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Knex Controllable Machine Gun Answered

This is where all future models of our machine gun will be posted. This is a project of a collaboration between me and theawesomestdude. We hope you enjoy. Suggestions and help and models and feedback are welcome.

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sonic broom (author)2015-02-03

So is this just a rubber band gun that fires one Rubber band for each trigger pull if so then maybe you should look at this gun it does the same thing but it has a much easier mech https://www.instructables.com/id/Knex-Rubber-Band-Gun-8/ i built it and it worked great.

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TheDunkis (author)sonic broom2015-02-04

No, that's exactly the limitation we're trying to get over. We want a fully auto, but also controllable, slingshot. Normally, if you just let all the rubber bands go, they fire incredibly fast, seemingly at the same time you could say. It's more of a shotgun in that sense. And that's assuming it doesn't even jam up. So, we've been studying different methods to make a "controllable" full auto, that is it would fire at a slower rate. One of the methods I proposed (and others such as myOmy may have independently as well) was to create a mechanism where the band that was just fired will trigger the gun after it reaches a certain point. The difficulty in this so far has been making a strong enough trigger mech that can take the stress of upwards 8 bands but still be actuated by the force of just one band. You can see where physics isn't our friend here.

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Mepain (author)TheDunkis2015-02-04

Try something like this:

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

Mechanism around 2 minutes in.

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myOmy (author)Mepain2015-02-07

I have a working prototype like the video shows, but youtube is being stupid right now . . . so yeah.

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TheDunkis (author)Mepain2015-02-04

Thanks, but I've no problem with the concept itself. I'm struggling to think up a trigger design in K'nex. I basically have the gist of what I'm trying to accomplish, a trigger mechanism that slides off the cog and catches it by like a hair, something easy for the power of one band to actuate. But I just can't figure out any combination of parts and layouts that do that. I ask for help and haven't seen a trigger like that yet. Meanwhile, people keep spitting out these proof of concepts and I get hopeful but then they say stuff like "It doesn't work well with more than 2 bands" and then it's back to the drawing board.

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myOmy (author)TheDunkis2015-02-07

I have a working prototype like the video shows, but YouTube is being stupid right now . . . so yeah.

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didexo (author)Mepain2015-02-04
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sonic broom (author)TheDunkis2015-02-05

The gun that i gave a link to is controllable it fires one band upon pull of the trigger and can hold more then 8 bands

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TheDunkis (author)sonic broom2015-02-06

But it only fires one band. That's called semi automatic. What we're talking if fully automatic, hold down the trigger and it'll keep firing at a consistent fire rate.

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sonic broom (author)TheDunkis2015-02-06

okay now i get it hope to see a working gun made with this if it's so awesome. but any way why not just use a motor connected to the cog to spin it at a constant rate and pull the trigger to switch the motor of and on.

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TheDunkis (author)oodalumps2015-02-04

Correct me if I'm wrong, but doesn't that work pretty much on friction? Like, he's only retarding the cog's spin, not actually controlling it? From the comments below, he's claiming it fires upwards 1200 RPM, still fairly fast.

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oodalumps (author)TheDunkis2015-02-05

No, he's using a piston that moves back and forth. Momentum limits the ROF.

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myOmy (author)sonic broom2015-02-04

Yep, precisely as TheDunkis said.

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knexguy237 (author)2014-10-23

This is pretty nice. I don't know if you've figured it out yet, but how will the full auto stop?

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myOmy (author)knexguy2372014-10-23

I abandoned this for about a month because it was pissing me off but in the past week I have got a little farther than before. As of right now I have a theory of how I will stop it but I am not sure because the full auto mech is not fully complete. As of right now, it looks nothing like it does in these two videos. I have mainly been trying out different ways to make it have less friction by designing different cog/trigger designs. I know you are quite mechanically inclined so if you want to give this concept a shot, please do.

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TheDunkis (author)myOmy2014-10-27

Keep at it, man. Yeah, I struggled to find a good trigger and cog mechanism that had low enough friction. Literally years and years have gone by. And my thoughts for a trigger mechanism is there'd be a "real" trigger that the piston operates and then a user trigger that either manually operated the cog or the piston once and then would let it fire uninterrupted until the trigger is let go, then it'd either stop the piston or stop the cog from advancing.

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knexguy237 (author)myOmy2014-10-24

Yeah, I was thinking of starting to make this is try it. I feel like it would be fun, but I'd probably destroy it after it made me mad, haha. But yeah, I'll try this mech after a couple of guns I'm working on right now. You seem to be doing really good so far with this though!

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didexo (author)2014-09-06
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JonnyBGood (author)2014-08-11

I'm intrigued.... I'm kind of interested to see how far you take this mech, mainly because it is a heck of a lot more complicated than I thought it was. You did however prove a theory that I've had for awhile now. I was predicting the first usable full auto would be a combination of both full auto and semi auto technologies. I'm just glad to see someone is fairly closer to figuring something out. Keep up the good work man!

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