14 replies to this topic

[Paragon]

I was originally planning on making a minigun but one of those is already being made so i drew up this design for an automatic belt fed machine gun. I made a short animation of it here:



A small electric motor is used to push the dart from the belt into the barrel past the small hole for the air resevoir. When the rod is back, another motor rotates and catches the next dart holder on the belt and moves that one into position. The barrel is sealed behind the dart and the air resevoir is unsealed accelerating the dart forward. Then the resevoir is sealed, the barrel unsealed, and the next dart put into the barrel which starts the process over again. The air resevoir would be filled with an air compressor.

There are three big flaws with this idea.

1) I don't know how I would go about sealing/unsealing the air resevoir and back of the barrel.
2) The timing on the motors has to be precise and while I've used servo motors controlled by a board programmed in C before, I do not have access to those and I do not know how to obtain those for cheap.
3) Whatever I missed.

I would really appreciate if someone knew a way to solve the problems with this idea. I'm going to try and make a simpler design if I can't think of anything to fix these problems.

Edit: Here is an idea for the sealing/unsealing of the barrel and air resevoir.

Edited by Paragon, 28 June 2006 - 10:10 PM.

[LastManAlive]

Unless you plan to use CO2 or something more compressed than just air in that little handle, you will not get anywhere.

[CaptainSlug]

I hate to be blunt but if you can't find a solution to the problem yourself you're not going to be able to overcome any potential problems you will come up against.
What you're proposing is very complicated.

And you cant put a hinged door in a round tube.

Edited by CaptainSlug, 29 June 2006 - 01:29 AM.

[Paragon]

The problem isn't that I don't know how to do it, the problem is that I do not know where I can obtain the materials. I've seen a hinged plug on a T-joint of a round tube so it must be possible. I realize that the current solution makes it semi-automatic and not fully automatic and I am thinking of simpler more reliable ways of going about this part of it.

I don't see how an air compressor fed into a 4 inch diameter PVC tube then fed into a 1/2 inch PVC tube would not produce enough pressure unless I missed something.

And I don't get why you are saying if i can't find solutions to the problems myself then i wont be able to overcome problems. I posted it on this forum for a reason, I could have just made the thing myself and posted the finished product when I was done. But if everyone is just going to say 'oh thats impossible' then why did I bother posting.

If I can get a hold of two servomotors and a programmable controller and a pressure sensor then I'll be ready to go. I know someone who has exactly what I need but I'm pretty sure he won't be willing to part with them. And so the problem is getting a hold of the materials I need.

You seem to think that just because I am new to this forum that I do not know what I am talking about. I have done things like this before but not all of it together. I've worked with servo motors and programming them to move in precise intervals at precise power levels. I've worked with making things that use compressed air to accelerate things. Based on my past experience with the things I'm using here, this design should work. I'm looking into simpler ways to do it because the simpler it is, the less things can go wrong during sustained use. However, I do not see how this is all that complicated.

[taz22]

there is only one problem.

you have now made your design and asked people for what they think.
in a few days you will think OMFG this is expensive ore hard to build and you won't build it.
now you just ask a lot of people to say what they think.
i know iv also did this a lot of times.

ok what i think. it won't work
1: the servos, sensors, motors will use a lot of battery so you will need something like 1 ore 2 car batteries.
2: the shells will be very hard to make, so you will only make 2 maybe 3 and then think OMFG this is expensive ore hard to build.
3: how will you be able to make sure all the motors will stop and turn around in time.
4: what will you need for air? you will need a compressor. you cant use a big one on so you have to use a small 12V one, and those thing does only make 4-5 bar. a good gun will only shoot at 10 bar.
5: how will you move that thing if you have 1-3 car batteries on your back? ehm.. not.
6: what if your batteries run out in a battle field?

so my advice. don't build it.


greats

[davidbowie]

You seem to think that just because I am new to this forum that I do not know what I am talking about. I have done things like this before but not all of it together. I've worked with servo motors and programming them to move in precise intervals at precise power levels. I've worked with making things that use compressed air to accelerate things. Based on my past experience with the things I'm using here, this design should work. I'm looking into simpler ways to do it because the simpler it is, the less things can go wrong during sustained use. However, I do not see how this is all that complicated.

You don't know what you're talking about. It's not difficult to program servos to move in precise intervals at precise power levels. That's what servos were designed to do. Also, if you're really experienced in robotics, you probably know that you can just go buy some servos, either from a hobby shop or online, and shell out $30 for a BS1 chip, which is all the computing power you would need for something that simple.

Making things that use compressed air to accelerate things? Everyone on this forum has used compressed air to accelerate things. That's a big part of why it's here. I'd bet you HAVEN'T had experience operating and sealing belt-feed, have you?

Here's the chip I was talking about:
http://www.parallax....oduct_id=BS1-IC

Get servos from a local hobby shop that deals in RC planes.

Everything else can come from Radio Shack.


Now.....GO!!!! build it.

[Pineapple]

I was originally planning on making a minigun but one of those is already being made so i drew up this design for an automatic belt fed machine gun.

....while I've used servo motors controlled by a board programmed in C before, I do not have access to those and I do not know how to obtain those for cheap....

...Whatever I missed.

I would really appreciate if someone knew a way to solve the problems with this idea.

You answered your questions yourself.

If you can't afford the components right now, you'd best wait til' you've got the goods on the table. Good intentions without actions are simply hot air.

Captain Slug is already working on his "minigun" themed blaster, and can tell you that it probably took a bit more resources than he anticipated. A project of that caliber requires a whole lot of extra financial and technological latitude to allow for errors and discrepancies that always occur between concept plans and workable product.

Anything automatic in nature will be difficult to take to final product stage. Flannel is still (after quite some time) working on his fully automatic Nerf stefan dart maker. It's still not making darts. The concept was great, but reality hems in the abilities both in the practical and in the financial sense. That's why so many of these concepts fail to get beyond mere pipe dreams.

I'm going to try and make a simpler design if I can't think of anything to fix these problems.

That's a pretty good idea. Carbon decided to simplify the masterful work of Boltsniper, and came up with his wonderful SNAP series of blasters. One (SNAP-3) of which sits unfinished at my worktable. Next to the unfinished FAR that I've been working on for over a year.



See, even I dilly-dally over these projects.

Nonetheless, good luck. Hope you can rise above the crowd of wishful thinkers with your shootin' machine.



-Piney-

[Paragon]

I have thousands of dollars and a full time job that pays for my housing and all the bills associated with housing. That means lots coming in, very little going out. I have the financial resources to do this.

taz, you seem to thing I am going to use some rediculously powerful motor in a place where a small servo is sufficent. The ones I have worked with could run for a long time on 8 AA batteries. The only thing that will take alot of power will be the air compressor and you can get over 250psi on some of those. I also don't do battles or anything like that, I'm making this just to make it and because it will be cool when I'm done with it. I don't need it to be that portable.

davidbowie, I'm not talking about working with compressed air for some some dinky little nerf gun. I'm talking about shooting baseballs and other similar objects using large air compressors. Since it was a group project I do not have that compressor nor would I want to use one that big for this anyways. And obviously, one of the reasons I'm doing this project is to get experience in making a belt fed gun. Also, you realize that you can't just shell out $30 and buy the chip. The chip is worthless when you don't have the stuff to program with it. So, it's more like shelling out $80. And while that is do-able, I am trying to keep the cost to a minimum and I have yet to find something in the price range I desire. I have all that money saved up because I don't just find what I need and jump on the first one, I look around and try and find the best deal.

Edit: Simpler trigger design (the light blue is air):

Edited by Paragon, 29 June 2006 - 04:24 PM.

[CaptainSlug]

Firstly I think you should stop trying to ram-load the dart into the barrel. That's where most of your mechanical complications are taking place. If you could instead focus on turning each belt link into a sealable part of the barrel you could simply your system greatly. Keep-It-Simple-&-Stupid is the way to go and if you can even unify the mechanism of advancing the belt with the one required to time the firing you'll be much closer to having a feasible design.

Captain Slug is already working on his "minigun" themed blaster, and can tell you that it probably took a bit more resources than he anticipated. A project of that caliber requires a whole lot of extra financial and technological latitude to allow for errors and discrepancies that always occur between concept plans and workable product.

And machining skill can't be overlooked. Especially when you're trying to get several moving parts to work in unison to perform a single operation cycle repeatedly without failing from wear. Just finding the time top make the intricate parts is proving difficult for me right now.

Your current plan is not mechanically graceful because each stage was interrupting the function of the other stages so your rate of fire would be pretty slow in comparison to a manual cycle. Plus you can't find solenoids with enough travel length to push a dart that far and other options would do it too slowly.
The other problem with belt-fed is that you have to load such a large number of darts in advance, and make a consistently dimensioned belt.

I can think of several way to accomplish a belt-fed compressor powered machine gun. But it's still far more complicated than even I would care to undertake because it would require servo timings or complicated valve systems.

Edited by CaptainSlug, 29 June 2006 - 05:17 PM.

[Paragon]

Actually, the common acronym is "Keep It Simple, Stupid". I am trying to get the design down to only one motor that advances the belt. I agree that the ram loading idea is problematic.

Edited by Paragon, 29 June 2006 - 05:34 PM.

[davidbowie]

Actually, it's more like $30 instead of $80. You need a breadboard and a serial connector to program it, which might get up to $10. Granted, something like an Atmel might be cheaper, but basic stamps are just so EASY. All the other electronics (resistors, battery connectors, wires) shouldn't cost more than $5. Servos are usually at least $15 each. That looks like about $75 for everything, minus PVC.

As for air cannon experience, we all love to bust out some Dual-Supah, 3" barrel, Twin Chamber nightmare, or a Coax with an 8" chamber and a full-port piston valve piloted by a 3" Irritrol and smash concrete block walls with bean cans and baseballs, but "some dinky nerf gun" would be many times more useful for this project than a big meaty standard air cannon.

Something else to check out is this:
http://neospud.com/c...es/cylbelt.html

There's a great description of the mechanism on the Spudtech forums, but the link wouldn't do you much good until you've registered there. Which you should do. Now.

[Carbon]

The biggest problem I see with your trigger designs (both of them, actually) is that they rely upon a full pull of the trigger to seal the action. In your revised trigger action, there will still be a time period where the air will be allowed to escape, but your trigger action will not be completely sealed against the bottom of your barrel...during which you'll lose pressure. The problem would be reduced by a fast (and hard) pull on the trigger....not something desirable in a trigger action.

[taz22]

OK, if you are olready using electris go for a electric sprinkler valve for the valve. and program it.
I like that one from the link, but do you see the belt? Do you see how complicated it will be to build one that can hold a lot of nerfs?

greats

[Paragon]

I figure if I'm going to make something belt fed, I should make it like the real belt fed guns and use the same kind of mechanism. So, here it is:

http://yoda_24.freep...elt fed mk2.mov

It's basically the ammunition belt feed system here: http://science.howst...achine-gun2.htm
I had looked at that page before starting any ideas but I first wanted to see if I could make something different that worked. But this seems to be the best approach.

[davidbowie]

Well, it works in theory, but I hope for your sake that you have a lot of CNC access.