Shahgazer,
I though I would add a few thoughts on the DS-4 scope.
The goals of DS-4 was to not compromise quality of a large scope, to have a scope that is easy to lift, to have a scope that has the smallest possible size, to have the lowest possible eyepiece height, and to have an easy to build design.
I went with a conventional design, instead of a Mel type Tridob for a few reasons.
* The Tridob looks like it is more complex to create. (Since I have not made one, I don't know this for a fact.)
* The Tridob, if it follows Mel's design where the mirror box can pass through the center of the ground ring, will probably have a larger footprint than a conventional design. Otherwise, it won't have as low of an eyepiece height.
* The Tridob will have more trouble with friction and dirt in the azimuth direction, when used on a dirt field.
* The Tridob will have a lower eyepiece height by about 4 cm than a well designed conventional scope. This was a design compromise.
* The Tridob will have smaller, lower, more compact bearings. I don't consider this an advantage, since bearings are so easy to remove.
As far as 6 vs 8 trusses, DS-3 (12" ultralight) uses 6 trusses. DS-4 (16" ultralight) uses 8. Both are totally rigid, and have no vibration or bending when in use. 8 trusses do have a few advantages. 8 trusses will hold a shroud out of the light path, 6 will not (assuming that the mirror box is small in design, and assuming you don't use other tricks). Another advantage is that 8 trusses fit in the corners of the mirror box well. 6 do not, thus requiring you to either increase the size of the mirror box, attach the trusses on the outside of the mirror box, or place one set of trusses on a cross brace between the bearings. Yuck.
Alan
http://www.xmission.com/~alanne/DS4Main.html