Siege engine generator Pro

A trebuchet or a catapult that really throws, with a range estimate before you cut.

Open Siege engine in the app Pro generator: explore its settings in the app; cut files come with Pro, $39 once, no subscription (coming soon).

A laser-cut plywood trebuchet: A-frame uprights, a long throwing arm and a counterweight box hanging from its short end

In short: Desk trebuchet with a hinged counterweight and a sling on a release prong, or a catapult powered by rubber bands or a twisted skein. One arm length sizes everything; a physics simulation estimates the range and sets the release. Checked through the whole swing and along the ball's flight.

The classic school physics project, designed for you. Pick a trebuchet or a catapult and an arm length, and you get a complete kit: a base, two uprights and a brace, a laminated throwing arm on a dowel axle, and a trigger pin you pull out to fire.

The trebuchet has a hinged counterweight box you fill with coins or nuts, and a sling that slips off a release prong at the end of the arm. A small physics simulation of the arm and sling picks the sling length that throws furthest and sets the prong's angle so the ball leaves at the launch angle you choose. Change the arm ratio or the counterweight and see the estimated range change.

The catapult runs on rubber bands or on a skein of twisted string wound up with winders outside the frame, and its arm stops against a bar angled for the launch angle. Weigh the pull at the cup with a kitchen scale for a range estimate.

Every part is checked for overlaps through the whole swing, and the 3D preview plays a shot.

You need: plywood, dowel for the pins, glue, string or rubber bands, and a ball. Never aim at anyone.

The trebuchet firing, slowed down: the counterweight drops, the arm swings over the top and the sling lets the ball go

Settings

All of these can be changed in the app, and the 3D preview updates as you type. The name under each setting is its key in a share link, e.g. https://laserpuzzle.app/app/siege-engine?kind=…; a link only needs the settings that differ from the defaults.

Siege engine

Setting	Default	What it does
Engine `kind`	trebuchet	Options: trebuchet, catapult.
Arm length `size`	240 mm	Length of the throwing arm, end to end. Everything else scales from it. From 120 to 800 mm.
Launch angle `launch_angle`	45 deg	Angle the ball leaves at. 45 throws furthest; lower is flatter. Sets the trebuchet's release prong and the catapult's stop bar. From 20 to 65 deg.
Ball diameter `projectile_diameter`	16 mm	A wooden bead, a marble, a ball of foil or modelling clay. From 6 to 40 mm.
Ball weight `projectile_mass`	3 g	Weigh it on a kitchen scale; only the range estimate uses it. From 0.3 to 100 g.
Engraved details `details`	on	Timber lines on the frame, trough on the base.

Trebuchet

Setting	Default	What it does
Arm ratio `arm_ratio`	4	Trebuchet: long arm / short arm. Higher throws a light ball faster but needs a heavier counterweight. From 2.5 to 6.
Counterweight `counterweight`	200 g	Trebuchet: what you put in the box (coins, nuts, washers, sand). From 20 to 5000 g.
Sling length `sling_length`	0 mm	Trebuchet: string from the arm's tip to the pouch. 0 = the length that throws furthest. From 0 to 1000 mm.

Catapult

Setting	Default	What it does
Power `power`	rubber band	Catapult: rubber bands pulling the arm's butt down, or a skein of twisted string the arm is clamped in (wound up with winders outside the frame). Options: rubber band, torsion.
Pull at the cup `draw_weight`	300 g	Catapult: what a kitchen scale reads when you hold the cocked arm down at the cup. Only the range estimate uses it. From 20 to 20000 g.

Pins

Setting	Default	What it does
Pin diameter `pin_diameter`	4 mm	Measured diameter of the dowel or rod used for every pin. From 2 to 8 mm.
Press-fit hole offset `press_fit`	-0.1 mm	Hole = pin + this, where a pin is fixed. Find it with the fit-test hole strip. From -1 to 1 mm.
Axle hole offset `axle_fit`	0.25 mm	Hole = pin + this, where something turns on a pin (the arm, the counterweight) or a pin has to come out by hand (the trigger). Larger turns more freely. From -0.2 to 1 mm.

Plus the material and machine settings every generator has: material thickness, kerf, slot clearance, sheet width, sheet height, part spacing, engrave part labels, cut line colour, engrave line colour.

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Pro