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Hey guys!

I just finished testing a boomilever I built. I expected it to hold full weight (following the calculations that Balsa Man (rest in peace) uploaded), but we were only going to test it to 10 kg. However, the boomilever only held around 3 kg. I suspect this is a construction error, as one of the compression members was starting to turn inwards. It seemed that I was not able to align the compression members with the tension members/base properly, which made it hard to set the boomilever up on my testing wall perfectly symmetrical. This led to the rotation of the compression member.

Here is a picture of the remains of the boomilever. As you can see, the compression members and the tension members did not flex at all, but the X bracings were broken because of the turning of the compression member:





When I built it, I first cut my compression members, put them next to each other, and attached the X bracings. I put some thick sticks of wood to make sure the compression members were roughly 5 cm apart to hold the loading block. (However, this time, I'm using clamps so the compression members don't move out of place.)

Then, I built the base and glued my tension members (with gorilla glue) to the base and clamped for 24 hours. However, I noticed that the tension members were not in the exact same plane-one was at a different angle from the base than the other. You may be able to see this in the picture. When gluing, I put the base in between the tension members, attached pieces to it, then added gorilla glue, and then clamped. I think the clamping may have shifted the tension members slightly out of place for some reason (which I noticed when I was building, but it was too late to change anything.

Then, I put the compression members on a flat surface, though the compression members were a little wobbly. The orientation of the compression members was like this:


I put the base/tension members above the compression members at around 13.5 cm(our height). Then, I connected the first tension member to the compression member and glued with CA glue. Then, I flipped over the boomilever onto its other side, connected the second tension member to the compression member, and glued with CA glue. Then, I added reinforcements to both joints and clamped.

Do you know any construction tips that can help with alignment? It seemed like because the tension members (which were the same length) were connected to the base at different angles, it pulled the compression members into an asymmetrical shape, which helped its premature failure. My base was also misaligned, probably because I tried to fix the alignment problem by gluing the tension members on slightly different spots on the compression members. This all also made it difficult to set up on the testing wall. If you have any tips, I'd really appreciate it!

Anonymous15 wrote:

Hey you might need to fix images

Keep in mind, Balsaman's calculations are very theoretical in nature and are much more helpful in guiding adjustments and getting a starting point. I had a projected 4200 tower last year and on its first test, it only got 420. There's lot's of ways to invent specific holding structures to put on bracing but that's a case by case scenario. I can help more after the images work!

PS: 200th post! Dedicated to Len Joeris

https://gm1.ggpht.com/rsAbn5mvOkUo6e9wj ... -ft-l75-ft

https://gm1.ggpht.com/Ykt966E6QNk8Hi3Sa ... -ft-l75-ft


Here are the links to the pictures. In my previous post, I put the url of the picture into the img BBcode-is that the right way?

Also, my boomilever weighed 9.02 grams and held 3 kg, so it got a score of 333.33, in case you or anyone else was wondering!

I also used 1/16*1/32 bracing, is that too thin?

Thanks for the help btw!

Anonymous15 wrote:https://gm1.ggpht.com/rsAbn5mvOkUo6e9wj ... -ft-l75-ft

https://gm1.ggpht.com/Ykt966E6QNk8Hi3Sa ... -ft-l75-ft


Here are the links to the pictures. In my previous post, I put the url of the picture into the img BBcode-is that the right way?

Also, my boomilever weighed 9.02 grams and held 3 kg, so it got a score of 333.33, in case you or anyone else was wondering!

I also used 1/16*1/32 bracing, is that too thin?

Thanks for the help btw!

Still can't see the pics, though that may be because of my school's filtering software. Could you share it via dropbox, if at all possible? I'd like to help out, but it's a bit hard right now.

I won't go into the math (because I'm stupid and I'll mess it up), but from your description of the building process I agree that this could have been a construction error. However, I've found that simply misaligned and tilted members won't take your load down to the point you described. I think there could be something you may have to review in the overall design again. As for the bracing, 1/16 by 1/32 is perfectly okay, but of course this depends on your bracing intervals and compression members. I myself have been using 1/16 by 1/32, except I carefully double layer them. Not sure if there's any significant tactical advantage in doing this, but from my experience it works better (increased glue surface area I guess).

https://www.dropbox.com/s/q0y2n9ja24sig ... 9.JPG?dl=0
https://www.dropbox.com/s/3wyoht2ihrtma ... 9.JPG?dl=0
https://www.dropbox.com/s/ticnped6sj6ha ... 9.JPG?dl=0

Do these work?

Also, what did you mean by double layering your bracing members? Do you mean putting one on top of the other or one next to the other? If you could share a picture, it would probably clear things up for me.

And sometimes my bracing members can break off, so increasing glue surface area definitely makes sense.

Here is another one that hopefully shows the misalignment of my tension members on my previous boomilever:

https://www.dropbox.com/s/4mb8hvhovikaf ... 1.JPG?dl=0

And this is one showing how I am planning to do my tension-base joints-I'll put gorilla glue on the tension members, then clamp it to the base. However, I did this last time and I think that helped misalign the members (Also my base and my tension members are a different height which also makes it harder to align). Do you guys have any tips?
https://www.dropbox.com/s/ji8caku1ivuyg ... 2.JPG?dl=0

Looking at the amount and size of the bracings, I think it would help to use 1/16 x 1/16 weighting 0.3 or 0.4 grams every 36in

Anonymous15 wrote: Do these work?

Also, what did you mean by double layering your bracing members? Do you mean putting one on top of the other or one next to the other? If you could share a picture, it would probably clear things up for me.

And sometimes my bracing members can break off, so increasing glue surface area definitely makes sense.

Yes, I am able to see the images now. Thank you! I'll send a picture of what I mean by "double layering" via PM, so be sure to check your inbox.

A few things about your boomilever:
1. Like Cow481 said, you need more bracing. I'd recommend thickening your bracing to 1/16 square or double layering the bracing like how I did in the pictures I sent you.

2. You are lacking ladder pieces. These pieces are strictly for keeping the two compression beams in place. They are very important since your bracing helps distribute force by transferring the immense force pushing against the wall into a "pulling apart" force for your compression piece. Adding ladders would help prevent your boomilever from splitting apart, like what is shown in one of your pictures.

3. When aligning your tension members, think of the sides of your boomilever as triangles you'd like to make congruent. If you have the same length tension and compression chords, then to make the 'triangles' congruent you only need one more member that is congruent. This is based on the idea of SSS. Basically, connect the tension member to your compression at the distal end, and give it a little bit of wiggle room. Then cut two identical lengths of the thing 'side' in order to have your tension members line up (by CPCTC).

This is all super helpful! Thank you so much!!

When you glue your tension members to the base, how you make sure they are in the same plane? I think mine were not, which could have led to more alignment problems. However, the points you mentioned make a lot of sense and I'll make sure to follow them as I build.