Boomilever B/C

[LoneMonkey]

What is the best way to connect the two tension members near the hook? I've just been putting a single 1/4 square piece under, but it seems to fall off every time.

What glue are you using, and is the 1/4" balsa or bass?

Purple CA, balsa

[knightmoves]

The problem with laser cutting is that all the grain still runs the same direction. Sheets of balsa are surprisingly weak when tensioned perpendicular to the direction of the grain, and they split. This tends to occur primarily on where the diagonal bracing would be.

This. I saw a beautiful laser-cut tower a couple of years ago. The thing was absolutely gorgeous - almost looked like a Sierpinski triangle. It held barely more than the bucket.

[MadCow2357]

What is the best way to connect the two tension members near the hook? I've just been putting a single 1/4 square piece under, but it seems to fall off every time.

What glue are you using, and is the 1/4" balsa or bass?

Purple CA, balsa

For the location you are talking about, use Gorilla Glue instead of CA (Titebond 3 apparently works too but I've never tried it?). You could consider using something like 1/2" by 1/4" balsa to increase the contact surface area as well. However, I prefer to use bass for the base (personal preference as of now)

[JZhang1]

https://www.desmos.com/calculator/efiabgnr7l
Here are some equations I made that model the efficiency vs number of bracings for trapezoidal prism shaped box boomilevers with X bracings and 1/8th square balsa columns. Green uses linear regression for the relationship of balsa critical load vs mass. Blue and purple use quadratic and exponential regression lines, respectively (both which I think are more realistic). There are also a few equations at the bottom which model div B towers from 3 years ago, which are surprisingly accurate based on personal experience. L is the load experienced by each column, w1 is the width at the distal end, w2 is the width at the wall, h is the height, m is the mass of the bracings per 36 inch stick. These equations are by no means a perfect representation of boomilevers, but can probably help as a general guideline for most. Real building is very different from theoretical building. Enjoy.

[dankdecidueye]

I know that tower chimney is one of the most prevalent designs, but are people going for a trapezoid type of tower chimney or making something like last season's one then adding two diagonal things to fulfill the 8 cm rule?

[seitanBacon]

The problem with laser cutting is that all the grain still runs the same direction. Sheets of balsa are surprisingly weak when tensioned perpendicular to the direction of the grain, and they split. This tends to occur primarily on where the diagonal bracing would be.

This. I saw a beautiful laser-cut tower a couple of years ago. The thing was absolutely gorgeous - almost looked like a Sierpinski triangle. It held barely more than the bucket.

That's too bad, we have a really nice lab and I'd love to be able to just use solidworks + ai to design and cut one.

[JonB]

The problem with laser cutting is that all the grain still runs the same direction. Sheets of balsa are surprisingly weak when tensioned perpendicular to the direction of the grain, and they split. This tends to occur primarily on where the diagonal bracing would be.

This. I saw a beautiful laser-cut tower a couple of years ago. The thing was absolutely gorgeous - almost looked like a Sierpinski triangle. It held barely more than the bucket.

That's too bad, we have a really nice lab and I'd love to be able to just use solidworks + ai to design and cut one.

You can use solidworks/autoCAD to still design and laser cut parts of the boomi, but not the whole thing. You could go as far as laser cutting all of the pieces individually (with the grain running parallel for all parts) and then put them together. You can also use the laser cutter to create paper templates to build on top of (set the power low enough that it scorches the thick paper- it is unbelievably accurate versus anything hand drawn). There are many ways to incorporate the laser cutter with boomi, but it simply will not work for cutting out the ENTIRE boomi due to the grains of the wood.

[MadCow2357]

This. I saw a beautiful laser-cut tower a couple of years ago. The thing was absolutely gorgeous - almost looked like a Sierpinski triangle. It held barely more than the bucket.

That's too bad, we have a really nice lab and I'd love to be able to just use solidworks + ai to design and cut one.

You can use solidworks/autoCAD to still design and laser cut parts of the boomi, but not the whole thing. You could go as far as laser cutting all of the pieces individually (with the grain running parallel for all parts) and then put them together. You can also use the laser cutter to create paper templates to build on top of (set the power low enough that it scorches the thick paper- it is unbelievably accurate versus anything hand drawn). There are many ways to incorporate the laser cutter with boomi, but it simply will not work for cutting out the ENTIRE boomi due to the grains of the wood.

The paper template part is an interesting idea that I might consider implementing myself, but would this be better than using a plotter/big printer?

Another issue of laser-cutting pieces would probably also be the varying densities since there is quite a bit of variation in each balsa sheet. Seems like it wouldn't be the most cost effective either.

[JonB]

That's too bad, we have a really nice lab and I'd love to be able to just use solidworks + ai to design and cut one.

You can use solidworks/autoCAD to still design and laser cut parts of the boomi, but not the whole thing. You could go as far as laser cutting all of the pieces individually (with the grain running parallel for all parts) and then put them together. You can also use the laser cutter to create paper templates to build on top of (set the power low enough that it scorches the thick paper- it is unbelievably accurate versus anything hand drawn). There are many ways to incorporate the laser cutter with boomi, but it simply will not work for cutting out the ENTIRE boomi due to the grains of the wood.

The paper template part is an interesting idea that I might consider implementing myself, but would this be better than using a plotter/big printer?

Another issue of laser-cutting pieces would probably also be the varying densities since there is quite a bit of variation in each balsa sheet. Seems like it wouldn't be the most cost effective either.

I am not sure that it is necessarily better than a large printer or plotter, we just do not have easy access to a large enough printer/plotter but we have full access to the laser system. Any differences between the two (laser vs plotter) would be negligible. However, the more comfortable and familiar our group is with the laser, the more they realize what they can actually do with it across the events.

There are definitely varying densities across sheets and even within a sheet but this is an issue for everyone despite how they build their designs. It actually is not too bad when it comes to cost (I am assuming you are referring to wasted wood after laser cutting?). If the pieces are all cut in a parallel fashion then very little of the sheet needs to be wasted. That being said, we do not cut all of our pieces with the laser. We cut some of our pieces with the laser (maybe 45% of the design) and the rest are hand cut.

[MadCow2357]

The paper template part is an interesting idea that I might consider implementing myself, but would this be better than using a plotter/big printer?

Another issue of laser-cutting pieces would probably also be the varying densities since there is quite a bit of variation in each balsa sheet. Seems like it wouldn't be the most cost effective either.

I am not sure that it is necessarily better than a large printer or plotter, we just do not have easy access to a large enough printer/plotter but we have full access to the laser system. Any differences between the two (laser vs plotter) would be negligible. However, the more comfortable and familiar our group is with the laser, the more they realize what they can actually do with it across the events.

There are definitely varying densities across sheets and even within a sheet but this is an issue for everyone despite how they build their designs. It actually is not too bad when it comes to cost (I am assuming you are referring to wasted wood after laser cutting?). If the pieces are all cut in a parallel fashion then very little of the sheet needs to be wasted. That being said, we do not cut all of our pieces with the laser. We cut some of our pieces with the laser (maybe 45% of the design) and the rest are hand cut.

Yeah I meant wasted wood lol. I like to test all of my pieces with SPFD before building, is there a method you use to sort your wood pieces after they are laser cut?