An open platform for turning cheap servos into smart actuators.
OpenServoCore (OSC) is open hardware and firmware that drops a CH32V006 control board into a $2-3 cloned hobby servo (SG90 and friends) and turns it into a DXL-style smart actuator — position feedback, current sensing, bus-addressable, programmable.
The thesis is the price point: at mass-production volume, an OSC swap board should add no more than ~$1 to the BOM of a cloned servo. Cheap enough that "upgrade every servo in a robot to smart" stops being a premium decision and starts being a default.
In active development. Nothing here is shippable yet. The firmware is being rewritten, the dev board is validated and integrating with firmware, and the swap board is designed but not spun.
- OSC Dev CH32 (
osc-dev-v006) — Rev B validated. Firmware integration ongoing. - OSC SG90 CH32 (
sg90-prod-ch32v006) — designed, not spun. Waiting on firmware v2 to be testable against. - Firmware v1 (
firmware-old/) — legacy. First pass was vibe-coded and got poor Reddit feedback. Kept as historical reference; not a target for new work. - Firmware v2 (rewrite) — in progress.
- tinyboot (OSC bootloader) — v0.4.0 shipped. Lives at
OpenServoCore/tinyboot.
open-servo-core/
├── hardware/
│ ├── boards/
│ │ ├── osc-dev-v006/ # OSC Dev CH32 — has its own README with pinouts, jumpers, bringup notes
│ │ ├── sg90-prod-ch32v006/ # OSC SG90 CH32 swap board (designed, not spun)
│ │ ├── servo-dev-board-stm32f301/# Retired hobby-phase STM32 dev board (legacy)
│ │ ├── encoder-board/ # Optional quadrature encoder breakout for J8 experiments
│ │ └── motor-mount/ # 3D-printable test fixtures
│ ├── shared.kicad_sym / shared.pretty / shared.3dshapes # Shared KiCad libraries
│ └── templates/ # KiCad project templates
├── firmware/ # Firmware v2 lives here once the rewrite starts
└── firmware-old/ # Legacy firmware (do not use)
The OSC bootloader, tinyboot, is a separate repo. It's part of the OSC firmware stack but versioned and released independently — its chip-support matrix (V003 / V00x / V103) is broader than the OSC boards on purpose.
OSC boards follow OSC <Form> <ChipFamily>:
- OSC Dev CH32 — dev board, exposes every rail and signal for firmware bringup. Directory:
osc-dev-v006. - OSC SG90 CH32 — swap board that physically replaces the SG90 factory PCB. Directory:
sg90-prod-ch32v006.
Engineering SKUs (osc-<form>-<chip>-rev-<letter>) appear in BOMs and schematic title blocks; the names above are what you'll see in posts and docs.
OSC standardizes on the CH32V006 — 48 MHz RISC-V, 62 KB flash, 8 KB RAM. Chosen because it's the chip that makes the ≤$1 BOM uplift work. No multi-chip roadmap; one chip, done well.
Each board has its own README with full schematics, pinouts, jumper behaviour, and bringup notes:
- OSC Dev CH32 — accepts any gutted hobby servo, USB-C / 1S-2S LiPo / WCH-LinkE power, full edge test-point fanout. Rev B validated.
- OSC SG90 CH32 — compact swap board, 10×12.5 mm, double-sided. Designed; not yet spun.
The Rust firmware is mid-rewrite. The legacy firmware-old/ tree contains the original architecture (multi-crate workspace targeting STM32F301 and partly CH32V003) and is kept for reference, but the v2 rewrite starts from a cleaner architecture targeting CH32V006 first. Plan: DXL-compatible register table, persistence, control loops, safety features.
Build instructions will appear here as the rewrite matures.
This is early — the most useful thing right now is following along and asking questions, not opening PRs.
- Discussions: github.com/OpenServoCore/open-servo-core/discussions — design questions, ideas, "is this on the roadmap?" go here.
- Build journey: posts at aaronqian.com document the design decisions, dead ends, and what shipped each week.
- Issues: open ones on this repo are scoped to specific work (README, LICENSE, board revisions). Pre-firmware-v2, contributor scope is small.
Dev boards are fabricated and assembled by PCBWay — sponsor since Feb 2026.
Five PCBA boards delivered. Build and assembly quality clean across all five — no fabrication issues. Bring-up turned up design issues on my side (VDD/VSS swap, silkscreen errors), but those traced back to my own schematic, not the manufacturing. The process itself was painless. A late BOM swap (RS1 shunt 100 mΩ → 10 mΩ) was accepted without fuss; the pre-fab assembly review caught a pad-clearance concern before manufacturing.
Full spin + bring-up writeup: CH32V006 dev board first spin.
Five PCBA boards delivered, May 2026. Validated. PCBWay's pre-fab manufacturability review flagged nothing, and build/assembly quality was again clean. A small bug found in the sponsored boards (shared nRST / OPN2 pin) didn't warrant another validation round — patched in-rev with a solder bridge. The published files include the patch.
Reference design available as a PCBWay community project for one-click ordering.
OSC is fully open. No dual licensing, no commercial gates.
- Firmware — MIT OR Apache-2.0, at your option (Rust ecosystem convention).
- Hardware (schematics, layouts, board files) — CERN-OHL-P v2.0.