Yellow plate is controlled by three step motors via ball screw drives, blue sliders and green bars.
Oblique angles of axes of three revolution joints on the plate are the same.
The video shows the plate motion when the sliders move with the same displacement, first one after another and then at the same time.
The plate is kept always horizontal and moves without rotation. By combination of positions of the sliders the plate can reach any position in 3D space. However, the calculation is not simple.
See a real tripteron:
/watch?v=gPnnYZwSM38