cs.ROMar 19, 2026

Introducing M: A Modular, Modifiable Social Robot

Authors: Victor Nikhil Antony, Zhili Gong, Yoonjae Kim, Chien-Ming Huang

Organizations: Department of Computer Science, Johns Hopkins University, USA · Department of Mechanical Engineering, Rice University, USA

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Abstract

We present M, an open-source, low-cost social robot platform designed to reduce platform friction that slows social robotics research by making robots easier to reproduce, modify, and deploy in real-world settings. M combines a modular mechanical design, multimodal sensing, and expressive yet mechanically simple actuation architecture with a ROS2-native software package that cleanly separates perception, expression control, and data management. The platform includes a simulation environment with interface equivalence to hardware to support rapid sim-to-real transfer of interaction behaviors. We demonstrate extensibility through additional sensing/actuation modules and provide example interaction templates for storytelling and two-way conversational coaching. Finally, we report real-world use in participatory design and week-long in-home deployments, showing how M can serve as a practical foundation for longitudinal, reproducible social robotics research.

Figures & tables

Fig. 1: M is an open-source, modular social robot platform designed for longitudinal, in-the-wild research. The platform features customizable embodiment ( e.g., accessories, face plate), expressive behaviors ( e.g., facial expressions, body gestures), multimodal sensing ( e.g., touch, radar, camera), and ROS2 software supporting reproducibility, extensibility and field deployments.
RobotCostModularMulti-SensorExpressivityOn-Board ComputeSim2RealField Readiness
Blossom [ 9 ]$250∘\circ∘\circ4 DoF--∘\circ
Poppy-H [ 10 ]$8-10K∙\bullet∙\bullet25 DoF, LCD-∙\bullet-
Ono [ 11 ]$350-575∘\circ-13 DoF---
FLEXI [ 12 ]$2.5K∘\circ∘\circ4 DoF, tablet∙\bullet-∘\circ
Reachy-M$299-449-∙\bullet6 DoF-∘\circ∘\circ
M (ours)$325∙\bullet∙\bullet5 DoF, LCD∙\bullet∙\bullet∙\bullet ∗
TABLE I: Comparison of Social and Expressive Robot Platforms
Fig. 2: Exploded view of M ’s mechanical design, illustrating the modular architecture. Key components include the head module (containing compute, audio, and display), head rotation and nodding modules, customizable face masks, articulated arms with magnetic attachments, camera, and body rotation module with weighted base for stability.
Fig. 3: Illustration of M narrating a children’s story with synchronized multi-modal expressive behaviors produced leveraging generative AI pipelines.
Fig. 4: M can be programmed in a simulation environment with complete sim-to-real parity. The GUI includes a 3D viewport with orbit controls, real-time joint state displays, and interactive manipulation controls.
Fig. 5: Illustration of M ’s modular sensing extensions: FMCW radar enables privacy-preserving human presence detection. Upon detecting a user (left), M initiates engagement through body reorientation and expressions (center, right), demonstrating M support for proactive engagement in privacy-sensitive deployment contexts.
Fig. 6: Illustration of M ’s capacitive touch sensing integrated beneath the exterior shell. The robot detects physical contact as an interaction signal: a brief tap (center) can indicate readiness to engage, while sustained contact (right) can be used for structured activities, enabling embodied interaction without additional visible instrumentation.
Fig. 7: Illustration of M delivering a two-way conversational positive psychology coaching session. M guides a structured gratitude practice through open-ended questions, empathetic listening with embodied acknowledgment, and context-aware follow-up dialogue maintained across multiple conversational turns.
Fig. 8: M in real-world deployment: participatory design workshops (left) and week-long autonomous home deployments (center, right).
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