Air Trajectory B/C

[retired1]

Our 3 teams went with a $4.50 basketball from Wall Mart. No problem throwing the practice golf ball the max distance with 1 kg of weight. We bought 10 lbs of steel shot from midwest at a reasonable price. Normally it is repeatable. Bought a cheap digital inclinometer on line to get repeatable elevations.
Works far better than last years bottles.

[Bazinga+]

I wouldn't use a soda bottle because it is very inconsistent. Also after using it a few times it can change shape and its just a very brute design imo. Try using something more consistent like a pump. You are allowed to move the trajectory anywhere inside the 1m x 1m box (as long as no part goes outside). Also remember that you can move it forward and back to adjust for lengths.

What exactly do you mean by a pump? I've tried to build a sort of air pressure chamber but it did not work out.

Some good pumps I have seen are stomp rocket pumps, either circular, or rectangular.

http://www.amazon.com/The-Original-Stom ... B0006O8Q7Y

I don't recommend using stomp rocket pumps since they have the exact same problems as regular bottles. Try hand pumps or foot pumps which are very consistent and don't wear out.

[kaziscioly]

Our team has a working apparatus with a kickball, and foam golf ball projectiles. The two biggest challenges were sealing a tube into the kickball, and finding appropriate sized tubing for the launch barrel.

So far, the first challenge was met with some metal coupling hardware, attaching the kickball to a shop vac style hose. The second, check out "furniture grade" PVC. As it turns out, they make plastic tubes in basically any size you can imagine - seek and ye shall find (for very little money, too!)

What size pvc were you able to find that could fit the practice golf ball, and where did you get it from? Even when searching furniture pvc I am only finding standard sizes. 1 1/2 inch was too small to fit the practice golf ball (which is around 1.7 inch diameter). Thanks

[retired1]

PM me and I will tell you what we use.

[SPP SciO]

What size pvc were you able to find that could fit the practice golf ball, and where did you get it from? Even when searching furniture pvc I am only finding standard sizes. 1 1/2 inch was too small to fit the practice golf ball (which is around 1.7 inch diameter). Thanks

https://flexpvc.com/Products/PVCPipe.shtml 1-1/2" is the way to go, but with sch. 40 PVC, the walls are a little too thick. There's thinner stuff available, with the same outer diameter

[SOCoach]

Having extreme consistency issues with our Air Trajectory and I am at wits end in how to help my students . . .

We have an ice cream bucket with a heavy piece of vinyl stretched over the lid and secured tightly. Our barrel comes out of the side of the bucket, again sealed tightly and attached to a metal pipe that fits a racquet ball. A 4 inch piece of pvc pipe is suspended above the bucket and our weight slides freely in the pvc tube hitting the vinyl on the ice cream bucket in the same place every time. The students adjust the distance thrown by changing the height from which they drop the weight. So they worked all last Saturday and dialed it in. They were consistent with all the shots within about 10 to 15 cm. We put the device away in the back room (not heated) for three days.

We took the device out again today to test . . . changing nothing . . . we are nearly 2 meters off our far targets and over 1 meter off our close ones. Nothing has changed!! This is the third time the students have recalibrated all of their measurements . . . gotten them where they like them and then came back a few days later and they are all wrong. Can temperature or air pressure really change the measurements that much? I can't think of any other variable that we haven't accounted for.

The kids are really getting discouraged and I don't know what to tell them to try.

[Bazinga+]

Having extreme consistency issues with our Air Trajectory and I am at wits end in how to help my students . . .

We have an ice cream bucket with a heavy piece of vinyl stretched over the lid and secured tightly. Our barrel comes out of the side of the bucket, again sealed tightly and attached to a metal pipe that fits a racquet ball. A 4 inch piece of pvc pipe is suspended above the bucket and our weight slides freely in the pvc tube hitting the vinyl on the ice cream bucket in the same place every time. The students adjust the distance thrown by changing the height from which they drop the weight. So they worked all last Saturday and dialed it in. They were consistent with all the shots within about 10 to 15 cm. We put the device away in the back room (not heated) for three days.

We took the device out again today to test . . . changing nothing . . . we are nearly 2 meters off our far targets and over 1 meter off our close ones. Nothing has changed!! This is the third time the students have recalibrated all of their measurements . . . gotten them where they like them and then came back a few days later and they are all wrong. Can temperature or air pressure really change the measurements that much? I can't think of any other variable that we haven't accounted for.

The kids are really getting discouraged and I don't know what to tell them to try.

I'm still a little unclear on how it works, namely the ice cream bucket and the venyl. If the PVC goes into the bucket and compresses the air inside then the problem is that the ice cream bucket can deform and air can escape so it's not reproducable. I think the best thing for air trajectory is a closed air chamber(ball, pump, etc) since it compresses almost exactly the same every time and has no air leaks. Please correct me if I misunderstood your system.

[SOCoach]

It is a closed system. The ice cream bucket is sealed with the vinyl on the top (only the barrel comes out the side). It looks like drum . . the only purpose of the pvc is to guide the weight so it hits the vinyl at the same spot every time. Does that make more sense?

[Bazinga+]

It is a closed system. The ice cream bucket is sealed with the vinyl on the top (only the barrel comes out the side). It looks like drum . . the only purpose of the pvc is to guide the weight so it hits the vinyl at the same spot every time. Does that make more sense?

So the ice cream bucket compresses? In that case the problem is that every time the ice cream bucket is crushed it deforms differently and you can't put it back to its exact original position. As I said something soft like a ball works better since it deforms more consistently and can be reliably put back into its original position. The air temp has little effect but if you want to minimize it I advise using heavier balls and a different air chamber. The air temp should never effect your consistentcy, just your accuracy.

[SOCoach]

The bucket is about the size of a ice cream bucket, but it isn't that kind of plastic . . . it isn't flimsy. The bucket doesn't deform at all. The vinyl acts like a drum and compresses the air. We can't seem to figure out what is changing. If it isn't temp. then I am at a loss.