Efficiencies

[lllazar]

Ok heres how you do it, from past bridge experiences it is the best.

Slowly bring it up to full speed, then just keep it at full speed. That's it.

[iYOA]

As for C division scores from the 2006 national tourney, this is what happened after having this event for 2 previous seasons:
1st place 4.18 g - loaded to 13.625 kg --> old score was 3260 and new score would be 44.4
2nd place 5.42 g - loaded to 15 kg --> old score was 2767 and new score would be 41.5
3rd place 4.53 g - loaded to 12.22 kg --> old score was 2698 and new score would be 33.0
4th place 5.44 g - loaded to 13.745 kg --> old score was 2527 and new score would be 34.7
5th place 6.19 g - loaded to 15 kg --> old score was 2423 and new score would be 36.3
6th place 6.05 g - loaded to 14.58 kg --> old score was 2410 and new score would be 35.1
7th place 6.56 g - loaded to 15 kg --> old score was 2287 and new score would be 34.3
8th place 6.29 g - loaded to 13.935 kg --> old score was 2215 and new score would be 30.9
9th place 5.14 g - loaded to 10.895 kg --> old score was 2120 and new score would be 23.1
10th place 6.47 g - loaded to 13.495 kg --> old score was 2086 and new score would be 28.1

I also computed new scores for places 11-30. The interesting thing is that after looking at 1-30 with the new system, the top 10 stayed the same, and only their order was changed. The third place tower from 2006 ended up in 7th with the new system and is the one that changed the most places in the top 10. In places 11-30 from 2006, the 19th and 21st place finishers would have ended much further down under the new scoring system, probably 2/3 to 3/4 of the way down the list. They were light towers that failed at low loads (4.92 grams and 6.815 kg for one and 3.83g and 5.065 kg for the other).

So, there you have it from 5 seasons ago. A grand total of 2 C division towers would have scores above 40 with the new formula. So, based on this, I'm changing my previous position and am agreeing with rjm in that anything above 50 will be breakout new technology. So, scores above 40 will likely earn medals in Wisconsin next May for both B and C.

Do you know what the ratios from 11th -18th place were? and where would a 1644 fit in with those?

[bmbw123]

Ok thanks, illazar. That makes sense

[iYOA]

So our tower doesn't hold more than 1 kg... efficiency less than 1 fail

that happened to a group for our team tryouts lol
it was because they did not let the glue dry

[lllazar]

I've been getting efficiencies in the range of 19-22 mil, and there has been an increasing trend. Now, they've all held the full load (im just building lighter as i go, i want to make sure it holds the max load), so by last years formulas my effiencies are 1400ish...i was just thinking, would tower efficiencies be naturally higher than bridge efficiencies? It'd seem so, since the forces are more vertical in towers than bridges, and towers generally tend to be lighter (or at they can generally be built lighter more easily).

Also, my towers have been in the weight range of about 11-10 grams, what have you guys been getting?

[iYOA]

well, we have been getting ratios in the 19.5 range. We have never had a tower hold all the weight. I think they can hold all the weight but they usually break for some stupid reason. recently we tested one that was 7g and held 12kg. it broke because the top part was too flimsy and usually, our top part NEVER breaks. now we are building even lighter towers( 6g-5.5g) because we feel that each tower we build CAN hold all the weight but it just doesnt.

[lllazar]

Yes i see where your coming from - it's not really your design that's flawed i think, rather just the uncontrollable strength variance in balsa. You'd really need to go through over a 100 sticks of balsa to get 4 that are light, strong, and all of the about the same stiffness, so that 1 isn't unnecessarily stronger than the others.

I have a suggestion, take it how you will, but build the tower stronger than it needs to be next time - even if it adds a bit of weight. Weighing 1 more gram but holding 1 or even more kg of mass would result in an improvement of your ratio.

Good luck!

[iYOA]

well, actually what happens is that we usually built 9-10.5g towers and they were fairly strong. but the reason they broke was because of connection issues with the top and the bottom. We ordered a new batch of wood and the wood was amazingly light. However we usually have issues with our base so we used lamination on the legs to make it stronger. Even though the base was about 1.5g lighter than usual, it still seemed extremely overbuilt and it was not the part that failed. We did not strengthen the top part in any way so that is why it broke. For the next tower with this kind of wood, we again laminated on the base and also laminated on the top. so if all goes well, this one will hold nearly all the weight. We are also crunched for time because an invitationals is coming up on the 8th and we want to have a 6g tower that holds all the weight by then(maybe even lighter, if possible).

[lllazar]

Ahh, well i wish you good luck at your invitational - btw where do you buy your wood?

I ask because no matter how simple i make my design, i don't think it could get below 7 grams.

[soccerkid812]

Ahh, well i wish you good luck at your invitational - btw where do you buy your wood?

I ask because no matter how simple i make my design, i don't think it could get below 7 grams.

yea, i have the same problem
i made a forum topic about it but only got a few replies

[iYOA]

thanks

i know what you two mean. We ordered our wood from the same place twice. The first time, the wood was pretty heavy and that is why our towers were 9-10.5 but then the second order was really light so we reduced the weight by about 3-4 grams. There is a slight bit of luck involved i guess but maybe you can talk to the people and ask them to send lighter wood?
http://www.balsawoodinc.com/

EDIT: Actually, you can customize your order. This is what it says on the site.
"We can hand select balsa wood to suit your needs. Balsa wood sheets are available in Soft, Medium, and Hard. Hand selection is not the same as weighing the wood to determine its weight. Please include your specifications in your order details. 30% will be added to the base price of your order."

[jander14indoor]

Even when you order specific weights, expect to sort AGAIN and still through out a lot of wood. Its just part of the normal variability of a natural product like balsa.

But, if you want to do really well, this is just a necessary part of the process. You can design the best structure, but unless you select the right materials its just junk.

Jeff Anderson
Livonia, MI

[soccerkid812]

Even when you order specific weights, expect to sort AGAIN and still through out a lot of wood. Its just part of the normal variability of a natural product like balsa.

But, if you want to do really well, this is just a necessary part of the process. You can design the best structure, but unless you select the right materials its just junk.

Jeff Anderson
Livonia, MI

If you do order light wood, how would you sort through them again?

[lllazar]

IYoa, that site looks very nice for pricing, but how much shipping did u end up paying? Specialized balsa charged us like 17 bucks - our order itself cost 17 bucks.

Also, where do you specify that you want hand selected wood? I don't see anything for that anywhere.

Thanks!

[dholdgreve]

I'm sure this is a relatively stupid/simple question, but is there a certain way you all pour in the sand. If a lever system is used to let the sand fall in, would you want to go slow, then faster, then switch back to slow? Letting the sand in slow seems like it would make your tower sustain the weight for longer times, but faster streams seems a bit all of a sudden.

And if there is a manual sand system, then I would assume you would try to pour the sand around the bucket evenly, so there are no mounds, and try to do it as quick as possible?

bmbw,
The age-old question... To level the bucket or not... The real challenge is to keep the bucket as still as possible. If the bucket leans one way or the other due to more sand being in one side than the other, that is fine... Do not try to level the sand in the bucket. The ojective here is to keep the chain as vertical and still as possible. By focusing on leveling the sand within the bucket, you will almost certianly lose focus on what is really important... Keeping the bucket from swaying, and keeping the chain still and straight. Even if the bucket hangs at a 45 degree angle, that's fine. With there being only one chain connecting the bucket to the loading block, all the load transfers through that chain. If there were two chains connecting the bucket to the tower, you would want to keep the bucket level, but with one chain it just doesn't matter where the swand is within the bucket, so long as the bucket isn't moving... What's it going to do? Pull harder on one side of the chain than the other?

As for the speed of which to add the sand, I think that is pretty much personal opinion... I agree that starting it with a thump is probably not a real good idea, and that a smooth, steady flow makes sense. I'd also suggest that with an automatic dispenser, you begin slowly, but quickly build to the maximum flow allowed by the device, and keep it pegged until the end... A couple of reasons... 1) As you mentioned, under a heavy load, a tower will only hold for so long... get as much in as possible during that time, and 2) Proctor's reaction time. If the automatic loader has a emergency shut off, it is probably triggered by an event proctor. i.e. as soon as the tower breaks, he pulls a disconnect, and a flapper or knife valve closes off the sand flow. Let's assume that this reaction time is .5 seconds. The reaction time would be the same whether the sand is flowing at full speed or barely flowing, but slightly more sand will flow into the bucket after the tower breaks if you are running it wide open.