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Direct Propulsion Crossbow

DP series blaster #3

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#1 hamoidar

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Posted 19 November 2012 - 09:42 PM

Again, all credit for the catch design goes to Meaker IV.

Also, I decided to go green, and used a bow drill for all the holes.

This blaster is a continuation of my direct propulsion series, which started with the cardboard pistol, and the DP pistol. I don’t really think that I can call this a gun, as it is quite literally, a crossbow. Now don’t you wish your middle name is Archer? (like mine)

I made this bow solely for testing the range capabilities of direct propulsion blasters.
Being a prototype, this bow is neither pretty nor clean, and I don’t really care. : )


PARTS:
˝” PVC
˝” thick cutting board
1/8” thick Polycarbonate
A few random screws
A small spring
A bow*
Electrical tape
Kite string

*I made the bow out of a straight branch found on a tree in my backyard. You could use ˝”CPVC, if you are totally lame. Let your inner caveman shine, and use real wood!

TOOLS:
Screw drivers
Drill + bits
Dremal + bits
Branch clippers
Band saw or scroll saw (you could use a hand saw…I guess)

Time to start. (Note: Before you cut, make sure your PVC is not bowed...)

First, cut a 16” long section of your ˝” PVC:
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Now, cut a 1/8” wide slot on either side, leaving about an inch of PVC at each end:
(I would say that cut is straight as an arrow…)
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Drill a 3/8” hole on one end, perpendicular to the slots:
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On the other side, drill a tiny hole (1/8”), and cut a ˝” by 1 ˝” slot:
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The holes should line up:
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Next, make two of these: (MAKE SURE TO DRILL ALL THE HOLES PICTURED)
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They need to be opposed to each other, like this:
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Cut a ˝” by 1/2” by Ľ” piece of cutting board:
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Bevel the top:
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Drill a hole through the side:
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Stick a nail through the piece pictured:
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Add the cutting board chunk that you just made:
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Make the catch:
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A better picture:
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You need to have a pole in the catch that sticks out 1/8” on both sides:
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Attach the catch to the piece which has the cutting board chunk on it, as pictured:
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Make the handle:
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Tape on a spring like the one in the picture:
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Now, screw the catch/cutting board chunk/side plate onto the handle:
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The spring should line up with the notches in the trigger:
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Make this:
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Screw it to the handle:
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Attach the second side plate:
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Drill a hole in the handle:
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Screw the handle/catch to the pipe:
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Add a small bow and you’re done!!!
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Here it is cocked:
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Close-up of the catch/string:
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I am currently working on testing the ranges with different darts, and bow tensions.
I should have the data finished by Friday.
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#2 Foam Ninja

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Posted 19 November 2012 - 11:28 PM

What kind of wood did you use as the bow?
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QUOTE(Soothsayer @ Jul 18 2010, 03:51 PM) View Post

Still haven't beat Foam Ninja in a sword fight


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#3 hamoidar

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Posted 20 November 2012 - 10:15 AM

What kind of wood did you use as the bow?


A branch from a Crepe Myrtle.
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#4 Meaker VI

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Posted 20 November 2012 - 11:42 AM

You, sir, are a prototyping machine! I wish I could get that kind of shop time. Looking forward to more data, good work otherwise.
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#5 Griever 2112

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Posted 20 November 2012 - 01:33 PM

Color me confused... how exactly does this fire a dart though? Either I am not thinking out of the box, or I just don't get it... anyway of getting a firing video?
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#6 BiwinningPanda

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Posted 20 November 2012 - 02:22 PM

Color me confused... how exactly does this fire a dart though? Either I am not thinking out of the box, or I just don't get it... anyway of getting a firing video?

I am pretty sure that the dart is placed in front of the bow string, and the momentum it gains propels the dart when the string stops moving.
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#7 Meaker VI

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Posted 20 November 2012 - 02:50 PM

I am pretty sure that the dart is placed in front of the bow string, and the momentum it gains propels the dart when the string stops moving.


This is correct. The dart is 'directly propelled' by the firing mechanism, rather than using them to compress air which fires the dart. Vortex blasters are an example of another method of direct propulsion.
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#8 Zorns Lemma

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Posted 20 November 2012 - 03:32 PM

Since your "barrel" has slots cut for the bow string, your dart is going to encounter disastrous energy losses that make this mechanism much less efficient than a pneumatic.

Kane has had the adventure already from Autobow (http://nerfhaven.com...showtopic=19632) to AAbow (http://nerfhaven.com...showtopic=20086)
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#9 hamoidar

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Posted 20 November 2012 - 03:45 PM

Since your "barrel" has slots cut for the bow string, your dart is going to encounter disastrous energy losses that make this mechanism much less efficient than a pneumatic.


I'm not quite sure what you mean when you say that the slots make the bow inefficient. Do you mean that the dart gets stuck/creats friction along the slots?
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#10 Meaker VI

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Posted 20 November 2012 - 05:31 PM

I'm not quite sure what you mean when you say that the slots make the bow inefficient. Do you mean that the dart gets stuck/creats friction along the slots?


I could see how that'd be an issue - unless you can sand the inside of the slots, they'll have burrs that stick out. I was planning on building a square barrel, as you've done previously, which would alleviate that particular issue.

Kane has done something similar, but his Autobow didn't use slots and had a plunger that pushed the dart rather than the bow doing it directly, adding the mass saved by not having a plunger back in (albeit, so that he could also use mags easily). Carbon pointed out that DavidBowie has also done basically exactly this in his KISS series, which he said got ~50-75' ranges.

Where I think this is an improvement is in your use of a dart-pusher (pencil, 1/8" steel rod, etc) that is connected to the bow/springs/bungies. You don't add much mass, but you do reduce friction and control the interactions between the darts, the trigger, and your power source better.
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#11 hamoidar

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Posted 20 November 2012 - 08:02 PM

I could see how that'd be an issue - unless you can sand the inside of the slots, they'll have burrs that stick out. I was planning on building a square barrel, as you've done previously, which would alleviate that particular issue.

Since the PVC is flexible, you can widen the slot enough to get sand paper/Dremal in there to sand the burs down. A square barrel may help with friction (somewhat), but I can say that with the PVC one, the ranges are around 70ft flat. (conservative estimate)
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#12 Paloose

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Posted 20 November 2012 - 10:40 PM

Its interesting to see the catch designs of this compared to those of historic crossbows. Granted, we're not working with a draw weight heavy enough to warrant a lever system, but its still cool none the less.

http://www.myarmoury...hlight=crossbow
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#13 Meaker VI

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Posted 21 November 2012 - 11:58 AM

Since the PVC is flexible, you can widen the slot enough to get sand paper/Dremal in there to sand the burs down. A square barrel may help with friction (somewhat), but I can say that with the PVC one, the ranges are around 70ft flat. (conservative estimate)


Doh! Totally forgot that sandpaper exists. Well, that was my guess as to the opposition; if it's getting 70'+, I can't imagine what the issue would be. That's great, and a clip/hopper/mag mech shouldn't be hard to figure out. If I'm reading DB's site right, I think he came to the same conclusion I did to solve that issue - rather than have a larger, heavier 'bolt' fire the dart and block the mag, use a secondary breech to block the mag. I was planning to rubber band a block or piece of PVC so it'd block the mag opening once the dart-pusher was released.

Its interesting to see the catch designs of this compared to those of historic crossbows. Granted, we're not working with a draw weight heavy enough to warrant a lever system, but its still cool none the less.

http://www.myarmoury...hlight=crossbow


I forget if Hamoidar and I were discussing that in PM's or the other topic, but traditional crossbow catches got brought up somewhere. Possibly good future inspiration, though I'm a fan of the pistol grip personally and traditional catches use a lever trigger that wouldn't fit the grip. Also, this trigger involves a minimum of work. If you find an interesting, easy-to-build catch, or one that is still cheap but uses off-the-shelf parts and isn't a clothespin, that'd be great though.
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#14 Foam Ninja

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Posted 21 November 2012 - 02:28 PM

If I were you (this is only a suggestion), I would eventually change that wood out to a Yew or an Osage Orange. Yew is softer and has high elasticity, but Osage is dense heavy and has the same properties. It all depends on how long you want your bow arms to be.
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QUOTE(Soothsayer @ Jul 18 2010, 03:51 PM) View Post

Still haven't beat Foam Ninja in a sword fight


QUOTE

1.The baby would blow up do to being made of pure fail.
2.I GIVE UP! I AM GETTING MY GAS ELSEWHERE!!
-Nerf Mafia

#15 wardrive

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Posted 22 November 2012 - 05:19 AM

That catch is beautiful, so simple and yet so effective.
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#16 hamoidar

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Posted 24 November 2012 - 12:39 PM

I'm afraid that I will not have the range data for another few days. : ( I was trying to increase the draw on the bow and ended up cracking it in half. I tried using my longbow, but it just smashed the darts. I'm going to Lowes soon, and will pick up some CPVC.
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#17 ProfessionalNerf

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Posted 08 December 2012 - 10:48 PM

man, beautiful concept, simple sweet. making the ordinary extraordinary, I like it
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