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Potato Gun Fun

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Dustin Holt

on 7 August 2015

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Transcript of Potato Gun Fun

Cause and Effect Diagram
Data and Charts
Experimental Factors
Our prediction was that the launch angle would have the biggest influence on the distance launched, but it was found that the main variable that effected our response was the barrel depth. From this experiment we successfully demonstrated how seemingly insignificant factors can have a large influence on a response variable. In other words, the barrel depth factor examined was not anticipated to be an important or significant factor, however in combination with the other three factors, it was shown to dominate the results, and the experimental analysis.

Potato Gun
ABS Pipe
Sparker/ BBQ lighter
Durability of Tube
Contamination of
tube with successive
Accuracy of distance measurement
Angle of launch
Amount of propellant

Ground Level

Amount of Propellant (A)
This was chosen for one of our main factors because when the propellant is combusted it produces a pressure forcing the potato out of the barrel. Thus more propellant in the combustion chamber would theoretically produce more force. This is true up to a point due to the stoichiometry of the combustion fluid with limited oxygen. Too much fuel and not enough oxygen will not combust as well as would the combustion of the same amount of fuel with excess oxygen, thus producing less/no force. To account for this and try to not add too much fuel we used a half a teaspoon of naphtha for the high value (1) of propellant. For the low value (-1), too much fuel wasn’t as big of a concern so we used a quarter teaspoon of naphtha. For the center point (0) we used three-eighths of a teaspoon. Once the fuel was added, the combustion chamber was capped and spun around to maximize surface area exposure and to ensure complete volatilization.

Low: ¼ teaspoon
High: ½ teaspoon
Center: 3/8 teaspoon

Length/Mass of Potato (B)
The size/mass of the potatoes that were used for the launch was determined solely by their length. For each run we used Russet potatoes which were jammed into the barrel of the potato gun to eliminate any gaps between the potato and the wall of the barrel. This minimized energy losses through the barrel after ignition of the propellant. All potatoes were cut to a standard initial length, and then cut to a desired length for launch. All potatoes in each category of size were loaded the same way in each run.

Small: 2 inches
Large: 4 inches
Center: 3 inches

The potatoes used for the center point runs were all shaped like cylinders, and potatoes used in the other two runs were shaped like bullets, and loaded just like a bullet would be.

Barrel Depth (C)
We predicted that pushing a potato further down the barrel of the gun would increase the distance of the launch, or at least create a more explosive launch. We used a barrel that was 3 feet long, with a 2 inch diameter. The combustion chamber, 2 feet long and 4 inches in diameter was attached to the barrel with a 4 inch to 2 inch reducing coupler, and then glued in place with ABS cement.

Minimum: 10 inches
Maximum: 30 inches
Center: 20 inches

We used a broom handle with taped markings for the minimum, maximum, and center point lengths to push each potato into the barrel. This insured that each potato was precisely placed in the barrel for each run. This eliminated any nuisance variables or uncertainty around this specific factor.

Launch Angle (D)

We knew that the angle an object was shot at (given the same force) would affect the distance it is launched. Too high of a launch angle and the potato will go high but not far, too low of a angle and the potato might not have a large enough arc to carry a long distance. This being said, the angle of the barrel when the potato launches should have a large impact on distance the potato goes. To set the angle of our launches we used an inclinometer, which told us the exact angle of the barrel. For the high setting of the launch angle we chose 35° to try and maximize the distance with minimal arc height. For the low setting we chose 15° to see how much the low launch angle effects the overall distance of the launch. Lastly the center point was set at 25° to give us an idea of the variation in the measurement.

Low: 15°
High: 35°
Center: 25°

Mixing of propellant
230.3 - 68.8 Amount of Propellant (A)*Amount of Propellant (A) 45.1 Barrel Depth (C) + 26.7 Mass of Potato (B) + 23.6 Amount of Propellant (A) + 14.7 Amount of Propellant (A)*Barrel Depth (C) - 9.2 Amount of Propellant (A)*Mass of Potato (B) + 8.9 Angle of Launch (D=ABC) + 7.3 Amount of Propellant (A)*Angle of Launch (D=ABC)
CODED EQUATION (Unrefined Model)
Fractional Factorial Design

Factors: 4 Base Design: 4, 8 Resolution: IV
Runs: 20 Replicates: 2 Fraction: 1/2
Blocks: 1 Center pts (total): 4

Design Generators: D = ABC

Defining Relation: I = ABCD

Alias Structure



Design Table (randomized)

Run A B C D
1 + - - +
2 + + - -
3 - - - -
4 0 0 0 0
5 - - + +
6 0 0 0 0
7 - + - +
8 + + + +
9 0 0 0 0
10 0 0 0 0
11 - - - -
12 + + + +
13 - + + -
14 - - + +
15 + - - +
16 - + - +
17 + - + -
18 + - + -
19 - + + -
20 + + - -


The primary objective in this experimental project is to determine the effects of four different factors on the distance of a launch from a potato gun. Repeated tests will demonstrate which factors have the greatest and least effects, and how the interaction of these factors affects the distance of a launch. Our predicted factor that will influence the distance the most is launch angle.

Launch Angle
Potato Mass
Barrel Depth
Amount of Fuel
CODED EQUATION (Refined Model)...

175.2 + 45.1 Barrel Depth

Materials List:
- 3’ x 2” ABS pipe
- 2’ x 4” ABS pipe
- 4” to 2” ABS Reducing Coupler
- 4” to 4” ABS Coupler
- 4” ABS screw cap and adapter
- ABS Glue
- Bag of Russet Potatoes
- Zippo Fluid (naphtha)
- Adjustable Launcher (wooden)
- Inclinometer (on iPhone)
- 100ft of String Marked in 1ft segments with 100ft pegs up to the 300ft mark
- Barbeque Lighter

Factorial Regression: Distance (ft versus Amount of Propellant, Length of Potato, Barrel Depth, ...

The following terms are totally confounded with the center point term and were removed:
Amount of Propellant*Length of Potato*Barrel Depth*Launch Angle

The following terms are totally confounded with other terms and were removed:
Length of Potato*Barrel Depth, Length of Potato*Launch Angle, Barrel Depth*Launch Angle,
Amount of Propellant*Length of Potato*Barrel Depth,
Amount of Propellant*Length of Potato*Launch Angle,
Amount of Propellant*Barrel Depth*Launch Angle, Length of Potato*Barrel Depth*Launch Angle
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