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Can anyone help me figure out why my boomilever broke. It only held about 10 lbs and it seems to have broken around the compression members.

It seems to me that since your tension pieces are mounted to the bottom of you box beam, and the block is on the top of it, the wood/bracing between the two got crushed between the two. You could fix this by reinforcing the vertical connection between the top and bottom of the box beam in the area directly under the loading block.

jinhusong wrote: ↑February 23rd, 2020, 3:11 pm This time, my son asked permission to setup a camera recording the boomi. From the video, we can see the distal end is continuously going lower and lower, maybe because of combination of J-hook bending and tension strips are stretching.

From 0-9kg, it dropped about 20mm (our base is pre-dented with 40kg pulling on the J-hook). This puts quite a challenge to 4-leg style.

Hope this information is helpful to others.

Tiger

Consider for a moment a steel bar-joist. Each bar joist is a webbed member with a top and bottom chord, but only the top chord is "bearing" in most cases. The top chord of the joist is in compression, while the bottom chord of the joist is in tension. They are connected with a heavier web extending from bottom chord to top chord at the wall, redistributing the load to the upper chord at the wall. Would something like this help in keeping all points to the wall?

I

Are you gluing the point where the tension arm crosses the upper compression beam? If so, technically you may be creating a lever of sorts, where that upper joint acts as fulcrum, and the loading block literally pivots off of that point. That's what it looks like to me anyway.

dholdgreve wrote: ↑February 25th, 2020, 7:25 am Are you gluing the point where the tension arm crosses the upper compression beam? If so, technically you may be creating a lever of sorts, where that upper joint acts as fulcrum, and the loading block literally pivots off of that point. That's what it looks like to me anyway.

Hmmm, should we not glue the connection between the tension arm and the upper compression beam? I have been doing so, and it hasn't created a problem for me yet.

top score @ regionals was 2.2k it didnt break, even after holding full load.

sneepity wrote: ↑February 29th, 2020, 3:42 pm top score @ regionals was 2.2k it didnt break, even after holding full load.

Do you have more information? (e.g. division, state, chimney vs standard, other scores?)

MadCow2357 wrote: ↑February 29th, 2020, 4:35 pm

sneepity wrote: ↑February 29th, 2020, 3:42 pm top score @ regionals was 2.2k it didnt break, even after holding full load.

Do you have more information? (e.g. division, state, chimney vs standard, other scores?)

It is not my boomilever to share, and I think the owner would rather not say. But, I have to say, it was a really great boomilever, and as I said, it never broke!!!
oh and my boomilever did not do very well and i took 12th. I tried fixing something right before the testing and the j-hook attachment snapped with little weight, so I suggest the j-hook attachment to either be very bulky or very light- stay consistent with your design, because my boomi was very strong but the j-hook attachment wasńt. Something I learned today!!!

sneepity wrote: ↑February 29th, 2020, 6:09 pm

MadCow2357 wrote: ↑February 29th, 2020, 4:35 pm

sneepity wrote: ↑February 29th, 2020, 3:42 pm top score @ regionals was 2.2k it didnt break, even after holding full load.

Do you have more information? (e.g. division, state, chimney vs standard, other scores?)

It is not my boomilever to share, and I think the owner would rather not say. But, I have to say, it was a really great boomilever, and as I said, it never broke!!!

Lmao is division and other scores really too much to ask? (I can understand not sharing if it's chimney or standard tho)