Banjoes.
By inserting a coupler into a shaft collar, you can create very versatile bracing joints. (see the variety of ways we used them on our robot) The banjo allows you to create braces at odd angles when screwed into a standoff. (the standoff being the primary structural member) If you use two banjoes in tandem, you can mount/brace something at any arbitrary angle… see our first picture.
From our school’s coach:
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If you make banjos you have to tighten the set screw against a short piece of shaft. If the thread is not tight, the loctite won’t cure properly. Tighten against the corner of the shaft, not the flat. When you take the shaft out, a short twist will loosen it. Then you have to run a drill through the hole to clean it up. It takes a numbered drill. #19, I think. You want the size that just matches the ID of the shaft collar.
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Use red locktite, and let it cure for at least 24 hours.
I prefer using banjo-standoff bracing as opposed to something like the below image. In the case of the below image, the use of bar is not bad since the bar(s) will only be under tensile stress. Banjo-standoff combos on the other hand, have great tensile strength aaaand a decent amount of compressive strength (though not nearly as much as the tensile)
View of rubber bands on a catapult, courtesy of 99904A – taken from BLRS Wiki.
Of course, there are probably a couple of other ways you could do this… but I figured I would let you know it’s an option – they could com in handy to you later on.