Kyle and I would like to construct a potato launcher. We enjoyed building the trebuchet, especially because it was fun to launch things. We think this will be a realistic challenge, and will be a worthwhile creation. We also figured that a project like this provides a good opportunity to take measurements like horizontal and vertical distance, time, and angle of launch, and make calculations like force and initial speed of launch.

Specific Project Goals

Kyle and I both think constructing things for physics projects is the way to go. We learn more about applicable physics through working with real materials and making real mistakes. It's much more fun and it makes it worth spending the time on it come exhibition time.

We intend of making a report explaining the physics of our project. It will include things like the afformentioned force and speed calculations and hopefully a simplified explanation on the mechanics of the combustion involved. We might also include a history and examples of potato launchers in the past.

Also, we hope to hold a demonstration for the class. It should be entertaining at the very least.

Justification

Kyle and I have worked on a few physics projects now and understand each others' schedule enough to make accurate estimates at time commitment. Though we are both busy people, working, performing, sporting, we know how to get things done extra-extra-curricularly. We usually end up working once or twice a week when we have the time. And when we are a little more pressed for time, until the project is due that is, then we make time as many days as we can, even if it's later at night after all of our activities are done.

As has been said, we expect to integrate our knowledge of projectiles as much as possible and calculate all possible values. It would also be interesting also to estimate force and speed values, calculate where our projectile should land, and aim for a target like we did with the trebuchets.

With a two person group, we found that both member must participate as much as possible for the project to get anywhere, so we anticipate equal contributions, as we've had in other projects.

Contact

Email Matt

Email Kyle

Email Mrs. McLean

-[Project Progress]-

Photos/Sketches Page

Documentation

3/24/03

Kyle and I met after school on Mon.

We simply took a shopping list to Lowe's and gathered all of the supplies we'll need. These include:

Materials
Recommended Part and Purpose	Part Aquired	Bills Shelled	Place Aquired
1 1/2"x36" SCH 40 PVC water piping for potato barrel	1 1/2"x10' SCH 40 PVC water piping	$2.15	Lowe's
4"x10" SCH 40 PVC water piping for chamber body	4"x5' SCH 40 PVC water piping	$7.67	Lowe's
2 4" PVC couplers for coupling 4" pipe with 4"x1 1/2" PVC bushing and clean-out adapter	2 4" PVC couplers	2x$1.38	Lowe's
4"x1 1/2" PVC bushing for connecting the 4" chamber body and the 1 1/2" barrel	4"x2" PVC bushing and 2"x1 1/2" PVC bushing (no 4"x1 1/2" bushings were available, so we mix 'n' matched)	$3.91 + $.48	Lowe's
4" PVC clean-out adapter and threaded plug for easy access to chamber body	4" PVC clean-out adapter with threaded plug	$5.24	Lowe's
PVC primer with dye for priming surfaces for PVC pipe cement	PVC primer with dye	$1.97	Lowe's
medium body PVC pipe cement for slappin' those suckers together	medium body PVC pipe cement	$1.74	Lowe's
2 #8x2 1/2" flat/round-head all-thread machine screws, any drive	1 6-piece #8x2" round-head all-thread machine screws, philips drive, and 1 4-piece #8x3" round-head all-thread machine screws, philips drive (#8x2 1/2" screws not available so we bought 2" and 3" and will see what works best)	2x$.78	Lowe's
'Red button' mechanical BBQ ignitor/striker replacement with sideburner for sparking the combustion	Electronic BBQ ignitor with sideburner (saves us the trouble of wiring the mechanical one)	$21.94	Lowe's
2' of 16 gauge or lower insulated wire for wiring the mechanical BBQ ignitor/striker	None (we bought electronic!)	$0
Electrical tape and duct tape (of course!)	You should never be without it!	$0	home
	Total w/ tax	$56.02

That's all we did today, though it took quite a while. We shouldn't need any more materials for the whole project excluding potatoes and the propellant.

3/25/03

Nothing was done today.

3/26/03

We met again on Wed.

We had all of the pieces we needed so we started construction. We proceeded to:
saw 10" of 4" PVC from the original 5' (chamber body)
- saw 3' of 1 1/2" PVC from the original 10' (barrel)
- file the sawed edges so it would glue properly
- prime and glue both 4" couplers to the chamber body
- prime and glue the 4" clean-out adapter and bushings to the 4" couplers

(image 1)

- prime and glue the barrel to the bushings
- wait ten minutes for it to set

(image 2)

- sober up after working with the solvents

(image 3)
That primer has got to be the most potent stuff on the face of the earth!

After waiting for the glue to set we added the means of ignition. We screwed to 3" machine screws (which conduct well) into the chamber body, stopping them about 1/4" apart. Then we connected the electrodes of the electric grill ignitor to the screw heads.

(image 4)

(image 5)

After testing out the connection a few times, the only things we really had to do were solder on the connection, and buy fuel and ammunition. Since the solder gun wasn't handy we decided to just let the glue dry, as had been suggested, a full 24 hours, and work more on it another day.

(image 6)

3/27/03

Nothing was done today.

Our prospective meeting on Fri. 3/28/03 was called off due to an extended pit orchestra rehearsal, and bad weather.

3/29/03

Nothing was done today.

3/30/03

We met around 11:00 on Sun.

We went out and got the materials we needed immediately. We picked up some wire to extend the ignition switch. We bought some suave hairspray and some aerosol deodorant (right guard was suggested, but we bought the cheaper walgreens brand). Finally, of course, we picked up two sacks of potatoes (10 lbs) and a couple sandwiches for lunch while we were at County Market.

We got back and soldered on the connection between the ignition switch and the screws. At first we connected 6' wires to the screws so we could stand back a ways and ignite it. However the multiple connections were a little faulty and proved to work much better with fewer and shorter wire segments.

So, that done, and lunch eaten, we grabbed everything we needed and headed out to Robeson park.

Once there we set up the launcher on a picnic table and got to work. While testing it out we found a few interesting flaws and quirks. We had forgotton to bring something to shove the potato down the barrel, but after a short search of the area, we found a metal pole that work well. Our first trial caught us a little unaware. We didn't really know what to expect, and the loud gunshot sound threw us a little off. The following is a table of trial info. we collected.

(image 7)

We found that the Walgreens brand deodorant didn't ignite. Most of it immediately condensed on the chamber wall, and when examined, didn't have the some of the ingrediants the hairspray did. We decided we'd buy the suggested Right Guard deodorant next time. However the next few trials with the hairspray after the first fluke also did not fire. We think the Walgreens residue had something to do with it, after wiping it off, and adding a little extra hairspray it fired again.

It was a little difficult to watch the potato as it flew, and even more difficult to find it after it landed. We decided to buy some bright spray paint to help us out next time. Also we'd get some flags to mark where they landed, as sticks were also difficult to see.

We didn't even think about the launch angle or air time until later in testing. We estimated the angles since we didn't have a protractor, and used a stopwatch rather crudely the only trial we timed it. We'll have a better system for timing and measuring next time.

3/31/03

Nothing was done today.

4/1/03

Nothing was done today.

4/2/03

Nothing was done today.

4/3/03

Nothing was done today.

4/4/03

Nothing was done today.

4/5/03

Nothing was done today.

4/6/03

Nothing was done today.

4/7/03

Nothing was done today.

4/8/03

Nothing was done today.

4/9/03

We got together on Wed. after school.

We decided we needed an accurate way to measure the angle of launch, so that we could, in turn, accurately measure the rest of the data. We drew out plans in class for a launch base of wooden planks and such. When we got together we routed through a bunch of my wood and found decent planks to make a base, arm and upright with. We had to make a quick trip to Ace Hardware to pick up a hinge, some 'L' brackets and screws. Then we put it together, with multiple distractions for phone calls regarding it being Matt's birthday, but didn't have time to finish it up before Kyle had to leave. We would have drilled a hole for some string and attached it as shown in some sketches in image 8 on the photo/sketch page.

4/10/03

Nothing was done today.

4/11/03

Nothing was done today.

4/12/03

Nothing was done today.

> 4/13/03

Nothing was done today.

4/14/03

Nothing was done today.

4/15/03

Nothing was done today.

4/16/03

Nothing was done today.

4/17/03

Nothing was done today.

4/18/03

Nothing was done today.

4/19/03

Nothing was done today.

4/20/03

Nothing was done today.

4/21/03

Nothing was done today.

Kyle, however, finished building the launch pad sometime while I was gone for spring break. He also did a few tests with it to try it out. He found that it was rather awkward to use. The big problems with it are that, a.) it's not very stable, so the accuracy is off a bit, and b.) it's very difficult to load the primed cannon into the launch pad quickly enough (the potato must be launched as soon as possible after the hairspray is sprayed or it settles and is not as effective or doesn't fire at all). The launch base is useful for finding the angle of launch however because you can set the gun on the ground and line up the barrel with th launch base arm.

Kyle also tried out some new propellants, however he didn't get any results because the ignitor battery apparently died. He did get a couple of potatoes launched though and had pretty good results, farther than anything we had previously done.

4/22/03

Nothing was done today

4/23/03

Nothing was done today

4/24/03

Kyle and I got together before school started at 1:30 (excellent).

We went straight to firing potatoes. We did a bunch of tests at different spray lengths. We used the suave first and lengthed the spray length until we decided that more spray wasn't doing us any good. Five seconds seemed to be the ideal amount. We got results over 400ft. and up to 453ft. We didn't record any air times because it's too hard to get an accurate time. It's almost impossible to fire the cannon while starting the watch, and even harder to hit it accurately if you don't know when the other person is going to fire it, and you can't count down to fire, because the ignitor is too inconsistent. It's also pretty impossible to stop the watch when you can't see the potato land, which is most of the time.

The other two new propellants we tried this time, rubbing alcohol and Axe spray deodorant didn't fire. We think it's because they don't burn fast enough. When we took the clean-out cap off and ignited them they both burned seemingly too weak to fire a potato.

Our recorded results can be seen in image 9 on the photo/sketch page.

4/25/03

Nothing was done today

4/26/03

Nothing was done today

4/27/03

Nothing was done today

4/28/03

Nothing was done today

4/29/03

Nothing was done today

4/30/03

Nothing was done today

5/1/03

Nothing was done today

5/2/03

Nothing was done today

5/3/03

Kyle and I got together before we headed to prom (not together).

We decided we had better wrap things up. It's been fun firing potatoes, but none of the data was really that useful. Once we found the maximum efficiency according to fuel type, how much was used, angle, etc. We really didn't need the testing anymore. We started writing a mechanics report, drawing a detailed diagram, and making calculations of the initial force, speed, and acceleration of the potato.

We didn't finish any of these. Me still need an accurately averaged potato mass, and non-rounded answers for accuracy. To finish these preliminary calculations, we needed the mass of a potato. And an accurate scale not being handy, we held an average potato in one hand, and held four Granola snack bars, each weighing 1 oz according to their packaging, in the other hand. The potato slightly out weighed the bars, so we guesstimated the potato to be about 5 oz or .17 kg.

Even so, we found initial force to be about 4128 N, initial velocity to be about 66 m/s, and acceleration to be about 2426 m/s^2, all of which sound reasonable.

5/4/03

Nothing was done today

5/5/03

Nothing was done today

5/6/03

Nothing was done today

5/7/03

Nothing was done today

5/8/03

Nothing was done today

5/9/03

After we averaged the mass of our potatoes (100g), we used many equations learned in class to calculate the average initial speed (when leaving the barrel), acceleration and time (while in the barrel), force on the potato during acceleration, and the work and power done on the potato. Calculations can be seen on image 10 on the photo/sketch page. These were our final answers:

Calculations
Angle (deg.)	Initial Velocity (m/s)	Acceleration in Barrel (m/s^2)	Time in Barrel (s)	Force (N)	Work (J)	Force (Watts)
40	28.6	447.8	.06	44.78	40.9	682
45	34.9	664	.05	66.4	60.7	1214

5/10/03

Nothing was done today

5/11/03

Nothing was done today

5/12/03

Nothing was done today

5/13/03

Nothing was done today

5/14/03

Nothing was done today

5/15/03

We wrote up the report on the mechanics, and posted the diagram. The diagram is image 11 on the photo/sketch page.

Here is the report.

There are two basic components to a potato launcher, the barrel and the canister. It is essential for both safety and effectiveness that these are solidly fused together so that there are no leaks. The first part of the launching process requires the potato to be rammed into the barrel so that it is positioned just outside of the canister. It is also very important the potato is pressed firmly against all sides of the barrel to prevent the combustive gases from escaping. The next step involves the canister. After the potato is in place the canister then needs to be filled with what ever flammable spray desirable. In our case we found Suave hair spray to be an effective fuel. After spraying the fuel into the canister it needs to be sealed quickly. Since the fuel is an aerosol spray it will escape the canister quickly if it is not sealed. That is also why it is vital that the canister and barrel be fused together leak free. Once the launcher is loaded and primed the only thing left to do is ignite the hairspray. We just press the igniter button which causes a spark to jump between the two screws in the canister causing an explosion. This combustive reaction creates a huge amount of force which forces the potato out of the barrel and several hundred feet away. There is also a very important ratio between the size of the canister and the size of the barrel. The volumes of the two need to be proportioned so that the combustive reaction is finishing just as the potato is leaving the barrel. If the canister is too large for the barrel there will be wasted combustive forces, and if the barrel is too long for the canister then the potato will slow down before leaving the barrel significantly decreasing the distance the potato will go. It has been calculated by potato enthusiasts every where that the prime ratio is a 1:1.5 ratio with the canister being the larger of the two.

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