Boomilever B/C

[Balsa Man]

The winning efficiency at nats in 2008 was closer to 2500. It was about a 6 gram boom that went to full load. A Kansas school won the event in both 2007 and 2008. In 2007, it was by a wide margin. It was much closer in 2008. At least this is what I recall. So, quite a bit better than Ohio at the time.

So, do your schools typically keep their best devices to start from when an event comes around again or have some other means of not recreating the wheel when an event comes back, or do you start from scratch?

Thanks for the info. Looking at the posted final 2008 results (http://soinc.org/sites/default/files/up ... ll_C08.pdf), Kansas team 26 did indeed get 1st, while Ohio team 7 got 35th in the event (although 3rd overall in the tournament).

Everyone should please keep in mind there is at least 1 significant change from the rules in 2007-2008 and now that will likely impact the abilities of the boomilevers. In 2007-2008 the device could be up to 20cm below the attachment holes. That's still true in B division, but in C the limit is now 15cm.

As I said a few posts ago, the 2008 specs (as in for 2007-2008 season) were 15cm, not 20. (with a length of 40cm)
So. for C-div, it's the same.
Quite certain on this- have a copy of the rules in my hands.

[chalker]

As I said a few posts ago, the 2008 specs (as in for 2007-2008 season) were 15cm, not 20. (with a length of 40cm)
So. for C-div, it's the same.
Quite certain on this- have a copy of the rules in my hands.

Thanks for the correction. I was looking at an electronic version of the rules from my files and must have pulled up the 06-07 season one.

[Balsa Man]

How are you guys connecting the tension members to the base?
I can't figure out how to drill the two holes that the tension members go in.

So back in 2000 when this was a trial event for the first time in B division at nationals, the team that won the event was from my current home town. I saw their device at the time and many times since. It used two anchor points to the wall, each with a custom drilled hole to match the dowel size and angle of the tension arms. The arms themselves were probably 1/8" diameter. I remember asking them how they did it, and the reply was that they had access to something that could drill compound angles. Their boom weighed something on the order of 25 grams.

Fast forward to 2008 where the winning boom at nats was more like 6 grams and went to full load. Our's was a couple grams heavier, did not go to full load, but we got 5th. We did NOT use dowels for the tension arms, but rather thin basswood strips that were simply glued to either side of a single base (and at the distal end too). There were no slits in the base or at the distal end for the tension arms to fit into either. So, this design eliminates the need to drill holes at angles that match those of the tension arms and also eliminates the need to create slits for flat tension arms. I strongly suggest going this way at both the distal end and at the wall mount.

Quick question on that 2008 Nat winner - were they (by chance to get that couple grams lighter) running a single tension member, or paired like you were running?

[thsom]

How are you guys connecting the tension members to the base?
I can't figure out how to drill the two holes that the tension members go in.

So back in 2000 when this was a trial event for the first time in B division at nationals, the team that won the event was from my current home town. I saw their device at the time and many times since. It used two anchor points to the wall, each with a custom drilled hole to match the dowel size and angle of the tension arms. The arms themselves were probably 1/8" diameter. I remember asking them how they did it, and the reply was that they had access to something that could drill compound angles. Their boom weighed something on the order of 25 grams.

Fast forward to 2008 where the winning boom at nats was more like 6 grams and went to full load. Our's was a couple grams heavier, did not go to full load, but we got 5th. We did NOT use dowels for the tension arms, but rather thin basswood strips that were simply glued to either side of a single base (and at the distal end too). There were no slits in the base or at the distal end for the tension arms to fit into either. So, this design eliminates the need to drill holes at angles that match those of the tension arms and also eliminates the need to create slits for flat tension arms. I strongly suggest going this way at both the distal end and at the wall mount.

Quick question on that 2008 Nat winner - were they (by chance to get that couple grams lighter) running a single tension member, or paired like you were running?

How in the world would you use one tension member?

[Balsa Man]

How in the world would you use one tension member?

Uh, attached to the center bolt, running down and attached to the distal end off the boom.....
Small piece cut from the sapwood of an old growth unobtainium vine.....by the light of the full moon, with the proper incantation; oh, yeah, and with the sacrifice of a virgin....

Seriously, though, yes, it can be done. We used 2 last time (in '08), but did (successful joints & member- at a competitive weight) testing w/ 1 and are.....looking closely at that for this year.
Tension force is about 43kg; that's a lot; definately a couple tricks to making it work - and being lighter than 2. It can be done. For obvious reasons, I'm going to stay away from the details till much later in the season....

[germinator]

For my two cents, as the boom bends it might load one side a bit more than the other and allow it to move either sideways or worse, UP. The smaller the boom, the more problem it might be. The boomilevers are not perfect, well most of them are not.

First try on a computer model only held 5Kg. Demoralizing.

what computer model would this be?

[fanjiatian]

I'm confused about the testing surface.
The rules ask for 3/4 " OD flat washers.

Does this mean that the inside diameter is 3/4 inch? If so, how'd it fit on the 1/4 inch bolt?

[Balsa Man]

I'm confused about the testing surface.
The rules ask for 3/4 " OD flat washers.

Does this mean that the inside diameter is 3/4 inch? If so, how'd it fit on the 1/4 inch bolt?

No, OD stands for outside diameter - not inside diameter (ID).
If you go to the store and ask for "1/4" washers"- the OD is 3/4". The hole in them - the ID - is actually a bit larger than 1/4" (~5/16")

[thsom]

I'm confused about the testing surface.
The rules ask for 3/4 " OD flat washers.

Does this mean that the inside diameter is 3/4 inch? If so, how'd it fit on the 1/4 inch bolt?

No, OD stands for outside diameter - not inside diameter (ID).
If you go to the store and ask for "1/4" washers"- the OD is 3/4". The hole in them - the ID - is actually a bit larger than 1/4" (~5/16")

does the competition provide everything except for the boomilever and the goggles, etc. So, do they provide the bolt, washer, etc.

[Balsa Man]

does the competition provide everything except for the boomilever and the goggles, etc. So, do they provide the bolt, washer, etc.

yes - Rule 2.c says the Event Supervisor must provide the testing apparatus. Rule 4 describes/specifies the testing apparatus. Rule 4. b. iii describes the bolts, washers, and nuts to be provided as part of the testing appaaratus. It's very clear.

Rule #1 is, of course - for this and all events - read the rules. Rule #2 is re-read the rules till you know and understand them.
No offense intended; this really is important; it's where you start....