Air Trajectory B/C

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bernard
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Re: Air Trajectory B/C

Post by bernard » February 18th, 2015, 7:11 pm

MC McGilicutty wrote:
bernard wrote:
MC McGilicutty wrote:Honestly, you don't even have to tape over the inside of the barrel. That could mess with too many things. Just tape the outside of it where you here the air leaking. If it is a pretty decent sized whole, you could invest in some super glue to just put a dab or two in the holes. Make sure it is absolutely dry before you test anything. But taping the inside of the barrel just seems like it could have a worse negative effect than just taping the outside.
I don't understand why you would tape the outside of the barrel. Could you explain it? For a barrel that is slightly larger than the projectile, taping the inside makes the inner diameter slightly smaller so the projectile fits better. Of course you would tape carefully to avoid wrinkles in the tape.
My bad. I thought you were talking about having a barrel that had air leaking out of it through places other than the end of it. A tape ring to make it tight on the inside of the barrel makes sense then. Sorry about that
No worries, I agree, taping on the inside of the barrel for other leaks is inconvenient and doesn't necessarily help.
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Re: Air Trajectory B/C

Post by TheGatesofLogic » February 19th, 2015, 11:11 am

People asked for hints regarding my elegantly simple solution to the problem of mismatched ball/pipe sizes. Here are two hints:

1. The French

2. Rocket Propelled Grenades

(I am not, however, implying that using rocket propelled grenades or French people in your device is either legal or safe in competition)


And in response to whomever mentioned the FAQ, I am fully aware of the total legality of HDPE golf balls. That's kinda why I use them?

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Re: Air Trajectory B/C

Post by iwonder » February 19th, 2015, 11:42 am

TheGatesofLogic wrote:People asked for hints regarding my elegantly simple solution to the problem of mismatched ball/pipe sizes. Here are two hints:

1. The French

2. Rocket Propelled Grenades

(I am not, however, implying that using rocket propelled grenades or French people in your device is either legal or safe in competition)


And in response to whomever mentioned the FAQ, I am fully aware of the total legality of HDPE golf balls. That's kinda why I use them?
That's not particularly helpful or funny.

Also, there is a difference between High Density Polyethylene (HDPE) and whatever High Density Polyurethane is (which is what I'm guessing you mean by HDPU?), I think that's what Chalker was trying to point out
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Re: Air Trajectory B/C

Post by joeyjoejoe » February 19th, 2015, 6:44 pm

Wait, HDPE balls are acceptable??
Too late for us as we already have our data with ping pong balls but I considered not using the poly balls as a setback. They were very dependable: The shot radius of 10 HDPE balls is less than a foot. For ping pong balls -try five ft.
I thought the packing material had to say "Plastic", "Golf" and "Balls" on it (but not in any order). I combed heaven and earth but could not find such a ball!

Also, I keep hearing about people not able to get a ball to go 8m. We launch a ping pong ball by dropping a mass of 700g and can shoot it over 9.5 m with just a 60cm drop.

Also, this is going to sound weird but is anybody seeing an optimal distance coming from some angle other than 45 degrees??
We get a maximal flight at around 35 degrees. Weird!

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Re: Air Trajectory B/C

Post by iwonder » February 19th, 2015, 7:32 pm

joeyjoejoe wrote:Also, this is going to sound weird but is anybody seeing an optimal distance coming from some angle other than 45 degrees??
We get a maximal flight at around 35 degrees. Weird!
YES! SCIENCE!
In a vacuum the ideal angle to launch a projectile at is 45 degrees, yes. In air, the angle shallows out a bit, because there is a acceleration in the X direction, namely drag. I would guess if you tried it with a golf ball of similar size you'd see the launch angle increase a hair because they have less wind resistance (that's why their dimpled).

I'm sure there're other reasons why it's shallower for your launcher, 35 degrees sounds almost too shallow for that, and I don't feel like doing the differential equation to calculate the actual numbers, but that's a pretty cool observation in my book.
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Re: Air Trajectory B/C

Post by GoldenKnight1 » February 20th, 2015, 3:41 am

iwonder wrote:
joeyjoejoe wrote:Also, this is going to sound weird but is anybody seeing an optimal distance coming from some angle other than 45 degrees??
We get a maximal flight at around 35 degrees. Weird!
YES! SCIENCE!
In a vacuum the ideal angle to launch a projectile at is 45 degrees, yes. In air, the angle shallows out a bit, because there is a acceleration in the X direction, namely drag. I would guess if you tried it with a golf ball of similar size you'd see the launch angle increase a hair because they have less wind resistance (that's why their dimpled).

I'm sure there're other reasons why it's shallower for your launcher, 35 degrees sounds almost too shallow for that, and I don't feel like doing the differential equation to calculate the actual numbers, but that's a pretty cool observation in my book.
Another factor that might not make it 45deg is the initial height the projectile leaves your device. I have seen a device that launches the ball at 0deg but from 1m up which wouldn't work if you just used the range equation.

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Re: Air Trajectory B/C

Post by hogger » February 20th, 2015, 4:32 am

iwonder wrote:
TheGatesofLogic wrote:People asked for hints regarding my elegantly simple solution to the problem of mismatched ball/pipe sizes. Here are two hints:

1. The French

2. Rocket Propelled Grenades

(I am not, however, implying that using rocket propelled grenades or French people in your device is either legal or safe in competition)


And in response to whomever mentioned the FAQ, I am fully aware of the total legality of HDPE golf balls. That's kinda why I use them?
That's not particularly helpful or funny.

Also, there is a difference between High Density Polyethylene (HDPE) and whatever High Density Polyurethane is (which is what I'm guessing you mean by HDPU?), I think that's what Chalker was trying to point out
I just went and read the rule clarifications again and while the HDPE golf balls seem to be legal, one of the answers say the word "plastic" must be on the package. Seriously? So I just took a look at my little cheap cardboard package that comes with my foam golf balls and it has no plastic word on it. It has the word practice golf balls but not plastic. So my golf balls are now illegal?

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Re: Air Trajectory B/C

Post by chalker » February 20th, 2015, 6:29 am

joeyjoejoe wrote: I thought the packing material had to say "Plastic", "Golf" and "Balls" on it (but not in any order). I combed heaven and earth but could not find such a ball!
That's EXACTLY the point I was trying to make. I've yet to hear anyone find HDPE golf balls that meet this criteria. If you have, congrats to you, but I'd highly recommend you bring the packaging to the competition.
hoggy wrote: I just went and read the rule clarifications again and while the HDPE golf balls seem to be legal, one of the answers say the word "plastic" must be on the package. Seriously? So I just took a look at my little cheap cardboard package that comes with my foam golf balls and it has no plastic word on it. It has the word practice golf balls but not plastic. So my golf balls are now illegal?
It's not that they NOW are illegal, but that they likely never were. The rules are pretty explicit in that they have to be plastic golf balls. We would have said 'foam golf balls' had we intended to include those.

As always though, this is not the place for official comments or clarifications.....
Last edited by chalker on February 20th, 2015, 7:07 am, edited 1 time in total.

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Re: Air Trajectory B/C

Post by chalker » February 20th, 2015, 6:35 am

TheGatesofLogic wrote:People asked for hints regarding my elegantly simple solution to the problem of mismatched ball/pipe sizes. Here are two hints:

1. The French

2. Rocket Propelled Grenades

(I am not, however, implying that using rocket propelled grenades or French people in your device is either legal or safe in competition)


And in response to whomever mentioned the FAQ, I am fully aware of the total legality of HDPE golf balls. That's kinda why I use them?
I assume you are referring to a 'sabot' (a french term used in anti-tank rounds): https://en.wikipedia.org/wiki/Sabot

A couple things I'd like to point out:
-Rule 3.f. explicitly says the projectiles must be unmodified. You can't glue or attach anything to them.
-Rule 4.c. explicitly says device parts must automatically return to or stay within the launch area. You can't have a 'fall away' sabot leave the barrel and fly outside of the launch area.

As always though, this is not the place for official comments or clarifications.

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Re: Air Trajectory B/C

Post by jennyk » February 20th, 2015, 4:23 pm

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.

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