I built my first heavy crossbow when I was about 13 years old. It was a quite powerful device, powered by a rubber sling - a 10mm O-ring I just 'found' on a public worksite - and armed with custom wooden darts. Steel heads, explosive heads, too dangerous heads - in the hands of a small me. I'm sure the holes are still in the steel garage door of my parents.
No wonder that one of the first skills I learned was changing glass windows. Rapidly. Invisible. I became a pro.

My crossbows were a great source of pleasure in my youth.
And of cave arrest, also. Too bad - for my parents - there was a lot of beer stored in that cave, also.
That's how, for the first time, I got insanely drunk.
Resulting in more cave arrest, my hands powertaped. And the company of the neighbours dog to keep an eye on me.
Sweet youth souvenirs...

Resuming: in my youth I learned to love crossbows, I learned to love beer, I discovered the resistance of duct tape and I started to hate dogs. JUST KIDDING!!!
More than 20 years later I'm still on bows, crossbows & slingshot stuff. Target shooting. Long range. 'Run, doggy, run!'.
Since the 80's I've built six arrow-shooting devices. This is number 7, I guess.

But today I see things a lot bigger. Crossbow's Revenge.

This project is about building a real heavy powerful 'badass' scorpio-style arrow shooter. It's not a crossbow, not a speargun, not a scorpio and it's definitely not a slingshot. It's a prototype.
My wife calls it 'That Heavy Thing That Keeps On Hanging Around In The House'.

I built it gradually. 'Sometimes it's good to look at your work' a member said once. That's also what I told my wife because that's exactly how I build this weapon. It all started with a piece of wood and some scrap metal I had to integrate in the project.
In other words: I got the ingedrients, but no idea of the meal I was going to prepare.
Experimental building.

This instructable isn't about howto, it's about custom made hardware. I'm not going to explain how to work wood & metal.
I'm giving you the plans of each device. Your job to make it. Or to improve it. Open source.
Download the plans (click on the pictures & get access to the original files). No CAD-stuff - I'm an old school guy...

Total length (winch included): 128 cm (4 feet) - look at those kitties to compare!
Max. widht: 21 cm (2/3 foot)
Total weight: too much

This IPAD is made of 12 components:
- stock
- drum
- trigger
- trigger rod
- trigger protection
- 'double decker' aka roller device
- stirrup
- lock
- winch
- driver
- sling
- sight

One step, one component. Let's have a look at all those pieces!

Step 1: Startup

This is the challenge I set to myself:

Build a rubber band powered device using rollerblade wheels and a reclaimed drum from a plane, capable to shoot regular carbon arrows at least as powerful as a 50-pound compound bow.

And

Use as much as wood & metal you can.

Why rubber bands? Because they are compact & powerful.
Why rollerblade wheels? Because they are ball bearinged. And cool.
Why that drum from a woodworking plane? Because it's a cool device, also, that's been waiting for years in my workshop to be used.
Why wood & metal? Because I don't like the actual abondant use and mis-use of composite materials. Back to good old basics.

Step 2: Some Helpful Vocabulary to Impress Your Friends

Spearguns. Common used in under-water hunting. They have a hardwood stock (most of the time), are powered by rubber bands, armed with harpoons and equiped with a fishing reel. Various sizes, going from one foot long to catch tiny goldfish to five feet or more for baracuda or alligator hunting.

Crossbows. Developed in the early cold war between bows and body armour. There was a time that armours became more & more efficient, and so opponent archers more & more frustrated. Some smart guys came up with a real steel bow. It was so powerful that it had to be mounted on a wooden stock to bring it under tension, forming a cross. Crossbows are armed with wooden darts & steel heads. They are insanely powerful and there's no skill needed to shoot them - in contrast to 'normal' bows. Exit armoured knights. Nowadays those weapons are made with a lot of composite material, making them lighter & more accurate than ever. But less beautiful, but that's my opinion.

Rubber band crossbows. Instead of a steel bow they use rubber bands as power. Nothing more to do with a 'bow'.

Scorpios (alsio called 'manu(hand)ballistas'). Greek invention, perfectioned by the Romans. Wooden stock. Instead of a steel bow they are powered by torsion springs aka tendons, leather straps or ropes - mounted in a kinda 'double-decked' device. Armed with arrows or darts. Used to wipe out infantry or cavalry.

Ballistas. Like scorpios, but much bigger. Often armed with stones. Considered as 'siege weapons' - used to destroy fortifications & whole cities. One of my favorite youtubes ever: The Ballista Project.

Step 3: The Stock

This project started with a nice piece of wood I found in our barn. It used to be a piece of a handle of a farm wagon, I guess.
I can be wrong, but it looks like Common hornbeam (Carpinus betulus) - a hard & heavy wood often used for pieces that have to be ultra resistant like stems, oars, the teeth of mill wheels and the skin of married men.

Try to find a piece of hardwood. I'm sure you can find a piece of scrap for free in a local sawmill. Just ask friendly, and pay a coffee to the employee.

Again, I'm not telling or showing you how to cut & dig this piece. If you're a woodworker you'll know.

Copypaste the plan - measures are metric (mm) - and use PMF aka multitasker, plane, jigsaw & router to get the job done. I even used a cutting disc to dig out the sleeve for the trigger plate. Non conformic but functional.

Oil the whole before continuing. Tung is good, walnut is nice. Varnish is for idiots.

IMPORTANT!

Don't add the 'shoulder' in the stock. I discovered badly that this is definitely the weakest point of the stock (see further). You're better off without.
During the trials (step 14) the stock broke and I had to reinforce it with two steel plates on each side. Those are bolted together and extend to the drum.

Step 4: The Drum

A while ago my plane got stuck and I decided to keep the drum, since I felt it had all to be a perfect device for a future crossbow release.

So here it is. It has two functional grooves. One for the trigger plate (downside groove) and one for the arrow (upside groove).

If you don't have a plane drum, copy the design to a full piece of aluminium, resin or hardwood. Use a clock drill.

I'm sure you can even cast one. Try this I'ble to find out how.

IMPORTANT!

After a few tests I decided to cut off the back teeth because they blocked the cocking. So, exit that part.
Note the heavy axis of the drum - a 10mm bolt. It's solidly maintained by the reinforcement plates on each side of the stock, dispersing the heavy torsion that (in the first concept) was acting directly on the small wooden zone.

Step 5: The Trigger

Trigger & drum form one device. When the trigger is in 'rest' it blocks the drum - safety first. When the trigger plate moves backwards the torsion of the sling on the drum makes it 'fall' into the 'trap' in the plate, releasing the sling (see picture).

The sleeves in the plate are designed to keep the device in place in its (stock) housing.

The plate has rounded edges because I used a grinder with a cutting disc to make the sleeve in the stock.

Note the rubber band attached to the plate. It is fixed in the stock to keep the plate in place in 'resting' position. Once fired it moves forward again, blocking the drum. You can use a spring if you want, or even a small piston on the back side of the plate. If you're not an idiot like me and you don't cut a 'shoulder' in the stock, there's place left to install a nice piston.

Made from an aluminium plate and a piece of scrap olive wood. Glued & riveted.

Step 6: The Trigger Protection

Designed to prevent the trigger from touching the ground in 'sniper' position.

Curved aluminium.

Step 7: The Trigger Rod

Optional device. It's an aluminium rod that goes all the way through the stock. Pull at the wooden 'finger' and the main trigger will move backwards.
I made it because I wanted to be able to activate the trigger at various positions - machine-gun style, you know.
Use an extended flat drill to get the (long) hole done. Here's how you make one.

Step 8: The 'double Decker'

The idea of using rollers in a slingshot device came from Joerg Sprave - credits to him. It permits you to use a longer sling than in a traditionnal shooter, resulting in more power.

Instead of basic rollers like our friend I chose roller blades.
Bacause I had them.
Because they have smooth ball bearings.
Because the sling is nicely guided between the two rollers on each side, giving more precision.
Because they are just cool to use in a weapon.

Mounted in a solid aluminium device.

IMPORTANT!

In the first tests the sling 'disappeared' aka got crushed between the two rollerblades, so I put a giant washer between them to fill the space and added some rounds of tape to fill it more. Crushing the sling results in more friction. More friction results in less power.

Step 9: The Stirrup

No crossbow without a stirrup.

Bended aluminium.

Step 10: The Winch

To get the weapon armed the string has to be pulled. You can do this with both hands - yeah right - but I prefered anticipating future frustration by including a pulling device.

So I set my mind on a - removable - winch. Clipped on the stock with the help of a metal piece this is the perfect device to pull the string all the way up. It works just perfect!

Step 11: The Sling

Made of rubber tube - 1/3 inch thick.
Helt together with paracord - sliding knots (they work just great).

I started with only one at each side (see later) but added one rapidly. You can put as much tubes as you want, just be careful that the whole structure can hold the (enormous) forces.

Step 12: The Driver

This is definitely the weakest point in the whole concept. It's actually not a driver, it's a joke (just a piece of plastic...).
I ordered a whisker biscuit. It's on it's way.

Step 13: The Sight

I'm using an adjustable small alu tube a sight. Simple & effective for the ranges I practice.
You're totally right. A real sight would be cooler.

Step 14: Trials

First run.
String: one tube each side - 15 inch long each
Distance to target: 30 feet
Target: solid pine plank
Penetration: 1/3 inch
Feeling: depressed (with my compound bow the arrows go straith through at 100 feet distance)
Remedy: doubling & shortening the strings

Second run.
String: four rubber bands - 10 inch long each
Distance: 30 feet
Target: solid pine plank
Penetration: 2/3 inch
After the second shot disaster striked. The armed weapon fell on the ground and with the enormous force of the string the stock broke on its weakest point: the area affected by wood beetles (hornbeam is good stuff, but that's also the opinion of those parasites) and exactly the point where the wood grain went straith into the smallest point of the stock.
Yep, I should have known better. My fault.
Feeling: depressed, again. And if that wasn't enough, also my camera gave up (these images were taken with my phone).
Remedy: some beer, glue, plates & bolts. No more time for half work.

Third run.
String: four rubber bands - 10 inch each
Distance: 100 feet
Target: 3 inch styrofoam, backed by a solid pine plank
Penetration: see picture
Feeling: quite impressed
Remedy: more beer. Not to forget, but to celebrate victory!

Step 15: Improvements & Evaluation

PRO's:
- it's heavy and thus stable
- it's extremely powerful (and not yet tested to it's limits)
- it's relatively accurate
- it's safe - no risk that the drum accidently moves
- I'm particlarly happy with the behaviour of the winch - pulling the string is just fun
- it's a modular design - you can change the double decker to a small bow to get a crossbow

CONTRA's:
- it's a really heavy weapon that should be shot from 'laying' position or mounted on a tripod
- when adding power by adding tubes (or dragging the tubes more) the trigger becomes harder to operate (more friction from the drum to the trigger plate)
- it's not yet accurate enough (with my compound bow I do a lot better) but that's probably because I'm not yet entirely used to it

To resume, it was great fun to build it and there's a lot of room for improvements. I'm thinking about experimenting with different rollers, different tubes or strings, adding a whisker biscuit instead of my poorly designed driver, mounting a sled to shoot darts etc.
If you have any recommendations let me know!

Thanx for watching!