PIC controlled air cannon

[MrDEB]

The area high schools had a technology fair recently and several high school kids I know were in the trebuchet contest. $5000 to furthest throw for their school.
Was talking to the kid Joey this morning about next years contest, putting an accelerometer, angle meter etc. on his trebuchet.
He stated that next year they want air cannons but get points for being "green"
he was considering solar powered electric valve, some sort of wood burning device to make sein? gas or ?? for running the generator to run the air compressor.
My thoughts-an angle (read trajectory) meter, air pressure meter, and ? what ever it would take to help the marksmanship of the air cannon (points for accuracy).
perhaps a laser distance meter??
we have a year to work on this.
any thoughts from this imanagitive groupe of people on this board??
oh yea Premiere Technology is the company awarding the cash.
you should have seen the trebuchet they brought on a flatbed truck. about 2 -3 stories high, threw a 3 pound water balloon 600yards+

 

[Sceadwian]

If you use a small smooth ball you can just about ignore air resistance, so the optimum angle is always going to be 45 degrees so no reason to measure it, so the ammunition you're firing is critically important.

If you want green, use a human being to power the air compressor, if you tweak the gearing optimally a human being can put out some decent power, remembering that maximum pressure is more a function of torque than speed if given an appropriate amount of time a human being can pressurize an air source as well as if not slower than a motorized device. To prove 'greenness' you can get them to learn and do the math to determine the amount of calorise required to deliver the same power with a gas powered source or compute the efficiency verse a solar powered electric source. People are pretty efficient as far as energy use goes, and if you consider the fact that the excercise a person does to power the device is good for the person involved the net efficiency and benefit is way higher than a pure fuel based system.

 

[MrDEB]

I like the bickle idea

I understand the ammo is a baseball or tennis ball?
wonder what would work better - the bike generating electricity or connected to an air compressor?
even contemplated steam or maybe a chemical reaction?

 

[Sceadwian]

Well you'll need an air compressor no matter what, it doesn't provide energy it just converts it for you. In one case you would have an expanding gas driving an engine that would drive the compressor, in the other you would directly power the compressor via a pulley system from the bike, you could also use the bike to generate electricity and use an elecrtical power to power the compressor, this would be advantagous in that you could use a transformer as a gear box instead of a more complex direct connection, but it would be higher loss.

Chemical reactions tend to slow down when the pressures increase so direct cehmical powering is probably not a good idea, steam is a good idea, lots of power to be had there, however you need to heat it with a combustible, which isn't very green.

Personally I like the idea of a well thought out and constructed gear system powering an air compressor directly from a bicycle. The single most important part is going to be the compressor itself, and the pressure containers it uses. As I said in my previous post nothing says 'green' more to me than using human power to derive kinetic or electrical energy. Most people need the excercise anyways so it's a health/longevity benefit to the person as well.