SpudFiles

boyntonstu wrote:A 150 pound crossbow pushing a .25" diameter piston 24" iwould create a a fairly high pressure.

BoyntonStu

I'll have the stirrup pump if its all the same.

1) You need to manually haul back that string

2) 150lb draw does not mean it puts out 150lb for the entire travel of the string


Of course if the purpose is to have a pulse of pressure to fire something... just use the crossbow itself, conversion doesn't improve efficiency.

Hotwired wrote:

boyntonstu wrote:A 150 pound crossbow pushing a .25" diameter piston 24" iwould create a a fairly high pressure.

BoyntonStu

I'll have the stirrup pump if its all the same.

1) You need to manually haul back that string

2) 150lb draw does not mean it puts out 150lb for the entire travel of the string


Of course if the purpose is to have a pulse of pressure to fire something... just use the crossbow itself, conversion doesn't improve efficiency.

Would you drive the piston and move the projectile immediately, or would suggest compressing the air and releasing the final pressure?

BTW I can see a way to individually pull multiple elastics for cocking a slide shuttle and generating much more than 150 pounds of force.

BoyntonStu

Hotwired wrote:

boyntonstu wrote:A 150 pound crossbow pushing a .25" diameter piston 24" iwould create a a fairly high pressure.

BoyntonStu

Of course if the purpose is to have a pulse of pressure to fire something... just use the crossbow itself, conversion doesn't improve efficiency.

The string has mass. After the crossbow itself fires the projectile, the string continues indicating not all the energy transfered to the projectile. In an ideal spring, air, projectile setup, it is possible to transfer all the bow energy to the air such the bow comes to a stop with no left over energy, which then transfers all of it to the projectile, which then reduces to atmospheric pressure as the projectile is ejected, giving all the energy to the projectile for a higher overall energy transfer efficiency.

Building it with everything the right mass, etc is another story.

Hotwired wrote:Would you drive the piston and move the projectile immediately, or would suggest compressing the air and releasing the final pressure?

Higher efficiency can be obtained without a valve by simply using the air as an efficient spring.

Technician1002 wrote:

Hotwired wrote:

boyntonstu wrote:A 150 pound crossbow pushing a .25" diameter piston 24" iwould create a a fairly high pressure.

BoyntonStu

Of course if the purpose is to have a pulse of pressure to fire something... just use the crossbow itself, conversion doesn't improve efficiency.

The string has mass. After the crossbow itself fires the projectile, the string continues indicating not all the energy transfered to the projectile. In an ideal spring, air, projectile setup, it is possible to transfer all the bow energy to the air such the bow comes to a stop with no left over energy, which then transfers all of it to the projectile, which then reduces to atmospheric pressure as the projectile is ejected, giving all the energy to the projectile for a higher overall energy transfer efficiency.

Building it with everything the right mass, etc is another story.

Hotwired wrote:Would you drive the piston and move the projectile immediately, or would suggest compressing the air and releasing the final pressure?

Higher efficiency can be obtained without a valve by simply using the air as an efficient spring.

More better!

Easier to make.

It's a really powerful simple blowgun.

Chamber/barrel diameter ratio?

1:1 or greater than 1:1?

BoyntonStu[/url]

boyntonstu wrote:

Technician1002 wrote:

Hotwired wrote:
Of course if the purpose is to have a pulse of pressure to fire something... just use the crossbow itself, conversion doesn't improve efficiency.

The string has mass. After the crossbow itself fires the projectile, the string continues indicating not all the energy transfered to the projectile. In an ideal spring, air, projectile setup, it is possible to transfer all the bow energy to the air such the bow comes to a stop with no left over energy, which then transfers all of it to the projectile, which then reduces to atmospheric pressure as the projectile is ejected, giving all the energy to the projectile for a higher overall energy transfer efficiency.

Building it with everything the right mass, etc is another story.

Hotwired wrote:Would you drive the piston and move the projectile immediately, or would suggest compressing the air and releasing the final pressure?

Higher efficiency can be obtained without a valve by simply using the air as an efficient spring.

More better!

Easier to make.

It's a really powerful simple blowgun.

Chamber/barrel diameter ratio?

1:1 or greater than 1:1?

BoyntonStu[/url]

No chamber in a traditional sense. Chamber is the moving compressing and expanding air between the piston and projectile. C/B ratio is simply determined by how much the final air compression is before it re-expands. Think Newton's cradle, but with air for springs instead of steel balls impacting for energy transfer. With a large mass in an elastic collision (air spring) the small mass can be ejected at higher velocity than the velocity of the heavier mass impacting it.

It works like this video with string, piston, air, and projectile,but the direction does not change but energy is transferred to the smaller projectile.
http://video.google.com/videoplay?docid ... 9464&hl=en

You can get the projectile up to speeds faster than the string can move simply pushing the projectile. Much like a stomp rocket, you can get projectiles traveling faster than your foot landing on the stomp bellows.

[youtube][/youtube]

Sounds like fun rag, ill make one to if i get around, it sounds really useful, what are you using as a piston material?

Oh look what i found, this is to pressuize water, but maybe could eb used for air too
clicky

john bunsenburner wrote:Sounds like fun rag, ill make one to if i get around, it sounds really useful, what are you using as a piston material?

Right now, spare PVC rod. That's why I'm not quite finished - it works, but something more robust would be welcomed.

If I do it, would you recomend alli or nylon?

Hotwired wrote:Would you drive the piston and move the projectile immediately, or would suggest compressing the air and releasing the final pressure?

Tech needs to work on quoting skills, boyntonstu said that not me.

Hotwired wrote:

Hotwired wrote:Would you drive the piston and move the projectile immediately, or would suggest compressing the air and releasing the final pressure?

Tech needs to work on quoting skills, boyntonstu said that not me.

Sorry. Posted after an all nighter graveyard shift.