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Vacuum Crossbow - No limbs, no rubber.


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Old 07-21-2014, 08:56 PM   #11
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If the pic seems strange:

Warmth and Temperature are two completely different things..
Warmth is infrared radiation; Temperature is telling how fast
molecules are moving (vibrating).. Gases under pressure are
less agile.. or colder..


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Old 07-21-2014, 11:15 PM   #12
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Here's how it goes together. The 'good' part start at about 5:00.

Do you understand what happens when the trigger is pulled?



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Old 07-22-2014, 12:26 AM   #13
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Quote:
Originally Posted by BeMahoney View Post
If the pic seems strange:

Warmth and Temperature are two completely different things..
Warmth is infrared radiation; Temperature is telling how fast
molecules are moving (vibrating).. Gases under pressure are
less agile.. or colder..

In the U.S. the unit for Heat is the BTU (British Thermal Unit)

1 BTU of Heat will raise the Temperature of 1 pound of water 1* Fahrenheit.

1 Calorie of Heat will raise the Temperature of 1 gram of water 1* Centigrade.


(12,000 BTU/hr/day defines 1 Ton of ice melt cooling.)
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Old 07-22-2014, 12:53 AM   #14
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I GET IT! You totally lost me with the numbers and the math but that second video was all I needed I get it now.
Seriously when you guys start with the numbers it's like you're speaking a different language at least I could understand the guy in the videos
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Old 07-22-2014, 01:07 AM   #15
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Quote:
Originally Posted by kohlqez View Post
I GET IT! You totally lost me with the numbers and the math but that second video was all I needed I get it now.
Seriously when you guys start with the numbers it's like you're speaking a different language at least I could understand the guy in the videos

The great thing about Math is that it is a universal language.

( IMHO Learning Math is a worthwhile goal.)

I could not understand a single word in the video except 'vacuum' but the video and the hand waving explained a lot.

A vacuum is begging to be filled. The neat thing is that there is infinite air available for each shot. Unlike compressed air.

The limitation on power is the diameter and length of the vacuum chamber.

Brilliant!
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Old 07-22-2014, 01:43 AM   #16
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Quote:
Originally Posted by BoyntonStu View Post
The great thing about Math is that it is a universal language.

( IMHO Learning Math is a worthwhile goal.)

I could not understand a single word in the video except 'vacuum' but the video and the hand waving explained a lot.

A vacuum is begging to be filled. The neat thing is that there is infinite air available for each shot. Unlike compressed air.

The limitation on power is the diameter and length of the vacuum chamber.

Brilliant!
I know basic, intermediate, and a little bit of slightly advanced math but I try to avoid math whenever possible as it causes me headaches. Also I'm pretty sure I'm dyslexic especially where numbers are involved
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Old 07-22-2014, 08:27 AM   #17
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Default One cubic meter of air weighs 1,293 kg!

SORRY! - I edited yesterdays post...

It was full of BullSH!T! - all numbers wrong..

But I corrected it (must say I tried to..)

greets,

Be

(Those forty grams are the amount of water one cubic meter of air holds at
40C, 80% rel. Hum. - like in Florida at 4p.m.?)
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Old 07-31-2014, 08:37 PM   #18
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For me, the results speak for themselves. And i think this design can be improved. I would take away the arms,and 4 out of 6 pulleys,thus reducing a bit of it's size,weight, some friction, cost,and stuff to break. I would take away the plug with holes for the cylinder,which lets atmosperic pressure push the plug. I think that cap with holes,slows down the airflow into the cylinder.
The rail could be lower placed on the cylinder,taking away a bit of weight,and size.
Here's a shooting video at 50m. If someone has an audio/video editing program,it would be possible to calculate the average velocity of the arrow at 50m by looking at the time from the launching sound to impact sound. But to me it sounds about 1 sec to get to 50m and those are probably the 55 gram arrows,described on their page. That's impressive power..
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Old 08-03-2014, 06:05 AM   #19
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Quote:
Originally Posted by jlasud View Post
And i think this design can be improved. I would take away the arms,and 4 out of 6 pulleys,thus reducing a bit of it's size,weight, some friction, cost,and stuff to break. I would take away the plug with holes for the cylinder,which lets atmosperic pressure push the plug. I think that cap with holes,slows down the airflow into the cylinder.
The rail could be lower placed on the cylinder,taking away a bit of weight,and size.
I guess the pulleys are needed as an aid system for cocking the "bow" to increase the leverage. The end cap is required to keep the rope centered and prevent it from scraping the grease from the vacuum chamber, all the other holes are required too to let the piston slide back and forth as they let the air out of the chamber when the "bow" is being cocked, and into it once more after shooting to return the piston to it's 1st position along side the vacuum behind it creating the required pressure difference that operates the weapon
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Old 08-03-2014, 01:20 PM   #20
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You could center the rope with the pulleys.. The end cap is there is to stop stuff getting into the cylinder i think.


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