GGLDNL Hexapod

Resolve the mechanical count before ordering

The hardware bill of materials lists 18 MG996/MG996R servos, 18 F686ZZ bearings, 92 M3 screws and 92 M3 inserts. Yet its notes call for 12 servo_mod housings while describing one per servo. That conflict remains unresolved: do not turn either count into a verified complete shopping list. The guide also requires top and bottom stiffeners to prevent frame flex. [S005]

The archive includes STEP parts and printable STL files. Filenames do not form a complete one-to-one mapping between those formats, and the hardware-shaped STL assets used by the simulation are not parts to print. No geometry, fit or assembly video was inspected. Without the optional PCB, the guide adds an electronics mounting plate, M2 inserts and screws, and servo cable extensions. [S005] [S007]

The maintainer's approximate €280 total is historical, with an additional €60–70 mentioned for the optional PCB. Those figures are not current checkout quotes and do not establish a delivered first-working budget, including printing, tools, charger and shipping. [S005]

Keep logic power and servo power distinct

The BOM specifies a 7.4 V 2S LiPo and two 8 A UBECs. Assembly instructions assign one regulator to the Pi/Servo2040 logic at 5 V and the other to the servo rail, mentioning 6 V subject to the actual servo datasheet. The battery mount is designed around the linked regulator shape; a replacement may require a mechanical change. The guide's alternatives are not verified drop-in substitutions. [S005]

The firmware documents UART1 on Servo2040 GP20 TX and GP21 RX, crossed to Raspberry Pi GPIO15 RX and GPIO14 TX, with shared ground. The default link is 921600 baud. The controller guide describes enabling the hardware UART and removing a conflicting serial console. These instructions were read, not applied to a board. [S008] [S011]

Calibration is not a motionless configuration step

The controller's calibration tool measures each bare servo at minus and plus 90 degrees, computes the midpoint pulse, and writes per-servo triples into the configuration. Structural joint trim, direction and range remain separate. Its “offline” label means separate from the normal robot controller: the raw jog implementation actually energizes the servo rail and drives a selected output even while the state machine is OFF. Calibrate with that behavior understood, rather than interpreting OFF as proof of unpowered servos. [S014] [S015]

The normal control loop runs on Servo2040: gait generation and inverse kinematics turn high-level commands into joint motion. The Pi provisions configuration and sends setpoints. The active-state watchdog implementation starts a sit-down sequence after the configured command timeout; this is more specific than an instantaneous power cut and has not been physically tested here. [S008] [S011] [S016]

Build dependencies and openness remain layered

The firmware guide uses CMake, an ARM toolchain, the Raspberry Pi Pico SDK and Pimoroni libraries to produce a UF2 image. The Python client needs its serial extra for a real board and its calibration extra for the configuration-writing tool. Ubuntu 24.04 is suggested for a possible later ROS 2 route, but that separate ROS integration and the simulation were not reviewed as working dependencies. [S008] [S011]

The mechanical repository supplies CERN-OHL-W-2.0 terms; the firmware and controller supply GPL version 3 license texts. Purchased boards, servos and third-party dependencies need their own treatment. The optional PCB is linked but not assessed here. This is source-based build research: no parts were printed, firmware compiled, board flashed, servo calibrated or walking performance measured. [S005] [S006] [S009] [S012]