Boomilever B/C

[bearasmith]

The first place score was 1330 for MD. We were 17 points behind it.

[inconspicuousmole]

How are you guys doing the struts between the tension members and compression base? My current design breaks around 12kg and looks somewhat like this. https://www.flickr.com/photos/123804914@N02/ Seems like the diagonal beams are pulling away from each other ultimately leading it to snap.

[JonB]

How are you guys doing the struts between the tension members and compression base? My current design breaks around 12kg and looks somewhat like this. https://www.flickr.com/photos/123804914@N02/ Seems like the diagonal beams are pulling away from each other ultimately leading it to snap.

I am going to assume you are using CA? Also, are you gluing them to the top of your compression piece, or side of the compression piece? Are your diagonals pulling away from the compression/tension piece or "each other" as you state?

[inconspicuousmole]

I am using tightbond 2. The struts are glued to the top of the compression plates with plates on the sides. It appears the struts are pulling away from the tension and compression pieces.

[iwonder]

It's definitely better to use CA(superglue). Wood glues require long dry times and clamping, which could damage really light balsa if you're not careful and really slow down the time it takes to build a boom. CA will be just as strong (if not stronger) and dry much faster without clamping, which means the odds of getting a good joint are a lot higher.

CA's also a lot lighter than wood glues.

[JonB]

I am using tightbond 2. The struts are glued to the top of the compression plates with plates on the sides. It appears the struts are pulling away from the tension and compression pieces.

So if I am visualizing this correctly- struts on top of compression and then a thin piece of balsa on the side that covers the entire joint and is glued to both strut and compression? That's not a bad way to go, but it might be simpler to glue the strut to the side of the compression piece (with CA glue). There should be a large amount of surface area to be glued and then you will reduce weight without using that extra wood. Just my opinion though.

[iwonder]

It also sounds like your fundamental problem is that your compression member is curving up and pushing the compression-tension connecting pieces out, when they're pushed too far they'll snap. It could also be some kind of misalignment in your tension member that settles when you reach a higher load, but since you're reaching 12kg that's probably not the case (you'd see settling in the first 5 or 10).

If it's the compression member, some suggestions are to make the compression-tension connectors bigger, make the compression member taller, or use denser wood (it's stronger) in either of those parts. Any of those make the compression member stronger and less subject to bending. If you can make it fail consistently about 16kg you're doing pretty well and can just focus on shaving excess weight.

[Buckstops]

Anyone have any word on efficiencies from MI or Ohio states yesterday?

[havenguy]

I'm facing a bit of a problem right now in that my tension members are shearing off right where they are glued to the base. Any suggestions on how to fix this? Would reinforcing the joint (for example, running another piece that's the same width down the tension member for about 3 cm) prevent it from breaking?

Thanks in advance.

[iwonder]

Try and make the joint area larger, maybe use the top and bottom of the joint as well (so like in a notch on the base). Also, if you're using superglue sand the parts smooth, use a tiny amount of glue spread over the whole area, and let it dry for a full 24 hours (when you're pushing the limits of the glue, which this does, the time really does make a difference)