Aha!! Yes, a bit of explanation might make things clearer for you. Think of an effector to be something like a glue gun: you put some solid stuff in one end, melt it and squeeze the glue out a hole in the tip. An equivalent can be the cartridges used by builders to apply silicone sealants, but they don't use heat. The reason for calling it an effector is that it is exactly the same as the cutting bit on a CNC machine or a tip on a plasma cutter.
The most common way of moving the effector about in 3D space in a 3D printer is to fix the orientation of the effector to be vertical and use motors acting parallel to each of the cartesian axes to position the tip just where it is needed. This leads to building up the 3D object in layers, with each layer being a series of (non-zero-width) lines, just so the effector does not run into prior build material.
Another way of moving the effector around is to have a plate supported from three 'points' using extensible rods, with each support being two rods acting as a parallelogram for stability and to control the orientation of the effector. This style is called a 'delta' printer.
Anyway, my idea came from seeing a design for a drawing machine with strings supporting a pen horizontally so it drew on a (nearly) vertical surface. In this design the motors were in the top corners of the board. Well, if 2 motors gives a 2D picture, then 3 motors gives a 3D picture. At this point, it became obvious to me that the size of the printer could be anything from a desktop to a football stadium. And, cameras flown about stadia on wires (just thick strings really!!) are common. Gee, it cannot be too hard can it?
Several years later, I can say that I have had a continuous education from this project. Yes, my prototype worked - at about a cubic metre, though the reproducibility was questionable. It is when I went to room-sized that the wiring became a real problem - and that has taken the bulk of my focus for the last couple of years. Now, I am back to the stability of the effector - because it just swings about in 3D space.
Effectively, the point of intersection of the extension of the 3 strings is well-defined, but depending on just gravity to constrain the orientation of the effector to be vertical is, well, idealistic. Making the centre of gravity of the effector further below the effective support point does increase the moments to keep the effector vertical - but only when it is not moving. Add in the inertial effect of actually moving the effector around just makes for a disastrous 3D print, further complicated by the surface tension of whatever is being extruded dragging on the tip. Mmm...time to do something to better understand the effects and what can be done to mitigate the 'wobbles'.
So, I decided that having two strings from each support might be the way to go. My intuition said to have the attachment points vertically positioned, in contrast to the layout used for delta printers (horizontal). But others have suggested otherwise. And what should the relationship be between attachment points and centre of gravity? And...
So begins my learning about simulation and a myriad of new terms - like FEA. Somehow, I found a link to simscale.com (maybe from another project on hackaday.io, but I cannot remember). I register, and then discover that I need to create a model offline. Well, I've used OpenSCAD to create STL files to 3D print, so how hard can it be to find something to produce STEP files? Constraints = for free, and I use Linux. So, I have a go a FreeCAD, but it took me a while to discover the button to make something that looks solid to actually be solid. In my defence, note that OpenSCAD is a solid modeller so coming to terms with a surface modeller has been another learning experience (and obviously, still underway).
Whew. I hope this background assists with your understanding of this problem space. Many thanks for all assistance. Even Vincent gave me some hints via chat last night - thank you.
Here's a couple of annotated diagrams to assist understanding: