Boomilever B/C

[thsom]

How, then, are students able to ensure that the boomilever will be perfectly horizontal to the ground? Seeing that the base will be able to move across the J-hook during the testing, won't the angle of said boomilever's compression board be moved as well resulting in uneven pressure?

[iwonder]

In all fairness, that sounds like one of the challenges inherent to the event

[thsom]

Understandable, however, when one could firmly attach the base of the boomilever to the wall, the issue of the angle of the boomilever wasn't due to the position of the base staying where it was placed. I feel as if with this J hook, the base could slide while testing messing up the boomilever's angles. With the old design, the base had not chance of moving and this allowed for much more fixed testing and predictable results, unless I'm imagining the setup of the J-hook incorrectly.

[iwonder]

I think once a little load gets on the hook it won't tend to slide except under extreme conditions. But yes, it's a small regression from last year, but I think it'll make everything go faster and we won't have to worry about washer sizes.

[penclspinner]

....the base had not chance of moving and this allowed for much more fixed testing and predictable results...

You're absolutely correct in that there will be some additional instability and maybe we'll see some students come up with clever ways to overcome this challenge. This might end up shaking up the event and might even lead to some unorthodox designs.

Speaking of fixed testing and predictable results, the students in Wright Stuff/Gliders want to have a word with you ^^.

[UQOnyx]

I was also having g problems in the same area. Where will the base of the boom stay. In other words should I design to make the base hooked on to the curve of the J or the straight part of the J? Even then, where on the curve?

[iwonder]

Well, I don't think you'll be able to get the boom to stay on the straight part of the hook. And remember that it will tend towards the point of the j hook closest to the distal end as the load is applied, so I think you should design the boom to sit right at the front bottom edge of the hook for a tension design. For a compression design, make it stay on the point farthest away from the testing wall. For something in between, it'll be in between honestly it'll probably take a few tries to get it perfect.

[Balsa Man]

Regarding the post about the eye bolt, I'd say continue at your own risk in October clarifications will open up and you'll be able get a real answer(hopefully) to your question. But don't let that stop you from working on a design, just keep in mind you might have to tweak it later on.

Speaking unofficially of course, I don't think we'll provide a rules clarification that specifies the eye bolt in more detail. Thus you are going to need to be prepared for any of the possible contingencies discussed here so far. of course you could always contact individual event supervisors before a tournament and try to convince them to provide a certain style eye bolt......

Hmmm… I must be missing something…. The lack of specification of the (minimum) shaft length for the load block eyebolt has, I believe, the effect of eliminating booms with a single compression member. Given that, and, if, in fact, no clarification is forthcoming, one has to conclude an intention to do so. That leaves me really curious as to why…. the powers that be would want to do that.

The shortest ¼” diameter (1/4-20) eyebolts commonly available have a 1” long shaft (2.54cm). With a 2cm block thickness, and a wingnut on top of the block, that has the top of the eye right up against the bottom of the block. With either a box section, or a tubular section compression member, where the load block sits on top of the compression member, that member has to have a vertical cross section dimension….as a practical matter, in the ¼ to ¾” range. So, if a particular event supervisor decides – which is fully allowable with the rule as written – to use a 1” eyebolt, with the eye up against the bottom of the load block, then the only designs they’re allowing are two compression member ones, where there’s nothing interfering with the eye. Looking at both Regionals feeding into State competitions, and State feeding into Nationals, a design that might be fine for one level of competition where the ES decided to use a 2” or 3” eyebolt, would be put in Tier 4 for the next – where the ES decided to use a 1”, and the boom “cannot accommodate the loading block.” Sorry, but that doesn’t make sense. Am I missing something, or is this indeed the intent?

[dholdgreve]

Regarding the post about the eye bolt, I'd say continue at your own risk in October clarifications will open up and you'll be able get a real answer(hopefully) to your question. But don't let that stop you from working on a design, just keep in mind you might have to tweak it later on.

Speaking unofficially of course, I don't think we'll provide a rules clarification that specifies the eye bolt in more detail. Thus you are going to need to be prepared for any of the possible contingencies discussed here so far. of course you could always contact individual event supervisors before a tournament and try to convince them to provide a certain style eye bolt......

Hmmm… I must be missing something…. The lack of specification of the (minimum) shaft length for the load block eyebolt has, I believe, the effect of eliminating booms with a single compression member. Given that, and, if, in fact, no clarification is forthcoming, one has to conclude an intention to do so. That leaves me really curious as to why…. the powers that be would want to do that.

The shortest ¼” diameter (1/4-20) eyebolts commonly available have a 1” long shaft (2.54cm). With a 2cm block thickness, and a wingnut on top of the block, that has the top of the eye right up against the bottom of the block. With either a box section, or a tubular section compression member, where the load block sits on top of the compression member, that member has to have a vertical cross section dimension….as a practical matter, in the ¼ to ¾” range. So, if a particular event supervisor decides – which is fully allowable with the rule as written – to use a 1” eyebolt, with the eye up against the bottom of the load block, then the only designs they’re allowing are two compression member ones, where there’s nothing interfering with the eye. Looking at both Regionals feeding into State competitions, and State feeding into Nationals, a design that might be fine for one level of competition where the ES decided to use a 2” or 3” eyebolt, would be put in Tier 4 for the next – where the ES decided to use a 1”, and the boom “cannot accommodate the loading block.” Sorry, but that doesn’t make sense. Am I missing something, or is this indeed the intent?

Boy, I can certainly see your concern Len, especially with the design you guys have "patented." However, also consider that any variation between the beam elevations on a double compression member is exacerbated with longer eye bolts.. an 1/8" difference between the 2 compression beams amounts to nearly nothing if the eye of the bolt is drawn up tight to the loading block, but now imagine that the eye bolt is 18" long (just to prove a point), The eye may be off vertical by as much as 3 or 4". This would substantially torque the boom and cause premature failure I'd guess...

I agree... there should be a set length for this eye bolt as well, to minimize the torquing created by different length bolts...

In other matters, I was somewhat surprised to see the rules give the distance from the end of the J hook to the testing wall, but not the distance from the apex of the hook to the wall... I would think this would be a much greater critical dimension than the clearance dimension furnished, as this dimension with impact the projection angle of the boom, where the clearance dimension will not. For those inquiring minds that must know, per the actual specs from National Hardware (Thanks Len), the apex dimension, from end of hook, to outer apex is .94 Inches. The diameter of the bolt is stated as .21 inches... therefore, the net is .73 inches, convert to cm = 1.9 cm, add to the 2.5 cm from test wall to end of hook, and you get 4.4 cm from test wall to bearing point of the inner apex of the hook. This is truly the critical dimension that should be designed to...

Many hardware stores buy these type bolts in bulk, without packaging... They may or may not be from National, and conform to their spec... I caution all Event Supervisors to be very careful when setting up their testing apparatus to make sure that the 2.5 cm clearance from testing wall to hook end is confirmed but that, even more importantly, the 4.4 cm from test wall to inside face of hook curve is also confirmed, as well as the 5/8" diameter of the hook arc. {Stepping off soapbox now}

[iwonder]

I think it's a safe assumption that 5/8" eye bolts will have the same clearence from apex to wall, but you raise a valid point.

I also completely agree that not specifying a minimum eyebolt length is not necessarily a good thing. I have a few specific designs in mind and without a minimum length the creativity and possibilities that could be explored are serverly limited.

I know it's more difficult to specify but a minimum length would really make the event more about design and engineering than who can construct a boomilever to the most exacting specification, which, to me(and I may be totally wrong) seems more to the point of science Olympiad.

As I've said before, I understand how much effort it takes and I really appreciate people who do this and volunteer their time to help out, I'm just pointing out something that I think could be easily improved.