Elevated Bridge B/C

[StampingKid]

We took first at Kentucky State Division B this past weekend with a 8.6 g bridge that held all 15 Kg.for a 1744 efficiency thanks to some careful reading of BalsaMan's recent posts. With better glue discipline and more time to get lighter balsa (ran out of one size making first model of this bridge which @ 10 g. held 13.6 kg for a 1360 efficiency), we may have been able to get that to the 7.0-7.5 range. Kentucky can be competitive with Ohio and other states as we have done well in events at the Magsig Invitational.

2007 Reg'l 1st Balloon Launch Glider
3rd Wheeled Vehicle

2008 Reg'l 1st Tower
2nd Balloon Launch Glider

2008 State 1st Tower

2009 Reg'l 1st Crave the Wave
Elevated Bridge

[StampingKid]

We took first at Kentucky State Division B this past weekend with a 8.6 g bridge that held all 15 Kg.for a 1744 efficiency thanks to some careful reading of BalsaMan's recent posts. With better glue discipline and more time to get lighter balsa (ran out of one size making first model of this bridge which @ 10 g. held 13.6 kg for a 1360 efficiency), we may have been able to get that to the 7.0-7.5 range. Kentucky can be competitive with Ohio and other states as we have done well in events at the Magsig Invitational.

2007 Reg'l 1st Balloon Launch Glider
3rd Wheeled Vehicle

2008 Reg'l 1st Tower
2nd Balloon Launch Glider

2008 State 1st Tower

2009 Reg'l 1st Crave the Wave
2nd Elevated Bridge
1st Physical Science Lab
2nd Robo-Cross
1st Wright Stuff

2009 State 1st Elevated Bridge
3rd Wright Stuff

[Balsa Man]

We took first at Kentucky State Division B this past weekend with a 8.6 g bridge that held all 15 Kg.for a 1744 efficiency thanks to some careful reading of BalsaMan's recent posts.

Hey, glad to hear it was helpful; that is what this board is all about, in my mind. Thanks.

That's a very good result; congratulations. You guys going to Nationals?

[StampingKid]

No Nationals for us. Maybe next year.

[Bridges and Bots]

I got back from the state competition yesterday and my bridge placed second overall with an efficiency of 1072. It weighed 14 grams and held the whole load. It was made of bass wood legs to withstand compression, and balsa tension pieces.

Nice job, i also just got back from states. I got 1090 and got 1st. My bridge was 5g holding 12 pounds. I got lucky because the bridge broke before it was loaded on the bus so i built one overnight. Which state did u get back from? I guess you are marshall from WI cuz u got 19th in mystery architecture. LOL i beat u guys barely, but my team sucked, waunakee. I did pretty well though getting 4 medals, ecology, bridge, stars, and meteorology.

Haha, yeah I am from Marshall. Waunakee did very well this year. Unfortunately, our team wasn't good enough to win though. Four medals? Good job. I got Three and a dumb little ribbon.

[nejanimb]

We took first at Kentucky State Division B this past weekend with a 8.6 g bridge that held all 15 Kg.for a 1744 efficiency thanks to some careful reading of BalsaMan's recent posts. With better glue discipline and more time to get lighter balsa (ran out of one size making first model of this bridge which @ 10 g. held 13.6 kg for a 1360 efficiency), we may have been able to get that to the 7.0-7.5 range.

That's very impressive! What kind of design schematic did you use? Did you actually use a similar truss design to what Balsa Man used?

[Balsa Man]

[quote="nejanimb"]Did you actually use a similar truss design to what Balsa Man used?

I'd be very interested (for obvious reasons) to hear on that, too. Thanks

[StampingKid]

Since this event may return next year,we'd prefer not to broadcast the actual design but it was not BalsaMan's. Ithough will respect BalsaMan's assistance to me and offer some of my own. It is a simple truss design with few vertical members with butt to butt joints except for the tension members running from the bottom of the legs to the top cross member at the loading block but no radical angles at the butt joints. The key is in the execution using gussets and maintaining symmetry. We first had to get away from the tower mindset that you had to use at most 1/8 balsa throughout and that 1/4 wood was huge. We used 1/4 for compression and the other in tension--wondering whether we could have done 1/32 here. The early designs were all blowing out at at the uppermost and outermost joints (the upper right or left of the bridge tying the top members to the legs) glued face to face and usings gussets and symmetry here proved to be the key. We did not have time to build BalsaMan's tower but on that first bridge we carefully supported the bucket at the handle when loading and we were amazed to see the side to side forces at work when the cross-bracing started to tighten in one direction and literally deflect out and up 1/4 inch in the other and in taking it to the limit it split straight down the middle with the cross members largely intact on the separated sides with the bracing split which told me a lot about those gussetts and joints. I easily repaired that bridge and had it with me as a back up. I am a scout and as you may know our motto is "Be prepared"--reading the boards I knew 1500 could be a very good efficiency. In loading towards the end we heard a couple of pops, I have not checked the bridge but I suspect that the popping was the cross-members flexing again.

2007 Reg'l 1st Balloon Launch Glider
3rd Wheeled Vehicle

2008 Reg'l 1st Tower
2nd Balloon Launch Glider

2008 State 1st Tower

2009 Reg'l 1st Crave the Wave
2nd Elevated Bridge
1st Physical Science Lab
2nd Robo-Cross
1st Wright Stuff

2009 State 1st Elevated Bridge
3rd Wright Stuff

[gandhiji]

i was just wondering if all the state competitions have happened already or if theyre all done cuz nats is only a few weeks a way

[Balsa Man]

StampingKid,
Thanks for the insights. Again, nicely done.