# Open source robotic arms for AI and teleoperation (2025-2026)

State of the art focused on data collection, imitation learning and leader-follower teleoperation.

## 1. The layer that unifies everything: LeRobot (Hugging Face)

LeRobot is the reference framework of the ecosystem (Apache-2.0 licence, PyTorch). It is not an arm; it is the common software layer: models, datasets, hardware drivers and training/evaluation tools. It natively supports a broad catalogue:

- Low-cost arms: SO-100 / SO-101 (single and bimanual), Koch v1.1
- Bimanual / humanoid: ALOHA-2, Hope-JR, Reachy-2
- Mobile manipulators: Stretch-3, LeKiwi
- Recent releases (v0.5.x) add Unitree G1 and OpenArm

The central mechanism shared by almost all of them: leader-follower teleoperation. LeRobot reads the joint positions of the leader arm and writes them onto the follower. That same loop is used to (1) record expert demonstrations for imitation learning (e.g. the ACT policy) with `lerobot-record`, and (2) run a learned policy directly on the follower. Live CLIs: `lerobot-teleoperate`, `lerobot-record`.

Practical implication: the choice of arm is secondary. If you are going to do AI/teleoperation, what matters is that the arm is integrated in LeRobot. Everything else (driver, dataset, training) is already solved.

## 2. Project comparison

Confidence legend: [V] verified by the research workflow (primary source + corroboration); [S] confirmed in a later targeted search; [G] domain knowledge / order of magnitude.

### Entry / low-cost tier (recommended to start)

**SO-101 / SO-ARM101** (successor of the deprecated SO-100)
- Servos: 6x Feetech STS3215 per arm (serial TTL bus). 5 DOF arm + 1 gripper. [S]
- Cost: ~110-130 USD/arm (follower); leader+follower set ~230 USD; bimanual ~550 EUR. [V cost band, S unit price]
- Software: LeRobot + Feetech SDK. Native integration, the de facto "star" arm of the ecosystem. [V]
- 3D printed structure; kits with/without printed parts. [V]
- Where: Seeed Studio, Hiwonder, ThinkRobotics, Waveshare, Amazon, AliExpress (loose servos). Design at `TheRobotStudio/SO-ARM100`. [S]
- Verdict: best price/community ratio to get into LeRobot today.

**Koch v1.1**
- Servos: Dynamixel (XL430 + XL330), not Feetech. More expensive but better control/quality. [S]
- Cost: original designer's DIY ~430 USD (leader+follower); commercial ROBOTIS kit ~670 EUR/arm, ~1346 EUR bimanual. [V]
- Software: integrated in LeRobot. [V]
- Where: official ROBOTIS kit; design at `jess-moss/koch-v1-1`. [S]
- Verdict: mid-low Dynamixel alternative. Better actuation hardware than the SO-101 at the cost of more money. If budget rules, SO-101; if you want premium servos, Koch.

**Bambot (timqian)** and mobile derivatives
- Essentially 2x SO-100 + LeKiwi base + a bamboo structure for height: an ultra-low-cost mobile bimanual, ~300 USD. [S]
- Built for experimentation and education on the same LeRobot stack. [S]
- Related: XLeRobot (dual-arm home robot for ~660 USD). [S]
- Verdict: the cheapest route to a mobile bimanual setup, assuming limited maturity and robustness.

### DIY middle tier (more DOF, more payload, more mechanics)

**AR4 (Annin Robotics)** - MK3 / MK4 (MK4 is the current version)
- 6 axes. MK3: 629 mm (24.75") reach, ~1.9 kg (4.15 lb) payload, 0.2 mm repeatability, 27 lb weight. [S]
- Actuation: NEMA stepper motors + drivers, bought directly from Stepperonline to cut cost. Aluminium structure + 3D printed covers. [S]
- Software: official ROS 2 driver (`Ekumen-OS/ar4`) with ros2_control + MoveIt 2. Not native to LeRobot, but its ROS 2 stack is mature. [S]
- Cost: combo kit on the order of ~2000 USD (excluding motors/printing). [G]
- Verdict: the most "industrial" of the accessible DIY builds. 0.2 mm repeatability and real payload. Better for pick-and-place / ROS 2 than for pure LeRobot.

**ARCTOS**
- 6 DOF. ~600 mm reach, ~2 kg payload. NEMA17/NEMA23 motors + GT2 belts. [S]
- Firmware: a GRBL variant, open source on GitHub. Free control app, Discord community (4000+ builders). [S]
- Licence: open firmware, but the hardware plans are a paid download (<40 EUR). Requires ~3 kg of PLA and a build volume >=200x200 mm. [S]
- Verdict: a cheap, eye-catching 6-DOF to print, but not on the LeRobot track nor industrial-precision. Hobby / mechanical learning.

### High end / research (bimanual, high budget)

**ALOHA / ALOHA-2 / Mobile ALOHA (Trossen Robotics)**
- Architecture: leader-follower with backdriving. ALOHA-2 uses Trossen arms: WidowX (leader) + ViperX 300 (follower), 6 DOF. [G, claim not re-verified by the workflow]
- Cost: ALOHA ~21k EUR (2x ViperX + 2x WidowX + cameras + frame + compute). Mobile ALOHA ~32k USD (adds AgileX Tracer mobile base). [V for ~21k; G for Mobile]
- Software: ROS 2 + LeRobot integration (ALOHA-2 natively supported). [V LeRobot support]
- Commercial evolution 2025-2026: the ALOHA line is rebranded as **Trossen AI**, with the **WidowX AI** as flagship manipulator. "Stationary AI" product: turnkey station with 4 WidowX AI arms for data collection. European prices observed between ~13,000 EUR and ~41,000 EUR depending on configuration. [S]
- Verdict: the de facto standard for serious bimanual research (ACT/ALOHA, Mobile ALOHA papers). Only makes sense with a lab budget.

### Others in the ecosystem
- LeKiwi: low-cost mobile base that turns an SO-ARM into a mobile manipulator; native LeRobot. [V]
- Hope-JR (humanoid arm), Reachy-2 (humanoid, Pollen Robotics), Stretch-3 (Hello Robot): all LeRobot-supported, outside the "cheap desktop arm" range. [V]
- reBot-DevArm (Seeed) and other 6-DOF clones: a growing wave of commercial kits repackaging the SO-ARM pattern. [S]

## 3. Recommendations by budget and goal

| Goal | Recommendation | Why |
|---|---|---|
| Enter AI/teleoperation at minimum cost | SO-101 (leader+follower) | ~230 USD, native LeRobot, largest community, easy spares |
| Same but with premium servos | Koch v1.1 | Dynamixel, better control, ~430+ USD DIY |
| Cheap mobile bimanual setup | Bambot / XLeRobot | ~300-660 USD on the LeRobot stack |
| Precise pick-and-place / ROS 2 | AR4 MK4 | 0.2 mm repeatability, real payload, mature ROS 2 + MoveIt 2 |
| Print a hobby 6-DOF | ARCTOS | cheap to print, active community (paid plans) |
| Serious bimanual research | ALOHA-2 / Trossen AI | papers standard, LeRobot support, lab budget |

## 4. Licences (summary)

- LeRobot: Apache-2.0 (software). [V]
- SO-ARM100/101: open hardware design on GitHub (TheRobotStudio). [S, exact licence to confirm in the repo]
- Koch v1.1: open design (`jess-moss/koch-v1-1`). [S]
- AR4: open hardware + open source ROS 2 driver; business model = selling the structure kit. [S]
- ARCTOS: open firmware, paid hardware plans. [S]
- ALOHA: hardware designs published by the authors (Stanford); the commercial route is Trossen. [G]

## 5. Methodological caveats

- The core verified against a primary source (LeRobot paper, arXiv 2602.22818v1, Sept. 2025) covers: what LeRobot is and what it supports, the leader-follower mechanism, the use of consumer parts + 3D printing, and the SO-101 / Koch / ALOHA cost band. Those four claims passed adversarial verification 3-0.
- The fine technical specs (exact DOF, payload, reach, repeatability per arm), unit prices and Trossen/ALOHA details come from later targeted searches [S] or from domain knowledge [G]; the original workflow did not re-verify them (a tooling failure in the verifier agents, not a real refutation).
- Prices are orders of magnitude, sensitive to date and sourcing (DIY vs commercial kit). The Koch case illustrates it: ~430 USD DIY vs ~670 EUR ROBOTIS kit.

## Main sources
- LeRobot paper: https://arxiv.org/html/2602.22818v1
- LeRobot docs: https://huggingface.co/docs/lerobot
- LeRobot repo: https://github.com/huggingface/lerobot
- SO-ARM100/101: https://github.com/TheRobotStudio/SO-ARM100 ; https://huggingface.co/docs/lerobot/so101
- Seeed SO-ARM100 kit: https://www.seeedstudio.com/SO-ARM100-Low-Cost-AI-Arm-Kit.html
- Koch v1.1: https://github.com/jess-moss/koch-v1-1 ; https://www.robotis.us/koch-v1-1-low-cost-robot-arm-leader/
- Bambot: https://github.com/timqian/bambot ; XLeRobot: https://github.com/Vector-Wangel/XLeRobot
- AR4 / Annin: https://anninrobotics.com/ ; ROS2: https://github.com/Ekumen-OS/ar4
- ARCTOS: https://arctosrobotics.com/ ; https://github.com/ArctosRobotics
- ALOHA-2: https://arxiv.org/html/2405.02292v1 ; Mobile ALOHA: https://arxiv.org/pdf/2401.02117
- Trossen AI: https://www.trossenrobotics.com/ai ; ViperX 300: https://www.trossenrobotics.com/viperx-300
- LeRobotDepot (community catalog): https://github.com/maximilienroberti/lerobotdepot