This was made at LVL1, Louisville's Hackerspace. (see more at http://www.lvl1.org) Be sure to check your area for a hackerspace, they're a great place to meet new people, learn new things and get access to awesome tools.
Having a laser cutter or CNC machine will really help with this build, but they're not required. The pics in this tutorial were all taken after the gun was built, so everything is its final colors.
When building my weapons I try to make my weapons scaled perfectly and worry about the details later. There are a lot of miniguns out there, but most of them are scaled horribly. To me, the details don't really matter as long as the weapon is scaled properly.
Laser cutter or CNC machine
hot glue gun
really long Phillips head screwdriver
Rough List of Materials:
1/2" foam board
3/4" PVC pipe 10'
1/2" PVC pipe about 3' long
1/2" conduit about 1' long
4" PVC coupler
4" to 2" PVC adapter
3" PVC pipe 1' long
2" PVC pipe about 2' long
12" long 3/8" diameter threaded rod
6x coarse 3/8" nuts
4x 3/8" lock washers
2x 3/8" fender washers
4x 3/8" washers
3/8" inner diameter bearings
belt (and pulleys if you don't want to make your own)
black and white paint
other bits of scrap wood
Step 1: Make the Barrel
Cut six 1" diameter PVC pipes to 19" in length.
Use 1/2" foam to cut out 6 foam supports (8 for a static barrel.) This file is for a laser cutter which makes the final part a little smaller so you might need to scale it slightly to work with whatever method you use.
- Print the file onto a sheet of paper, glue to foam, cut out with a knife.
- Same thing, as above, but use a band saw or jig saw.
- Laser cutter
- CNC machine
- Mind bullets (advanced users only)
Four of these only need to look pretty, two need to fit snugly in the end. On all of them, the pipes should fit snugly; our entire barrel assembly is held together with nothing but friction and paint. If you're cutting the holes manually it is also easier to hide mistakes if the holes are slightly smaller instead of too big.
Test fit all of your foam pieces, then add a layer or two of Mod Podge. I know this sucks and it takes forever to let every foam bit dry, but if you don't Mod Podge the foam it will melt when you paint it.
The wood pieces are smaller and have a center hole for the axle. If you aren't going to make the gun spin you can skip the wood pieces and make two extra foam supports. Our first revision of this gun didn't spin and the barrel was just held in place by the friction of the foam in the funnel bit and a single screw on the top.
Fit all of the foam pieces together as best as you can. To get the individual barrels even cut a scrap piece of 1" thick wood to fit inside the end so you can press the barrels down against it.
Bolt the wood bits onto a 12" long 3/8" wide threaded rod (our axle). As you can see in the pics, I only used hardware to secure the very end support and then used the second support as, uh, support. The hardware I used was
nut - lock washer - washer - fender washer - support - fender washer - washer - lock washer -nut
Once the wood supports are attached to the axle, slide the wood pieces onto the barrels. This is kind of hard, I ended up pressing down on the wood support and spinning each individual barrel up into the support a little bit at a time. When you're done you will probably have to readjust all the foam supports again.
Step 2: Make the Ammo Barrel
Mark a line down the short side 1/2" from the edge. Every 1" to 1.25" or so put a mark for a rivet. We made ours unevenly spaced on purpose to match the game gun. Drill holes for the rivets on one side, the roll the sheet into a circle and rivet together. Once you get the rivets in it should naturally form a perfect-ish cylinder.
Trace the end onto a foam board and cut out three circles to help it hold its shape. One will be put in the front permanently, you can make this one as tight as you want. After you put it in, hot glue it into place from the inside.
The second one will be for the back end, but this one you will take in and out to access the inside of the gun. I made mine slightly big and tapered the edges. After a few fits it started to naturally sit in place. I would recommend putting a single drywall screw in it to pull it out..
The third piece will be for the middle, it will be a little looser and will need to be modified later to get around the backbone. It will be less for holding shape and more for keeping the barrel from deforming too far when the end piece is out. With the end piece out this barrel is very weak, be very careful with it so you don't deform it too much.
Step 3: Create a Backbone
Cut down two other scraps of wood to 8" long for the servo mount. These will be attached to the backbone and will support the servo (see pic for the complete part).
Also be sure to drill some largish (1/4-3/8") holes sideways through the backbone. This is so you can ziptie the battery down, if you forget this step you'll be taking the gun apart later...
Attach the backbone to the gun with a couple drywall screws through the ammo barrel. Be sure to pre-drill the holes so you don't split the backbone. Pay attention to where you place the backbone as this will determine where the seam lines up on the side of your gun. If you look at the minigun from the front you'll notice that the barrel is off center. I forgot this fact so our rivet seam ended up slightly higher than it should have been.
Step 4: Make the Main Tube
Just make some shallow cuts with a chop saw then use a drill or something to break the middle piece out. When you're cutting the slits do NOT let go of the trigger until the blade is all the way back up. If you let go while trying to balance the blade in just the right spot it will jerk down as it stops and ruin the part. This part doesn't need to be very exact, as long as the belt has some room to move.
Cut a small scrap of wood for a spacer. I used 3"x1"x5/8"
About 2.75" back drill a hole in the top (opposite side of the slit) for a screwdriver to fit through. On the other side drill a hole for a drywall screw, cram your hand into the tube, get the screw started in the hole on the bottom, then use a screwdriver through the hole in the top to attach it to the backbone of the gun. You'll want to pre-drill the spacer also so it doesn't split.
You don't have to attach it yet, you just need to know where this screw is going to go so that you don't cover it up with a bearing mount.
Cut round pieces to support the bearings of your choice. I went with some really cheap plain bearings from Lowes and the servo was able to power through the added friction but I would highly recommend getting some flanged ball bearings instead.
Once you cut the bearing blocks screw them into place with a single drywall screw. Be sure to leave them a little loose so they don't bind on the axle. In my pics I screw the the blocks into place from the top, you can probably do this from the bottom instead without making it harder to take apart.
Put the rear mount in front of the screw hole you drilled earlier (so you can take apart the gun later) and put the front mount about 1.25" back. For a exact fit press the PVC adapter in and butt the bearing block up against it (see first pic of next step for what I mean).
Once the bearing blocks are in test fit it on the axle to make sure it spins correctly.
Step 5: Mount the Main Tube
Hopefully your main tube should be tight on the top of the adapter. This will let us adjust the angle of the height of the main tube relative to the adapter. The barrel is so heavy, it will bend the axle slightly and the barrel is tight enough in the adapter that it this slump will cause it to rub. To compensate for this we'll add a screw on top of the main tube that will push down the adapter relative to the main tube. Once this is set correctly the gun will only spin when you're holding it properly, lay it on its side or hold it upside down and it'll set against the adapter enough to prevent movement.
When picking a set screw make sure to get something that isn't pointed on the end, otherwise you'll end up going through the adapter too.
If you're feeling really freaky you can try what I'd like to do for revision 3; make the barrel support and adapter into one giant custom ball bearing. This is how real mini guns are supported. I've included a rough sketch of the idea if you want to try it.
Step 6: Make the Front Handle
You can round the corners if you want, I was a little lazy and skipped this step.
Next cut a piece of 3/4" conduit for the front handle. I would cut it long, bend it, then cut the ends down to length. If it's a little off don't worry, the game gun is slightly lopsided too. (It's not a bug, it's a feature!)
To attach the pipe to the wood, we'll need to screw into the open end of a hollow tube (which generally doesn't hold for very long). To make the handle stay attached longer, jam a bunch of wood into the ends. Just cut some taper shaped pieces of wood and hammer them into the end of the tube until you can't cram anything else in there. Cut off the excess and then run a screw into the end of the pipe without pre-drilling. This will make all the stuff you crammed into the pipe even tighter and will create a stable way to mount the handle.
Mount the handle 1.25" from the edge.
Cut the V piece. This is where I really deviate from the game files, the method I show here for the V and the rear handle don't match the game exactly, but they were quick and easy to make. Revision 1 of this gun was finished at the con so I had to cut a few corners to get it done and this is one I never went back and fixed. It's a part nobody really looks at and there are other improvements I'd rather do first. If you can come up with a better solution let me know, if not plow on ahead!
Cut the V, and then bolt it to the top of the front handle base. I kinda cheated and used screws that looked like bolts.. :/
Step 7: Cut the Rear Handle
Use the attached file to CNC or hand cut the handle.
You should also cut the bottom piece now. This will be glued to the back foam piece for easy removal of the back piece.
Step 8: Mount the Handles
If you're going for a non spinning barrel don't trim the screws, they'll help hold the barrel in place.
Fit the rear handle in place, it should be pretty tight under the V. If it's too tight just sand down the end until it fits nicely. Drill a pilot hole from the top of the V through to the main tube. Remove the rear handle and make the hole bigger, this part is the most likely to split.
For the back of the rear handle, I just ran a screw from the inside of the main tube into the handle. This held pretty well, even with the foam since the back part of the handle gets pushed down in order to balance the gun. Most of the weight is held by the front handle.
Once the front and rear handles are in place, hot glue the bottom piece of the rear handle to the foam so it looks like a continuation of the rear handle.
Step 9: Get the gun ready to hold the barrel
Add two nuts and a lock washer to the axle about 1.75" from the last wood support. Just hand tighten for now, you'll probably need to adjust this soon.
Carefully slide the axle into the main tube. Make sure the nuts are back far enough that they're hitting the bearing before the barrel is hitting the back of the adapter. As you can see in the pictures, my front wood support is all the way out of the adapter.
Pick up you gun and see if the barrel spins nicely. If not:
- Check the alignment of your adapter
- adjust the adapter height adjustment screw covered in step 5
- back out the nut stops so the barrel is further out from the gun
- verify the inside of the adapter is smooth
- loosen the screws that hold the bearing blocks and make sure they're not binding
- double check that your axle is strong enough and isn't sagging too far
- give up and pretend you were working on a static, non spinning barrel all along
Hopefully you don't have to go with the last option...
Once you're happy with where your barrel, is tighten down the nut stop at the front, put the barrel back on the gun and then add a rear stop (nut, lock washer, nut). It's a little tricky to get it in there but it's doable. I wouldn't worry about getting the lock nut flat, otherwise you'll never be able to get it off.
From now on when you store the gun, always put some foam under the end of the barrel so it's supported. The axle holds up alright, but I wouldn't trust it to not bend permanently after a couple weeks of storage.
Step 10: Get some pulleys and a belt
If you'd like to go the belt and pulley method, find a belt about 9" long. To generate the pulleys I used an OpenSCAD library I found on Thingiverse at http://www.thingiverse.com/thing:16627 Attached to these steps are various file formats of the pulleys so you don't have to dive into OpenSCAD (you should) if you don't want to.
The bottom pulley has been modified to fit on a servo.
Step 11: Modify a servo
TL;DR: rip out all the electronics besides the motor, attach leads directly to the motor, cut off the stop tab on the big gear.
I blew a couple servos when working on the gun, mainly by testing to see how much power they could handle. 18v is the danger zone, 25v is a burnt up servo. 12v works pretty reliably and spins the barrel at a decent speed.
Step 12: Mount the electronics
Mount a momentary switch on a the handle and mount a 12v battery to the backbone (or somewhere inside the ammo barrel).
Wire everything up and test it out.
Step 13: Add the details
Side tubes -
Cut a 2" diameter PVC pipe to 5.5".
Cut foam end caps and rings, Mod Podge and paint.
Once dry, hot glue to the ammo barrel.
Side Thumbscrews -
I just cut these out of 1/2" foam and hot glued them to the side of the front handle mount.
Bottom Pipe -
*Do not glue this on until everything is painted!*
Cut a 1/2" diameter PVC pipe to 8.5" long and another 15.5" long. Put a coupler on top end and 90 degree joint between the two. Make a foam block with a hole for the bottom pipe and attach it to the bottom of the ammo barrel. Make a pivot for the front out of foam or print the attached .stl file on a 3D printer. Yes, printing that piece is overkill (and takes forever) but everyone knows that anything made with a 3D printer is automatically more awesome.
Everything else -
There are many pieces we never got around to making, look around at source pics and fill in all the stuff we missed. Craft foam is a good, easy to work with material to add details.
Step 14: Paint
Stuff some paper towels in the main tube to protect the bearings and put a garbage bag over the axle then paint everything black. Be sure to get all angles so the gun doesn't look funny from the bottom like ours does.