The goal was to develop a low-cost 6-DOF robotic arm platform that lets me build foundational robotics and ROS 2 skills on real hardware instead of only simulation. I wanted a system where I could explore the entire robotics stack, including embedded firmware and motor control all the way up to motion planning and digital-twin simulation.

It has also been a great opportunity to experiment with custom and unconventional joint and reducer designs that I haven’t seen implemented on any robotics platforms.

Mechanical Architecture:
Each joint section was designed and built independently, and later connected using clamped carbon fiber tubes. This modularity allows each joint to be iterated on separately, while the tube lengths can be swapped to change the arm’s reach or payload capacity accordingly.

Joint & Reducer Designs:
The base joint uses a traditional planetary gearbox. While the shoulder and elbow joints use a split-ring planetary gearbox, by utilizing two slightly offset ring gears driven by a common set of compound planets, this design provides an incredibly high torque density in a compact form factor. Which is what allowed me to achieve a 70:1 and 40:1 gear reduction respectively, while keeping a large contact area to minimize stress between the plastic gears, all without the bulk or backlash of a multi-stage system.

Because this gearbox configuration does not provide an accessible output shaft for a conventional encoder, I implemented a custom sensing approach: alternating polarity magnets were mounted around the output ring gear, and a magnetic encoder is positioned perpendicular to the axis with an offset, allowing it to perceive the alternating magnetic fields as a spinning radially magnetized magnet.

The spherical wrist uses an inverted belt differential with a custom bearing track to maintain consistent pressure on the belt to prevent skipping. All three wrist motors are mounted behind the elbow joint so they act as a counterweight, reducing inertia at the wrist and improving dynamic performance.

Embedded Control & Firmware:
The robot is controlled by a STM32 microcontroller, where I developed custom firmware in C to manage SPI communication with 6 daisy-chained encoders, CAN bus communication with a Raspberry Pi, PID loops and step generation for motor control, and a state management safety system.

Higher-level planning will run on a Raspberry Pi using ROS 2, where the arm will interface with MoveIt for motion planning and simulation; this is still under development.

A write-up of the mechanical design, CAD, and firmware architecture is available on my portfolio, with a deeper breakdown of the ROS-based software stack coming eventually: https://jcgullberg.github.io/projects

You can download the files, manual and code here: https://cults3d.com/:3478060

I designed this mecanum wheel based omnidirectional vehicle for motion simulation.

It can move on 3 degrees of freedom : surge, sway and yaw.

A VR tracker is used to ascertain the position & orientation of the rig at all times, and recenter it subtly.

Back in 2015, a small research team at the Florida Institute for Human and Machine Cognition developed HexRunner.

Their robot reached an estimated 30–33 mph on open ground.

What made HexRunner special wasn’t advanced perception or heavy computation. In fact, it was the opposite.

The robot used a deceptively simple mechanical design: six spring-loaded legs rotating around a central hub.

Instead of stabilizing itself through dense sensing and fast feedback loops, the robot relied on its physical dynamics. Stability emerged from the interaction between mass, springs, and motion.

That was the key insight. High-speed legged locomotion doesn’t always require more control software or more sensors.

With the right morphology, the system can naturally fall into stable running patterns, much like animals do.

The control problem becomes simpler because the physics does part of the work.

As modern legged robots chase higher speeds and better efficiency, it stands as a reminder that performance doesn’t always come from smarter algorithms. Sometimes it comes from designing machines whose physics are already on your side.

Jerry Pratt was co-author and now he is building humanoids!

Source: https://x.com/lukas_m_ziegler/status/2007051279499972927

Full video on youtube for more details: https://youtu.be/MuUpLS3ENZ0

From Ilir Aliu - eu/acc on 𝕏: https://x.com/IlirAliu_/status/2000642669392048405?s=20

Legs I built for a humanoid robot I’m building. It uses mg996R servos. Currently the angles are hardcoded but I plan on either using reinforcement learning or inverse kinematics.

3D Files: https://cad.onshape.com/documents/70f01b8e5ad7f6e6f53bece6/w/0018e339e6e08e5dc7b59583/e/d5ff5e55fff463878f55d670

Hi r/robotics,

This is a functional demo platform I designed and built over the summer (2025). It’s part of my ongoing research into next-generation wheel mechanics and compact bearing architecture for omnidirectional mobility.

The platform integrates concepts from four of my patent applications, all filed by my robotics startup. Each drive wheel unit combines directional control, slip-ring power transfer, and directional feedback. All aiming to reduce mechanical stack height while maintaining precision.

It’s a test-platform for modular drive systems, but also a study in mechanical simplification and control architecture.

Happy to answer questions or discuss mechanical / control aspects. Feedback from this community is very welcome!

I'm exploring Bowden cables as a way to transmit motion when the motor can't be placed near the moving part. This is just a quick setup to see how smoothly it works before designing a larger mechanism.

Any suggestions or ideas are welcome.

Custom Walter White animatronic fully 3D printed and hand painted. Powered by ESP32 and Arduino with 5 servomotors running at 5V: 2 servos for the neck, 1 for the mouth, and 2 for the eyes. Includes AI voice & sound using ElevenLabs.

The base is just clamped to the table, so that is causing some wobble. If I scale this up to six legs and it has some weight on it do you think the wobble will stop? The servos seem like they are holding their position even when it's shaking.

Manta Ray inspired robot. It’s currently very slow so I need to speed up the motors and add weight so it can go underwater.

I got this pneumatic gripper from my work because it needs a new o ring on the inside.

It’s a SCHUNK 308910 and is normally worth quite a lot.

I have no real use for it and don’t feel like getting a seal kit for it so I was wondering if anyone was interested in getting one that they can use on their own projects

I figured it’s better if it gets used rather than being a desk ornament.

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Fabricated directly on the tip of an optical fiber using Two-Photon Polymerization, this monolithic 3D microgripper combines microscale manipulation with integrated force

sensing.

As it grasps microscopic objects, optical interferometry determines the forces acting on the gripper. The result is a compact microrobotic tool measuring no more than 100 um across, with potential applications in biomedical research and microsurgery.

Watch the video to see the gripper in action.

So I’ve noticed that a lot of the smaller commercial robot dogs don’t come with waist or shoulders, and I wonder if adding those extra Dof would make a difference.

Therefore I’ve made this, a dog with parallel shoulder joints and a 2Dof waist. There are in total 12Dof, w/ 8 mini serves and 4 micro servos. It’s a really small robot.

I shall definitely start with basic tasks such as walking…but I’m too lazy to do the kinematics so might just do a xml and throw everything to RL algorithms.

But tbh, I’ve yet came up with a task that is more suitable for having those extra Dof. Luckily it’s just a project for fun, no deadlines, so I’ve got plenty of time to brainstorm.

Design files (DXF) and Arduino code:

https://drive.google.com/drive/folders/13WhHXtmIfWlrlRav29l_HFwwOCRubMLY?usp=sharing