Military Tank, Drivable With T-shirt Cannon

Recently, I was asked to build a tank for a men's event I was helping with at my church. The only parameters I was given was it had to fit through a double set of doors and it had to be able to shoot t-shirts and beef sticks. I had an old mobility scooter I could use, was given some metal unistrut (strut) and electrical conduit, and told we could get some coraplast to make the skin of the tank.

The scooter was the kind that turns on a dime (just like a tank!) and is operated with a joystick. Unistrut is metal that is basically square tubing, but with a notch in one side. It's often used for suspending things like pipe and electrical in buildings. The unistrut and conduit were left over from previous projects and helped to keep the cost down for this one. The coraplast is short for corrugated plastic; pretty much plastic cardboard and is similar to foam board.

My goal was to make it drivable with the operator completely hidden, allow the turret to spin, and have reloadable "shells" for the cannon.

A good reminder is that you can build great things even if you aren't proficient with programs such as CAD. This whole project was built out of some table talk, a great idea and some scribbles on a piece of paper, which was lost before the tank was even finished!

Some safety precautions before we begin;

-T-shirt cannons are a lot of fun but could blow up or break something. Be careful.

-Welding fumes suck. Welding galvanized metal sucks even more. If you choose to use conduit and unistrut, there's a good chance you'll be welding galvanized metal. You should try to avoid breathing in any fumes and a respirator is absolutely necessary. While I thought I was taking all the appropriate steps to avoid breathing in the fumes and had welded galvanized metal countless times before, I still messed up and took my mask off too early while cleaning up and ended up with zinc poisoning. I was home sick from work, throwing up with what was basically the flu. Be careful with fumes!

So with all that out of the way, Let's build a tank!

Step 1: Create a Design

The first thing I did was get online and look at loads of pictures of military tanks. I looked at modern ones as well as old ones. While I like the look of modern tanks, I figured the shorter turret would make things difficult to fit a driver, as well as the barrel, and also have room to reload. I finally settled on the classic Sherman tank as it has a taller turret and there's plenty of pictures to study.

I printed out a few good pictures as well as the dimensions and went old school with a measuring stick and pencil and came up with the rough dimensions I would use. Measuring the picture and referencing it to the actual dimensions allowed me to come up with the scale I would use. I settled up on a roughly 3:1 ratio.

I wasn't too worried about making it look exactly like the pictures. I knew as long as I had the basic shape, people would love it.

Step 2: Cut Up a Scooter, Bend Some Metal and Let the Sparks Fly!

First thing to do was remove the batteries, controls, seat and plastic pits. I saved all the parts except for the plastic because I knew I could end up using them later for other parts of the tank. I decided I would use the unistrut for the frame and structural portions of the tank and use the conduit to give it the proper shape.

With the scooter now free from all the extras, I cut it in half and widened it to just under 4' to give me a good wide base. The plan was to make the motors hide in the tank tracks.

After widening the base, I cut two pieces of strut to about 7.5' and welded those onto the base. I now had a rough shape of the tank and a solid frame to build off of.

I took the seat from the scooter and simply welded that onto the frame. It took some guess work to get a good angle. I figured it would be a tight fit once the tank was complete, so I angled the base of the seat back a fair amount so my legs wouldn't take up too much space.

Next, I took some conduit and bent them into what seemed like a good shape for the tracks. No need to make the perfect shape, remember we're working off a measuring stick and pencil. With my four pieces of track, I elevated them off the ground by and inch or so and tacked them in place. The individual sections of conduit can easily be joined by taking scrap metal and putting that inside the ends of the conduit so that you have more material to weld.

Step 3: Build a Turret and Add Power Sources

With a good frame to work off of and a seat, it's time to move on to the turret. Once again, I was able to reuse scooter parts. The seat was on a post that spun 360 degrees. This works perfectly to allow the turret to pivet. First, I took some strut and built it to the height I needed and then I welded on the pivoting seat post. Next was to start to build out the shape of the turret. I welded the two sides of the turret and then front portion where the barrel would hang from. One thing I had to watch out for was keeping the clearance tight between the vertical tank frame and turret frame, but not so close that they would hit.

On the frame of the turret, I welded a step to allow me to climb up into the turret to enter the tank.

At this point, I extended to wires for the right side motor. This was simply done using crimp connectors. I was able to route the wires through the unistrut and under the seat to keep them safe from getting dragged along the ground or rubbed by anything. There's four wires going to each motor two for power to the motor itself and two thinner gauge wires that turn off the parking brake.

Next I had to figure out where the batteries for the scooter and the co2 for the cannon would go. The batteries went just to the right of the seat inside of the tread. The batteries get wired up in series to provide 24vdc.

The co2 tank was able to sit on the frame by utilizing the scooter foot rest as a base and some scrap conduit as vertical supports.

Step 4: Whats a Tank Without a Cannon!?

One of the most difficult parts of this build was figuring out how to build a cannon that could be quickly and reliably reloaded from inside the tank itself. I looked online trying to find something that someone else had tried but couldn't seem to find any good ideas. I knew I wanted to use pvc, so I started looking at fittings and ended up settling on camlocks and threaded pvc. Camlocks are a quick connect fitting that is often used with hoses and is readily available online or in some hardware stores. At first I thought I would use camlocks on both ends of my shell but cost ended up making me change to threaded pvc.

With 3" pvc, I glued a female threaded fitting the one end of what would be my barrel and set it aside to attach to the tank. Next I took a section of pvc and glued a female threaded fitting to one end. On the other end, I used reducers until I was able to screw in the 1" camlock. I now had the shells I could preload with t-shirts and quickly swap out.

Next step was to get the barrel mounted to the turret. Utilizing a hinged bracket from the scooter foot rest, I was able to weld up a bracket that would attach to the barrel using some 3" U-bolts. The bracket is basically angle iron that hugs the pipe and provides a structure for the bolts to clamp onto. That was welded to the turret frame and gave the barrel a nice lateral range of motion.

Step 5: Make a Functional Cannon!

Building a t-shirt cannon is fairly easy by itself. All you need is a source of compressed air, a valve and a barrel.

Knowing I wanted to be able to shoot multiple shirts, I opted to use co2. Since I used pvc as my barrel, I can't safely hook it straight to the co2 tank as they run about 800 psi. For reference, an air compressor operates in the somewhere around 90-125 psi. First I need the co2 tank to go through a regulator. This limits the pressure to 150 psi and keeps me within the limits of the pvc. After the regulator, it needs to go into my (relatively) low pressure expansion tank. This tank builds up the pressure that will fire the cannon and is build from a piece of pvc about three feet long. To fill this, I have an electric solenoid that opens and fills the tank with regulated co2. On the expansion tank, an important piece I have is a blow off valve set to 150 psi. This allows excess pressure to release should the regulator fail. From the expansion tank, there's a 1" diameter hose that runs to the main 1" solenoid valve on the camlock. From there, it's the shell and cannon.

While putting together the co2 system, I ensured all parts had a working pressure of at least 200 psi. The only exception to that was the camlock which had a lower pressure rating but seemed worth the risk. All pipe threads were wrapped in plumbers tape and and hose fittings got a pipe clamp or two.

The wiring of the valves was pretty simply. I found an plate that fit on an electrical box that had two buttons on it and used that as my "fill" and "fire" buttons. Simply wire one button from the battery to their valve and you're set. Just for good luck, I added a light switch before the buttons to serve as a safety lockout. In the picture you can see that there's a keyed switch. While that would've been nicer than the light switch, I didn't have the key so it wasn't wired up.

Step 6: Make It Look Good

Finally we have a solid frame, working motors and a functional cannon. Time to make it look like a tank. For this step I had some excellent help to cover it in coraplast. We were able to source large 4x8 foot sheets which made the large surfaces easy to cover.

First step was to cover the tank treads. For the side of them, they were traced and cut out. The actual tread was cut to length and then slit every inch or so to give the appearance of real treads. The rest of the tank was a lot of measuring, cutting and zip ties. To add some texture, holes were slit and bolts pushed through.

It's hard to keep pvc painted, so a piece of coraplast was cut to length, slit so it would bend and then wrapped around the barrel. Once again, zip ties help this all together.

Step 7: Load Your Shells and Go!

At this point I had a (almost) life size tank that not only drove but also shot t-shirts, beef jerky, and whatever else I wanted to load in the shells. This project was a great success and crowd pleaser. I was able to shoot shirts over 50 feet!

I had a good amount of the supplies just sitting around and the amount spent on this project was less than $400. I encourage you to go out and push your personal limits and make something great!

Well this not only completes my first ever instructable but also my childhood dream of having a powerwheel to drive around!