Introduction: Air Trajectory for Science Olympiad

My 13 year old daughter designed this project for the Science Olympiad competition. Although designed to meet certain requirements, it is a nice project for any STEM, 4H, Boy/Girl Scouts activity.

This was my daughter’s plan; so I had to resist the urge to make it “better”. I did try to convince her to add a few enhancements but they failed (see below). So the old adage (KISS) still applies. My daughter and her teammate are currently taking data by adjusting the launch angle and weight height. The results will be posted after the competition.

Video of it in action

Launch at Competition

Step 1: ​Competition Overview

In preparation for competition, the teams will design, construct, and calibrate a device capable of launching projectiles. At the competition, each team will be shooting at targets 2 to 8 meters away.

Rules:There is a two page description of the rules/contest. Below is a simplified version.

  • Launching force must supplied by gravitational potential energy (PE) from a falling mass (5kg max).
  • Gravitational PE must be converted to air pressure, which is used to launch the projectile.
  • Max size: 1m x 1m x .8m
  • Mass must be detachable (impounded prior to event)
  • The launcher must have a triggering device. Competitors must remain at least 1m away from launch area during launch.
  • Tennis, racquet, ping-pong and /or plastic golf balls can be used as projectiles.

Competition:

  • Launch area is 1m x 1.5m.
  • The competitors must not be within 1m of the launch area while triggering the device.
  • Targets are placed in front of the launch area at distances between 2m and 8m.
  • Shooting into a 1 to 5 gallon bucket gives bonus points.
  • As is typical with scoring, high score wins.
  • Final score = Best Close Target Score + Best Short Target Score + Graph Score – Penalties + Bucket Shot. See website for complete list.

Step 2: Build Overview

A weight (wood block) drops on a 2 liter bottle. The bottle is connected to a PVC pipe through a flexible hose. Air from the bottle propels a ping-pong ball out through the pipe. Weight height and launch angle are adjustable.

Step 3: Tools

  • Saw
  • Drill or Drill Press
  • Bits
  • Hole Saw (2 1/2” Diameter)
  • Screw Driver
  • Scissors

Step 4: Materials

  • Plywood: 34” x 20” x .5”
  • 2x4 by 20” Long
  • 1x6 by 18” Long
  • PVC Pipe: 1.5” nominal size by 12’
  • End Cap, PVC, 1.5” (x6)
  • 90 Degree Fitting, PVC, 1.5” (x6)
  • Tee Fitting, PVC, 1.5” (x2)
  • PVC Pipe Cement
  • Pipe Clamps (x9)
  • Screws
  • Eyehook
  • 5/16” Diameter threaded rod x 8” Long
  • 5/16” Flat Washer (x2)
  • 5/16” Rubber Washer (x2)
  • 5/16” Wing nut (x2)
  • 2 liter bottle w/cap
  • Flexible hose (2” inner diameter) – used old shop vac hose
  • Ping-Pong Ball (40mm)
  • Duct tape
  • Clear Tape
  • Paper Ruler
  • Sharpie

Step 5: Build

You will be building to this drawing.

Step 6: Base

Cut plywood for the base of the launcher. We used 1/2" thick to keep the weight down. Keep in mind the overall size requirements (1m x 1m x .8m) during this step.

Step 7: PVC Pipes

Cut pipes as shown. You might want to hold off on the 3” long pieces until final fit check.

Step 8: Drill Holes

Drill 5/16” clearance holes through the center of 3 of the 12” pipes

Step 9: PVC Assembly

Assembly the PVC pipes/fittings as shown - don’t glue yet! For the launcher tube, feed the 5/16” threaded rod through the holes. We used rubber spacer for the inner interface. Flat washers and wing nuts were used on the outside. Note that this rod also is used for the ball stop. Optional – add another through rod to the a few inches from the bottom. This will give the vertical sections more support.

Step 10: Weight

Depending on PVC fit, the dimensions might not match the drawing. Remove the top piece and use it as a template for the slider holes on the 1x6. Use a drill and hole saw to make these holes. Note that it took us two iterations for this step. For the first try, we had holes that were only slightly bigger than the outside diameter of the PVC pipe. This seemed nice until the trial phase. The board would catch and not fall about 25% of the time. We increased the diameter to 2 ½” and it now works every time.

Step 11: Additional Weight

Attach the 2x4 to the bottom side of the slider for additional weight.

Step 12: Eyehook/Cord

Add the eyehook to the top side (centered in both directions). Tie a cord to the eye hook.

Step 13: Hose

Run a flexible hose between the bottle and PVC launching tube. Duct tape was used to attach the hose to the PVC tube.

Step 14: Bottle Connection

The bottle will most likely need to be replaced (good for ~ 100 hits). You can either use tape or try the replaceable feature which we modified based on seamster’s instructable. We chose the replaceable option. Connect the end cap assembly to the other end of the hose with duct tape.

Step 15: Failure

I tried to make a tape free version using only fittings. Although it looks nice, the flow restrictions limited the performance of the launcher. So, we were back to my daughter’s original idea with a “Dad, I told you so!” thrown in.

Step 16: Glue It Together

Once you are happy with the setup, glue pieces together with PVC cement. Note that we didn’t include this step since the assembly needed to be broken down for transport. Each joint was pressed together tightly and duct tape used for additional strength.

**DON'T GLUE THE TOP SECTION - THIS PART NEEDS TO BE REMOVABLE SO THE MASS CAN BE IMPOUNDED**

Step 17: Attach PVC to Base

Attach the completed assembly to base as shown with pipe clamps.

Add an additional clamp a few inches away from the 2 liter bottle. This does two things: locates the bottle under the weight and helps with angle adjustment.

Step 18: Launch Angle

Again, we took the simple approach for this step. A 2x4 was placed between the launching tube and bottle as shown. The closer the 2x4 was place to the bottle, the lower the launch angle. Four board locations were marked off.

Step 19: Weight Height

A paper ruler covered in clear packing tape was added to the rear to mark the weight height. An optional approach would be to use a sharpie to mark the tube directly.

Step 20: Ready to Fire

    Set the angle.

    Drop the ball onto the tube.

    Raise/drop the weight

    Step 21: Update 1 - Added a Trigger Mechanism

    Add two eyehooks to the weight. Pull pin used for the release.

    Step 22: Update 1 - Added a Trigger Mechanism

    A cord/latch was used from an old book bag to lock in the weight height.

    Video of the trigger:

    Step 23: Update 2 - Video From the Competition

    Step 24: References

    Comments

    author
    SwaggerFul Swellow (author)2015-02-16

    Very nice! Build instructions are very clear and detailed. As for the design, I love it! Very cool and also very simple. I hope your daughter does well in the competition!

    author

    Thank you!

    author
    PVidmar (author)2016-03-25

    I made this for our Science Olympiad with some slight modifications. I added weights to the board and made it out of 1 1/4 inch PVC except for the launch tube. Our team took second at regionals! It was the first time our school participated in Science Olympiad. Thank you for great instructions and a great idea.

    author
    mtairymd (author)PVidmar2016-03-27

    Congratulations and thank you.

    author
    akrshyam (author)2016-03-15

    If we try to blow into the pvc pipe after the soda bottle has a dent, it doesn't return to regular shape, and after a while there are many dents and it alters the results, and makes the distances very different. By upto 53 cm(which was happened in the competition, but luckily the next shot was only 11.9 cm away, but we had to increase the wood height by an inch).

    author
    mtairymd (author)akrshyam2016-03-15

    The bottle for this version returned to the original shape each time. You might want to look into another style bottle. However, this will require you to retake your test data :(. For calibration, my daughter took 3 data points at each height and angle. The data was then averaged and curve fit. Good luck.

    author
    akrshyam (author)mtairymd2016-03-15

    How did you connect the bottle to the pvc pipe

    author
    mtairymd (author)akrshyam2016-03-15

    The bottle for this version returned to the original shape each time. You might want to look into another style bottle. However, this will require you to retake your test data :(. For calibration, my daughter took 3 data points at each height and angle. The data was then averaged and curve fit. Good luck.

    author
    akrshyam (author)2016-03-15

    My partner and I have made it to states and got 6th place in air trajectory in regionals, but it wasn't very consistent. Your bottle shape didn't change at all when the weight dropped. Could you explain the steps and materials to attach the bottle to the pvc pipe instead of using tape.

    author
    mtairymd (author)akrshyam2016-03-15

    My daughter tried a variety of bottles. She found the 2 Liter Sprite bottles to be slightly more durable which allowed them to take more hits and return to the original shape easily. Whatever you choose, make sure your backup bottle is the same shape/style. I tried to make to make the connection better (step 15) against my daughter's wishes. It didn't work at all - stick with tape. Take your time taping the joint and make sure you have a nice seal.

    author
    akrshyam (author)2016-01-05

    Thanks for the advice, what did you do for your 4 graphs, my partner and I are still in the thought process of what to do.

    author
    mtairymd (author)akrshyam2016-01-06

    Use excel or any other spreadsheet program. Make sure to follow the data/plot directions (data on page, axis labels, etc.) per the Science Olympiad instructions. I posted a sample graph on a comment below.

    author
    akrshyam (author)2016-01-04

    How did you make the bottle not even Change shape when hit by the wood. Ours is self inflating but after some time the bottle is not in the same exact shape. I'm not sure what to do because we can't drink lots and lots of soda just to get the bottles.

    author
    mtairymd (author)akrshyam2016-01-04

    The bottle isn't required to self inflate. You can blow into it between shots. With that, it will get back to the original shape.

    author
    mtairymd (author)2016-01-03

    @krshyam. A 2 liter bottle was used. This size is most common and seemed to work the best.

    author
    akrshyam (author)mtairymd2016-01-04

    ok thank you, that clears some confusion.

    author
    KrystalM10 (author)2015-12-30

    do you happen to know if this design will work in the 2015-2016 competitions?

    author
    mtairymd (author)KrystalM102016-01-02

    I would assume so. Read through the 2015/16 requirements to verify.

    author
    VansBuilders (author)2015-11-02

    Hi

    I am trying to get started with this project for my science Olympiad. I tried the basic design ( PVC pipe connected to 2 liter soda bottle) and how do I return the bottle to its original shape before every launch? Thanks.

    author
    mtairymd (author)VansBuilders2015-11-02

    It doesn't have to be self inflating. You can blow into the PVC pipe to get the bottle back into its original shape.

    author
    VansBuilders (author)mtairymd2015-11-02

    Thanks for your prompt response. I did what you suggested. It worked for 2 hits. Then the bottle won't go back to its original shape. I connected the bottle directly to the pipe using duct tape. May be I will connect using a flexible hose and then try. So far anything I am doing wrong? Thanks again.

    author
    mtairymd (author)VansBuilders2015-11-02

    It's most likely your seal - make sure you have enough tape. This one was hit over 100 times and came back to original shape each time. You could also try another 2 or 3 liter bottle. BTW, make sure you have 2 of the exact style bottles in case you need to exchange one in the competition.

    author
    VansBuilders (author)mtairymd2015-12-26

    During the competition are you allowed to blow into the soda bottle ( before loading the ball after each hit, I blow through the PVC pipe end ) to return it to original shape? thanks.

    author
    mtairymd (author)VansBuilders2015-12-26

    Yes

    author
    VansBuilders (author)mtairymd2015-11-09

    I improved the seal. It works fine. Thanks a lot.

    author
    mtairymd (author)VansBuilders2015-11-09

    Yeah, the seal has caught a few people - see other comments. Good luck.

    author
    VansBuilders (author)mtairymd2015-11-17

    Hello, I was able to collect some data with the basic setup. I took data with 3 drop weights, 3 drop heights, 2 angles -varying only 1 parameter at a time. I wanted to get some idea on what graphs / charts are typically presented for this event. Any pointers would be very appreciated.

    author
    mtairymd made it! (author)VansBuilders2015-11-17

    See picture. Use excel or any other spreadsheet program. Make sure to follow the data/plot directions (data on page, axis labels, etc.) per Science Olympiad

    data_example.PNG
    author
    VansBuilders (author)mtairymd2015-11-28

    The graph is for a fixed launch angle and fixed drop weight, it shows how the drop height affects the range. Is my understanding correct? Is this the typical calibration graph? Thanks for your time.

    author
    mtairymd (author)VansBuilders2015-11-29

    The weight is constant. The two variables are angle (4 positions, A thru D) and drop height. Shown above is position B (locked) while varying the drop height. This plot was repeated for the other angles (A, C & D). This data must be shown prior to launch since it is part of the scoring.

    author
    VansBuilders (author)mtairymd2015-11-29

    We are using Ping pong (plastic) ball so far. My team mate wants to go for racquet ball. What is ideal for the competition?. Thanks for your time.

    author
    mtairymd (author)VansBuilders2015-11-29

    My daughter tried the racket ball. First, it was hard to find a tube that matched the ball diameter - it needs to be snug. Second, it takes more force to move the racket ball. I think the racket ball would be more consistent in flight if you can get it to work. Give it a try in a small scale mockup to see if it works.

    author
    Drjeremy97 (author)2015-03-18

    ok so I took off the duct tape on my bottle connection that connects to the flexible tube and put it back on and now it works and like you said shoots way over 8m

    author
    mtairymd (author)Drjeremy972015-03-19

    Glad everything worked out!

    author
    Drjeremy97 (author)2015-03-18

    the 2x4 block didn't work either and I don't know what else to do im starting to doubt a 2 liter bottle can make a ping pong ball go anywhere

    author
    mtairymd (author)Drjeremy972015-03-18

    It works - see video. My daughter's was shooting way past the 8 meter mark. It was a challenge to meet the short distance (2m). Also note that a 2L bottle is used in most cases - google Air Trajectory Science Olympiad. Try stomping on the bottle. Can you get it to shoot in any way? Did you check the ball fit? Obvious question - is it sealed tightly between the flex tube and bottle/pipe?

    author
    Drjeremy97 (author)2015-03-17

    so I made mine sorta I just haven't added the wooden block that falls on my soda bottle but before I put that on I took a 4 lb book and dropped it on my soda bottle and it barely budged what do you think I did wrong ( I'm posting a picture now)

    author
    mtairymd (author)Drjeremy972015-03-17

    Looks correct. Let's start troubleshooting. What size (not weight) book did you drop on the bottle? Spreading 4 lbs over a large area might not compress the bottle. Note that the 2x4 is only 3.5" wide.

    author
    mtairymd (author)mtairymd2015-03-17

    Try dropping a 2x4 (or equivalent size) onto the center of the bottle from the desired height. That's lighter than the final weight but it should give you some results. The bottle should deform about half way over the 2x4 area. Did that solve the problem? If not, check the fit of the ball into the pipe. It should be a tight fit but the ball should freely move in the pipe. I know a tight fit is subjective so here is my definition - when you hold your hand over the top of pipe, it should take the ball much longer to fall through the tube than when it's open on both ends.

    author
    Drjeremy97 (author)mtairymd2015-03-17

    I think your right the book was very wide so I think if I were to use the 2x4 it would work better so thank you!

    author
    Drjeremy97 (author)2015-03-17

    here it is

    image.jpg
    author
    Drjeremy97 (author)2015-03-12

    sounds interesting there is this one school project I have to do and this sounds perfect but if I had to decrease the side length that's 34 to about 29 do you think that would be possible and if so how do you think I should go about doing it

    author
    mtairymd (author)Drjeremy972015-03-13

    The length isn't very important. However, per the Science Olympaid rules, you must not exceed 1 meter (39.4"). Reducing the overall length will make the hose connection harder if you need the flexibility to adjust the launch angle. My daughter used an old shop vac hose which wasn't very flexible. As for how you should do it, just shorten the 22" long PVC pipes by 5".

    author
    Drjeremy97 (author)2015-03-11

    how does the air not just go around the edges of the ping pong ball?

    author
    mtairymd (author)Drjeremy972015-03-12

    It's a very tight fit and works very well - see video. She had to limit the weight and drop height to stay within the 8 meter limit. See comment below about the ping pong ball and PVC pipe dimensions.

    author
    airmanT-28 (author)2015-02-15

    I was told by SO officials that the bottle had to reinflate automatically, so we had to scrap the entire design and go for a design with a sort of bicycle pump. I wonder if it's different for you in Maryland than it is here in Michigan.

    author
    mtairymd (author)airmanT-282015-02-15

    Thanks.

    Yes, there is a requirement:

    "All device air chambers must start each launch at ambient air pressure and must automatically return to ambient air pressure".

    That might be a problem. I will have her ask the team lead.

    Her weight is ~ 2.5lbs so the bottle doesn't start any deformation until closer to the 6 meter distance. Even at the highest hit, the bottle only deforms slightly. Requires a little squeeze to go back to full shape.

    author
    georgesun (author)mtairymd2015-02-26

    Ambient air pressure means the air pressure inside the bottle is similar to the air pressure in the room. Even if the bottle does not re-inflate, if it is open to the room (i.e. not plugged) it will return to ambient air pressure on its own.

    author
    mtairymd (author)airmanT-282015-02-15

    It's funny - she's putting on her lawyer hat now. She says it doesn't say anything about touching the chamber after the shot - just that it needs to return to ambient air pressure, which it does.

    author
    airmanT-28 (author)2015-02-15

    Yes, I realize that it doesn't say anything about touching the chamber, just about the bottle or other launching device to return to it's original shape after launch. You're not supposed to touch it. Anyway, my forte is Astronomy and Aeronautics, so I will refer this to my teammates who actually work on this event. I only supervise. I'll let you know what they think.

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