Quote:
Originally Posted by bojan
How did you go with flexure calculations and how did you implement it in your design?
Obviously, for Serrurier truss to be what it is meant to be, the amount of sagging of primary mirror cell and the secondary-eyepiece assembly must be of the same amount.
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The idea of the design is that the two ends of the telescope are suspended from a center pivot, and thus the amount of sagging of the two sections can be made equal under the influence of gravity if the trusses are balanced. The heavier mirror sits in a shorter truss, but it also puts more load on the truss tubes and vice versa - so the sagging becomes equal and the Serrurier design does its job automatically as long as the central brace coincides with the point of balance.
Though, there may be more to it than that as I think the big observatories also use truss tubes of varying diameter, so it's probably a bit more than a simple balancing act - but for a 10 inch it should be close enough.
In comparison, a traditional truss tube dob is effectively only a half Serrurier. The disadvantage is that the triangles become very long with narrow angles (the key to truss strength is the triangle base-to-height ratio). Of course if the telescope is to be regularly dismantled and transported one would then have double the amount of truss tubes and connectors to deal with in the Serrurier design, but for a permanent setup I think the original Serrurier design is superior in every aspect.