redHEX Hexapod Robot

Robot Anatomy & Kinematics

A hexapod is a six-legged robot where each leg is controlled independently. In the case of red.HEX, each leg has three degrees of freedom (DOF) controlled by three separate servo motors, allowing for complex, life-like movement.

• Coxa: The joint that connects the leg to the main body (abdomen).

• Femur: The "thigh" of the leg.

• Tibia: The "shin" of the leg, which makes contact with the ground.

With 3 joints per leg, the robot utilizes 18 high-torque servos for locomotion. The inverse kinematics—the complex calculations that translate desired movements into specific joint angles—are run on a connected Android phone using the open-source Chica software.

The Build Process: From Digital to Physical

The construction of red.HEX was a multi-stage process involving advanced manufacturing, intricate electronics, and meticulous assembly.

1. 3D Printing

The project required printing over 100 individual parts. Initial attempts using a high-end Prusa XL 5T printer resulted in continuous print failures. After re-evaluating, a revised set of part files was found that were optimized for reliability.

To meet the challenge, a small "legion" of three Bambu Lab printers (X1 Carbon, P1S, and A1 mini) were run simultaneously. After 48 hours of non-stop printing, all 100+ parts were successfully completed. Approximately 70% of the parts are multi-material, using black and red PLA filament to achieve the robot's signature look.

2. Electronics & Wiring

The heart of the robot is a Pimoroni servo2040 board, an 18-channel controller that interfaces with all the servos, sensors, and power systems. The core components include:

• Power: An 8.4V, 6200mAh Lithium Polymer battery.

• Control: A Pimoroni servo2040 microcontroller board.

• Switching: A 5V relay switch to safely control power to the high-torque servos.

• Servos: 18x high-torque, high-speed servos, each capable of exerting roughly 80 lbs of torque.

Each of the 18 servos had to be individually calibrated using a dedicated servo calibrator to ensure precise movement, with the values recorded for the control software.

(Suggested: Use the wiring diagram image and a photo of the messy workbench)

The wiring diagram, designed by MYP, uses smaller, modern components for a compact layout.

The final wiring harness during the testing phase.

3. Mechanical Assembly

Parts are assembled using M3 metric screws and a combination of hex and flat square nuts. The use of square nuts allows screws to anchor against a metal surface inside the 3D-printed parts, creating a much stronger overall build.

An early improvement was replacing the stock plastic servo horns with metal ones to prevent overshoot and increase the durability of the leg joints under the high torque of the servos.

Close-up view of the assembled leg, showcasing the multi-material print and servo placement.

The Modular Head Unit

The head unit is a major custom component that houses the electronics, provides a mount for the future t-MTU, and dictates the robot's overall aesthetic. The primary design challenge was accommodating the large Android phone required to run the control software.

The first revision served as a functional base for testing but is being iterated upon to improve the form factor and better integrate the phone into the body.

The first revision of the custom head unit, designed to house the electronics and the Android phone.