Tabletop Kinetic Sand Rebuild
I spent three days or so recreating the original sand robot from scratch. I have access to a much larger 3D printer now, so I'm able to fully print everything in one piece, except the acrylic that the sand rests on.
Originally, the robot used a 2-DoF SCARA arm to maneuver the ball around, however I didn't like how much vertical space was used up by this mechanism.
The robot uses a central gear with 238 teeth to drive the rotation angle. It's driven with a stepper motor off to the side with a 500mm timing belt. They're spaced appropriately to keep adequate tension.
The linear axis rotates off of the central gear and is a basic rack and pinion type drive. The stepper motor in the center goes all the way through the central gear and has the pinion gear attached to the top.
I was honestly really surprised at how well it was turning out so far!
While I was waiting for the main housing to finish printing, the remaining components came in the mail.
Since the robot has no "stop points," I couldn't use typical endstop sensors. I decided to use magnetic sensors mounted on the base, with magnets embedded in the printed pieces to determine the home position.
There's also a SD card to store pattern files, a pair of TMC2209s to drive the steppers, and a TSL2561 breakout board to sense ambient light.
And of course, I'm using my favorite microcontroller to power this thing, the humble dual-core ESP32!
I ordered a large kit of different JST connectors so I would be able to easily connect everything up to the circuit board, which was also currently on the way from JLCPCB. It's a pretty bare-bones design, and I just used one of the spare boards that I had left from the Coffee Table project.
Even though I've used the same Trinamic drivers in other projects before, I ended up frying SIX of them simply because I forgot to plug in the motors... They're all shown on the top side of the robot here :p
I was lucky enough to have most of the firmware written already from the coffee table project, however I had to design and implement a new abstraction layer for this robot's new mechanism design.
I'll skip the boring parts, but essentially, I needed to convert the Cartesian coordinates sent by the higher level classes into polar coordiates, and then use a series of conversions to find the amount of steps needed to move the gear. For the rho (linear) axis, it was a bit weirder. The movement of the rotary axis actually affected the position of the rho arm, so I had to compensate for this in my calculations, and compensate for it again when the robot recalculates it's Cartesian position based on the current step counters around 20-30 times a second.
The motion abstraction code is in the RobotSandTableRotary.cpp file in the repository.