noobforce wrote:thsom wrote:Hey guys, how can I make the base for my boomilever lighter? My base is currently...3-4 grams... Waaaayyyy too excessive... I use one layer of a 3/16 balsa sheet and 2 layers (on either side of the balsa) of 1/16 bass sheet. this base is about 6 cm by 3 cm... This is currently what holds my boom weight from breaking 10 grams...
Curve your tension members inward so that the part where your tensions members touch the base can become smaller. This will allow you to reduce the width of the base.
I would seriously caution against that approach. Yes, you want the attachment plate/block as small as you can. Yes, with many/most "conventional" designs (i.e., 2 compression members, with the outsides 5cm apart, so the load block sits on them), that means distal ends 5cm apart. but building a bend into tension members is asking for trouble, and means the tension member(s) will need to be heavier than they would if done without a built-in bend.
The tensile force on the tension member(s) will act to pull them straight. As you get toward full load, there's a lot of pull- tensile force - at work. Adding bend to tension will reduce the tension load the member can carry. The only way around that is to make it bigger or denser, to get higher tensile strength. Also, at one end or the other, or both, as the force tries to straighten the t-member out, that will put a "peeling" force on the glue joint - not just pulling along the t-member, but pulling the t-member away fron the glue joint. Glue joint will be much weaker against peeling than in pure (straight) shear.
However, if you angle the t-members so they can run straight- from the narrow separation at the wall to the wider separation at the distal end, you avoid those problems. Yes, to do that, you have to have angled holes/slots/faces in the wall block/plate, and angled pieces on the compression members for the straight t-members to be glued to.
For a wall block/plate - it only needs to be, and you want it only to be big enough to hold the t-member(s) right next to the washer. Think about it - there is a lever effect at work. The bolt holds the center of the block/plate down - acts as a fulcrum. if there is a tension member- let's look at one side - out from the fulcrum(bolt) by just the width of the washer (3/8ths"+), it takes a lot of force- pull- on that t-member to bend the wall block/plate. If you move that t-member out 3cm (1/2 your 6cm width), it takes much less force to bend the wall attachment piece.
The other thing to consider is thickness of that wall piece. With what you describe, it's only 5/16ths" thick. The glue area you have to hold against the t-member(s) being pulled out is limited by that thickness. Thin also bends easier than thicker. If you were to go to like 1/2" thick, with end-grain orientation- grain running perpendicular to the wall, with thin skin wall side, and outside side - 1" (2.5cm) square would be more than enough. "Thin skin" meaning 1/64th - if tou can't get 1/64th, sand down some 1/32nd... It would be a lot stiffer, a lot lighter, and give you a lot more glue strength....
