# Cylinder Force Calculation

How much pressure is needed to pop these poof ball into the center goal with a 2" bore and 4" piston from the tip of the ramp? Is it possible? What equation can I use to find this out? HELP!

What kind of mechanism is the cylinder affixed to? A lever arm of some sorts?

The force a clyinder puts out is just pressure times area. Area being pi*r^2 For force on the retract, subtract the cross sectional area of the rod.

Also, have you guys already ruled out a spinning wheel shooter? It is not as hard as it may seem. You can build it it one day if you were focused on it.

We want the ball hitting directly with piston.

Itโs more an issue of flow and volume, I would suggest printing out the manual and setting up a test situation and see if you can get what you are thinking about to hit the ball fast enough and hard enough to get what you are hoping for. You may be surprised by your results.

Thanks, I am planning on doing that as soon as I have the math down. Time to contact the math teachers and physics teacher.

the equations you are looking for relate force, mass, acceleration, velocity, distance and time

you need to specify the length of the cylinder-throw, the mass of the ball, and the velocity you desire

the pressure will then fall out as the calculated force divided by the area of the face of the (circular) internal piston plate.

Force = mass times acceleration

distance = 0.5 * acceleration * time^2

velocity = acceleration * time (and you can average the velocity = final speed / 2) to get the time

remember that mass is kilograms and force is newtons. (or slugs and pounds).

something else (that has been discussed in other threads): the flow of air through the valves and hoses in the kit of parts is not that fast - probably not fast enough to laungh a ball. You will most likely need to hold the cylinder back with a release pin (a pin that blockes its forward motion) and precharge the cylinder with air, then pull the pin to fire the launcher. This means if you want a 4" throw you might need an 8" cylinder, with the release trigger pin half way down its travel.

and you might also need to take the fitting off the far end of the cylinder, to allow the air to escape without restriction.

We did some empirical testing with this method, and ruled it out pretty quickly. With a large diameter cylinder, you get the most force, but it takes a lot of air to fill the cylinder, so the speed is way too slow. We got much better speed with small diameter cylinders, but the force was only enough to push the ball about 4 feet.

saw the same thing a few years back. Thats why the cylinder needs to be mechanically held back while its pre-charged

then released

when you implement this way, is like an air-spring

decided to draw a diagram

1. the release pin is blocking the cylinder from extending more than half way

2. the cylinder is charged with 60PSI

3. the release pin is pulled. The business end of the cylinder has no fitting, so the low pressure air flows out freely

4. the ball is launched into tomorrow!

5. a mechanical stop prevents the end of the piston from slamming the inside end of the cylinder (not shown)

6. use a spring or surgical tubing to pull the piston back when the pressure valve is closed (not shown either)

Say we didnโt want to preload it, just have the air flow in instantly when the piston is drawn back. Then would it work?

all the testing that teams have done (over the years) says no. The air cannot flow through the little openings in the solonoid valves, fittings and tubing fast enough.

Ever see the pumpkin-chuckers, the giant air cannons that launch a 10" pumpkin about a mile away? they have huge air valves that someone pulls with a foot long handle.

we dont have those valves, so you need to get the air in the cylinder first (precharge) and then pull the mechanical pin out of the way.

2" bore 4" stroke and a 12V solinoid with 60PSI wont work!?

try it and see for yourself. The cylinder will not fill up fast enough.

I know a cylinder with 60psi slamming it back and forth looks fast, but not compaired to something like pulling a spring back and letting it go.

By precharging the cylinder, blocked half way, you are creating an air-spring. scroll back up and look at the drawing in post #9 in this thread.

What if it was a springloaded piston? I have seen them on McMaster?

you can only use pneumatic cylinders that are on the Bimba purchase list, and none of those have internal springs

you could use an external spring, and use a cylinder to retract it.

Say if I modified the bore and stroke length? Would that make a difference? a smaller volume means it will get filled up fast right?

you are not allowed to disassemble the cylinders or modify them in any way - but you can build them into a mechanism that alters its behavior (adding an external spring-return, or an external trigger release.

No matter what the bore and stroke of the cylinder is, the air flow is controlled (restricted) by the valves and fittings and hoses. There is nothing you can do to the cylinder to make air flow through the valves faster.

And you cannot use other valves, or modify the ones in the KOP.

By mod i meant like change sizes, I know you cant mess with the parts. I just want to make less volume to cover, to it fills up faster, but I guess that doesnโt work.

a smaller diameter cylinder will fill up faster, but it will have less force on its pushrod. The force a cylinder generates is equal to the surface area of its internal; piston plate times the pressure of the air you feed it with.

So, yes, a smaller diameter cylinder will pressurize faster, but the trade-off is less output force.

Is there some reason why you dont want to implement the release-trigger like I drew in the diagram? its probably the easiest way to make a pneumatic shooter.

I think a lever would be a better idea. Where a bar has a pivot on one end, then have the piston in the middle then the other end of the bar hits the ball.