[coldlegs (Stephen)]

Recently my “pseudo” serrurier truss underwent a major re-build that included adding heim joints and turning it into a “true” serrurier truss. Then I started to discover things about it that I'm not sure I like at all. You see I normally park any scope pointing west so it fits under the closed roof of the observatory and the camera is nearest the door and easy to collimate/work on etc. So the collimation was done facing west but when I rotated the scope east it lost collimation as the cats-eye triangles were quite spread out. Think I finally worked out why. When the scope rotated the camera changed position relative to the center of mass of the front cage and the front half of the truss moved in a slightly different direction to the back half hence loss of collimation. This means that there has to be a weight equal to the camera train and focuser assembly somewhere on the opposite side of the front cage. That would be about 2.7kg. Here's where things start to get ugly. If I add the weight my balance is up the creek and the strut lengths have to be re-done or I add about 3kg to the rear making the scope around 5.7kg heavier. With the scope weight currently at 15.5kg with the new welded center and all the mods plus 2kg camera/onag etc giving 17.5kg then I'll be up to 23.2kg on a neq6pro mount. Not good for the old girl! The other choice is to re-do the struts and save 3kg which is more practical. The other big ugly is when I ditch the camera /onag and install a webcam for planetary imaging. I will need to have a weight on the camera side to make up for the weight disparity and it will need to be where the center of mass of the camera/onag setup was to work right.
At this point I'm thinking a “true” serrurier truss is a “pain in the mass”. Rolf and quite a few others do excellent imaging with “pseudo” serrurier trusses that have the struts permanently fixed and that's the way I'm heading back to as well.


Cheers
Stephen