Lego Airsoft Gun (LAG21A): The World's Most Advanced Lego Gun Yet

Focus of project: Rate of fire, bullet speed/strength, ergonomics

So after obtaining a whole lot of experience with airsofting, I began researching lego guns in an attempt to find a legitimate handheld lego rifle. Unfortunately, the closest I came to was not what I was looking for, as the mechanism wasn't very orthodox and firepower was extremely weak. However, it was impressive nonetheless. Here's one of the various links to this weapon: http://mocpages.com/moc.php/87986 The weapon's creator is none other than Jack Streat, the internet's most famous lego gun smith.

A couple years ago, I embarked on a full-auto "brickshooter" project, for which I quickly threw together a prototype, whose main component was the firing pin. The firing mechanism was mostly inspired by the mechanism used in airsoft gearboxes:

As you can see, airsoft gearboxes utilize a sector gear combined with a spring-loaded rack gear. The area of the sector gear that has no gear teeth gives the rack gear a moment to launch forward and shoot the pellet, using an air-compressed funnel to intensify the pressure. However, Lego never released a sector gear element, and I wasn't about to break the teeth off any of my gears. Suddenly, I recalled a gear element that I knew I would never use, possibly from some old Bionicle set. I had it cut up, and then I sanded away the excess plastic. The part ID is 32311:

Be aware; these are the only custom elements I ever used to build this creation. Without them, the entire mechanism would not work. There are ways to make similar mechanisms while avoiding making custom parts, but I decided to take it easy this time since I planned to make the rest of the gun quite complex, as you will see below.

Unfortunately, I was having loads of homework at the time, not to mention a summer job and other, much larger lego projects, such as the second-generation Battlebots and the Arm Rover, and thus I wasn't able to finish the gun for at least two years. I should mention: the gun featured in this blog post was originally intended to be mounted on the Arm Rover, but I had to disassemble the robot to make the Battlebots. Also, if you look back at the Arm Rover post, you will see a skeleton of the lego rifle in the bottom-right corner of one of the pictures. Anyway, here's the first video I ever posted about my gun. If you are watching this video because of this blog post, ignore the annotations:

So, that version of the gun us cool and all, but I was having a big problem with the firing mechanism. The problem was that, since the firing pin shoots the bullets directly out of the clip, the first few shots would have less range than the last few. This is because the clip pushes the bullets upward, and so the first few bullets are under the pressure of all the bullets below them. As the clip would empty, the shots would shoot further and further. At that I realized that I needed to come up with a mechanism that feeds every shot into a firing chamber before it gets launched. I began reseaching feeding mechanisms, both in real guns and in lego guns. I also tried very, very hard to find a motorized brick shooter that features a feeding mechanism, and soon I realized that I would be the first person in the world to make one. I found plenty of lego guns that had interesting feeding mechansisms, but every single one of them had to be recharged after every shot. I also came across hundreds of "automatic" lego guns, but nearly all of them fired rubber bands, which do not constitute as "bullets" in my book.

Before you continue: Just to confirm some "brick jargon", keep these definitions in mind. Lego fans can skip this section:

                                                         Left: "Brick"      Middle: "Technic Brick"       Right: "Technic Beam"

Also, since bricks can be stacked, there are thinner variants of them called "plates":

Left: "Plate"                     Right: "Flat Plate"

Three plates can stack to match the height of a brick.

After drawing a few primitive diagrams of what I wanted the final mechanism to look like, I decided on how to build the feeding pin. There was only one problem; the pivot joints that were in the feeding pin had to fit a frame made in Lego, meaning that I couldn't just place levers on levers wherever I wanted (as you will see, the feeding pin consists of three levers). And so I made "The Grid", a Brick-Technic interface that provided layered rows of Technic pinholes, in the medium of studded Legos. This technique is widely used in lego creations that combine brick parts and Technic parts. The methodology for making one is quite simple: between every layer of Technic bricks, place two layers of plates, like so:

Left: Technic bricks and plates              Middle: A small Grid             Right: The Grid with a VERTICALLY placed Technic beam

It is obvious that you can always place Technic beams in parallel with the Technic bricks they are mounted on, but to mount them vertically, the Grid method above must be used.

After tinkering around for a very, very long time, I figured out a way to place all the pins in the proper places to lay the angled "mag well", feeding pin, firing pin, and ratchet (or, as they are in airsoft gearboxes, the "anti-reversal latch"). I filmed a very long "update" video explaining how they all work, but it's over 17 minutes long and I talk too much, so I'm going to skip it here. Then, after almost a year of academic subjugation, I finally resumed building the rifle. I added the mechanism that I had the most trouble with: the trigger assembly. The reason I had so much difficulty with it was because I strongly avoided expanding the Grid I had already made, as I feared the stock, which would house the batteries, would be too far back. Originally, the trigger was meant to be directly connected to the batteries, but that didn't work very well. The parts that now activate the motors are a pair of PF switches. I needed two because the motors on the left side needed to spin in the opposite direction as the motors on the right side, and the control switches have a small black sliding switch on them that changes the direction of the circuit, which was very useful:

 When I thought about how much trouble I went through the last time I attempted to lay the trigger switches, solely because I did not want to expand  the Grid, I basically thought, "To hell with it," and I made the Grid longer. It only took a few minutes to get the perfect trigger mechanism that held the trigger at the perfect pressing angle, as you can see in this next video:

Then I ordered two more XL motors, raised the gear ratio, and perfected the ratchet release mechanism (all such guns need ratchets, because if you let go of the trigger when the mechanism just loaded a bullet without firing it, it will unwind and load a second bullet into the same chamber next time you fire, possibly exploding the gun). All these upgrades are in this next short video:

After that I rebuilt a mechanism I attempted to make before, which I call the "blocking door". Basically, it is a small piston that pops up to hold the bullet from falling out of the firing chamber, and it goes out of the way the moment before the bullet fires. This allows for the gun to fire at all angles that point downward, because otherwise the bullets just fall out before the firing pin slams into them:

As you just saw, I experimented firing with a Technic barrel but found that it caused too much friction. In Lego guns, that's unfortunately the case; the longer the barrel, the shorter firing range you get. In real steel guns, longer barrels allow the explosion to propel the bullet further, and in airsoft guns, the air compression has more room to launch the bullet (and barrels with smaller inner radii also propel the bullet with more strength). In Lego, however, although they provide more accuracy, barrels only cause friction with every shot. I figured out a simple solution to this problem: remove the top and bottom slices of the barrel. That's right, make it a rail-gun. Except without the magnets. This minimizes barrel friction while retaining accuracy on the horizontal axis, as vertical accuracy is never exceptional with Lego guns anyway. Also, I finally made a Grid for the right side of the gun, which was the most difficult step because I had a shortage of parts. I had to get creative and and use solid bricks wherever I could to harvest some extra plates and Technic bricks I needed to use elsewhere. In fact, this step was so tricky, I had to create a digital map of the Grid in LDD as an aid for the process:

Using that 3D model, I was able to completely disassemble the left-side Grid and rebuild both of them fully with black parts. Thank you Lego Digital Designer! Anyway, all the upgrades I just mentioned can be seen in the next video:

Shortly afterward, I did some body work, and "cut the corners" of most of the right-angles in the hull design. I also added sights on the hull and the barrel to add to the realism. I also perfected the ugly stock design from the last video, and made it much more convenient to turn the battery boxes on and off. Basically, I finished the gun, and I named it the LAG21A, meaning Lego Airsoft Gun, 21 round magazine, model A (as I hope to make B and C models). I also got some help from my family to film this video:

After I posted that video online I felt the need to open it up and show what's inside, and so I filmed this video of how all the internal mechanisms work. It's a long video, but at least watch the first few seconds since I spent so much time making the "laggy" intro. :)

So that's it. You have just read everything about the world's most advanced fully-automatic Lego brick shooter (yes, it really is the most advanced AUTOMATIC Lego gun, that is until someone takes this mechanism and makes it better, perhaps myself). Please leave comments if you so desire.

Lego Airsoft Gun (LAG21A)
PF Contents:

2 Battery Boxes
4 XL Motors
2 Control Switches