Introduction: Pollen MicroDuck and Open-Source Embodied Intelligence

Learning objectives: understand what MicroDuck is, how the Sim2Real paradigm operates, why the original is difficult to obtain in China, and the rationale behind the community replica's servo selection.

1.1 An Open-Source Robot Duck That Can Walk

In 2025, Pollen Robotics — a robotics team under Hugging Face — open-sourced a bipedal robot duck named MicroDuck. It is compact (≈0.7 kg) and affordable, but its core value lies not in the hardware itself but in how it moves: a gait trained via reinforcement learning.

Traditional quadrupedal/bipedal robots (such as Spot and Atlas) rely on complex kinematic planning: first build a precise dynamics model, then solve joint torques frame by frame. MicroDuck takes a completely different route:

  1. In a GPU simulation environment (MuJoCo-Warp), a "digital duck" falls and walks randomly;
  2. A PPO reinforcement-learning algorithm, guided by a reward function, teaches it to stand, walk, and self-recover from falls;
  3. The trained policy is exported as an ONNX model and deployed directly onto the physical duck's "brain" (an RK3566 board);
  4. The physical duck reads IMU and joint angles at 50 Hz, runs ONNX inference to obtain target servo positions, and closes the control loop.

This is the complete Sim2Real (simulation-to-reality) loop. It does not require engineers to hand-design gaits; it only requires a well-designed reward function and simulation environment.

1.2 Why "Simulate First, Deploy Later" Is a Paradigm Shift

DimensionTraditional gait planningSim2Real reinforcement learning
Modeling costRequires a precise dynamics model; error-sensitiveUses domain randomization to tolerate model error
Source of gaitHand-designed by engineersDiscovered automatically by the algorithm
Disturbance robustnessDepends on precise feedback; fragileHas seen various disturbances in training; robust
Complex terrainHard to plan by handGuided by the reward function

The essence of Sim2Real is not "simulation" itself but how to close the gap between simulation and reality — the central problem this book revisits from Automated Onshape→MJCF Modeling through The Sim2Real Closed-Loop Iteration.

1.3 Why the Original Is Hard to Buy in China

The original MicroDuck uses Dynamixel XL330 servos with an official pre-order price of 399 USD. The more critical constraint is the supply chain:

  • Official direct-shipping regions: US, Canada, EU, UK, Norway, Switzerland, Japan, South Korea;
  • Mainland China is not on the direct-shipping list, requiring freight forwarding or proxy ordering;
  • 399 USD plus international shipping, tariffs, and customs clearance makes the actual landed cost significantly higher than the list price;
  • New orders have an estimated 4–6 month wait.

These real-world constraints make it hard for domestic hobbyists and university labs to obtain an original robot duck at low cost. A domestic replica therefore becomes an engineering proposition of genuine value.

1.4 Servo Selection for the Domestic Replica: Why the Feetech HD1910

The original's core actuator is the Dynamixel XL330, a serial-bus servo. Domestic alternatives fall into two main categories:

ServoTypeTorque @ 4.8 VWeightCommunicationPrice range
Dynamixel XL330Magnetic-encoder bus servo~6.5 kg·cm~16 gTTLHigh
Feetech HD1910Magnetic-encoder TTL bus servo9 kg·cm21±2 gTTLLow

Key specifications of the Feetech HD1910:

  • Model: HD-1910-C001, dual-shaft magnetic-encoder TTL bus servo, coreless motor, metal gears;
  • Operating voltage: 4.8–8.4 V;
  • Stall torque: 9 kg·cm @ 4.8 V;
  • No-load speed: 0.137 sec/60° (≈73 RPM) @ 4.8 V;
  • Weight: 21±2 g;
  • Communication: TTL bus, baud rate up to 1 Mbps, 360° magnetic encoder, multi-turn position readout.

⚠️ Selection warning: the torque, friction, bandwidth, and backlash parameters of domestic servos differ dramatically from the original. The original's pre-trained gait model cannot be directly transplanted; the servo model must be re-calibrated and the policy retrained (see BAM Actuator Modeling and Identification).

1.5 The Community Replica Landscape

RepositoryNatureServoCompanion assets
pollen-robotics/microduck_rlOriginal RL coreXL330Training code only
UnitClaw/microduck-wwduckWWNTRobotics-optimized editionHD1910Training + CAD + firmware + image + engineering optimizations
fanhao375/microduck-replicaComplete replica projectXL330 + HD1910Training + CAD + firmware + image
fanhao375/microduck-replica-cadMechanical drawingsXL330 + HD1910SolidWorks/STL
LuwuDynamics/xgoduck_hardwareFeetech-partner robot duckHD1910Standalone robot

Boundary note: 晨芯时代科技 is a domestic hardware solution provider that adapted the original for domestic hardware, but it has no standalone MicroDuck GitHub repository, delivering only RK-platform images and BSP. Feetech has likewise not published an identically named MicroDuck repository.

1.6 Goals of This Book

This book completes something the community has not yet done in full: building, from scratch, a reproducible MicroDuck full-stack engineering loop using domestic Feetech HD1910 servos, while specifically addressing five shortcomings of the original replica project:

  1. Dynamics modeling: replace manually estimated inertia parameters with the Onshape→MJCF automated pipeline (Automated Onshape→MJCF Modeling);
  2. Servo modeling: identify the HD1910's BAM actuator parameters via bench measurement (BAM Actuator Modeling and Identification);
  3. Training robustness: extended domain randomization + curriculum learning to shrink the Sim2Real gap (Domain Randomization);
  4. Engineering: Docker environment, automated validation, experiment management (The MuJoCo-Warp Simulation Environment);
  5. Hardware closed loop: real-robot gait iteration and system identification (The Sim2Real Closed-Loop Iteration).

Chapter summary: You now understand the value of MicroDuck and the necessity of a domestic replica. In the next chapter, we run the simulation end-to-end with one Docker command, building first-hand intuition for the entire pipeline.