The __P4__ - Pnuematic Potato Projectile Producer





Introduction: The __P4__ - Pnuematic Potato Projectile Producer

About: Just making things.

Old idea with maybe a few twists that might interest others. We went for an automatic valve (cheap 24V sprinkler valve), a pressure gauge, a triggering box and a firing platform with adjustable angle. The first picture is the rendering of the 3D model. The second photo is the completed P4. The mpeg file shows how the parts decompose.

Step 1: The Plan

The "P4" (Pnuematic Potato Projectile Producer) started as a duel project - a school project for the kids and a chance to make a documentary movie together.

I also saw this as an opportunity to start to train them how to plan and manage a project. So, the first image is our schedule and resource plan. The second one is a list of the things that could be learned from the project.

The third image is my original attempt to draw out the circuit for the trigger. I will describe it in a later step. The fourth is of our plan for making the documentary and the supplies we would need. The next is the rest of the supplies list. The next shows the design layout for the gun and the trigger box, with the parts list for the gun. The last shows the prep'd raw parts for the gun.

Step 2: Chamber

The first step was to create the chamber. Here are the steps:

1) Measure the openning size for the pressure gauge and the valve, then drill end caps and insert them. The pressure gauge was (if I remember right) was a water pressure gauge with "1/4" fitting. I drilled the hole as if I was tapping it, then screwed it in and put a pipe fitting on the other side to hold it. The valve is a standard auto tire valve (I walked into a local tire shop and asked for one - they just warned me that they had a 120PSI limit).

2) Cut, clean and glue together the main chamber shafts with the PVC fittings.

Step 3: Barrel

The idea we had for the barrel was that, if it was in two pieces and culd be unscrewed, we could try different size barrels in our testing.

The main thing to do on the barrel is to bevel a sharp edge on the end of the barrel so that is cuts the potatoes down to a cylinder when you breach load them.

We also made a matching ram for loading. We used an old table leg (from a X Mart round wooden table) that already had a threaded shaft on the end. We drilled a hole in a 3/4 pvc end cap and screwed it onto the ram.

The final picture shows the completed chamber, two pieces of the barrel, the ram and the parts for the trigger and valve.

Step 4: Testing

Once the gun parts were done, we did a pressure and valve test on it.

The initial test showed a slight leak in the pressure gauge fitting. So, I think we either epoxied the fitting or used silicon caulk.

Then we tested both the auto valve and a manual valve. The auto valve was triggered with a single 9-volt battery.

Step 5: Trigger

This diagram was by one of my sons showing the schemetic for the trigger, the physical layout for the box, and some ontes about our testing. The schemetic shows the design idea:

a) Three 9-volt batteries in series to provide the 24V that the circuit should safely need.
b) A power safety-switch for a two-step firing sequence (poswer up, then fire).
c) An indicator light to show when the power is on.
d) An intermittent switch for firing the valve.
e) Everything linked together on a terminal strip (all of the components have spade terminal leads).

The secret to the circuit was the diode in paralell with the firing switch. This made the light come on when it was powered-up shorting the firing switch.

Here are the construction steps:

1) Lay the trigger box components.
2) Measure where the external ones will go.
3) Drill the openings and test the fitting.
4) Add the interlocking connectors to the pig tail of the valve and the end of the trigger power cord.
5) Add leads to all of the components.
6) Wire it all together on the terminal strip.
7) Test the fit of the box.
8) test the circuit to make sure everything is flowing right.

It worked great, at least for a few weeks. It got us through the school fair and a bunch of firings at home. Alas, eventually the wires on the intermittent switch somehow shorted out or just got bent off hitting the terminal block. I have a larger project box in the garage to put it all back together some day. This time I will probably also add some battery holders.

Step 6: Platform

The platform was meant to provide a heavy, stable, adjustable base for the gun. We design it to aim the barrel at 4 angles - 0, 15, 30, and 45 degrees. The straps in the back allowed the gun to pivot while staying stable.

The first pictures shows my son's rendering of the plan and steps.

Step 7: Firing

It is really great to have an empty 5-acre lot across the street from your house. Notice flag poles marking every 100 feet (and showing any wind). We got good enough to aim and hit the steel roof of the barn across the street everytime (80PSI at 30 Deg. and adjust the directions for wind). The last picture was our intial test results.



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    Wow ur instructable makes the gun look like a really really hard nuclear powered Electromagnetic launcher. What with all the plans and stuff lol. Nice gun though, but i dont like the shape of the gun. The shape is only good for massive guns that arent handheld.

    I made a similar gun, but I used the classic potato cannon design, but with a shroeder valve as an air intake and a ball valve to release the pressure

    Frame3 is a particularly dangerous drilling technique. It is always better to clamp something down rather than hold it with bare hands. Whatever is being held can release and turn the holding hands into finer pieces of sliced flesh. No matter how long it takes, the time is well spent to do this safely. All ten digits will be useful.

    1 reply

    Good catch! Since it is a smooth and round object, it is less dangerous than if it was something else. But, still not a good idea - I should have had them clamp it.

    The "T" shaped gun is not the best approach because air escaping from two opposing sides decreases efficiency. That is unless you want to be compact, but i'll take quality over quantity(size of gun) any day.

    Well the PSI rating is on the side of the PVC I think it 450. You may want to use a pressure gauge to be sure.

    No sorry most of what I make is just a picture I have in my head. But I will see what I can do.

    1 reply

    Thanks, I suppose I only really need to know what sort of pressure the system can handle so I dont pump in too much air.

    do you have a plan or schematic diagram that you could email

    For a a better valve use the chrome ones.

    It is a blow gun trigger. You can find it at almost any hardware or car store.

    Hi Coffe Bean, what sort of valve and trigger does it have?

    Yes nice. I did a gun about a year ago but it shoots nails. I know I it is crude but I 11

    Getting both valves to open at the exact same moment in time is rough. Better to use more air and a bigger valve. On my large artilley cannon I used 4" PVC (18 c.f. of air) and a 4" ball valve, actuated by a garage door spring and a trip mechanism.I then necked it down to a 2" barrel. Lemons are the perfect ammo, and I can launch them about 800 yards now.


    Wow, nice and detail writeup..if the PVC is rated at 120 psi, can we just make two separate chamber with two valve connecting to the barrel in order to get higher pressure?

    Looks great, I like the motar like setup over the traditional gun approach. It should be noted for others that schedule 40 PVC is only rated at 120 psi and I would recommend staying around 100psi because PVC shatters when it bursts. One final note milk caps make great sabots.