Knex MG 3252 Prototype (UPDATED 5/31/2011)




Introduction: Knex MG 3252 Prototype (UPDATED 5/31/2011)

About: I paint, write music, and used to build knex guns. I have a Bachelor's Degree in Studio Art. - updated 5/7/2014
First of all, watch the video and study the pictures, my explanation below primarily explains what they leave out.

This gun is powered by elastics attached with string to a wheel, which in turn is attached (by the same string) to a white connector that acts as an anchor and spools the elastic around the wheel. When the trigger is released it spins a series of gears which are set up to multiply the speed of the spinning gears at the front of the gun (6 times faster at the front row than the back row). It fires gray connectors from a magazine by making the rounds come in contact with a treaded spinning wheel. The friction from elastics pushing up the rounds against the rubber treads provides enough friction to push the connectors out at speed. Currently, however, it has 1 foot of range. This is because a: a lot of energy is lost by spinning the crank when it fires, and b: the tan connector that holds the gear in place on the rod with the crank attached pops off it there is too much pressure, so I can't increase the elastic tension. I tested this without the crank and it got about 4 feet of range. If the crank and tension limitations can be overcome 20 feet of range seems achievable. I didn't bother putting a lot of work into the way that the mag attaches to the gun because I decided to ditch this version.

I'm posting this because I wanted to throw it out there for people to think about. There are a handful of new concepts within this design. I think I'm going to be tearing it apart to build a derivative version based on what I've learned here.

UPDATE: New photos and a new video is up. The new photos start at picture 15. I made the crank capable of being slid back and forth to disconnect it from the gear system and eliminate the problem of wasted energy. I made the gun wider at the back to make room for more structurally stable mechanisms. I changed the gear that the crank rotates to a smaller one so that it is easier to crank and is capable of winding the elastic back further. I estimate that the treaded wheel is now spinning about 4 or 5 times faster (just a guess). However, the gun still gets 4 feet of range. This seems to indicate that the treads on the tire only provides enough grip to fire 4 feet no matter the speed. Therefore, I will be creating an alternative firing mechanism. But don't worry, I have some ideas that should work. 20 feet of range is looking more and more attainable.

Here's the new video;
For some reason, embedding isn't working right now.




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    70 Discussions

    I'm on version 7 at the moment. I've made 3 mlcad models, created 3 hard-copies, and done 14 pages of drawings for this so far. I'm going to keep working on this until it's the best that it can be.

    I've mostly completed an "alternating" trigger design on the computer that will make the semi-auto trigger 100% reliable. I'm reworking gears back into the design to accommodate for the new trigger mech, as well as to split up the mechanisms to allow certain mechanisms to be thicker and sturdier to support the full tension of the firing elastic. The new version will be thicker to allow more space for the mechanisms as well as the addition of the gears. There's probably more to say than that, but that gives you some idea of what I'm doing now. The gun will likely fire 6 gray connectors 30 feet semi-automatically when version 7 is complete (I got 30 feet of range in a test on version 4 firing a single shot [but the gun had mechanical problems that would not allow multiple rounds to be fired, that is why I have been fixing them and beefing them up]). However, when I finish version 7, I plan to make a version 8 that will give the gun the ability to be cocked while a mag is in, allowing the user to cock and fire 1, 2, 3, 4, 5, or 6 rounds at a time as opposed to be being forced to cock for 6 every time, allowing the user to fire quickly while under attack in a battle. Sorry I don't have any good images to show you of the current version, it exists partly in drawing, partly in computer model, and partly in hard-copy. But here's a couple of mlcad images of version 5;

    SA 3252 2.jpgSA 3252.jpg

    You could make the crank a ratchet if you're still using it. That would reduce the energy lost from spinning it and the gun would shake a lot when going full auto. (I think)

    Dear Oblivitus,

    what if there were two wheels instead of one and they were slightly closer together which might cause pressure with the friction to shoot it out at faster speeds?

    1 reply

    Thanks for the reply. That would work, but I've already overcome the low friction problem, thanks.

    Hey man just made my mac-10 its more of a replica but still holds 20 rubber bands

    can u take a look and build my new full auto rbg that holds 20 rubber bands and shoots 2 a sec

    1 reply

    I got it firing 15 feet with the full auto trigger, the last round to fire got 7 or 8 feet because of tension loss as it spins. But it only fired 8 shots, while I estimate that the firing mech spins about 30 times, I reason that this is because the rounds were not fed into the chamber quickly enough. Therefore, I could have a 30 round capacity. However, because of the range reduction, I find it wiser to have an 8 round capacity AFTER the problem is fixed so that it will have minimal reduction to range (it will only be firing the first 8 out of 30 spins).

    So I developed a semi-auto trigger, but while the trigger mech works perfectly (a true semi-auto), it puts a lot of extra pressure on the crank because I used gear reductions to make the mech spin at the same rate as the firing mech to make it semi-auto, and it can only wind the elastic 1/4 the distance it was doing before and now fires rounds 5 feet. I was considering doing another gear reduction on the crank, but realized that the gears where the crank used to be would be subjected to the same amount of pressure regardless of this design improvement and I'm short on space for more tan clips and gears to divide the tension. I have a couple other ideas to fix the problem however.

    Regardless of the difficulties, I still have high hopes for this gun, if it doesn't work out for me now, it can still work for someone else later because it has essentially no limits. The bigger you make this thing, the more powerful it will become, even if that means adding multiple giant elastics to power it and making multiple sets of gears, all linked together in one system.

    If I get stuck, I'll post another slideshow to open it up to advice from the community again.

    if u could be able to deattach the crank after cranking it would be much more powerful

    Oblivitus, you are a true genius with K'nex! I am thinking about building a shotgun using the green rod method you had mentioned in one of your ideas posts.

    By the way, are you using some kind of gear-reduction style system for this?

    1 reply

    Great, I've been hoping someone would build that. Yes, I used a two stage gear reduction setup. And thanks for the compliment!

    UPDATE- 6/3/2011- Now fires 15 feet. (each consecutive round decreases in range down to about 8 feet. I'm working on getting more range next and will be trying to make it semi auto instead of a shotgun (it fires so fast right now).