It’s a fake!
@Whosa_whatsis This is my new front runner for a backpack printer. Hinge it, add some lid stays, and put a place to fasten the effector under the bed. What do you think? It wouldn’t be a great printer but it could be serviceable.
You could put a magnet where the effector would fall with the carriages all the way up and the tension on the line release. When you finish a print, just move to the top and off to the back of the build space and the effector will lock itself in place for transport.
BTW, at this point, I’m just coming up with more ideas to goad you into building it 
It reminds me of a metal-cutting CNC machine I saw a couple years ago on youtube (can’t find the link now). It offset the center column vertically from the other two, and the machining surface plane was parallel to the carriage plane, not at right angles to it. It made for a large XY area with limited Z, which doesn’t seem too bad for a lot of the 3D printed stuff I do.
@Charles_Steinkuehler I think I saw the same video but for the life of me can’t find it. I did find this. http://www.parallemic.org/WhosWho/Companies/Profile001.html
It isn’t the robot from the video but it is very similar.
@Whosa_whatsis My conceptual stab at this would be to take two towers of the square delta and then run a string from up top between the towers. (One bonus of this design could be the ease of switching the arms from angled down to angled up. I probably don’t have a hope of doing this accurately enough but if I could then you can use almost all of the vertical space with some weird cut outs in the build volumn for arm clearance.)
Speaking of the maths, how can a firmware determine the physical limits of the carriages? For example at home-position you have no horizontal freedom in the effector, but this gradually increases as Z moves down. I would also like to be able to limit the carriage positions so that at any Z height they can’t move beyond reasonable heights over Z. Thus, if you ask for an “illegal” position, the firmware can either forbid the move, or just put the effector at the nearest “legal” position. Essentially to prevent damage to a delta in the case where crazy coordinates are given to it.
Ha that’s actually really cool