Pneumatic Launcher / catapult doesn't work well... needs your input

Go to https://www.youtube.com/watch?v=sLy256p7KMo to see a vid of out current pneumatic launcher testbed. As you can see in the video the large ball doesn’t launch very well. What do we need to change? We currently have 2 dual acting pistons, 1 res., and 100 PSI.

How far away from the cylinders is your solenoid valve? If the tubing connection is too long, you might be introducing too much of a pathway for the air to move quickly enough to get full power. Just a thought.

You need to lower the height at which the large ball rests on. Make the catapult arm about 5-10 holes longer. And improve your piston mounting. The pistons should be completely straight.

Straight as in parallel to the floor?

Also keep in mind how the little “bean bag” weight inside the ball affects the dynamics of launching the ball. There is a considerable amount of weight in that bean bag, but in your present configuration, when your arm punches the ball, the arm is hitting far above the bean bag. To me, it looks like this causes the ball to roll rather than launch since the ball wants to rotate closer to its center of mass.

However, one of the problems with punching the ball directly at the bean bag is that you might end up with an effect similar to something you see in Newton’s Cradle. http://en.wikipedia.org/wiki/Newton’s_cradle

In other words, because you are “punching” the ball rather than accelerating it over some short distance, you might transfer most of your momentum to the bean bag rather than to the ball+bean bag. You can demonstrate this by holding the ball in one hand and punching it with the other directly at the bean bag. Under some circumstances, you can cause the bean bag to jump up inside the ball while the ball itself remains almost stationary.

My suggestion would be to try to configure this somehow so that you don’t punch the ball but instead try to accelerate it as closely as possible to where the bean bag might normally rest. But I’m going to guess this suggestion isn’t something you want to hear since you’ve got the thing assembled already. In any case, I hope this helps somewhat.

Straight as in parallel to each other and not skewed like you have them right now.

You want the ball to rest on the bar. That way it can travel up the bar and get more height/distance. Right now it’s just hitting the top of the bar and going down. Are you still doing Toss Up? I can send you some pictures of our launcher: http://youtu.be/Qy0o8lOOjrk

yes please email them to kxtperformance@gmail.com

The ball should roll up the bar as you catapult to get the right trajectory. If it starts at the end of the bar it wont get the same height as it doesn’t have the same vertical momentum at the end of the shot. If it is too close to the fulcrum it won’t get any movement as you have now.

Your walls seem to be hindering the resting position of the ball.

yeah…the catapult is slapping the ball, the ball needs to touch the catapult bar for you to get any distance

We have modified our pneumatic launcher, but we are still having problems with trying to get the big ball to go higher. I have changed the placement of the ball by resting it on the launching bar instead of above it where it only smacked it. We have also changed the length and the width of the launching bar from the original that we had. We now have the big ball placed at the top of the robot now instead of in the middle. Please check out the new video (https://www.youtube.com/watch?v=ISFMJImp79M) I need suggestions and ideas on how to make it go higher and or farther, thank you.

The video said it was private and would not let me see it. :confused:

link should be good now.

Where is/are your solenoid/s located? How far from the cylinders (actuators)? How far from the reservoir(s)?

If there is a long path from the solenoid to the actuator, then the air pressure must build up in the entire length of the hose before it reaches the actuator. At the same time, the air on the other side of the double-acting piston must find its way down another piece of hose to the solenoid before it can escape. If you have long hoses, then it might be reducing the performance of your system.

Also, are you using a pressure regulator, and, if so, are you sure you have it adjusted for max pressure?

The height comes from the ball sliding along the catapult arm. The resting position of the ball is too high and needs to allow the ball to be impacting by the catapult arm the entire shot.

as tabor said, instead of placing the ball too high along the catapult place it more like 3/4-1/2 of the way up the bar from the hinge.

We are going to shorten the hose lengths considerably tomorrow. (they are long now) Also we are using 1 solenoid that is T’ed off afterwards to the cylinders. Is it best to use 2 solenoids instead?

Also will be adjust ball height tomorrow. Will be uploading another video tomorrow afternoon.

I can’t say from experience (so I hope the geniuses above will input on this) but if each actuator could have its own solenoid positioned as closely as possible, that would be better under ideal conditions. However, I don’t know how close together in time your computer code can fire both solenoids. If both solenoids can fire virtually simultaneously, then that would be your best configuration.

In essence, you want to reduce as much as possible the path that the air must travel going to and from your actuators to the solenoids.

Good luck! :slight_smile:

In testing with our catapult, my team found that there was a slightly noticeable difference between one and two solenoids, so that may improve flow.

If you slightly increase the angle between the pistons and the launching bar, you should see more height. This way, the end position of the bar will not be directly vertical and will instead give the ball an earlier release point, allowing it to reach a higher point. We did this on my team’s Toss Up robot.