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iamscottym
02-06-2011, 03:33 PM
Has anyone given any consideration to building an airsoft gun from scratch for their mech? I was heavily into airsoft about 10 years ago so I'm very familiar with the mechanisms in AEG's (automatic electric guns) as well as gas guns.
Here's an animation of the internals in an AEG.

http://en.wikipedia.org/wiki/File:AEG.gif

The motor drives a sector gear that acts on a rack on the bottom of the piston which compresses the spring. The tappet plate (long thin black piece) is actuated by a pin on the sector gear (shown as a very small black circle on the sector gear in the animation) and loads the next bb in place. The front of the tappet plate has a hollow nozzle that allows air to pass through to fire the bb.

I have a design for light, simple gun I'll be CAD'ing up and building this week. Its essentially a hybrid gas and electric design. It would use a crank-slider linkage in lieu of the gear mechanism in an AEG to move the nozzle back and forth to load the bb's. The bb would be fired using compressed air or green gas injected with a solenoid valve. I'm a big fan of SMC's "one touch" air line fittings and their small solenoid valves. I have some of them laying around I'll use to build a prototype.

I'd like your input on this.

Slugman
02-06-2011, 04:35 PM
I considered it, as I cannot get airsoft guns. I worked out how to build a pellet gun with a high rate of fire, using just one motor, 4 cogs & one servo, but it would be still be classed as a firearm by my local authorities, so I haven't made it & probably never will. :sad:

I was looking at the "Bowling machine" method of imparting energy to the pellet, which should get the pellet to about 15-20m/sec with the motor at approx 10,000rpm - Probably OK for short range stuff like Mech warfare. Pellets would have gravity fed into the two spinning wheels, so rate of fire would be as fast as the pellets could get into the chute once the servo let them in... :happy:

cire
02-06-2011, 04:43 PM
I think everyone has thought about it, but I think that at this current stage in the existence of mech warfare most people are more focused on getting the rest of their robot working before they start making guns from scratch. Additionally, right now you are only allowed to use electrical power for shooting your BB's in the air soft league which most people are competing in. More powerful guns could shoot through the mesh that protects the audience, so they are only allowed in the "hardcore" version.

Regardless, I don't think the current options for guns in mech warfare are very great, they are heavy and hard to mount. Personally I want to look into something different next year if i can get some better manufacturing capabilities.

sarendt
02-07-2011, 04:27 AM
I am interested in this subject as well. I concur with Cire about needing a working bot first. I'm not in a position to start building a complete bot at the moment so as I build up a inventory of parts I am learning how to use them and also working on the very basic design. In general I am attempting to design the bot before I build it in an attempt to have a efficient design.

I am also very excited about what the future of mech warfare holds, in five years we could be having some wicked cool fire fights!!

Cheers,
Scott

iamscottym
02-07-2011, 08:40 AM
I guess I don't see what's so difficult about getting a quad up and running (running well is another matter). Granted I've only built a hex before but that was back before all the nice pose capture software and dynamixel servos. I'm just waiting on some parts so I can put together an all RX64 quad. pyPose + NUKE should get it walking in a weekend. I suppose I could go with an EX106 design and just slap a full sized airsoft gun on it but that's not a very elegant solution.

sarendt
02-08-2011, 01:15 AM
iamscottym, clearly your budget constraints aren't the same as mine, that's been my biggest hold up, that and a nice space to work on it.

It would be cool to see some CAD drawings of a home brew airsoft weapon. I was also curious about the possibility of using a solenoid (http://en.wikipedia.org/wiki/Solenoid) to fire the airsoft gun instead of a spring? I don't know enough about these to know if it is practical though.

My idea was basically to use each 'stroke' of the solenoid to push air out of a chamber. You could then tie those chambers to a single barrel or to two different barrels. I think this might be better than how the air soft guns currently work, but with out trying it I don't really know.

iamscottym
02-09-2011, 12:15 AM
Sarendt,
A solenoid would not be fast enough to generate meaningful pressure to fire a bb. I suppose with a big enough solenoid it might work but it'd be a 5lb+ unit and far too heavy for most quads.

I talked to Andrew and got the bad news about using compressed air. Its back to the drawing board I suppose. I bet I can still improve on the little defender guns.

sarendt
02-09-2011, 02:51 AM
Iamscottym - What is the typical spring constant for the springs in airsoft guns? Is it possible that we wouldn't need such a large force as airsoft guns are looking at a typical range of 20-30 ft vs. mech's I would guess need something along the lines of 5-10 ft?

-scott

edit: here are some links to a Solenoid that seems like a possibility: little over a lb and produces between 0-25 lbs of force depending on stroke length etc. The first link has general data, the second link is force chart for the same solenoid.

http://www.solenoidcity.com/solenoid/tubular/S-29-150hp1.htm

http://www.solenoidcity.com/solenoid/tubular/s-29-150hp2.htm

iamscottym
02-09-2011, 11:06 PM
sarendt,

I don't have a spring handy to check but an M100 in a regular aeg is about a foot long and requires 10-12 lbf to compress it. That puts ks= 1lb/in. A spring in the little defender guns is a lot shorter and weaker. I'd put those about 4" long and maybe 3lb force.

As I said before, its not that the solenoids can't generate enough force its that they're not fast enough. A solenoid has a heavy steel plunger it has to accelerate. Meanwhile, a very little pressure will build up behind the bb as the steel plunger starts to move. The bb will start to move and will be out of the barrel before the steel plunger has accelerated enough to generate the larger pressure required fire the bb quickly. A conventional spring airsoft gun has a piston that weighs a fraction of an ounce that can accelerate really quickly. Thus he piston creates high pressure in the cylinder before the bb has a chance to get moving down the barrel. Does this make sense to you?

billyzelsnack
02-10-2011, 09:05 AM
Pellets would have gravity fed into the two spinning wheels, so rate of fire would be as fast as the pellets could get into the chute once the servo let them in... :happy:

This is pretty interesting if it worked reasonably well. You could definitely make this mechanism compact and lightweight.

sarendt
02-10-2011, 10:27 AM
iamscottym,

I think I get what your saying now! Thanks :*)

scott

Slugman
02-10-2011, 05:18 PM
billyzelsnack - I actually started making it a while ago, but when I looked at motors & their speeds, I had to abandon the original geared up design with skinny cogs, as a typical 10,000rpm motor would have spun it to bits - The wheels would have been trying to reach 40,000rpm - Am looking at using thicker cogs with almost no gearing (40-tooth to 36-tooth, as that was what they had available), & have simplified the original design to bare-bones - I don't need 8 rotating barrels around the central shaft which is actually the real barrel. :happy: AX12 will still move a lever to lift one end of a chute, which lets/stops the pellets go into the tube leading to the wheels. Chute will be 1/2 times the diameter of the pellets to try to prevent jamming etc etc
I cannot get to Mech warfare, but if I can set off an arms race by putting an idea out there, then I can say I have helped in the bringing of Judgement Day.... :tongue:
I don't need to mention that everyone should be concentrating on getting their mechs moving first before worrying about this sort of thing, do I? :rolleyes: Unfortunately that lets the guys with already developed mechs leap further ahead of the rest, but it gives everyone else something to aspire to.
FYI - Currently using Traxxas #3953 & #3955 gears, & radio-control aircraft landing wheels (More rotating mass, & they are rubber so will grip the pellet) so the thing is actually pretty big - Still working out how to lock the thing together at the moment.
Since you have thought about it, & hopefully can visualise what it would look like, can you imagine what a certain large biped would look like with one of these on its arm? :eek:

The only problems I can see with using it on a robot would be;
1 - Not able to hold enough pellets in the hopper - May be able to get smaller pellets? - Kinda like using an M16 instead of a 50-cal. I am designing for 4mm beads, which I can get cheaply, which also fit inside a 5mm thin aluminium tube, which I already have. The holes will stuff up long range accuracy, but who cares! It's about getting more plastic down-range quicker.
2 - Lag between starting the motor & getting the wheels up to speed, but that just needs either a time lag between starting the motor & moving the chute, or use a seperate trigger to "arm" the gun by starting the motors when you know you are going to need it soon.
3 - gyroscopic effects from the 4 cogs & two spinning wheels - They are spinning opposite to each other in pairs, so as long as you keep the whole thing horizontal, then it should be OK - Could turn left-right, but tilting up-down could be more difficult.
4 - The Hit-Point rules for Mech Warfare would have to be re-written to let single shot mechs be on an equal footing...

PS Shhhhhh. Don't tell anyone else, the design can be our little secret.... :tongue: