Plan B Forum

One thing I miss about being old is that I don't get to have fun high school physics projects anymore

But, I get to live vicariously through my kids!

This is how we spent our time during the hurricane and the school closings that came from it.

We made a catapult for my daughter's physics class. We did some fine-tuning today and got it within spec (needed to launch a tennis ball 40 feet at a height of 2 meters).




A video of the test fire. We need to rig it so that it doesn't move like that (see how the back pops up?)

http://www.youtube.com/watch?v=BlWj2WbztGE

That looks great Eddie...

Now all you need are a few squirrels to load up your catapult with, and you're in business...

Great fun.

You can stake the feet to the ground (screw angle brackets to the bottoms of the legs and pound stakes through the holes now flush with the ground) or attach a heavier base to it. Based on how how hard you are pulling on the lever in the video I would guess that it will take a lot of weight or longish and well-placed stakes to reduce the movement to an acceptable level.


yrs,
rubato

Great idea, rubato. The only problem is that, when she brings it to school, she is firing it in the gym. They would frown on me staking it down in there. I was thinking that either I would attach another long board to the back that the launcher would stand on or have two volunteers with a rope stretched across holding it down.

Full disclosure - the design is not mine. We found it online. I just did some fine tuning.

eddieq wrote:"... I was thinking that either I would attach another long board to the back that the launcher would stand on... "

Sounds like a good plan. Post the video, if you get a chance.


Speaking of building prototypes I've wound up making 5 different containers for a catalyst in a reaction, and still counting. I thought this was going to be dead easy too!

1.
Fluoropolymer bag heat-sealed with 75 micron openings.

Worked, sort of. But the catalyst clumped together and the product structure was changed.

2.
Switched back to smaller bead-size for the catalyst.

3.
PEEK bag* heat-sealed into container with multiple small 'pockets' and 35 micron mesh openings to overcome clumping.
Bag turned 90 degrees sideways and made several smaller 'clumps'.

4.
Realized that I needed something to hold the container into an open volume so that the catalyst would float freely in the solution. Made an FEP framework by cutting out most of the sides of a 60ml FEP (its basically like teflon) bottle and then heat-sealing the 35 micron mesh around it. Worked pretty well but the EtOH evolved by the reaction made the bag 'float' so that less of the free volume was filled with liquid than optimal.

5.
When 4 was done again on a 2x lager scale I added 12g of glass rasig rings to weigh them down (used two to accommodate the larger scale). Worked! The bags sank anyway but the stir-bar now hit them so often that the bags broke open negating the whole thing.


Shit! And we're already scaling up this reaction to a 5L jacketed reactor with an even more vigorous and damaging stirrer so this has to be fixed!

Ok so for the next round I'm making a framework to go INTO the mesh bag and hold it open and a framework to go OUTside the bag to protect it from harm from the stirrer. Now I'm a research chemist and REALLY impatient so I usually just look around the lab for something I can cut up and make into what I want and this is getting more challenging. AND what I really need to be doing is developing the material properties of this stuff which means changing the chemistry not making some damn container that in the RW I'm just going to pay someone to fabricate for me.


Yrs,
rubato

* the vendor stopped making the fluoropolymer bag in favor of PEEK which is similar in most properties but does not heat-seal as well.

Nice one Eddie, thanks for sharing...

Good to see you but of course we need a doggie update.

Sorry for the bump, but now she's on to making a Rube Goldberg machine in my basement. I got my Christmas tree last night, but I cannot put my trains up yet because the locomotive is "in use" for this physics project. It has been turned into a deadly weapon for the purposes of popping a balloon that holds back a rope attached to a pulley and weight. When the train pops the balloon, the rope lets go, the weight (one of my mallets) falls, pulling the cord to turn on a light and also smashing a piece of fruit and squirting toothpaste out. The fruit will be on the end of a lever which when pressed down, the other side flips a switch turning on my leaf blower, which will blow a yoga block down, landing on another switch, which will power up an electronic keyboard.

I'll have to post the video when it's all done. 12 energy transfers, 5 "simple machines", 4 electric switches, a pendulum and a partridge in a pear tree...

My locomotive...

I forgot to mention. Elegant design on the spring for your catapult. Twist the cord until you have the spring tension you want and then pop in a dowel to hold it there.

Very clean.

Looking forward to the video of the latest.

yrs,
rubato

rubato wrote:I forgot to mention. Elegant design on the spring for your catapult. Twist the cord until you have the spring tension you want and then pop in a dowel to hold it there.

Very clean.

Looking forward to the video of the latest.

yrs,
rubato

Thanks, rubato.

The video of the RG machine in action. A "gag reel" is included.

http://www.youtube.com/watch?v=DAaGRIc0yIA

Great! I love the use of the leaf blower and the little musical refrain at the end. Maybe you could work the catapult into it? Throwing a water balloon?

yrs,
rubato

rubato wrote:Great! I love the use of the leaf blower and the little musical refrain at the end. Maybe you could work the catapult into it? Throwing a water balloon?

yrs,
rubato

Well, the catapult was the wooden structure that was holding the balloon back Does that count?

That's way cool Eddie!

Well done! Loved the video and the blooper reel!!