The toughest part of this build had to be the arms themselves. Early versions of the linkage design ran into joint limits and self-collisions in simulation, so extra degrees of freedom had to be worked in before anything could move properly. Getting past that hurdle is what makes the finished machine so satisfying to watch: a hexapod on a Stewart platform, balancing and juggling a table tennis ball on a paddle, with the ball kept bouncing continuously through control of its position.
The construction is where the craft shows. Every part was modeled in Fusion 360 across three project files covering the six arms, the base, and the central triangular end-effector, then cut from 3 mm 6061 aluminum on a desktop CNC mill driven by Universal G-code Sender. Each multi-joint arm goes together with bolts, nuts, and ten bearings, which sounds like a fiddly assembly repeated six times over.
The motion side is handled by six NEMA 23 steppers through 10:1 planetary gearboxes on StepperOnline CL57T drivers, all fed from a 36V 14A supply, with a Teensy 4.0 running the show. The stepper movements come across as smooth. For sensing, two See3CAM_24CUG cameras track the ball, and the machine computes its 3D position from that image data at 120 FPS, while the tracking views themselves report frame rates above 400 FPS. A Windows machine with a GPU runs a Unity application that mirrors everything on a connected screen as a real-time 3D simulation alongside the stereoscopic tracking views.
What stands out most is the math made visible: handwritten derivations in a notebook flow straight into C# scripting, and a 3D animation explains how motor angles come from intersecting circular and spherical paths of the linkage joints. The open question for me is endurance. The machine juggles steadily on camera, but nothing stated tells us how long a run lasts before the ball drifts off the paddle, and that seems like the next thing worth measuring.
Project by Electron Dust. Watch it on their YouTube channel: