Introduction: DIY Ping Pong Ball Launcher
Kids will get to use 3D printed parts, a hammer, maybe a saw (it depends how you feel about this, you can cut the wood down for them if you want), and glue guns to create a standardized ping pong ball launcher. Using their tool they can measure out distances on the sidewalk and test how far it launches at different angles and enter their data into a community spreadsheet to try and find a correlation (but this is only if you want that extra learning bit).
These launchers can launch about 15-18 feet and build in an hour of class time (if you have 10ish students), or about 30 minutes if you have a small group of kids.
Step 1: Print Your Parts and Gather Your Supplies
I printed these with walls 3 layers thick and at 10% infill, each set took about 3.5 hours to print, so if you are printing for a class make sure to plan ahead. I was able to fit 4 sets onto an Ender 3 bed which helped in getting the prints done for 48 kids!
Note: If you are doing this with a lot of kids, make sure to take the sets off the printer one at a time and store each set in ziplock bags. The two dowel holding end pieces are mirror images, so if you dont keep them together you will spend a lot of time sifting through your box looking for the matching peice...and Murphy's law is you will pick out 10 right handed pieces until you finally find the left handed piece you're looking for.
Step 2: Measure Your Middle Line
I have to admit, this step was harder than I thought, so plan to really teach kids how to use a ruler, draw a line with a ruler, and line the ruler up.
Since 2x4s are not actually 2x4, AND they have a rounded edge, it is hard for kids to measure the 1.75in in for a center line. Instead I had them use their rulers to draw two "X"s on their board. This would end up being the top of the board.
To draw the "X"s we first learned how to line up the ruler from the top left corner to the bottom right corner. Make sure to tell kids to hold the ruler in place and use the ruler to draw a line. I had a lot of kids line the ruler up beautifully but then just draw a line near the ruler, which sort of defeats the purpose.
Repeat the with another line top right to bottom left and you should have one huge X on your base piece of wood.
To draw the second "X" I had the kids measure 2 inches down from the top of the board and draw a line from the top left corner to the right dot that marked 2 inches. Then repeat from top right to left dot at 2 inches. This gives you a second smaller "X" on your board and the two midpoints of the "X"s will give you a center line.
You will likely need to help them learn how to draw the dot at 2 inches (I work with K-4 kids so this hopefully won't be an issue if you have older kids)
Step 3: Hammer in Dowel Rod Holders
The dowel rod holders are the two pieces that look like right angle joints with a tube attached. These are mirror images of each other so you will have to play with them to find the right orientation. Kids should hammer these into the bottom of the 2x4 (ie the side that does not have the centerline we drew in the previous step).
Orient the holders so the dowel holding tube is along the long 9.5 inch side of the 2x4. I had students stand their 2x4 on end and hammer in the top nail first to hold it in place, and then do the bottom nail. This helped to ensure the holders were flush with the 2x4.
Check out the photo for the correct orientation. The short side with the dowel holders is not the front of your launcher.
Step 4: Hammer in the Trigger Holder
The trigger holder is what ensures we all pull back to (mostly) the same distance and it is aligned so the ping pong ball launches straight ahead.
Using your center line place your trigger at the back of your launcher (9 inches opposite from the dowel holders). The trigger holder has a foot that extends from the bottom with a nail hole. Hammer this foot about 1 cm from the back end of the launcher on the centerline.
Once hammered in the trigger will still rotate, use hot glue to glue it along the centerline as well.
Why is the trigger important? If we pull back to different lengths then we can't compare the distance the ball flies with angle because we won't know if it is the extra pull or the angle that is changing the distance. We will pull the launcher all the way back through the trigger holder until it hits the 3D printed ball holder.
Step 5: Prepare the Ball Launcher
Preparing the ball launcher is pretty easy - just thread a rubber band through a hole on the 3D printed ball holder part. Pull it about halfway so that there are two holes, one on each side of the holder, that the rubber band makes. Take one side and thread it through the hole on the otherside and pull to lock it in place. No knots/glue/etc is necessary.
Repeat this on the other side to have your launcher ready!
Step 6: Add the Front Dowels
The dowels might need a little twisting to get in place, but one goes through each dowel holder like the photo above. To prepare your launcher just to launch (and not take data), just add a rubber band loop onto each dowel rod - your ball holder should have the flat "skis" on the bottom, if you find they are facing up, flip over the piece and put your rubberband loops on the corrected dowels. The student in this photo has their launcher flipped over and was corrected after this launch!
Step 7: Protractor for Community Data Collection
If you want to add data into our community graph you will need to know what angle you launch at. To do this we will add a protractor to our launcher. Cut one protractor from the template and hot glue it to the top of one of the tall dowels. Make sure you glue the right angle corner to the top and have the 0 degree marking along the dowel.
Then take a 3-4 inch piece of floss, tie a bead to the end, and hot glue glue the non beaded end to the top of the same dowel. The bead will make the floww hang down, where the floss hangs is the angle reading for your protractor!
Step 8: Setup for Community Data
We used masking tape to mark out a starting line and every foot increment out to 16 feet. This helped students see the distances their balls were going and allowed them collect a measurement for our data pool. We guestimated between the feet, so many students got results like 5.5 feet, or 5 feet 2 inches, etc. It doesn't have to be perfect, just close :)
Step 9: Launch!
You will need to launch a LOT of times to gather more and more data - the more data we collect, the better our results will be!
Step 10: Input Community Data
If you made your launcher identical to ours (ie used the same rubber bands, have the trigger in the same place, and have the same length 2x4) then you can add data into our public spreadsheet and see a graph of our results so far!
To add your own measurements go to our community data collection form
Select your angle (to the nearest 10 degrees) and the distance your ball went to the first bounce. So don't include how far it rolled, or where it hit the second time etc. Watch for where it first hits the ground - that is your distance. Input your data in inches, there are "feet" markings every 12 inches to help you scroll quickly.
To see current results you can find the data chart and graph here. For teachers, this can be a great way to open the conversation and compare what you find as well!
First Prize in the
After School Challenge