Elevated Bridge B/C

[Aia]

does anyone know if, at nationals, you will have to pour the sand by hand or by a machine?

I've loaded a tower and a boomilever the last two years at Nationals, and I was given the choice between handloading or using the machine. The loading mechanism works well. The only two times I've ever used a machine to load a balsa structure were at Nationals, and I thought it was much easier than hand loading.

[croman74]

i think they use the same hopper as they use in NY: http://www.newyorkscioly.org/SOPages/Newsletter1.html I'm not sure though.

We use those at my comps. They're really good and very easy to use.

[rjm]

For EB at Nationals we will be using sand hoppers identical to the ones in the picture from New York and the ones used in Michigan. They will be loaded with clean, dry Lake Michigan dune sand. You will also be given the choice of scooping the sand into the bucket instead of using the gravity delivery system. A few teams prefer to place the sand by hand; we believe that the teams should load their structures in whatever manner they are most comfortable doing. There is no specific loading method required by the rules, and allowing teams to choose between a continuous flow gravity delivery or carefully placing a scoopful of sand at a time really just lets the teams perform according to their preparation and comfort level. We do not believe that there is any unfair advantage in offering these choices. However, we will not be prepared to offer any other alternatives.

The test bases will be leveled prior to competition with a 9" spirit level. It is sufficiently accurate for this; there is little or nothing to be gained by leveling with more sophisticated instruments. No one will be allowed to use their own level to check the setup. We will assure that everyone competes under the same conditions and we are not interested in quibbling about whether some team's level is better than ours.

Bridge height will be measured with a Mitutoyo digital height gauge reading in increments of 0.01 mm. For the purposes of qualifying a bridge for Tier 1, a measurement up to 150.5 mm will be accepted and anything taller will be Tier 2. For the purposes of second tie-breaker, the reading of the gauge will be recorded and used at face value to determine the which bridge is taller or shorter. The test bases have lines scribed into them measured such that structures must not touch the lines. We will be looking for some "daylight" between the structures' bases and the lines.

The rules state that students will be given 10 minutes to load sand, and the time will be made available. The folks who scheduled the tournament put start times seven minutes apart, so we may occasionally have to do a little catch up. Most tests take less than five minutes total and we've never had a problem keeping up. In Michigan we had 48 teams in each division and we had plenty of time. At full speed, the sand runs through in 27 seconds. There will be four test machines and either division can run on all machines. It won't be a problem.

Team members will be allowed to steady the sand bucket while the sand flows, if they wish to do so. They must touch with fingertips only, on the smooth sides of the bucket, not on the ribs at the top of the bucket and never at the bottoms of the buckets. We will apply the rules as literally as possible.

Hope that helps. There should be no surprises.

Bob Monetza
Grand Haven, MI

[nejanimb]

Wow - thanks so much for the details!

Two more important questions:

1. For testing, will the competitors be allowed to "filter" the sand through their fingers as it comes out of the spout before it falls into the bucket? I know some supervisors allow this, others do not. We tend to like to do it if possible, since we feel it helps to decrease the impact force of the sand and it lets us direct the position of the sand in the bucket.

2. Will the test base allow for the bridge to be oriented in either direction? Some competitions have allowed us to keep the spout's position relative to the bridge in either way. We prefer that the spout be in line with the long axis of the bridge, so that any sway of the bucket due to the sand streaming out at an angle (though we try to mitigate this with balancing) will be along that axis, where the bridge it more stable. At States however, we were forced to load along the short axis of the bridge, and this caused premature failure as even the minor sway of the bucket could cause some amount of instability in the bridge. If we are allowed to "filter", as per question 1, this issue becomes less of a factor, but I'd still hope we can orient the bridge in either direction. What will the setup provide for?

Thanks for much for the info!

EDIT: one more I forgot: how will "1/4 by 1/4 in cross section" be operationally defined? And how strict will the enforcement of this rule be? Our design includes wood that is 1/4 in one of the directions, and it came to purchased as 1/4in. If there is some amount of excess width somewhere in the piece - say, .03cm, only measurable by the careful use of vernier calipers or something like that - due to the tolerances of the company we buy from (a reputable one, for sure), will that result in a Tier 2 ranking?

[rjm]

You will be allowed to redirect sand as it flows out of the spout. You must keep your fingers apart, so that no sand is held in your hand and then dumped. You may not touch the sand which has already landed on the bottom of the bucket, since it is already applying load to the bridge. Once sand has started flowing, we don't allow further adjustments or unloading/reloading of the bridge, unless the judges have made an error in the set up. If you like to "filter" the sand through your fingers, you also take the risk of nudging or bumping the bucket and causing other problems, but that will be your call.

The test base will be oriented so that sand flows perpendicular to the long axis of the bridge. Sorry, no exceptions. Our equipment doesn't leave room for setting the bridge up the other way. The movements induced in the bucket by flowing sand are the only reason we allow manual steadying of the bucket at all.

We will measure the size of the wood if it appears that it is close to 1/4" in any cross section dimension. We may use a digital caliper if we feel that's necessary. Wood which is purchased as 1/4" is generally accepted if it is really close and if you convince us that you didn't cut it yourself. Don't push it, though; if we measure it as more than 1/4" we get to make the call.

Bob Monetza
Grand Haven, MI

[croman74]

I like how EB is run at my comps. rjm, you and the others that run it do a very good job. It's very smooth and efficient. One thing that I was happy to see at states was that you guys allowed bridges to be 15.05 tall. I saw that and chuckled to myself. For bridge builders on this site, don't worry how it's run; it's run very nicely.

[rjm]

Croman74, I ran your test station at State. Nice to meet you.

Bob Monetza
Grand Haven, MI

[croman74]

You were the guy that helped me? Cool! I was wondering which one of them was you. I was disappointed with how the bridge went. It broke a while earlier than expected. Then I made it too long accidentally. I was the one pouring the sand.

[nejanimb]

rjm, thanks very much for the info. It's great to know all of that now rather than just on Friday (or Saturday) so we can plan accordingly. We'll practice loading this week using those conditions, and I'll double, triple, and quadruple check to make sure our bridge meets specs. Though I'm sad to hear the bases only support one orientation, it certainly sounds like things will be handled very professionally and fairly. Thanks!

[dragonfly]

Along with nejanimb, thank you rjm, that is very helpful to know prior to competition. Apparently the question I'd asked was already answered...so nevermind about the calipers.