (standard event interface)

• No glue for the wooden base assembly

• Compact footprint: 170 × 170 mm base, overall height about 171 mm

How It Works

• Load a foam ball (Nerf-style).

• Arm the internal carrier (pulled by elastic bands), lock it in place.

• Trigger the release using a manual pull-string.

Event Constraints

This design was made to comply with the Medieval Challenge constraints:

• Laser-cut base plate: 170 × 170 mm, 5 mm thick, with a 10 mm reserved margin around the edge.

• The machine fits within 200 × 200 × 200 mm in the loaded position.

• Energy source: elastic deformation + gravity only (no electricity, compressed air, combustion, etc.).

• Trigger: manual pull-string ~50 cm (per event rules).

• Manufacturing: only MakerSpace digital fabrication processes (3D printing + laser cutting). Fasteners are allowed.

• CAD-designed, rigid axes, no improvised tape/hot-glue structures, and no loose/unstable parts.

To build one mini siege machine you’ll need:

Printed parts:

• 1× Base (Base - Base.stl)

• 1× Gear 1 (Base - Gear 1.stl)

• 1× Gear 2 (Base - Gear 2.stl)

• 1× Gear 2 axle (Base - Gear axle 2.stl)

• 1× Knob / crank (Base - Knob.stl)

• 1× Barrel (Barrel.stl)

• 1× Ball carrier / internal support (Ball carrier.stl)

• 1× Carrier lock / latch (Carrier lock.stl)

• 1× Barrel base (Barrel base.stl)

• 2× Towers (Tower.stl)

Laser-cut parts:

•  1× Wooden base plate (5 mm thickness, 170×170 mm) (DXF in Découpe Laser)

Additional parts to buy:

• 2× Wood screws 3.5×50 mm (for fixing the towers)

• 1× M4 screw + M4 nut (for the main gear/base axis)

• String (manual trigger line) ~50 cm (per event rules)

• Elastic bands: 2× (cut from a longer band; trim after fitting)

Tools:

• Screwdriver

• Drill (to open the tower holes from underneath if supports are not removable)

• Small file (for minor fit adjustments)

Notes:

• Elastic bands: start long and trim only after test-fitting. If it’s too hard to arm, loosen by increasing length.

• Threading elastics through the small carrier can be tricky: slightly melt the elastic tip to make it thinner, or use a needle.

Print Settings

Printed on a Bambu Lab A1 Mini using PLA.

• Nozzle: 0.2 mm

• Supports: Tree supports (as needed)

Assembly

1. Print all 3D parts and laser-cut the wooden base plate (DXF in LaserCut).
2. Assemble the gear mechanism:
  - Mount the large gear to the wooden base using the M4 screw inserted from underneath.
  - Place the M4 nut in the top cavity so it locks into position.
3. Install the small gear and secure it using the printed axle (Base - Gear axle 2.stl).
4. Finish the base module:
  - Assemble the wooden base (press-fit, no glue).
  - Add the knob/crank (Base - Knob.stl) to the small gear.
5. Build the turret:
  - Fix the first tower to the turret base using a wood screw.
  - Slide the barrel through the first tower.
  - Slide the second tower onto the barrel, then fix it to the turret base with the second wood screw.
6. Place the turret assembly onto the main axis / base so the rotation engages with the hidden gear mechanism.
7. Prepare the internal carrier:
  - Attach the two elastic bands to the carrier (Ball Carrier.stl) before inserting it into the barrel.
  - Insert the carrier into the barrel and install the locking part (Carrier lock.stl).
8. Add the pull-string (about 50 cm) to the release mechanism, then perform a gentle test to verify:
  - the base rotates smoothly,
  - elevation holds its position,
  - nothing is loose or unstable.

Important: Keep the elevation joint slightly “stiff” (friction fit). If it’s too loose, the barrel may drop during use.

⚠ Safety & Responsible Use

This is a game prop / educational mechanism and should be used under supervision.

• Foam ball only (Nerf-style foam ball)

• Never aim at people or animals, and avoid aiming toward fragile equipment (PCs, monitors, glass, etc.)

• Keep fingers away from moving parts and tensioned elements

• Before each use, check that no part is loose and that nothing has excessive play