Boomilever B/C

[Flavorflav]

The rule actually reads: “The loading block must be supported at a height higher than 5.0 cm below the contact depth.” Very different than “5cm above contact depth” – so, no, it doesn’t exclude either tension booms, or the single compression member configuration this discussion’s been around

Thank you, that is a very important difference - foolish error on my part.

[maxsd]

Does anybody know what the stabilization stick is all about? This is my first time and I cant figure it out... If anybody has a diagram that would be great. Great thanks!

[jander14indoor]

Any swinging of the bucket drastically increases the stresses on your boom tending to cause premature failure.

In the past, students were allowed to stabilize the bucket with their hands with the proviso that they could not do it in a way to support the bucket (reducing load on the structure). At nationals this was controlled by limiting the students to only using their finger tips on the side of the bucket., I think only one finger.

Apparently there was a concern that some students were at least percieved by the ES to be supporting the bucket. So the sticks were introduced to allow stabilization and make sure no support could be provided. Think of it as formalizing the fingertip rule.

In practice, one of the two competitors would hold one stick in each hand and use them to stabilize the bucket. They are configured such that no effective vertical force could be applied to the bucket as long as you stay on the sides. I note the rules don't specify where you touch the bucket, if you held the sticks under the bucket you might be able to relieve some load. I suspect most ES would rule this as illegal via a spirit of the rules interpretation.

Jeff Anderson
Livonia, MI

[ishoottrap]

Given the lack of recognition of the potential problem, it also seems fair/reasonable to assume there was no intent to build in a wild card effect- where someone using such a design could sail through one level of competition, and show up at the next and get Tier 4’d.

So, what does recognition of the issue that has now emerged mean, in light of the ... let me call it somewhere between apparent and possible reluctance to provide clarification?? Is this a “game breaking” constraint/wild card? One could argue that either way. Rather than go down that path, I would have to argue that, because of the now recognized consequences of the rule as written, a decision to not clarify and provide a minimum length would have to come from an intention to rule out a design approach, and impose a wild card factor. If such intentions are not there, not at work, with all due respect, it seems to me there is only one reasonable way to proceed.

Len,

I'm not sure I can get there. Certainly with a load block of typical thickness, washer and wing nut, the practical length the eye bolt protrudes from the load block could easily be made zero; that is the eye itself contacts the load block. I see no reason to be vague about the rule here, let's standardize the test apparatus for all competitions. This really needs a clarification.

-Scot

[Balsa Man]

Scot,
I think we're on the same page, but not certain (re: "I'm not sure I can get there").
What I'm saying is, for instance, you have a boom - like our last year's design - w/ a 5/8" diameter compression member, where the eyebolt comes up through the compression member, the block sits on top of the compression member, the eyebolt goes through it, nut and washer go on the end of the eyebolt. If the ES decides to provide a 1" shaft eyebolt (perfectly allowable as the rule is currently written- and actually as it was written last year), you don't have enough shaft length to get through compression member, and block. If you can't attach the load block w/ the eyebolt provided, you go to Tier 4. Specifying some minimum shaft length would avoid the problem of showing up and unexpectedly finding your design couldn't be loaded...

[dholdgreve]

... I might add... being tier 4ed while being fully in compliance with all aspects of the rules as written... talk about breaking a kid's (and coach's) heart! And the worst part is, that since the eyebolt is technically part of the load, it should not be swapped out to remedy the situation, since other competitors have probably already used the short eyebolt to load their booms. The only correct remedy is to prevent the problem from happening ahead of time through an official clarification.

[UQOnyx]

Maybe adding a pretty please will help

[fanjiatian]

Any ideas on building a jig for the trusses?
For towers it was easy because you could just slide the structure off but you can't do that with boomilevers unless if you leave one side unconnected.

[dholdgreve]

Any ideas on building a jig for the trusses?
For towers it was easy because you could just slide the structure off but you can't do that with boomilevers unless if you leave one side unconnected.

You are correct, with towers, one could build a single 3-D jig to assemble the entire structure around, then slip it off when complete... with Booms, think 2-D... build each side independently, verify they are exact mirror images to each other by holding them next to each other, then connect the 2 sides... The trick is how to build the 2 sides exactly the same... Think template...

[iwonder]

Another way to approach this (and an easier way in my mind) is to build a compression member and put it on a jig where you can attach the tension members to it. I believe balsaman described in great detail the jig I use in the main thread last year, it's basically a backwards testing wall, where I can mount a base, set the compression member down, and simply strong tensions members in between.