Requesting help with the design of a Homemade Bow

Good afternoon boys and girls, I'm in the middle of designing myself a homemade bow, and want to bounce some ideas off you. Included below is a diagram (excuse the mspaint :roll:) Everything will be made of pvc tubing, bar the homemade plunger head, which will be made of Chuck Norris's hair, for the perfect seal. Seriously though, if you wanna see how I'm going to do it, look for Aj's vaccuum loading triple shot. Instructions are there.


Here is the diagram for your added convenience.
<a href="https://2img.net/r/ihimizer/i/bowprototype.png/" target="_blank"><img src="https://2img.net/r/ihimizer/img413/9159/bowprototype.th.png" border="0"/></a>

The plunger tube, plunger, and arms are all made of PVC, with the arms likely being 1/2-inch, and the body being 3-inch, and liberal use of 45 and 90-degree couplers where appropriate. The whole shebang is powered by bungee cord, with stronger bungee denoted as red, and weaker bungee (mostly for aesthetics), drawn in blue. I will most likely rscb clip it, but I also want to be able to fire my homemade arrows too.

I have thought this through, and am likely to actually build it in the next week or so, and am wanting to get some opinions on it. Will it work? Will it explode and wipe out all life?

(side note: I for one do believe in the importance of style, so I'm going to paint this metallic blue, and use it at wars )
(side note #2: I'm a big guy, with quite some strength, so I'm going to use some serious bungee, which results in this thing having an elephant-load of power behind it)

Discuss.

Right, well this sound like a cool build and ill help by giving my 2 cents.

First off (i am not 100% sure of this) but that is a slingshot as you are getting power from the cord and not the elastic energy from the pvc... but for the purposes of this build lets just refer to it as a bow, mainly because it looks like a bow

Ok, so now that that's out of the way, lets look at how we get power. I am no physicist and i have never done it in school, but i am sure that these two chamber designs will yield different power levels. (keep in mind that they have the same volume.)



Like i said before, PVC pipe has quite a bit of flex, and due to this, it has quite a but of elastic energy building up inside of it... however with that many bungee cords i think the draw weight will be higher the the elastic limit of PVC causing elastic deformation (the point when you bend plastic and it starts turning white) or rupture (snapping) so i would recommend making it out of steel.... or change your design to a more simplistic bow design. the design which i propose is below it consists of:

>> A wooden grip (which i think should be varnished so go with oak) (dark red)
>> 13mm steel arms. For safety reasons fill the tips with hot glue. Arms can be bolted to grip with 2 bolts each (total 4) (blue)
>> 1 and 1/2 inch chamber. (green)
>> plunger (cast epoxy or hot glue). plus plunger rod (red)
>> Guidance sleeve (cyan)
>> Barrel (orange)
>> rubber tube/sheet or bungee cord (purple)



Feel free to take any of the ideas listed above, you do not have to take any of the ideas, they are just suggestions

Appreciate the input, but its a little unclear to me. When you talk about the elastic stress causing the pvc to fail, which part in particular are you referring to? The arms? The plunger? If you're referring to the arms, the way I've designed them, they won't actually bend that much at all when the weapon is used. They are there pretty much just there for looks. At the base of the arms, where the strong bungee attaches, those stubs of pvc will be reinforced with steel/aluminium tube.

If it's the plunger, I've been thinking of using aluminium tubing, but it's difficult to find where I live.

Thanks for the help!

I found this video on youtube of some guy's homemade bow. It might help for inspiration.

https://www.youtube.com/watch?v=Kzz4kvZsepM

Yeah, I've already seen that one. Thanks though

Key:
Red is compression
Cyan is tension

If you are reinforcing the limbs of the bow then it should be fine.

I'd again recommend reinforcing the base of the arms, the plunger system I designed does have a little friction, but I'm sure the bungees will overcome it.

Mounting the bungees off of the plunger tube means the amount of force they pull the plunger forward with will decrease over the length of the stroke, something to be mindful of, though with a plunger tube of that volume I doubt it'd matter. Seeing as you're going to have to put come kind of endcap or reducer on the back end of the PT to center the plunger rod, why not throw a spring in also?

Finally if this is true pull and release with no catch then having a rolling grip on the pull back handle will make a huge difference, if you don't know what I mean I can try n find a pic but its a pretty common thing in modern bows, simply allows you to release it smoother and faster, which translates into a much better plunger stroke.

Best of luck, the aesthetics look awesome

Aj

>>Aj: thanks for the tips. I might throw a spring in there, although I have to check out what springs I can get at the local Bunnings. I found some nice steel brackets I could use to reinforce the arms with, and they're not too huge, so they don't throw off the aesthetics too much 8). Only problem, thanks to a busy work schedule, I won't be able to get down to Bunnings for close to two weeks

Still, I can't wait to get started on this baby, she's gonna be a blast!

Its been a few weeks, any update on this?

I too am awaiting some results/updates, even if they are only preliminary.