Building a Budget BD-X Droid, Part 1: The Plan

The BD-X is the small, two-legged droid that Disney revealed in October 2023 at Galaxy’s Edge, and that Jon Favreau said will appear in The Mandalorian and Grogu. You can’t buy one. But there’s an open-source project that rebuilds the idea at 42 cm, for a fraction of the cost. I’m going to build it, and you can follow along, one small step at a time.

No robotics background? No problem. You don’t need to know what a servo or a microcontroller is yet. I’ll explain every new word the first time it shows up, tell you what each step does and why, and show you how to check that it worked.

Who Is This Series For?

• Beginners. If you can follow a recipe, you can follow this series.
• Younger builders. Go for it, but do the soldering and the battery steps together with an adult.
• People who want to see the real thing. I’ll show the mistakes, the real costs and the parts that didn’t work the first time.

How Every Part Works

Every part follows the same pattern, so you always know where you are:

1. What you’ll do in this part, and what you need.
2. Safety first, before any step that needs it.
3. Numbered steps. For each one: what to do, what’s happening, and why.
4. A check after each step: “Good result” and “Bad result”, so you know if you can move on.
5. If it didn’t work: the common problems and how to fix them.
6. Words explained at the end of each part.

What Is the Real BD-X?

Disney Research and Walt Disney Imagineering built the BD-X as a character, not as an industrial machine. According to their paper, it stands 66 cm tall, weighs 15.4 kg and has 14 powered joints in the legs, neck and head.

Its walking is learned with reinforcement learning in simulation: a computer practices walking millions of times in a virtual world before the real robot ever takes a step. A human puppeteer steers the character live. Disney’s own words: start with the character, and let the technology serve the story.

What Is Open Duck Mini?

Open Duck Mini is an open-source project by Antoine Pirrone and the community, released under the Apache-2.0 license. The robot is about 42 cm tall, uses 14 Feetech STS3215 servos and runs on a Raspberry Pi Zero 2W.

It’s not a Disney product and not an official copy. It’s a fan project that rebuilds the idea.

What Will It Cost?

The official v2 bill of materials comes to €398.10. I’m adding two spare servos, so one broken motor doesn’t stop the project.

A 3D printer, a soldering iron and an Xbox controller aren’t included. These prices come from the project and may be out of date, so I check them when I order.

What I Want to Achieve

1. A robot that stands and walks with the ready-made walking program.
2. Then some character: antennas, LED eyes, sound, and a few animation layers like Disney uses.
3. If that works: train my own walking program.

What I don’t expect is the dynamics of the original. The servos are far weaker than Disney’s actuators (about 1.9 N·m against 24 to 34 N·m, although Disney’s robot is also bigger), so recovering from a push or making fast moves is out of reach with these servos. Stronger motors exist, but they would make this a different, much heavier and far more expensive robot.

What I Don’t Know Yet

• Whether the Raspberry Pi Zero 2W has enough headroom for eyes, antennas and animation on top of walking. I’ll measure that in Part 7.
• How long the servos last before they overheat.
• How complete the build guide really is. The assembly guide calls itself incomplete.

The Plan in Nine Parts

Each part is published when the step is finished. That means you’ll see my mistakes too, and the plan may change along the way.

Words Explained

• Servo: a small motor that turns to an exact position and holds it. The robot has 14 of them, one for each joint.
• Raspberry Pi: a tiny, cheap computer. This one is the robot’s brain.
• Reinforcement learning: a way of teaching a computer by trial and error: it tries, gets a score and slowly gets better.
• Policy: the “walking program” that comes out of the training. It looks at what the robot senses and decides how every joint should move.
• Open source: the designs and code are public, so anyone can build, study and improve them.

Conclusion: A Small Droid with a Big Idea

A Disney-style droid doesn’t have to cost a fortune, as long as I’m honest about what it can and can’t do. Next up: ordering the parts and printing a test piece before I print all 36 files.

Small droid, big plans. Happy hacking!

Unofficial fan project

BD-X and Star Wars are trademarks of Disney/Lucasfilm. This site is not affiliated with, endorsed by or sponsored by Disney. The robot in this series is based on Open Duck Mini by Antoine Pirrone and contributors, released under the Apache-2.0 license.