Using a pneumatic cylinder or syringe to compress air and move a payload very fast 1

[3dmapmaker]

I plan on using a syringe that has a diameter of 1" and a 2.5" stroke. The needle is 0.25 diameter and 10" long. The syringe pushes air not liquid. I have a 2 gram payload in the needle at the junction of the syringe and the needle. how do I figure out how much force and speed to apply to the plunger of the syringe to move the payload in the needle to a speed of 10,000 inches per second as it exits the end of the needle?
I was thinking of using a pneumatic cylinder in place of a syringe. I am unsure how to do the math for this to size the cylinder and motor to drive the ram.
Any suggestions?

 

[LittleInch]

250 m/ sec eh?

Force=mass times acceleration is a start.

But that's air gun speed

No way is your design going to work practically. IMHO.

You would probably need to hit the end of the syringe with a sledge hammer to generate the force and velocity of the main plunger to get even close.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3dmapmaker]

I should be able to get 600 psi from the cylinder or piston in a tenth of a second using the proper motor. But I am unsure the proper way to calculate the actual required pressure and cfm required. I would rather not use a sledge if a small ball peen will do.

 

[srini1785]

The max speed of a Pneumatic cylinder of 40mm dia (1.5") is roughly 3m/sec. No way you are going to get a speed of 250m/sec using a pneumatic cylinder. Try firing a bullet type projectile.

 

[hydtools]

Look into a pellet gun construction.

Ted

 

[LittleInch]

Your biggest issue is that to much of this a transient behaviour.

So, e.g your pellet will start to move as soon as you start to move the big cylinder and then accelerate.

Air guns work by doing the air pressure increase as a separate activity and storing it and then releasing a set volume in a very short space of time.

To get your 600 psi you need the main piston to be essentially at the far end as you need a compression ratio of over 40.

Your system essentially gives you 1:16 force multiplier. Work out what force you need to accelerate your 2g payload from 0 to 250m/sec over 250mm. Simple physics and maths but I last did that 40 yes ago.

Then you can see what force you need on your other piston.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hydtools]

https://www.cse.iitk.ac.in/users/amit/courses/371/brijes/index.html

Ted

 

[LittleInch]

Ah - Always wondered how they worked.

The alternative is of course a paintball gun pistol which uses CO2 pulses of gas.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[btrueblood]

Paintball guns and similar precharged pneumatic rifles use a bash valve, basically the trigger releases a small spring loaded weight that bumps a valve open briefly to release a small amount of high pressure air into the chamber. A third method, used for light gas guns in research (these can get up to 10 km/sec speeds) is to pressurize against a burst disc that opens at a fairly reliable high pressure.

 

[3dmapmaker]

Interesting information. Since everyone sees this as a airgun I resized my syringe and needle to be comparable to what hydtools linked to. Nice link by the way. Never seen that before.
If my calculations are correct I come up with:
Cylinder diameter: 0.22 inches
Cylinder length: 16 inches
Load mass: 2 grams
Load travel distance: 16 inches
Plunger diameter: 1 inch
Applied pressure: 348.11 psi
Stoke of Plunger: 1.0526 inches
Speed of Plunger: 12.6301 ft/s
This takes into the compression of the air in the syringe. There is not much volume needed. Most of the stroke is to get the pressure up from atmospheric.
I will be using s linear motor to control the plunger not a spring and no valve.

 

[hydtools]

You could use work=energy. F*d = 0.5*m*v^2
F;force to move the mass
d;distance over which the force acts
m;mass
v;velocity of the mass

Ted

 

[akkamaan]

The difference between your concept and the airgun is that in your concept you store the energy in the compressed air and in the air gun the energy is stored in a compressed spring. And the spring pushes the piston that compresses the air when shooting the pellet. The stiffer spring and the longer stroke of the spring the more energy behind the pellet and the higher V0-velocity you get. The key is to make all the stored energy in the compressed air hit the pellet during the shortest possible time. Compare this with a gunpowder-driven bullet. The faster the powder can burn/combust the more instant energy behind the bullet...