Atmospheric pressure is all around us, and capable of providing a great deal of force when used properly. As Otto Von Guericke demonstrated with his Magdeburg hemispheres over 350 years ago, simply removing air from a chamber to create a vacuum can have astounding results. More recently, [Tom Stanton] has used vacuum to power a small 3D-printed dragster.
In the dragster build, a typical plunger syringe is plugged at the end, and the plunger pulled back. Atmospheric pressure acts against the vacuum, wanting to push the plunger back towards its original position. To make use of this, a string is attached to the plunger, causing it to turn a gear as it moves forward, driving the rear wheels through a belt drive. With the correct gear ratio on the belt drive, the dragster is capable of spinning its tires and shooting forwards at a quick pace.
The work is a great follow on from [Tom]’s earlier vacuum experiments, using syringes as small rockets. It reminds us of the classic CO2 dragsters from high school competitions, and would be a great project for any science class. Video after the break.
That’s pretty cool…it’s a cross between a mousetrap car and a co2 car.
My “Tech Ed” teacher and I had a yearly grudge match with both from 7th through 12th grade.
By the final race in co2 cars, we both had made entries that were just above the minimum specifications allowed by the rules. Just before the final race we were walking around with c02 cartridges in our armpits trying to gain an advantage. I won by 0.010 seconds.
The “mouse trap” cars were the real spectical though…by the end we were using rat traps, replacing the paddle with long rods, adding extra turns to the springs, trepanning 10″ diameter wheels (we both had the same idea independently), cutting the traps out for lowest weight without the car folding in half, and making overdrive transmissions. The typical “student” cars went 50′ or so, while ours were going a few hundred feet…to the point where when the cars hit the end of the hall, there was still spring left in them…we had to declare a draw.
If it wasn’t for that one teacher, I wouldn’t be a machinist today.
That teacher sounds like the best kind of teacher.
I did the CO2 car race in 8th grade, and my car placed fairly well. I used my limited plastic model building skills to give it a nice “desert camo” paint job, and used my fascination with aircraft to give it what I thought was an aerodynamic shape. I still have the thing.
Good teachers are a rare treasure.
He was by far the most influential teacher I had…i wish there were more teachers that saw a students potential and actively engaged them.
The single biggest I had in school was staying engaged…the normal classes were to dumbed down (to the point where I passed with mid 90s and never did homework) and the AP classes were too advanced unless you had a private tutor.
The second most influential teacher was my calculus teacher, she saw some drawings I had done trying to mathematically explain the relationship between valve timing and the effective compression ratio of an engine…then helped me find the solution. The math we came up with holds solid against commercial software.
My first couple of co2 cars were works of art…beautiful lines and I used “monokote” to cover any spaces that would increase drag. Then the “pissing match” began and we both worked down to them minimum requirements to be “legal”. One year both cars broke when they hit the end of the track, so we designed a “soft trap”. The following year it was an arms race to figure out where we could reduce the cars mass without it breaking. I still have the winning car out in my garage somewhere.
Damn it you two.. Now I’m peeved.. No such thing in school here in my experience (teachers or interesting projects like that)… I did have a few alright teachers – but largely they were alright because they would occasionally go beyond the exam requirements when asked good questions and didn’t kick up a fuss when I paid their lesson very little attention being so dumbed down and slow…
I take it the CO2 ones are a flat drag race over fixed distance, but what about other rules (is it just a CO2 powered rocket/piston/turbine or any method at all, the distance to cover, guidance method?)?
I think the mouse trap is a little more explained but expansion on that would be interesting too.
So basically the co2 cars have rules for minimum weight phisical dimensions…a c02 cartridge for a bb gun/tire inflator goes in a hole in the car’s body. A soleniod punctures the cartridge and it goes off rocket style…each person holds a button and there is a “Christmas tree” like in drag racing. Once you get down to the minimum requirements, it’s all reaction time and doing goofy things like warming the cartridges.
Guidance is simple, each car has two eyelets screwed into the bottom and a simple piece of high test fishing guides the car down the track…sometimes it breaks or the car flips over.
The mousetrap cars are property what you imagine…you get a kit with some balsa wood, wheels, hardware and a mousetrap. The first version is just a string wrapped around an axle driving the wheels and is boring. Then you start making it go further with bigger wheels, then make it longer so it doesn’t flip over, modify the trap, make it lighter…on and on. In the end we were using RC car gears to make simple transmissions and making our own giant wheels. We just ran them down the longest hall in the school.
Wow. This kind of teacher can really make the difference and make you love (or hate) the topic they are teaching
So, there’s no onboard energy storage is there?
There is onboard energy storage…i haven’t looked up the math but, it’s roughly the pressure difference across the syringe’s plunger squared times the volume of the syringe divided by two. It’s anagoulous to the stored energy of a capacitor…(V^2 x C) /2.
There’s energy stored in the vacuum. The vacuum is pulling on the plunger in the syringe, trying to pull the plunger into the syringe.
The way I understand it is the energy is in the atmosphere, not in the vacuum. Right? Like, if you put the car in a vacuum chamber and launched it, nothing would happen, if you put it in a pressure chamber, and gradually increased the pressure in the chamber, the performance potential of the car would increase, but you wouldn’t be putting more energy into the car.
All energy outputs are based on the environment.
You don’t give a rock more distance from the ground on the moon than here but its got alot less energy in that environment. Same thing when dealing with a pressure or charge differential. Its the differential to atmospheric that defines how much energy you get out yes, but the energy is most definitely stored onboard – there would be no potential difference to drive the mechanism without the vacuum, and a stronger/weaker vacuum under the same conditions directly changes the energy stored…
Perhaps this thought will help – If a force is ‘negative’ that just means its working in the other direction, not that its not there.
All energy outputs are based on the environment? What about radioactive decay? Combustion of browns gas?
Even when the energy source doesn’t require anything from the environment to function the actual output will change for one reason or other because of it. Often less dramatic though not always, some things behave very strangely when very cold/hot,pressurised or exposed to something else.
And even if the environment you are doing the reaction in doesn’t meaningfully change the reactions output the harvesting of that energy is usually more directly tied to the surroundings. So the reaction can go on just as it always would, it just doesn’t achieve as much.
It’s essentially the weight of the air above the surface area of the plunger, minus the ratio of the air that’s still left in the syringe. If it was a “total” vacuum, it would be the weight of the air. Under water it would be the weight of the water, plus the air. It’s a lot of force, usually going unnoticed. If you go up a mountain where the air is thinner, the car will have less energy available.
well, yes but also no. it’s a vacuum-actuator using ambient counterpressure against a vacuum plunger. so the prime mover of a plunger is drawing a vacuum when armed, replacing a spring in function
This is opposite of vacuum power, but reminded me of the Tomy Air Jammer Road Rammer toy from the 80s.
https://youtu.be/uafQObTMawU