With the delay in the video between moving the arm and the press moving, I’m pretty sure the one being shown off is pneumatic. [Ruchir Chauhan] calls it Hydraulic, but on the build page says it ...

Valley Middle School eighth-grader Jarett Huard manipulated water-filled syringes attached to hoses that served as a hydraulic system for a mechanical arm he built out of wood, cardboard, plastic a… ...