Catapult!

[JohnnyEgo]

My son is in 5th grade, which means it's science fair time in this county. After ruling out all the ideas that were improbable if not impossible, such as the robot butler and the hoverboard, and the things I was not willing to do, like the paper mache volcano or winding 40 feet of copper around a motor armeture, we stumbled across ballistic trajectory as a topic. Which totally called for catapults.
Had my son draw up a design first:

Then grab some scrap out of the bins:


He crosscut the maple base and frame arms with the sled.



Then he cut the finger joints on sled jr.


I did the single rip cut because it was fairly narrow, then he took over with the walnut for the multi-angle base.

[JohnnyEgo]

Drilled holes in the frame for the pivot arm.


Drilled holes for the angled base.


I trimmed up the lever arm on the bandsaw. I won't let him anywhere near the router, so I also knocked the edges off with a roundover bit. Then back to him for glue and clamps.




Two wiped on coats of Danish oil for the win.





We originally used 4 rubber bands, which ended up launching the ping pong balls something like 20 feet. I down-powered it so we could run the experiments at a reasonable scale in the garage.


We used video to determine the horizontal distance and elapsed time. In the context of his algebra-less experiment, that was enough to prove which launch angle sent the ball the furthest. I showed him how to use the kinematic equations to resolve vertical displacement and the component vectors of velocity, but I wouldn't say he was highly interested in that. But we had fun making the catapult and shooting ping pong balls all over the place. And when Mom wasn't looking, we launched cherry tomatoes all over the kitchen as well.

I am proud of the fact that his project represents both his actual levels of understanding and effort, and I look forward to seeing it between the projects of the kids who home-sequenced the genome of their dog and the one who built a functional model of the Jarvik heart.

[Irving]

I am proud of the fact that his project represents both his actual levels of understanding and effort, and I look forward to seeing it between the projects of the kids who home-sequenced the genome of their dog and the one who built a functional model of the Jarvik heart.

This is me. I tried to get my daughter to do a super awesome project, where I'd come up with the experiment, but make her put everything together, and she was never down. I wanted to do a solar powered aquaponics project. She always picked stuff more realistic and appropriate for her age though, so it was for the best.

[JohnnyEgo]

That is not a real shop, it is WAY to clean.

Love reading these kinds of posts. Yup, in the long run he will look back and smile.

Sadly, it's definitely a garage, not a shop. Everything is on wheels so my wife can park her car back in there in the evenings, and she frowns upon piles of sawdust gently raining down every time the garage door opens, so it is kept clean out of necessity and fear.

This is me. I tried to get my daughter to do a super awesome project, where I'd come up with the experiment, but make her put everything together, and she was never down. I wanted to do a solar powered aquaponics project. She always picked stuff more realistic and appropriate for her age though, so it was for the best.

It's an interesting balance. One of my son's friends is doing a bridge experiment, where you design different bridges and see how much weight they will support. I remember a friend of mine doing something very similar way back when we were in 5th grade. The difference is that my son's friend's bridges were clearly designed in Solidworks and accompanied by finite element analysis prints. Even more impressive to me is that the bridges were 3D printed somehow with a color spool such that they have the FEA color map printed on the surface. I am not sure I could do either of these things, let alone a 10 year old. Coincidentally, his dad's a mechanical engineer, but I am sure that has no bearing. I go back and forth over whether I do too much or not enough on this type of thing, but at the end of the day, I still end up frog-marching him towards active involvement in his own education, even when it would be faster, less stressful, and there would be much fewer obscenities uttered by either of us if I did it myself.

[Great-Kazoo]

Sadly, it's definitely a garage, not a shop. Everything is on wheels so my wife can park her car back in there in the evenings, and she frowns upon piles of sawdust gently raining down every time the garage door opens, so it is kept clean out of necessity and fear.



It's an interesting balance. One of my son's friends is doing a bridge experiment, where you design different bridges and see how much weight they will support. I remember a friend of mine doing something very similar way back when we were in 5th grade. The difference is that my son's friend's bridges were clearly designed in Solidworks and accompanied by finite element analysis prints. Even more impressive to me is that the bridges were 3D printed somehow with a color spool such that they have the FEA color map printed on the surface. I am not sure I could do either of these things, let alone a 10 year old. Coincidentally, his dad's a mechanical engineer, but I am sure that has no bearing. I go back and forth over whether I do too much or not enough on this type of thing, but at the end of the day, I still end up frog-marching him towards active involvement in his own education, even when it would be faster, less stressful, and there would be much fewer obscenities uttered by either of us if I did it myself.

As i'm reading your always interesting post. I flash back to one project in 9th? grade. Myself and a friend since kindergarten, did what we thought was not only factual but humorous project.

Titled The Appian Way, 500 years later.

Very detailed and lifelike of how it looked in present times. Many hours spent laying out the details and finally the finished project. 4"w x 12" long row of 1/2" broken tiles stuck on a board, held together with clay. Then a handful of dirt over it.

Clearly the teacher had no imagination, as we barely got past a c+ for effort. Even then, the education system was rigged.

[Skully]

That friggin cool!

Now, on to a full size one for the front yard and capable of launching farm animals.................

[Irving]

I didn't make a catapult until 11th grade physics. A few years ago we picked a science fair project that got the school district, and the state involved, and all the other group member parents bailed their kids out of the project. Nicely done.

[JohnnyEgo]

I didn't make a catapult until 11th grade physics. A few years ago we picked a science fair project that got the school district, and the state involved, and all the other group member parents bailed their kids out of the project. Nicely done.

That must have been a hell of a project!

[MrPrena]

That is 1st prize for sure!

[copfish]

Awesome project! Looks good too! Let us know how it was received.