Creating pneumatic launchers

[billbo911]

Originally Posted by AustinShalit

Anytime you use a large bore the speed is going to decrease. You might want to try using a smaller bore.

In order to have an equal amount of force, use multiple cylinders with smaller bore rather than a single large bore for greater speed.

Perfect example.
1 1 1/2" dia. cylinder with 60psi of air pressure applied produces 106Lb of force.
2 1 1/6" dia. cylinders with 60psi of air pressure applied produces 106Lb of force.

[Rick Wagner]

We have a successful prototype using two two-inch diameter, three inch stroke cylinders on a lever catapult. The cylinders are attached three inches from the catapult lever pivot, and the ball is placed 20 inches from the pivot. The catapult moves from horizontal through 45 degrees. We have a reservoir downstream from the 60 psi regulator and a reservoir upstream from the regulator at 120 psi. Each cylinder has its own solenoid. The tension side of the cylinder is open. The ball goes into the high goal reliably.

[waialua359]

Originally Posted by Rick Wagner

We have a successful prototype using two two-inch diameter, three inch stroke cylinders on a lever catapult. The cylinders are attached three inches from the catapult lever pivot, and the ball is placed 20 inches from the pivot. The catapult moves from horizontal through 45 degrees. We have a reservoir downstream from the 60 psi regulator and a reservoir upstream from the regulator at 120 psi. Each cylinder has its own solenoid. The tension side of the cylinder is open. The ball goes into the high goal reliably.

Rick,
when I first heard what you folks were doing, I was very skeptical it would have enough force (speed).
But as Ether has pointed out, the lever arm is the key.
I saw a video clip of the prototype.....nice work.

[ToddF]

Originally Posted by billbo911

Perfect example.
1 1 1/2" dia. cylinder with 60psi of air pressure applied produces 106Lb of force.
2 1 1/6" dia. cylinders with 60psi of air pressure applied produces 106Lb of force.

Note that with the same stroke length, it takes the same volume of gas to fill both of these configurations. With only a single solenoid valve supplying the gas, they fill in exactly the same time. The thing that allows the second configuration to fill faster in a FIRST robot is the ability to use two valves to fill the same volume.

In the real world, using a single large cylinder and filling with two valves would be more weight efficient than the second configuration mentioned. I hate seeing people tossing around generalities like "larger cylinders are slower" without stating the underlying assumptions behind the specific application that makes it so. I fear we're teaching our students design "rules" which are only true in the restricted world of FIRST robotics, but are completely reversed in the real world.

Another approach would be to use the single cylinder from configuration 1, and use a faster flowing valve, a perfectly valid option this year. People are finding legal valves with more than twice the flow capacity than previously legal valves.

[falconmaster]

we are using (2) 1 1/2 bore 10 inch stroke and we seem to have no problem https://www.youtube.com/watch?v=fljCPwHhnHw

[billbo911]

Originally Posted by ToddF

Note that with the same stroke length, it takes the same volume of gas to fill both of these configurations. With only a single solenoid valve supplying the gas, they fill in exactly the same time. The thing that allows the second configuration to fill faster in a FIRST robot is the ability to use two valves to fill the same volume.

In the real world, using a single large cylinder and filling with two valves would be more weight efficient than the second configuration mentioned. I hate seeing people tossing around generalities like "larger cylinders are slower" without stating the underlying assumptions behind the specific application that makes it so. I fear we're teaching our students design "rules" which are only true in the restricted world of FIRST robotics, but are completely reversed in the real world.

Another approach would be to use the single cylinder from configuration 1, and use a faster flowing valve, a perfectly valid option this year. People are finding legal valves with more than twice the flow capacity than previously legal valves.

As long as you are taking my comments out of context, then you are right. That said, I was only giving an example of equal force provided with two commonly available cylinders.

In FIRST, access to a large variety of parts is a given. Although, many teams are on restricted budgets and thus can not afford to by valves just to attain a higher flow rate. These teams need to be creative with what they do have access to.

There are ways to actually exceed the flow rate that is available from even the highest flow valves that are legal within the rules this year.