Open Tennis Robots is an open design for a ball machine and a robot that collects balls. Its CAD is code (build123d), so every number a fabricator needs comes from a parameter file, and the build refuses to finish if a check fails.
This week we added the part that moves balls from a storage tub to the launcher wheels. Writing the checks first showed three things a sketch would have hidden:
- Gravity cannot do the feeding. The launcher head tilts up to 45 degrees nose-up, so the last stretch to the wheels is uphill. The design became a printed shuttle with a ball-sized pocket that a linear actuator pushes to the wheels. Its solid back shuts the ball column while it moves, so one ball leaves per stroke.
- The hose moves a lot. The hose joins the head 430 mm above its pivot, so tilting the head swings that end about 450 mm. A 600 mm hose copes, with a bend radius of 171 mm against the 150 mm the hose tolerates. A shorter hose would kink.
- The open front is not a gate. At negative elevation a ball can roll forward on its own. A front retainer is next.
The package (laser DXFs, printable STLs, STEP, cut list and bill of materials) is in the repository under ventures/open-tennis-robots/manufacturing/feeder. Nothing has been built yet, the hose and ball-rolling numbers are assumptions, and the machine throws balls at over 30 m/s: read hardware/safety.md before powering anything you build from it.