Here's a close up of where the channels intersect. There's a X-fitting which my plumbing supply didn't have so I used a T and a two-hole piece.
You can see a nut where the 1/2" rod goes through the cross, there's a matching nut on the underside of those metal fittings to keep it tight. Also, the nuts you see going into the fittings are coarse 1/2" made by unistrut, they mate with unistrut bolts with springs.
Cost for the 10' piece of channel was $22.70, the T fitting was $12, nuts and bolts $5.40. So, $40 for unistrut. Too expensive really but OK for prototyping. If this were a larger implementation, say 10-20 mirrors, it could be made into a grid so as a system it could be stiffer. To cut costs, smaller channel pieces (13/16") could be used, or maybe a cheaper, plastic substitute. Also, the L and T pieces are pricey and in a grid it might be possible to use flat 3-hole pieces. All in, $20/ device (per square meter) for an easily installed base might be the target.
The threaded rod was a 2' piece of 1/2" -13 from Osh. This costs about $1.50/foot. It would be better to cut it down to 1' for stiffness (the mirror doesn't require 2' for clearance), but leave it at 2' when first building -- it's easier to get under it to work.
Here's a pic of where the 1/4"-20 rod is coupled to the 1/2". The 1/4" isn't stiff enough to use for the whole length, but 1/4" is needed to fit through the hollow shaft of the servo gearbox. The 1/2"-13 to 1/4"-20 reducer coupling nut is an oddball. I found it at tannerbolt.com, here's the link. I had to buy a box of 50, but they're 50 cents each in quantity. I have 49 left. The bolt you see in the picture is what the gearbox will rest on. Will tackle that in a next post.
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