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Unread 11-01-2006, 00:29
KenWittlief KenWittlief is offline
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Re: pneumatic launch velocity

dont say no too quickly

the problem with using a pneumatic cylinder to launch things is the small size of the tubing and valves. You cant get a fast enough inrush of air to move the cylinder piston as fast as you need to

but dont give up, there are ways around this

one would be to rig up a stop, or trigger/release pin about halfway down the cylinders length. To shoot something you would pressurize the cylinder against the trigger pin. That will build up a volume of air inside the cylinder at 60PSI

then you pull the trigger out of the way. There will be nothing to slow down its movement this way, except the ball that is being launched.

I must point out, these cylinders are not designed to be slammed into their own ends, so if you do something like this you must put a mechanical bumper or stop that limits the motion of the piston, so it cannot slam the end internally. If not, sooner or later the end will blow out of the cylinder, with a great deal of force: someone could be seriously injured.

there are other ways - brainstorm the concept: use the cylinders to load up some other form of energy storage/release mechanism.
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Unread 11-01-2006, 00:41
Rickertsen2 Rickertsen2 is offline
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Re: pneumatic launch velocity

Quote:
Originally Posted by KenWittlief
I must point out, these cylinders are not designed to be slammed into their own ends, so if you do something like this you must put a mechanical bumper or stop that limits the motion of the piston, so it cannot slam the end internally. If not, sooner or later the end will blow out of the cylinder, with a great deal of force: someone could be seriously injured.
Of course, BIMBA does make cylinders with two types of internal bumpers so that they can tolerate this sort of use, but FIRST does not allow the. With some trickery we have gotten a ball to a cylinder to launch a ball at 8m/s, with plans to go higher in an entirely FIRST legal setup. It can be done.
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Unread 11-01-2006, 00:45
KenWittlief KenWittlief is offline
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Re: pneumatic launch velocity

I should add: you would have to leave the fitting out of the far end of the cylinder, or it will restrict the air as it flows out.

this means the cylinder can only be pressurized from one end, so you will need a weak spring to retract it for the next shot. maybe surgical tubing?
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Unread 11-01-2006, 21:51
greencactus3 greencactus3 is offline
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Re: pneumatic launch velocity

Quote:
Originally Posted by KenWittlief
I should add: you would have to leave the fitting out of the far end of the cylinder, or it will restrict the air as it flows out.

this means the cylinder can only be pressurized from one end, so you will need a weak spring to retract it for the next shot. maybe surgical tubing?
nah. have the next ball push it back.
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Unread 11-01-2006, 00:43
sciguy125 sciguy125 is offline
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Re: pneumatic launch velocity

Aside from the actual speed that the piston moves (I hadn't thought about that until now), I don't think that it would be practical to launch the balls this way.

E=0.5mv^2
To get the ball to 12m/s, we need to supply it with 13J. This assumes no spin and minimal friction losses.

W=Fd
A 2" cylinder at 60psi will be able to give this 13J with a ~6" stroke. That's a huge volume of air. Your fire rate wouldn't be that great.

Of course, if your goal isn't the full 12m/s, some pneumatic mechanism might work for you.
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Unread 11-01-2006, 01:06
KenWittlief KenWittlief is offline
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Re: pneumatic launch velocity

Quote:
Originally Posted by sciguy125
Aside from the actual speed that the piston moves (I hadn't thought about that until now), I don't think that it would be practical to launch the balls this way.

E=0.5mv^2
To get the ball to 12m/s, we need to supply it with 13J. This assumes no spin and minimal friction losses.

W=Fd
A 2" cylinder at 60psi will be able to give this 13J with a ~6" stroke. That's a huge volume of air. Your fire rate wouldn't be that great.

Of course, if your goal isn't the full 12m/s, some pneumatic mechanism might work for you.
using F=M*A and V=A*t my calculations indicate you only need 19 lbs of force over a distance of 6" to accelerate a 0.175 kg ball up to 12m/s

the acceleration is 480M/S^2, and the time to get from 0 to 12m/S is 25mS
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Unread 11-01-2006, 09:07
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Re: pneumatic launch velocity

You are over constraining the problem. There is no need to have the piston directly provide the full range of motion required to accelerate the ball. Use a 2" diameter x 1" stroke piston. The piston is connected to a range-multipier lever with a 1:10 ratio. The piston will provide 188 pounds of force over 1" as input to the lever. The end of the lever will travel 10" with 18.8 pounds of force. As noted in Ken's post above, there is more than enough energy here to launch the ball.

-dave
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Unread 16-01-2006, 16:58
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Re: pneumatic launch velocity

Quote:
Originally Posted by dlavery
You are over constraining the problem. There is no need to have the piston directly provide the full range of motion required to accelerate the ball. Use a 2" diameter x 1" stroke piston. The piston is connected to a range-multipier lever with a 1:10 ratio. The piston will provide 188 pounds of force over 1" as input to the lever. The end of the lever will travel 10" with 18.8 pounds of force. As noted in Ken's post above, there is more than enough energy here to launch the ball.

-dave
What is a range-multipier lever with a 1:10 ratio???? what do you mean?
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Unread 16-01-2006, 17:17
KenWittlief KenWittlief is offline
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Re: pneumatic launch velocity

an 11" lever with the pivot point 1" in from one end will have a 10:1 multiplier

ten times the distance (speed) on one side vs the other, with 1/10th the force available.
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Unread 16-01-2006, 17:57
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Re: pneumatic launch velocity

Quote:
Originally Posted by KenWittlief
an 11" lever with the pivot point 1" in from one end will have a 10:1 multiplier

ten times the distance (speed) on one side vs the other, with 1/10th the force available.
Is this a mechanical lever or is some kind of pneumatic device, because I am seriously lost.
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Unread 16-01-2006, 18:32
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Re: pneumatic launch velocity

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Unread 16-01-2006, 18:50
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Re: pneumatic launch velocity

Ahhh! what if you were to take that 1" stroke piston 2" diameter and fire it directly to the ball. Would that be enough to fire it to the center goal??
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Unread 16-01-2006, 20:07
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Re: pneumatic launch velocity

probably, if you have enough pressure in the cylinder

and you preload the cylinder with pressure, and use a mechanical release like I talked about on page one

the only caveat, a 1" piston throw may not deform (dent) the ball enough to transfer all the energy quickly. You might need a bowel shaped plate to keep the ball from deforming as the cylinder punches it.

a 1" piston throw into a 1:10 lever: definitely!
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Unread 16-01-2006, 20:09
Rickertsen2 Rickertsen2 is offline
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Re: pneumatic launch velocity

wow... Release latches, lever linkages etc.. Yall are making this way too complicated.
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Unread 16-01-2006, 20:10
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Re: pneumatic launch velocity

Quote:
Originally Posted by Rickertsen2
wow... Release latches, lever linkages etc.. Yall are making this way too complicated.
Do you have some alternative to offer?
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