Not Stiff Enough

Not Stiff Enough

Big Bertha 2.0 isn't stiff enough. It won't hold collimation as I move it across the sky. A little experimentation with the laser collimator in place, watching where the laser spot moves on the diagonal mirror, suggests that the 4" wide aluminum channel is stiff enough--but the 1" square aluminum tubes are not.

There's a reason that Serrurier truss designs are so popular--and I guess that I just didn't want to accept that there was a reason for this. A Serrurier truss (like the example shown at Moonlite Telescope Accessories) is a series of triangles that hold the two ends of the telescope in the correct position. Because they are triangles, they hold the parts in tension.

I'm still learning, but the most obvious solution for me is to buy two double ball and socket blocks to put on the focuser cage, and four single ball and socket blocks to put on the mirror cage. (Since I already have to have the 4" wide aluminum channel to mount the telescope to the equatorial mount, and this is very, very stiff, I'll leave it place.) The aluminum tubes fit in between these ball and socket blocks. The total weight of these parts is quite small--comparable the square aluminum tubes that I have on there now. It will mean putting a few more holes in the two cages, but perhaps I will be able to patch over the existing holes when I am done.