123445 wrote:Whats the best way to keep the distal end from bending downwards. On most of my booms once it reaches ~10kg the distal ends start bending down which causes it to fail. I've tried added vertical bracing but it doesn't really help. Should I just go for stronger tension members?
Well, from the sound of the distal end bending it sounds like compression is the problem, not tension.
Look at the size of your compression. Compression that is built super thin (even with vertical bracing) can cause bending.
And by thin I mean how tall the compression is, not how wide (built for the loading block size) or long (built to the 40-45 cm parameter) it is. Usually people have the height or size of their compression supports as 1/4 to 1/2, but even that can result in bending at the distal end. I personally have built my compression 45 cm by 5 cm by 3/4 in
. Having those sizes or something close to those sizes usually makes bending at the distal end very unlikely. This method is what i like to call "bulking up your compression". Bass by itself with no vertical bracing is very very strong. One of the most important things in boomi is getting equilibrium, including finding a balance between the strength of your compression and tension. Having a strong tension and a weaker compression obviously causes compression to fail because it is weaker. Bulking up compression is something that has helped me to make sure the bend of the compression doesn't happen. You can bulk by just simply trying to make the masses of compression and tension match, or even better, building a thicker compression to match the great tension strength of bass. I keep mentioning bass as tension, so quick disclaimer, yes. I highly recommend bass for tension. It withstands so much better than balsa. Bass without ANY vertical bracing to me is so much better than balsa with a bunch of unnecessary vertical bracing. Also, when I say "bulk up your compression" I don't mean to abruptly change the mass of your compression. Keep the goal of a boom under 10 grams under your belt.
But let's turn into a whole different lane and say that its not your ENTIRE compression piece that is bending, but your situation or problem area has become JUST the distal end and the boomi fails because the end that is holding the block just snaps off. This too has happened to me. You have all the requirements met in the first paragraph of this post, but this distal end just snaps off. So my solution to this is that your tension pieces (I'm saying pieces because I assume you use two pieces connecting to the distal end) aren't as close to the distal end as possible. This ties in with why I think 3/4 compression is good, because not only is it good as a basic design, it gives you room to move your tension as close to the end of compression as possible. I never have personally been a fan of not having the entire block resting on the boomi. Having for example like 1-2 centimeters of the block hanging off the side or end has so so so much more room for error because once again EQUILIBRIUM. If the block is even a little lopsided or off it could cause the whole boom to break as well. But back to the tension not being as close to the end as possible. Let's say your tension doesn't extend far to the right, or a better description of this is when you put the loading block, directly under it the tension isn't there. Having tension not meet up to where the block is placed makes the pressure of the weight go straight down on the boomi instead of into the testing wall. Make sure that your tension is as close to the distal end as possible. This makes sure that compression and tension are working together. Don't have enough room to make that happen? Do the compression size switch said in the first paragraph. It will for sure give you much more room.
1. Check the size of your compression and if it's too thin make it bigger
2. Bulk up compression
3. Make sure the strength of compression and tension are equal (or at not not too far off)
4. Have compression and tension work together into the testing wall
5. Make sure the distal end isn't putting pressure straight down
6. Bass >>> Balsa for tension