Hardware
========

.. image:: media/figures/a2_product.png
   :width: 70%
   :align: center
   :alt: Unitree A2 Industrial Quadruped Robot
   :class: mbsrounded

|

Component Overview
------------------

The Unitree A2 is a four-legged industrial robot composed of a sealed central body and four identical legs.
Each **leg provides three degrees of freedom** — hip abduction/adduction, hip flexion/extension, and knee
flexion — for a total of **twelve actuated joints**. The legs use high-torque electric joint actuators with
integrated reduction and dual-encoder feedback for precise, dynamic locomotion across rough terrain.

The body houses the onboard compute, dual hot-swappable batteries, the IMU, and the perception payload
(LiDAR and camera). External panels are sealed to **IP56**, while internal compartments reach **IP67**,
allowing the robot to operate in dust, rain, and extreme temperatures.

Degrees of Freedom
------------------

+----------------------+------------------------------------------+
| **Category**         | **Specification**                        |
+======================+==========================================+
| **Total DOF**        | 12                                       |
+----------------------+------------------------------------------+
| **Per Leg DOF**      | 3 (Hip Roll, Hip Pitch, Knee)            |
+----------------------+------------------------------------------+
| **Legs**             | 4                                        |
+----------------------+------------------------------------------+

Joint Actuators
===============

The A2 uses Unitree's self-developed electric joint actuators, engineered for high torque density, thermal
robustness, and precise closed-loop control. Each actuator integrates dual encoders, providing high-resolution
position and velocity feedback required for dynamic gaits, balance recovery, and accurate state estimation.

+-------------------------------+----------------------------------------------+
| **Parameter**                 | **Specification**                            |
+===============================+==============================================+
| Actuator Type                 | High-performance electric (PMSM)             |
+-------------------------------+----------------------------------------------+
| Peak Joint Torque             | Up to 180 N·m                                |
+-------------------------------+----------------------------------------------+
| Feedback                      | Dual encoder (position + velocity)           |
+-------------------------------+----------------------------------------------+
| Count                         | 12 (3 × 4 legs)                              |
+-------------------------------+----------------------------------------------+

.. note::

   Joint ordering, limits, and reference frames used by the control SDK are defined in the official
   `A2 SDK Development Guide <https://support.unitree.com/home/en/A2_SDK_Development_Guide>`_. Always
   confirm joint indices against the SDK header definitions before sending low-level commands.

Perception
==========

.. figure:: media/figures/a2_dual_perception.png
   :width: 100%
   :align: center
   :alt: Unitree A2 dual LiDAR 360-degree perception
   :class: mbsrounded

   Dual LiDAR providing 360° spatial coverage

|

LiDAR
-----

The A2 integrates **dual industrial LiDAR** units — one forward-facing and one rear-facing — providing combined
**360° horizontal coverage**. This configuration supports real-time point-cloud generation for SLAM, mapping,
obstacle detection, and autonomous navigation in unstructured environments.

Camera
------

An **HD camera with an integrated front LED light** delivers visual perception for teleoperation, inspection
imaging, and low-light navigation. The illuminator enables operation in dark indoor areas, tunnels, and night
patrols.

Proprioception
--------------

An onboard **IMU** combined with the per-joint dual encoders provides the proprioceptive sensing required for
balance, contact estimation, and stable locomotion control.

Onboard Computer
================

The A2 ships with an **embedded octa-core CPU** for motion control and standard autonomy workloads. For
perception-heavy or AI inference tasks, an **optional Intel Core i7 computing module** can be fitted to provide
additional processing headroom.

+--------------------------------------+--------------------------------------------------------------+
| **Parameter**                        | **Specification**                                            |
+======================================+==============================================================+
| **Base Compute**                     | Embedded octa-core CPU                                       |
+--------------------------------------+--------------------------------------------------------------+
| **Optional Compute**                 | Intel Core i7 module                                         |
+--------------------------------------+--------------------------------------------------------------+
| **Networking**                       | Gigabit Ethernet, USB-C, Wi-Fi 6, Bluetooth 5.2              |
+--------------------------------------+--------------------------------------------------------------+
| **Optional Networking**              | 4G LTE, GPS                                                  |
+--------------------------------------+--------------------------------------------------------------+

.. important::

   For security reasons, change any default login credentials after first access and follow proper shutdown
   procedures before performing hardware or software modifications.

Power System
============

The A2 is powered by **two 9,000 mAh batteries** that support **hot swapping**, allowing one pack to be replaced
while the other sustains the robot. This enables continuous, 24/7 operation in inspection and security
deployments without a full power-down cycle.

+-------------------------------------------+----------------------------------------------+
| **Parameter**                             | **Specification**                            |
+===========================================+==============================================+
| Battery Configuration                     | Dual 9,000 mAh packs                         |
+-------------------------------------------+----------------------------------------------+
| Hot Swap                                  | Supported                                    |
+-------------------------------------------+----------------------------------------------+
| Runtime (unloaded)                        | ~5 hours                                     |
+-------------------------------------------+----------------------------------------------+
| Runtime (full load)                       | ~3 hours                                     |
+-------------------------------------------+----------------------------------------------+

.. warning::

   Always verify that each battery is fully latched before operation. If the A2 will be stored for an extended
   period, remove the battery packs. Handle batteries according to lithium-battery safety guidelines.