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DIY_guy 04-27-2020 03:31 PM

3D printed arrow launching device (weapon)
 
I have a passion for making homemade weapons and taking game with them. Ive taken both deer and black bear with all homemade traditional archery gear. A longbow I designed and made myself with arrows Ive made using the wing feathers from turkey I'd killed that I converted into fletchings and I even made my own broadheads from old saw blades. I really enjoy hunting with homemade hunting gear. My homemade bows have typically been 48 to 50 lbs draw weight and have always done the job resulting in short blood trails.

To that end, I've tinkered with other human powered weapons in the past and some worked very well while others I was never satisfied with. Regardless of the human powered weapon type, its the force with which the projectile is propelled that determines lethality.

So I find it interesting the Wisconsin hunting regulations state that the minimum draw weight for bows is as low as it is. Sure it gets smaller and weaker and younger people into bowhunting but is the low standard good for the sport of bowhunting?

This if what I copied from the WI deer hunting regulations.

Definitions:

Bow: "Any bow, drawn and held by and through the effort of the person releasing it, not including crossbows.

Bows must have a draw weight of 30 pounds or greater, and metal broadheads must be at least 7/8 of an inch wide and kept sharp. Stone arrow heads may be used."


The regulations and definitions are pretty short and simple but the min. draw weight has always concerned me as its pretty low and the energy that such a bow delivers is also very low.

Here is one of my youth bows that, at my draw length is exactly 30 pounds.



Its and old Ben Pearson jetbow.



Using this bow, I shot some arrows through my chronograph. Here was the average speed. 121.3 Feet per second.



If I were to take this bow afield in WI, this would be perfectly legal.


Over the past winter, while recovering from a recent back injury, I was using a variety of therapeutic, elastic bands, while using these bands I got a desire to make a 3D printed (mostly 3D printed) weapon that is human powered and delivers an arrow. This weapon will have a draw weight in the 47 to 50 pound draw weight range since that is a draw weight Im comfortable with when no let-off is involved. It will incorporate these elastic bands, many 3D printed parts as well as wood and metal parts.

*****Disclaimer*******

There are arrow launching weapons on the market (Slingbow and Chief AJ are a couple) that incorporate elastic bands BUT I dont care for the designs as they require a lot of wrist and grip strength to overcome the draw weight that takes place above the wrist. As I age, my grip and wrist strength is not able to comfortably and accurately handle the forces that are all above the wrist. I can easily shoot a 65 pound compound since the draw is balanced above and below the grip and it can even be shot open handed but a weapon of the type Ive seen puts the draw above the hand only and while there are versions with a bracer that transfers some of the forces to the forearm, every attempt to use them as resulted failure at the draw weights Im shooting for.

I designed this arrow delivery system in my CAD software since I will need 3D CAD files in order to print the components on my 3D printers. This is what is will look like.



This design will be more like a bow because the design balances the draw weight both above and below the wrist as well as bracing off the forearm. I expect it to allow for open hand shooting meaning grip strength will not be an issue.

This prototype currently does not have limbs but I hope to design a later version with short limbs as well as elastic bands to propel the arrow.
At this writing, I dont know exactly how many bands and of what power it will take to achieve a draw weight of between 47 and 50 pounds but I ordered many different weights of Thera bands (resistance bands for physical therapy that I used during my recent PT for my back).

I ordered natural, red, yellow, green and black thera bands for this project as these are the bands I used while I rehab'd my back during the winter. Black was the most powerful but I have designed enough locations to attach the bands that I could include a variety of colors to reach my goal draw weight.



Using my 3D printers, I made the parts needed to assemble this arrow launcher. Here are some photos of prototype #1

3D printed, Rubber tube plugs so I dont have to tie knots in the rubber and I can quickly swap out all the colors of bands as I test the draw weight.



Once they are pushed into the hollow rubber bands, and slid into the yoke, they wont allow the rubber to pull through but the slots in the sides of the yoke allow the bands to easily be changed. The final design may not need the slots at all.



At the other end of the bands (where the pouch is) I have designed and printed similar devices the are held by the rubber and attach the arrow flinging pouch.



I made a very short bow string that I sandwiched between to layers of leather and I added a "D" loop for a mech. release.





The assembled bands.



Other 3D printed parts that are joined with metal rods and a wood riser.





The 3D printed arrow rest.





here is a short video of my printers making the parts.


4 black bands developed 47 pounds of draw weight for my length draw. (17 pounds more than the Wisconsin Min) here is the speed the black bands produced.



This prototype already develops more speed and momentum than the Wisconsin legal minimum bow so Im seeing the validity of such a device but more importantly I can handle the draw weight and even more importantly, I can draw it with an open hand and very little wrist fatigue.

Now its time to do some shooting and to see if things like a kisser button and even a sight can be added to improve accuracy but after shooting a few times, this is every bit like shooting a bow and arrow. Ive added a level because I will shoot with a "cant" or tilt to the right style of hold.



More to follow.

Oldtimr 04-28-2020 02:01 AM

I suspect if you check with your game department the device would not be considered a bow but a sling shot. The definition you posted from your state's regulations simply defines a mandated bow draw weight and minimum measurements for a broad head and must be drawn and held by hand. They will turn to Webster or other dictionary for a definition of what is a "Bow". The definition starts by saying "any bow" it is not a definition of a bow per se, but it defines what is a legal bow to hunt with. Your sling is interesting and it certainly is a weapon, but I would not hunt with it until you check with your game department

archeryrob 04-28-2020 04:23 AM

I got to agree with oldtimr. It will do the job, but it's not a bow.

An Atlatl is a big arrow thrown from a stick and is not legal anywhere that I know off.

DJfan 04-28-2020 04:47 AM

Do you sell those?

DIY_guy 04-28-2020 01:57 PM


Originally Posted by DJfan (Post 4374779)
Do you sell those?

No. In just experimenting.

bronko22000 05-09-2020 01:59 PM

I've shot wrist rockets (slingshots) with the forearm brace. At a 40-50 lb draw that forearm support will really bruise your arm. But I think you'd have a legality issue hunting with it.

wallhangr 06-03-2020 05:36 AM


Originally Posted by archeryrob (Post 4374778)
I got to agree with oldtimr. It will do the job, but it's not a bow.

An Atlatl is a big arrow thrown from a stick and is not legal anywhere that I know off.

Actually, here in MO it is. Can be used during " Alternate Weapons Season" that used to be just for muzzle loaders.

LINK_84 06-04-2020 05:44 PM

What kind of weight in the arrow are you pushing to get the fps shown...? Its a neat idea but I wonder if it would pack enough energy as the bands would quickly lose force as they contract and without a very heavy projectile, am not sure you'd have the energy for big game. Still got me curious though!

LindaSkync 08-09-2020 06:18 AM

3D printed arrow launching device weapon
 
Just thought i would ask if u guys out west use the wisker biscuit arrow rest. It is what i use here in arkansas for tree stand hunting and it seems like it would be prefect fit for spot and stalk.


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