Paleo-legal compound

Just thought some people here might be interested about -

Something I've been building and playing with recently






A compound cross-bow done according to so called "paleo-legal" or "abo-legal" rules.
All wood. No glue , no metal.
Cables and string natural fiber - flax with cotton serving.
Juniper limbs , birch tiller, hawthorn cam levers.
All relevant shapes in wooden parts are designed in a way that could be reproduced using mesolithic tools- splitting,drilling,grinding,chiseling.

Draw weight and length is easily adjustable. For testing I've been mostly using 46 kg with 185mm stroke (~100#/7").

I have not had a chance to chrono this, but trajectory and penetration tests make it look reasonably fast for something made from backyard pruning waste.
Throws 0,7 g (11gr) piece of bbq stick appx couple hundred m/s (600-700fps) - that is 700 fps for 10 pounds per grain or so.

Trigger is Indo-Chinese style notch and lever.

Fun toy. Very air gun like ballistics.
Still a bit under construction. I have been testing various sight arrangements and other accessories.

Now this is just plain cool! Thanks for posting. Can you give us some rough dimensions? How hard or easy is it to span? It looks like it would be an ideal survival weapon, far easier to make with just simple or even improvised stone tools (splitting a river cobble for instance), then even a quick sapling bow. I can see making one of these with say salvaged materials from from bombed out city or after a massive man made or natural disaster. Ever think of making one with more refined components? I do like the all paleo approach and philosophy, though.

Dane

I like it!

Don't think it shoots 700 fps though. It certainly does look like it has potential.



Todd

stoneagebowyer wrote: Can you give us some rough dimensions?

Limbs 25x18mm mid limb.
Prod length 52 cm front
47 cm rear
Arms 10cm long 8x22 mm middle, 5x20mm tips - tapering edges.

String length can be varied , but 42 cm for 105#.
A bit longer 45 cm string 80# weight seems to be more efficient with ultra-light bolts.

How hard or easy is it to span?

Just step on the rear bow and pull off the front bow.

Assembly and dissassembly goes in couple seconds.

It looks like it would be an ideal survival weapon, far easier to make

Second easiest

String tied to simple knotted cables allows measurable power stroke with practically zero limb movement. Meaning prod can be made of very low quality material as they don't need to bent much. As a bonus comes good mass efficiency and high bolt velocity.

Ever think of making one with more refined components?

Sure. This is not the first one.
Just the first with nothing new. And with decent ergonomics.
First prototype

was published January 2004 in Paleoplanet or Primitive Archer forum. That one and all other previous ones had some untried features wich did not work as well as they could.


The next one will have something new .
A separate modular prod unit. Just plain block of wood between the bows. This should allow more freedom designin the "user interface".

Limbs could be made faster with longer power stroke. This would put less strain on the cables and throwing arms allowing them to be lighter.

This latest unit here has calculated dry-fire speed ca. 250/ms or bit less. And this design is intended for sport shooting in camping environment. It is optimized for durability,ease of use and transport - not speed or power.

If the effective inertia per stored energy can be sqeezed to quarter of what this has( technically feasible), the dry-fire speed can go up to 450-500m/s. Allowing practical projectile speed of mach 1.1 or so. -We don't need a chrono to hear that.


And one nice feature about this arm-cable system: This can be safely dry fired. The throwing arms have enough mass to absorb practically all energy from limbs and cable. They are not fixed to the cables, only hooked there. So if there is too much energy left after bolt the arms and string simply fall off.

Some of the bolts used .

From left
Heavy Birch shaft , lead filled paper tube blunt used for comparison during initial testing.
7cm bamboo stick , glued air-gun pellet point plastic strawer vanes.
Bamboo skewers with masking tape vanes.
25cm 2mm diameter,
30cm 3mm dia,
30cm 4mm,
30cm 3mm shaft with glued paper reinforcement.

4 target bolts with blunt paper mache points for actual use.

Thanks for taking the time to answer my questions. Good of you to do that. I may have to put something like this together for my annual stone age skills celebration this coming October. I'll let you know how that comes out, if I can find the time to make something like this.

All the best,

Dane

Some test shooting results.

6 bolt group , about 40 meter distance

Paper cup is 5cm diameter.
Accuracy is adequate, keeping in mind that this is basically a pistol without proper sights. Shooting instinctive "from the hip" sort of.


some idea about the speed:

Right 0,9 gram bolt with 0,5g air-gun pellet point completely buried into wood.
Left a control shot taken with regular air-rifle doing the usual 150-170 m/s. Similar pellet sticking out over half of its length.

The crossbow made a cavity 10-20% larger, indicating 100-120% more kinetic energy, with just 80% more mass.
This indicates the bolt would have been maybe 10% faster than my old air rifle. 160-190 m/s or so.

50 m hit

A 1,9 gram bamboo skewer arrow went over target and hit a small light dry pine branch hanging from a bush.


Range testing:
0,7 gram dart launched 2 meter high, 0 degrees over calm water along beachline ditched 85 meters away -> mean velocity over 130 m/s.

5 gram bolt ~7 degree elevation 120 m.
12 gram arrow 60 degrees - 150 m.
( I had only 200 m clear field for testing - had to limit the range )

Nerd,

That is impressive palio-engeneering. Did you invent the toggle-and-two-bow idea? Its shear genius.

Mac

The basic lay-out is sort of a hybrid between Ming Chinese double crossbow and medieval European "cube springald".

The idea to use levers to twist cables is probably my own. At least I came up with it myself while trying to figure out how the Chinese multi-bow compounds were rigged. And how to build a reliable compound bow without precision manufactured metal parts.
But it is inspired by some late medieval siege gadgets.
A documented case that used allmost same approach is a Leonardo da Vinci designed "clokwork catapult" .

Nerd Flintstone wrote:
A documented case that used allmost same approach is a Leonardo da Vinci designed "clokwork catapult" .

I am unable to bring that one to mind. Have you got a pic, or a link to one?

Mac

mac wrote:

Nerd Flintstone wrote:
A documented case that used allmost same approach is a Leonardo da Vinci designed "clokwork catapult" .

I am unable to bring that one to mind. Have you got a pic, or a link to one?

Mac

Here is a model kit
http://www.italeri.com/scheda.asp?idProdotto=1983&idCategoria=16&idSottocategoria=0


http://www.wonderlandmodels.com/products/italeri-leonardo-da-vinci-catapult/


I remeber seeing somebody build a full size one a while ago.
Possibly in thehurl.org .

I guess we can call this one finished.

I wrapped the cables and stirrup rope with boiled birch bark, Siberian style.


There is now also a tacticool sinister looking detachable high tech assault commando tactical buttstock system feature.

As comrade Kalashnikov says "everything good is simple". Believe or not - It actually took me several months to develop this. I had thought about a folding butt since the start. But the first prototypes were much more complicated, with cheeck-plates, integrated quiviers etc rubbish. In the end a stick is all it takes.

An adjustable sight system


Rear sight plugs a hole filled with rough sand. Amount of sand can be changed to adjust elevation.
Bark tube is shading a bead. The bead is a peg wedged in a larger hole. Changing position of the wedge adjusts horizontal aim.

The diopter holes have enough fresnel to fix my -2 vision so I can aim this without glasses. Wich goes with the paleo-philosophy.

After all that experimentation, have you come up with any rough and ready design parameters such as length of toggles to the length of the prods or tiller, optimum toggle hanging distance, centered or off center toggle hanging, etc?

The last one you posted, on Jan 19, looks almost "square" from the top, with equal size prods, and the uncocked toggles and and cables forming nearly straight lines. Any more insights?

kenh wrote:After all that experimentation, have you come up with any rough and ready design parameters

c - the longer the better,
at least c > 2b - to get enought clearance to prevent moving parts hitting each other

b < x if long draw is desired - othervise arbitary ,
but x:b ~ 2 has proven practical

x:y - arbitary - same effect to stack and accuracy as with any bow

b:a - arbitary, but such that desired draw length x is achieved without exeeding safe tip movement a.

Forward bow should be slightly stronger than rear bow for equal tip movement. Exact ratio depends on other parameters. Equal bow-tip movement is optimal for efficiency , but othervise not necessary.

Fabulous! Nicely summarized, Nerd, and your efforts are appreciated. One of these is definitely on my Build List.

Nerd I have to admit that I didn't really get what you were going for with this until recently, this project is really cool! A long time back I played a computer game called "Clive Barker's Undying," and there was a section in it where you fought brutish proto-humans that used complicated, rigged contraptions to launch small spears at you. I thought it was a silly idea at the time but you've really changed my mind. Do you plan on making any bolts with knapped flint points?
Gnome

Quartz michrolithes would be more suitable native material for the neighbourhood.
Anyway, at close range I have poked holes to soup tins with those paper tipped bolts. So even fire-hardened sharpened wood seems like over kill.
When snow is gone, i have to try some round pebbles for bolt tips. Sort of stabilized bullets.

I would have to see chrony shots to believe the arrow speeds you are claiming.

Very cool project, original and inventive. Now lets see a high tech version.

I saw pictures of a Field Expedient Bow once...

It's like it was a Bow, with a somewhat shorter secondary bow pointing the other direction fastened to the Front.

Bending the Main Bow would Straighten the Secondary Bow—but presumably it had some desire to return to it's bent mode.

Maybe you could so a Crossbow using that principle.


Saxon Violence

Your "field Expedient Bow" wwas a design invented by the Penobscot Amerindians.  It does give a certain amount of increased power, but not nearly to the extent that Nerd's design does....

Depends how one defines increased power.
Penobscot has fat power curve, while I have been going after maximum dry-fire speed.
In archery terms in-swinger type projectors are somewhat "inneficient" because the first 1-2 inch of draw has light draw weight.
Efficient F/D-curve is desirable for longbows, but less important in a crossbow because draw weight and power-stroke length of a crossbow are not as much limited by physique of the operator.

Very academic.It is hard for me to understand .