Re: PICTURES, SCORES, VIDEOS!!

[sneepity]

Select better, lighter wood, check for wood grain and density for maximum effectiveness, reduce the amount of glue you are using.

sorry for the question, but how do I check wood grain and density?

At this point in your progress, don't bother with worrying about wood grain or the amount of glue. The first step, once you have a reasonable design (check Google, and maybe most importantly, read theses forums from last year's boomi event; the rules were different, but many of the concepts still apply this year - for good general technique and process read the towers and bridges forums as well), focus on proper material selection. We like to cut (or buy) pieces to some normalized dimension - or actual dimension if you want, and create a "library" of materials. Accurately weigh every piece and record its mass on the piece itself. Balsa can easily have a 4x range in density. Within most of that range, strength will increase linearly, but at both ends of that curve it's not linear. The really light stuff, which feels almost spongy is not a good choice to use for anything really. For everything else, you'll have to figure out what the best mass/strength to use based on your specific design. That is the majority of the work for this event to compete at a high level.

A couple quick tips for basic boomi success. Make sure your build is symmetric with respect to material choice. If one side is using a 3g piece, make sure the other side is as close to that as possible. Build precision is extremely important. At the very least, build your device on graph paper pinned to cardboard. Even better, build an accurate jig to help get it as precise as possible. Also record everything that goes into your boomi wrt materials. dimensions, mass of components, etc. so you'll be able to reproduce the device and have a record of what you changed to get to your final build/design.

Good luck!! You will need to build a lot of devices to get really good, but everyone starts somewhere!

I really appreciate your help! The fact that you actually wrote an essay, lol
thanks a lot! ill be sure to use these tips in my boomi. bet youre extremely good at building a boomi!

[sneepity]

what is your guys´ opinion on a x-bracing on the top? I put a singular x-bracing on top of the tension members, and its like long and extends from the start to the end of the tension members.

[dholdgreve]

what is your guys´ opinion on a x-bracing on the top? I put a singular x-bracing on top of the tension members, and its like long and extends from the start to the end of the tension members.

Tension members should never require X bracing... only compression members. X braces as used to resist buckling created from excess compressive forces. In fact, we actually brace off of our tension members to help resist the buckling forces on the compression beams.

[jgrischow1]

what is your guys´ opinion on a x-bracing on the top? I put a singular x-bracing on top of the tension members, and its like long and extends from the start to the end of the tension members.

Tension members should never require X bracing... only compression members. X braces as used to resist buckling created from excess compressive forces. In fact, we actually brace off of our tension members to help resist the buckling forces on the compression beams.

Awhile ago, maybe back in the 13-14 rotation, someone, possibly Len, mentioned it was more efficient to have rectangular cross section compression beams (i.e. "taller" than they were wide) rather than brace vertically to protect against vertical buckling. Do you disagree?

[MadCow2357]

what is your guys´ opinion on a x-bracing on the top? I put a singular x-bracing on top of the tension members, and its like long and extends from the start to the end of the tension members.

Tension members should never require X bracing... only compression members. X braces as used to resist buckling created from excess compressive forces. In fact, we actually brace off of our tension members to help resist the buckling forces on the compression beams.

Awhile ago, maybe back in the 13-14 rotation, someone, possibly Len, mentioned it was more efficient to have rectangular cross section compression beams (i.e. "taller" than they were wide) rather than brace vertically to protect against vertical buckling. Do you disagree?

Not dholdgreve, but I believe it depends on your design. For tower chimney booms, it'd be hard to attach vertical bracing at all. Tension booms allow this possibility, but building around the Contact Width Lines makes it difficult to attach vertical bracing in general this year without having the angles be weird and stuff. If Len was still here (bless his soul and rest in peace ), I think he'd emphasize taller compression beams over vertical bracing even more than previous years. However, I'd be extremely interested in his scientific opinion on standard tension booms vs chimney booms.

Wish he was still here to guide us

[dholdgreve]

what is your guys´ opinion on a x-bracing on the top? I put a singular x-bracing on top of the tension members, and its like long and extends from the start to the end of the tension members.

Tension members should never require X bracing... only compression members. X braces as used to resist buckling created from excess compressive forces. In fact, we actually brace off of our tension members to help resist the buckling forces on the compression beams.

Awhile ago, maybe back in the 13-14 rotation, someone, possibly Len, mentioned it was more efficient to have rectangular cross section compression beams (i.e. "taller" than they were wide) rather than brace vertically to protect against vertical buckling. Do you disagree?

By making your compression beams taller and not so thick, it allows you to vertically brace at greater intervals, and decrease the interval distance on the horizontal bracing. This was huge last year as the horizontal distance was much less than the vertical distance. With the 8 cm no touch area this year, it is less so, but still remains an advantage. I've seen a number of teams going with 1/8" thick x 3/8" to 1/2" high compression beams and have been very successful.

[jgrischow1]

Tension members should never require X bracing... only compression members. X braces as used to resist buckling created from excess compressive forces. In fact, we actually brace off of our tension members to help resist the buckling forces on the compression beams.

Awhile ago, maybe back in the 13-14 rotation, someone, possibly Len, mentioned it was more efficient to have rectangular cross section compression beams (i.e. "taller" than they were wide) rather than brace vertically to protect against vertical buckling. Do you disagree?

By making your compression beams taller and not so thick, it allows you to vertically brace at greater intervals, and decrease the interval distance on the horizontal bracing. This was huge last year as the horizontal distance was much less than the vertical distance. With the 8 cm no touch area this year, it is less so, but still remains an advantage. I've seen a number of teams going with 1/8" thick x 3/8" to 1/2" high compression beams and have been very successful.

Thanks!

[jinhusong]

Hi,

I read comments about 4-leg chimney boomilevel from Balsaman. Quite complicated to build, especially only the top 2 legs should touch the wall initially. Still, when we gave it a try and not much paying attention to weight of wood, we still ended up with a boomi not heavy (same as the 2-legs we tried pretty hard to reduce weight and holding almost the same weight).

So, we decided to give it another chance and this time, we will try to use lighter wood. I will report back after Saturday Golden Gate.

Tiger

[FrogLegs]

Tiger, what weight sticks are you using for the main compression pieces on your chimney design? For Towers we were going down to around 1g per stick, so with 4 in a chimney boomilever design I was thinking it would be about the same.

[MadCow2357]

Tiger, what weight sticks are you using for the main compression pieces on your chimney design? For Towers we were going down to around 1g per stick, so with 4 in a chimney boomilever design I was thinking it would be about the same.

Just note that boomilevers experience higher tensile/compressive forces than towers (due to mechanical advantage and stuff).

Iirc div b has ~33kg on the compression and div c has ~41kg