General Discussion

[deezee]

i guess the taller it is, the more prone to swerving and instability it is. So you're taking a risk by building a tall tower, since the efficiency favors taller towers.
(Weight held/weight of tower)x(height of tower - 25)

[rjm]

Tipping of the bucket as the sand flows in, as it piles up unevenly in the bottom of the bucket, will be taken up in the movement between links of a chain. So, all those hinge points in the chain make it unnecessary to distribute the sand in the bucket or worry about pivoting of the bucket at its handle while bucket fills. Swinging like a pendulum, from the sand pushing the bucket sideways, is different. There is no tendency for the links of a chain to pivot with respect to one another, except at the head of the eyebolt, unless the swing is so extreme that the weight of the bucket can't maintain tension on the chain. It would be the same as swinging on a string or rope. So, I think the swinging bucket scenario is still a real problem in unevenly loading the tower. You still have a lateral force to resist.

If a rigid rod were used instead of a chain, the swinging bucket could actually lift the block from two of the tower legs. That would be devastating. A chain can't develop a bending moment and so it can't act like a rod. The rules do not permit an event supervisor to use a rigid rod for loading for that reason.

I like the animation. I thought it was interesting to watch the lag in movement of the top of the tall tower as the bucket swings back.

Bob Monetza
Grand Haven, MI

[Balsa Man]

Good analysis (of course) on bucket swing, RLM.
Bucket swing can, and needs to, be controlled.

There is another factor that comes into play, and is exagerated with a tower to the tall end of the range, that I'm not sure how to control.
That factor is the levelness of the testing platform. If you build a perfectly true tower, and load it on a perfectly level surface, the load is centered, and the load is equally distributed between the legs. If the test surface has a slight tilt, one or two legs are disproportionately loaded; the taller the tower/the more the tilt, the bigger the effect.

While a non-level surface would "be the same for all competitors", it would penalize someone who built very competitively (i.e., had legs that would just barely carry 1/4 of 15K (assuming a 4-leg tower)), and would give an advantage to someone with a heavier, "over-engineered" tower, with enough leg strength not to buckle under the extra load induced by the tower not being vertical.

I'm sure at Nationals a great deal of care, with suitable tools, will result in a very level "playing field", but at State, and certainly Regionals, the chances for a less than level surface will be much greater. Any thoughts on how best to manage this out of the builder's control variable?
Len

[jander14indoor]

You mean other than the best method of helping the tournament directors find competent event supervisors???

Not sure how to approach analytically from first principles, but practically, test your towers at small deviations from level. See if some designs drop off less in strength then others. This can be done objectively by something called experimental design, specifically Taguchi design where you are trying to make your design robust to noise (in this case non-level surfaces).

This is a risk reward game. Do you select a design that is more efficient when perfectly level, but that drops off quick with minor errors, or a slightly less optimal design that is stronger as things tilt. Common issue in engineering.

Jeff Anderson
Livonia, MI

[nejanimb]

This is a question mostly for coaches and other Supervisors --

I'll be supervising this event at least once this year and have concerns with what the best way to measure the heights of the tower would be. Last year, even when they only thing I had to do was check if it met a height threshold, I felt bad because I didn't have an accurate enough measuring method / materials set to disqualify some of the participants I could tell were millimeters over the margin, but couldn't prove it beyond a reasonable doubt with the materials I had. Now that height is a factor in the score too, it's even more important to measure accurately. Any ideas for an easy way to accurately measure height? I'm working on very little budget and materials, too...

[Littleboy]

Heres an idea: You will make many towers throughout the season. Some will be stronger than they need, some will be about perfect and other too weak. Why don't you take your best one and a stronger one that will hold up with errors. When you get there see waht it is like and decide on the best tower for the conditions then.

[chalker]

This is a question mostly for coaches and other Supervisors --

I'll be supervising this event at least once this year and have concerns with what the best way to measure the heights of the tower would be. Last year, even when they only thing I had to do was check if it met a height threshold, I felt bad because I didn't have an accurate enough measuring method / materials set to disqualify some of the participants I could tell were millimeters over the margin, but couldn't prove it beyond a reasonable doubt with the materials I had. Now that height is a factor in the score too, it's even more important to measure accurately. Any ideas for an easy way to accurately measure height? I'm working on very little budget and materials, too...

Just brainstorming here (I'm sure someone like Bob M. will chime in with a very elegant solution), but I'd suggest a long dowel rod with a small piece of cardboard the size of the loading block on it. Hold the dowel vertically and place it into the middle of the tower (basically treat it like the chain that would support the bucket). Have the team slide the cardboard down until it rests on the top (mimicking the loading block). Lift the whole thing out then hold it against a yard stick to get a precise measurement.

[Balsa Man]

I'd suggest a long dowel rod with a small piece of cardboard the size of the loading block on it.

That would work. A threaded rod, with a nut attached to a loading block sized plate (cardboard, balsa sheet, plastic sheet) might add a bit of precision.

[iwonder]

Or for a larger contest I'm sure someone would allow you to borrow a metric version of the height measurement apparatus on a doctor's scale... just don't press down on the tower to hard.

[jschrep20wba]

unless you have express permission to make an online copy. I think I remember seeing one like that.

I'm rather sure you remember wrong. That said, there are online copies of TRIAL events on the soinc.org website, and some of the states run modified versions of the events and post modified rules for those. But in terms of the actual national standard rules for a given year, they are copyright registered and not allowed to be distributed in any other form.

As a side note, I've been pushing for 2 years for the creation of a smartphone app version of the rules that could be bought in various app stores (and actually have created a prototype one that's been shown to various national committee members). I'm sure it'll happen eventually.

I'm curious though (and I realize this is a non-scientific sampling), but would you all be interested in such a thing? What price would you be willing to pay? Would you want to be able to buy individual event rules, or just the whole rule manual? What platform would you use (i.e. iOS, Android, BB, etc)?

Hello. I think that is a brilliant idea! I happen to own an iPhone, and it'd be much easier for me to whip that out instead of lugging around the rules. I think it would be easier if all of the rules were in one app. There could be a simple list of events for the year, and you could navigate from there. Every year the app could be updated to accomidate the new rules. I wouldn't mind paying 99 cents or even $1.99 for an app like such. It'd be much more efficient and productive, and it'd limit our paper use. If you could please update me on how this process is going for you; I am quite intrigued.