Air Trajectory B/C

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SOCoach
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Re: Air Trajectory B/C

Post by SOCoach » January 10th, 2015, 2:02 pm

I need an opinion (I realize this forum isn't for rule clarifications, but I just want an opinion). Do you think it be legal to pull a pin, drop a falling weight and have it fill an air cylinder. Then pull a second string, opening a valve, releasing the stored air and shooting the projectile?

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Re: Air Trajectory B/C

Post by mej710 » January 10th, 2015, 2:04 pm

If we make 4 graphs for this event, do they have to be 4 graphs that show 4 different types of data we measured with our device, or are they supposed to be 4 different types of graphs that show the same set of data?

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Re: Air Trajectory B/C

Post by retired1 » January 10th, 2015, 2:43 pm

My thought is that you want the graphs to be useful. 4 variations of the same data is not going to be very useful.
What are your variables going to be?
Distance is the desired data, but vs what?? drop height or drop weight of angle or elevation of the barrel or a combination of all of them.
Our variable is going to be drop heights so we will have a number of entries which will be spread across 4 graphs to get the graph points.

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Re: Air Trajectory B/C

Post by retired1 » January 10th, 2015, 2:53 pm

SO Coach- That will depend a lot on the ES. My first thought was no. Then I reread the rules. You might have a bit of trouble with rule 3.c.

Considering leaks in the system, how are you going to have a precise pressure to release the chamber pressure? Electrical components are not allowed and aneroid pressure indicators are going to be a bit difficult to read. Also, the pressure release valve is very probably not going to release exactly the same each time.

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Re: Air Trajectory B/C

Post by SOCoach » January 10th, 2015, 3:22 pm

I thought a ball valve. Adapting a PVC cannon idea . . . A pvc chamber with a ball valve on the end. Drop the weight and load the 1st chamber and then open the ball valve and release the air. At the moment of release the air pressure in the mechanism would be normal room pressure because the chamber would be open to the room. My fear is that the weight dropping once will not "load" enough air into the chamber to push out a racquet ball. My students and I were discussing dropping the weight several times (loading more air into the chamber) before opening the ball valve but I think that would violate the spirit of the rules.

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Re: Air Trajectory B/C

Post by zyzzyva980 » January 10th, 2015, 4:37 pm

I just got back from running Air Trajectory at the Northland invite in the Kansas City area. Lots of stuff on my mind about Air Trajectory, so I better get it all down before I forget.

1. Air Trajectory is much tougher than Trajectory. Things were easier when I was around.
2. Consistency is key. Every single team at Northland missed on at least one shot. To win this event, you need a device that will shoot consistently, that you can practice with over and over until it produces the same results. Nobody had that today, and that's probably because it's early, but not a lot of devices looked promising.
3. Distance is also important. Most teams didn't come close to hitting the far target (6.8m because I'm a jerk of an event supervisor and used the national format). Those that did medalled.
4. If you aren't using your graphs to interpolate (or at least confirm) every single shot you're not doing this event right. They're as much for your use as they are for the judge to score.
5. 0-for-1 on bucket shots. Just one team even tried. If you get a relatively close score (I'd say 200mm or less) there's no reason not to at least take a shot. (This is where a calculator comes in handy).
6. I saw way too many ping pong balls. All of them died well before reaching the far target, and many of them didn't even make the near target (3.1m). I get why teams use ping pong balls (they're light and easy to acquire) but you need to find a way to get enough air pressure to launch a denser projectile (racquetballs, tennis balls, etc). They won't die in midair, and are much easier to aim.
7. For those using the two-liter bottle approach: In general, the longer the tube, the less power the projectile had. There are various reasons for this, but keep in mind how important it is to conserve as much of the air pressure as possible.
8. THERE IS SAND EVERYWHERE.
9. Literally. There is sand on my phone. My phone was nowhere near the targets.
10. Nobody ever crossed into the target area. Maybe the rules have changed since I did Trajectory, but I was constantly in the target area, helping my partner aim and checking the measurements after the first shot to see how to best adjust our device. There is so much information to be gained there. (You just can't be in that area when you shoot.)
11. For that matter, no one used sights or lasers (heh) either. I was mildly surprised by this. I guess get the fundamentals down first, and then start trying to be more precise.
12. Practice, practice, practice. Every night you can. (See #2. And then see it again. It is that important.)

Anyway, you guys probably already know most of this, but I thought I'd share what was on my mind from the tournament.
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Re: Air Trajectory B/C

Post by SOCoach » January 10th, 2015, 4:57 pm

Did anyone attempt throwing a racquet ball? My students can throw a plastic golf ball across the gym, but it is highly inaccurate. We want to throw a racquet ball but can't generate enough air pressure to get to the max distance.

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Re: Air Trajectory B/C

Post by zyzzyva980 » January 10th, 2015, 7:26 pm

Nope. All ping pong balls and golf balls. One coach/parent I was talking to said his team planned to use a racquetball, but didn't have enough time before this competition. Generating air pressure is the real challenge. I saw a few designs that looked like they might be able to pull it off, but I couldn't say for sure.

EDIT: I should point out that the design that would be most capable of pulling it off was, well, also illegal. With a few modifications it could possibly work. (They used a swinging arm to hit a plunger that was holding back compressed air. But their mass wasn't detachable. Whoops.)
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Re: Air Trajectory B/C

Post by bernard » January 10th, 2015, 7:38 pm

SOCoach wrote:I need an opinion (I realize this forum isn't for rule clarifications, but I just want an opinion). Do you think it be legal to pull a pin, drop a falling weight and have it fill an air cylinder. Then pull a second string, opening a valve, releasing the stored air and shooting the projectile?
This question was discussed earlier in October. Here is what chalker said about it. To see the context of this comment, click here.
chalker wrote:You should also keep in mind rule 3.c. This was one we wordsmithed very carefully as we want to minimize the danger due to pressure vessels. For example, a design where the competitor pulls a string to drop a weight, building up pressure in a chamber, then pulls another string to open a valve to release the pressure, would likely be prohibited because that doesn't allow everything to AUTOMATICALLY return to ambient pressure.

Of course, as always, this isn't the place for official statements or comments. VIsit soinc.org for that.
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Re: Air Trajectory B/C

Post by sjwon3789 » January 10th, 2015, 11:26 pm

Overall, I think soda bottles are inefficient because after numerous tests, the bottle dents a bit. We're definitely switching our design.
Has anyone successfully used the piston design? The idea that it'll get caught due to friction makes me think it'll be so inconsistent.

Do you guys think it's more efficient to scale the design such that we use as much as, but below, 3.5kg? Because we used 3 pounds lol.
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