Six-legged walkers have always seemed like a compromise to me: more servos, more cost, more assembly pain. PrintedRobotics clearly felt the same, and the answer here was to strip two legs off a hexapod and rebuild it as a proper four-legged dog. The result is lighter, quicker and more nimble in several ways, and it costs considerably less to build since fewer parts are involved.
The hardware is tidy. A single ESP32 S3 runs everything, paired with a PCA9685 servo driver, an MPU6050 IMU and a voltage sensor board. Twelve DS3218 high-torque servos do the moving, down from eighteen, fed by two 15A adjustable buck converters, one per pair of legs, plus a dedicated 5V 3A converter that keeps the microcontroller isolated. Power distribution is solderless and PCB-free, with a Wago connector tying it together. The central chassis had to be shortened for the four-leg layout, and about a hundred M3x8 screws plus twelve ball bearings hold it all together.
Two details stand out to me. First, the 3D-printed servo horn mounts and hip rails act as sacrificial breakaway points, protecting the internal gears and the main body when the robot takes a fall. Second, the 2-inch TFT screen shows animated eyes and menus, which gives it real character.
It walks on a diagonal trot gait and a four-phase walking gait, with body height and pitch adjustments and an idle breathing animation. Puppet mode uses a phone's gyroscope to steer the torso in real time. The gait still looks mechanical though, and reinforcement training is planned to replace the inverse kinematics solver with something more fluid. At around 200 USD and fully open source, that next step is one worth watching.
Project by PrintedRobotics. Watch it on their YouTube channel: