Air Trajectory B/C

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SDCoach
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Re: Air Trajectory B/C

Post by SDCoach » February 20th, 2015, 6:20 pm

jennyk wrote:I thought that the FAQ clarification "The most common type of plastic golf balls are plastic dimpled and plastic with holes and HDPE foam types are legal" meant that HDPE (foam) was a type of plastic. At regionals, the event judge questioned the HDPE golf balls, so the chief official in charge had to intervene, telling the event judge that the reason why "practice" golf balls were specified was that real golf balls could injure someone. He also decided that the FAQ stating that HDPE was definitely "legal" overrode the other FAQ that said the packaging had to say "plastic" on it since HDPE is a type of plastic. Actually, I haven't found any practice golf balls that list what they are made of on the packaging-- they just say "practice golf balls". Guess that's b/c it's not a manufacturing requirement.

Anyway, is there a reason why they have to be "plastic" and not foam? Tennis and racket balls are not plastic either. I would think as long as the balls aren't made of a material that would put someone's eye out that anything soft would be acceptable.
Unfortunately, there is no such thing as an HDPE foam practice golf ball. HDPE is high density polyethylene, which is a completely different polymer than the polyurethane foam that is used to make practice golf balls. I suspect that polyurethane foam balls are not allowed because they provide a significant advantage over the projectiles that are allowed. Ping pong balls and plastic golf balls lack the density to shoot accurately to 8 meters. Racquetballs and tennis balls are hard to throw that far with the limitations on the falling mass. At 10-15 grams, the foam balls are easy to throw 8 meters and they are dense enough to fly pretty straight. No foam balls were allowed at the San Diego Division B Regional (116 teams) and a ping pong ball shooter took first place.

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Re: Air Trajectory B/C

Post by hogger » February 20th, 2015, 6:50 pm

Yes the foam balls would definitely be easier to work with and provide many advantages over the other types of balls. They are very light, not as light as ping-pong ball but much lighter than other types of balls, so it takes a lot less energy to move them. They have solid core with dimples so they fly pretty straight and more predictable. Another important quality for us is that they are very soft and flexible, you can easily put them in smaler pvc pipe and create pop gun effect without too much work on modifying the size of the barrel/pipe. I guess higher degree of challenge is desirable here since it is really not an advantage for anyone if everyone can use the foam type balls. Here's to going back and redo a lot of work that we have already done.

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Re: Air Trajectory B/C

Post by ImNotSmart » February 20th, 2015, 11:41 pm

Ok, so I'm competing in this event and I have a couple of weeks to pull together something good. So far, I really haven't had the best time and I'm pretty stumped. This event is pretty new for me and out of my comfort zone - I'm more of a balsa builder or a good studier. As a result, I've used up pretty much all of my creativity. What's an idea I can base my design off of that will be consistent and able to fire up to 8 meters? Any general tips? Thank you to anyone who replies!

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Re: Air Trajectory B/C

Post by bernard » February 20th, 2015, 11:53 pm

ImNotSmart wrote:Ok, so I'm competing in this event and I have a couple of weeks to pull together something good. So far, I really haven't had the best time and I'm pretty stumped. This event is pretty new for me and out of my comfort zone - I'm more of a balsa builder or a good studier. As a result, I've used up pretty much all of my creativity. What's an idea I can base my design off of that will be consistent and able to fire up to 8 meters? Any general tips? Thank you to anyone who replies!
A stomp rocket or something made out of a 2-Liter bottle is something I've seen a lot at competitions probably because its simple to do. However, I prefer using a bike pump because it falls consistently. I'll give you a brief overview of the materials I'm using. For my barrel, I'm using 1.5-inch PVC, cut to about a foot in length. At the end I have an cap with a brass barb adapter on it (I drilled holes and fit it on). Put some tape where your ball goes so it fits tightly. Pretty simple. The bike pump has a mass attached to it (you need to separate the handle and mass for impound). Pretty simple, but that's good since there's not too many factors or places to mess up. You'll want to make a reliable way of angling your barrel. The Image Gallery for Trajectory (an older, slightly different event) has some good images of what people have done in the past.

Hope this helps, and if anything is unclear or doesn't work, let me know and I'd be happy to help.
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Re: Air Trajectory B/C

Post by jennyk » February 21st, 2015, 6:20 am

Unfortunately, there is no such thing as an HDPE foam practice golf ball. HDPE is high density polyethylene, which is a completely different polymer than the polyurethane foam that is used to make practice golf balls.
Well, the FAQ stating "HDPE foam" was very confusing for those of us w/o chemistry degrees. It simply should have stated HDPE plastic was legal, HDPU foam was not, if that is the case. There were no reasons stated in the official rules as to why only plastic golf balls are allowed, SDcoach and hogger are just speculating as to why.

Anyway, since foam golf balls were allowed at some regionals b/c of the confusing "HDPE foam" wording, it seems unfair to disallow them again. To be disqualified at state for something that was ruled "legal" at regionals would be extremely unjust. Even if you do change the FAQ again to correct the "HDPE foam" to HDPE plastic, not everyone follows this wiki or will read the FAQs after regionals since you would assume any rules infraction would be pointed out at regionals. Good thing we do follow the wiki and and can rethink our launch device.

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Re: Air Trajectory B/C

Post by chalker » February 21st, 2015, 8:13 am

jennyk wrote:
Well, the FAQ stating "HDPE foam" was very confusing for those of us w/o chemistry degrees. It simply should have stated HDPE plastic was legal, HDPU foam was not, if that is the case. There were no reasons stated in the official rules as to why only plastic golf balls are allowed, SDcoach and hogger are just speculating as to why.

Anyway, since foam golf balls were allowed at some regionals b/c of the confusing "HDPE foam" wording, it seems unfair to disallow them again. To be disqualified at state for something that was ruled "legal" at regionals would be extremely unjust. Even if you do change the FAQ again to correct the "HDPE foam" to HDPE plastic, not everyone follows this wiki or will read the FAQs after regionals since you would assume any rules infraction would be pointed out at regionals. Good thing we do follow the wiki and and can rethink our launch device.
I'd like to chime in on a couple things:

1. We have limited space in the printed rules. We can't explain the reasoning behind all the various choices / limitations we put in place
2. The FAQs regarding plastic golf balls were issued Oct 25 and Nov 25 and clearly state that what's on the packaging is important - you don't need a chemistry degree to follow those requirements. Teams have had many months to address this issue.
3. There are hundreds of regional tournaments all over the country, each with it's own volunteer event supervisors. It's hard to ensure complete consistency from tournament to tournament. In fact, quite often the competitors know far more about the rules than the regional event supervisors.
4. Is it less unjust to teams that saw the FAQ and designed their devices appropriately to show up at a state tournament and find other teams didn't follow the FAQ and are allowed to compete?

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Re: Air Trajectory B/C

Post by hogger » February 21st, 2015, 9:27 am

In our state competition, there are simply wide range of students/coaches/parents that compete and it is not uncommon that many of them do not carefully follow the websites or forums such as this. I am not a coach of this event so I was not fully aware of the details, I just started helping out a few weeks ago and when I read the rule, it did not even occur to me that different type of practice golf balls would be illegal. I don't have any problem with the intent of the ruling but I wish if there was this rationale from the beginning, why not just spell it out? Foam balls are illegal, don't even think of trying to use it?

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Re: Air Trajectory B/C

Post by drcubbin » February 21st, 2015, 10:09 am

I have not seen this questions yet, so.... Do the years and events listed at the bottom of the profiles/questions/answers apply to "school" participation, or "individual" participation? :oops:

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Re: Air Trajectory B/C

Post by chalker » February 21st, 2015, 10:34 am

drcubbin wrote:I have not seen this questions yet, so.... Do the years and events listed at the bottom of the profiles/questions/answers apply to "school" participation, or "individual" participation? :oops:
You can put anything you want in your signature There isn't any set rule regarding this, as indicated by mine below.

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Re: Air Trajectory B/C

Post by ImNotSmart » February 21st, 2015, 12:33 pm

bernard wrote:
ImNotSmart wrote:Ok, so I'm competing in this event and I have a couple of weeks to pull together something good. So far, I really haven't had the best time and I'm pretty stumped. This event is pretty new for me and out of my comfort zone - I'm more of a balsa builder or a good studier. As a result, I've used up pretty much all of my creativity. What's an idea I can base my design off of that will be consistent and able to fire up to 8 meters? Any general tips? Thank you to anyone who replies!
A stomp rocket or something made out of a 2-Liter bottle is something I've seen a lot at competitions probably because its simple to do. However, I prefer using a bike pump because it falls consistently. I'll give you a brief overview of the materials I'm using. For my barrel, I'm using 1.5-inch PVC, cut to about a foot in length. At the end I have an cap with a brass barb adapter on it (I drilled holes and fit it on). Put some tape where your ball goes so it fits tightly. Pretty simple. The bike pump has a mass attached to it (you need to separate the handle and mass for impound). Pretty simple, but that's good since there's not too many factors or places to mess up. You'll want to make a reliable way of angling your barrel. The Image Gallery for Trajectory (an older, slightly different event) has some good images of what people have done in the past.

Hope this helps, and if anything is unclear or doesn't work, let me know and I'd be happy to help.
Thanks for your help! As of now, I've been using a barrel very similar to yours - a 1.5 inch PVC pipe about 10 inches long that can be angled easily. However, I tried using a bike pump when I first started working on the event, but none of my pumps could produce enough pressure to even move a ping pong ball. Could I ask what type of pump you're using? Also, I'm having some trouble visualizing how you would connect the bike pump to the barrel - could you maybe post a picture of how it looks? (If you don't want to reveal your design to me, I'm perfectly fine with that.) Thanks again for the helpful response!

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