DIY Humanoid Robot Astrix: A 3D-Printed, Raspberry Pi-Powered Project with 23 Degrees of Freedom

One Person's Robot Dream

At a time when humanoid robots have become a focal point for tech giants — with Boston Dynamics, Tesla Optimus, Figure, and others pouring hundreds of millions into bipedal robot development — one maker on Reddit has independently built a DIY humanoid robot called "Astrix" using nothing more than a 3D printer and a Raspberry Pi.

In his latest update, the developer shared that he has just completed most of the wiring on the robot's legs, with only the power cables left to connect. Once finished, the entire physical body will be complete. What started as a personal 3D printing experiment is now closing in on a critical milestone: getting the robot to walk.

Breaking Down Astrix's Core Specs

Based on the technical details the developer has shared, Astrix already has the makings of a functional humanoid robot. Here's a look at its core specifications:

Physical Parameters

• Weight: Approximately 15 kg
• Height: 1.65 m (close to the average adult height)
• Body: Fully custom-designed and manufactured using 3D printing

At 1.65 m tall with a self-weight of just 15 kg, the robot's structural design is highly weight-optimized. This is partly a natural consequence of using 3D-printed materials (typically plastics like PLA or PETG), and it also reduces the actuation load needed to achieve walking.

Motion System and Degrees of Freedom

• Degrees of Freedom (DOF): 23 active DOF, with 7 others eliminated from the design
• Actuation: Fingers and neck use servos; all other joints use linear actuators

23 degrees of freedom is quite impressive for an amateur project. For context, the human body has over 200 DOF, while commercial humanoid robots typically range between 20 and 40. The developer's choice to use different actuation methods for different body parts — servos for the dexterous fingers and neck, and linear actuators for load-bearing major joints — reflects a pragmatic engineering trade-off.

A linear actuator is a device that converts the rotational motion of a motor into linear back-and-forth motion. Common forms include electric push rods and ball-screw drives. Compared to rotary servos, linear actuators have a natural advantage when outputting large push or pull forces, making them well-suited for weight-bearing joints like the hips and knees. However, they are generally slower and have limited travel, making them unsuitable for joints requiring fast, wide-range rotation — such as fingers or the neck. For lightweight DIY projects like Astrix, linear actuators offer another practical benefit: they're more affordable than high-torque servo motors and require no additional gear reduction assemblies, resulting in a cleaner, more integrated structure.

Sensing and Computing Platform

• Computing core: Raspberry Pi 4
• Sensors: Camera and speaker already installed; microphone to be added later

Using a Raspberry Pi 4 as the robot's "brain" is a quintessential choice for DIY robotics projects. While its computing power falls far short of the specialized platforms used in commercial robots, it's sufficient for basic motion control, visual recognition, and voice interaction.

From 3D Printer to Humanoid Robot

What makes this project most compelling is where it began. The developer freely admits that Astrix was started shortly after he bought his first-ever 3D printer — initially just "a fun idea to see if it was possible."

This perfectly reflects the maturity of today's maker culture and open-source hardware ecosystem. A decade ago, building a humanoid robot was a domain accessible only to university labs or tech companies. Today, with affordable 3D printers, open-source platforms like Raspberry Pi, and standardized servos and actuators, individual makers can build functional humanoid robots at home. The continuously falling hardware barrier is transforming robot development from "out of reach" to "within grasp."

Bipedal Walking: Astrix's True Challenge

Completing the physical body is only the first step. The developer has made clear that the next goal is "to try to get it walking" — and this is precisely the most central and most difficult problem in humanoid robotics.

Bipedal walking involves complex dynamic balance control. The robot must sense its center of gravity in real time, adjust joint angles, and respond to ground reaction forces — any delay or error in any of these steps can cause a fall. Even well-funded commercial teams have invested enormous effort into gait algorithms and balance control. For Astrix, which relies on a Raspberry Pi 4 for computation and 3D-printed structural components, achieving stable walking is a formidable challenge.

Structural rigidity, actuator response speed, sensor feedback accuracy, and control algorithms — all of these will be decisive factors in whether Astrix can take its first step.

The core challenge of bipedal walking lies in dynamic stability control. Static stability — where the robot's center of gravity projects within its support polygon while stationary — is relatively easy to achieve. But during walking, the robot passes through an unstable "single-leg support" phase with every step, requiring continuous prediction and correction of the center-of-gravity trajectory. Common engineering approaches include: Zero Moment Point (ZMP)-based gait planning, Model Predictive Control (MPC), and reinforcement learning-based gait strategies that have gained traction in recent years. Commercial teams like Boston Dynamics spent decades achieving biomimetically fluid locomotion, backed by high-precision IMUs (inertial measurement units), torque sensors, and high-performance computing hardware. The Raspberry Pi 4's computing power is roughly 1% that of a commercial robot controller — figuring out how to achieve even the most basic stable gait under this constraint will be Astrix's most technically demanding milestone.

The Broader Value of DIY Robotics Projects

Astrix may not be able to compete with Optimus, but its significance goes far beyond the technology itself. It demonstrates that, with open-source hardware and 3D printing technology, individual developers can enter the cutting-edge field of humanoid robotics.

Projects like this are often the best testament to the democratization of technology — they lower the barrier to innovation, spark broader interest in robotics, and may inadvertently give rise to unexpected solutions. We look forward to seeing Astrix take its first steps, and to seeing more individual makers, in their garages and home offices, push robotics technology toward the mainstream.