Trajectory B/C

WAMSCoach
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Re: Trajectory B&C

Postby WAMSCoach » March 4th, 2009, 7:59 pm

Help! I have an urgent question before regionals this weekend. I'm a coach for a B-division team, and we are having a rules question. We have essentially built a trebuchet, but are wondering about this:

"3a) The launching force must be supplied by non-metallic elastic solids such as rubber, wood, plastic, rubber bands, bungee cords, rubber tubing, etc."

How does this affect us? The devices we saw at an invitational seemed to be similar and use concrete as weights.

If we have a metal lever arm and our weight is supplied by sand in bags, is this in violation of that rule? Should we find a way to use bungee cords instead?

starpug
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Re: Trajectory B&C

Postby starpug » March 4th, 2009, 8:04 pm

Help! I have an urgent question before regionals this weekend. I'm a coach for a B-division team, and we are having a rules question. We have essentially built a trebuchet, but are wondering about this:

"3a) The launching force must be supplied by non-metallic elastic solids such as rubber, wood, plastic, rubber bands, bungee cords, rubber tubing, etc."

How does this affect us? The devices we saw at an invitational seemed to be similar and use concrete as weights.

If we have a metal lever arm and our weight is supplied by sand in bags, is this in violation of that rule? Should we find a way to use bungee cords instead?
Wait the sandgags power the catapult? That will get you DQ'd in a hurry, go with the bungee cords if that's the case. It's ok to use the sandbags to hold your device down to keep it from moving, but you can't use it to launch the projectile.
Last edited by starpug on March 4th, 2009, 8:06 pm, edited 1 time in total.
Get your facts first, then you can distort them as you please. - Mark Twain

andrewwski
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Re: Trajectory B&C

Postby andrewwski » March 4th, 2009, 8:05 pm

YES! That's absolutely a violation of the rule. Your launching force is gravity, not a non-metallic elastic solid.

ONLY a non-metallic elastic solid such as those listed in the rules is an acceptable launching force. Using a trebuchet powered by gravity is a really easy way to be Tier 2'ed.

Definitely find a way to use bungee cords or surgical tubing or whatever you can get your hands on, even if it sacrifices performance. A device that meets Tier 1 specs but doesn't fire will be ranked above a Tier 2 device that hits all targets dead on.

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Re: Trajectory B&C

Postby rman » March 4th, 2009, 9:27 pm

Has anyone had a trajectory competition out doors on a windy day? It would seem that with the limits on balls this year that the wind would make the event largely a crap shoot. I can see no practical way to calibrate for ground level winds (near the ground winds are highly variable), so you would just have to guess and hope for the best.

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Re: Trajectory B&C

Postby WAMSCoach » March 4th, 2009, 9:58 pm

Thanks for the clarification; I actually should have dug through the thread because the answer was there. It's an easy change to bungee cords.

soroco120
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Re: Trajectory B&C

Postby soroco120 » March 6th, 2009, 5:42 pm

How many graphs do I need for trajectory C, and wut do they look for?

andrewwski
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Re: Trajectory B&C

Postby andrewwski » March 6th, 2009, 5:45 pm

I shouldn't even be answering this. It's stated plain as day right in the rules.

You need four graphs, and they look for a completed data table, a completed graph, the graph to match the data table and for them to be on the same page, and proper labels (team name, title, labeled axes, and increments with units).

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Re: Trajectory B&C

Postby soroco120 » March 6th, 2009, 6:42 pm

What's the point of four graphs?

rman
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Re: Trajectory B&C

Postby rman » March 6th, 2009, 10:11 pm

What's the point of four graphs?
It depends on your point of view. If you don't actually use the graphs, because your calibration data is in a tabular format or an equation, then the only purpose of the graphs is to maximize your graph score. If you don't have compete tabular data for every possible distance and elevation then the graph can be very useful for quickly determining the setting for your trajectory device. Without the graphs, and assuming you don't have every possible elevation and distance in a tabular format (you would need 1680 distances and elevations for C division or 660 for B to cover every possible combination at Nationals), you are going to have to interpolate or extrapolate to get the correct setting for your device. You can also use the graphs to give you an idea of how much correction to apply after your first shot. For example, if your first shot goes 12cm too far then you need to be able to see how much of a change of setting is required to decrease the range by 12 cm. With you graphs that should hopefully be relatively easy to do. At regionals the graphs may actually be more important to many teams because the only possible ranges are 2,3,4,5,6,7,8 (9,10 for C), so you could quite reasonably go to competion with only 60 total data points. If your first shot misses by the same 12 cm I mentioned above then you would have to interpolate between two widely spaced data points, whereas hopefully your graphs would give a reasonable approximation of the required adjustment.

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Postby fee6 » March 7th, 2009, 2:04 pm

LA regionals were outside, as someone else said. However, there was no wind so everything was alright.


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