Air Trajectory B/C

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SOCoach
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Re: Air Trajectory B/C

Post by SOCoach » March 4th, 2016, 4:36 pm

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.

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Re: Air Trajectory B/C

Post by Bazinga+ » March 4th, 2016, 5:09 pm

SOCoach wrote: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.
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Re: Air Trajectory B/C

Post by SOCoach » March 4th, 2016, 5:13 pm

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?

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Re: Air Trajectory B/C

Post by Bazinga+ » March 5th, 2016, 4:27 am

SOCoach wrote: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.
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Re: Air Trajectory B/C

Post by SOCoach » March 5th, 2016, 4:59 am

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.

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Re: Air Trajectory B/C

Post by chalker » March 5th, 2016, 11:11 am

SOCoach wrote: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.
I'm having a little difficulty visualizing this design, however based upon your description, it sounds like the vinyl doesn't move very much (i.e. maybe an inch?). If so, your system appears to be working primarily upon IMPULSE WAVES transferred through the enclosed air system, versus MASS/VELOCITY of the air being moved (e.g. it's a drum instead of a plunger). I'm surprised you are getting reasonably good consistency with the design to begin with. Impulse waves are going to be naturally somewhat chaotic and very susceptible to slight changes in the conditions (i.e. think about how many things go wrong when you hit a golf ball with a golf club, which also generally is an impulse wave).

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Re: Air Trajectory B/C

Post by SOCoach » March 5th, 2016, 4:31 pm

We figured it out!!!

Believe it or not it was the ball. I would never have believed that racquetballs vary in diameter, but they do. One is slightly larger thus creating a better seal in the barrel and therefore getting more air behind it and traveling further. When we found the same ball that they used before their measurements were once again correct. We are using impulse waves but the shots are accurate within about a 30 cm area for the most part.

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Re: Air Trajectory B/C

Post by Bazinga+ » March 5th, 2016, 4:55 pm

SOCoach wrote:We figured it out!!!

Believe it or not it was the ball. I would never have believed that racquetballs vary in diameter, but they do. One is slightly larger thus creating a better seal in the barrel and therefore getting more air behind it and traveling further. When we found the same ball that they used before their measurements were once again correct. We are using impulse waves but the shots are accurate within about a 30 cm area for the most part.
Wow, I would never expect such consistency from using an air impulse launcher, not to mention being able to reach 8 meters. Good luck at your competition!
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Re: Air Trajectory B/C

Post by SOCoach » March 5th, 2016, 4:58 pm

It was the kids idea . . . I didn't think it was going to work either but with the max weight (4.87 kg) and dropping it from nearly the max height they can get about 9 meters.

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Re: Air Trajectory B/C

Post by AirTrejectors » March 6th, 2016, 8:04 am

Is a trebuchet allowed in air trajectory?

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