Personal project · In progress · Started approximately September 2026
5-DOF desktop robotic arm
Developing a 5-DOF arm with a planetary shoulder transmission, a cycloidal elbow transmission, and stepper motor control.
- My work
- Joint design, additive manufacturing, and motor control
- Result
- 15.16:1 shoulder transmission design
- Status
- Shoulder testing; elbow and controls in development
From gearbox to robotic joint
What began as a compact planetary gearbox has grown into a project to build a five-degree-of-freedom robotic arm. I’m developing the mechanical joints, stepper-driven transmissions, and a custom control board as one integrated system.
- 5 DOF
- Target arm architecture
- 15.16:1
- Shoulder design reduction
- Cycloidal
- Elbow transmission in development
Shoulder actuator (Joint 1): building and testing
I’m currently building and testing the shoulder actuator (Joint 1). It uses two fixed-ring planetary stages in one PETG housing. A 4.737:1 first stage and 3.2:1 second stage produce the 15.16:1 overall reduction. The arm link bolts directly to the output flange, while an 80 × 100 mm thin-section bearing carries the link’s bending load.
Elbow actuator (Joint 2): cycloidal transmission
I’m building a cycloidal gearbox for elbow actuation at Joint 2. This extends the arm’s drivetrain development beyond the two-stage planetary transmission used at the shoulder.
Controls in development
I’m designing my first custom PCB in KiCad around an ESP32 and four stepper drivers. The controls work builds on an Arduino and A4988 breadboard prototype used to test the NEMA 17 motor and motion profiles.
Develop and assemble the Joint 2 cycloidal transmission for integration into the elbow joint.
Engineering takeaways
Support the structural load independently of reduction
The link bolts to the output flange, while an 80 × 100 mm thin-section bearing supports its bending load. The 15.16:1 planetary transmission addresses speed reduction; the bearing and housing address structural support.
Resolve manufacturing and assembly interfaces together
The two planetary stages share a PETG housing. Bearing fits, shaft alignment, axial retention, and running clearances need to work together so that assembly constraints do not introduce unwanted friction.
Validate the joint before the full arm
The shoulder transmission is being built and tested while the cycloidal elbow transmission and custom control board remain in development. Joint-level testing comes before claims about the complete arm’s payload or positioning performance.