Lesson 2 · 20 min
Your program does not call a robot function: it publishes and subscribes to messages on a DDS bus. In this lesson you set up the manufacturer's bench (simulator, SDK, and CycloneDDS 0.10.2), bring up the simulated G1, and read the first state message, through the same path you would use with the real robot.
Start the lesson
Goal: set up the manufacturer's bench (simulator, SDK, CycloneDDS 0.10.2) and read the G1's first state message over DDS.
Click each block.
Swapping the simulator for the robot changes the domain and the interface, not your code.
Click each one.
High level: the manufacturer's locomotion controller walks and you ask for a velocity (LocoClient in the "sport" service: SetVelocity, Move, Damp, ZeroTorque).
Low level: you command each motor through rt/lowcmd. First, the official example releases the internal controller (MotionSwitcherClient, CheckMode and ReleaseMode), otherwise the two fight over the motors.
The simulator uses domain 1 on the lo interface (config.py in unitree_mujoco). The SDK examples use domain 0 and the name of the network card connected to the robot.
A program and a robot on different domains can't see each other: the script waits and the robot looks dead. The "Common error" tab shows the message.
The unitree_ros2 README puts the PC on a fixed IP in the 192.168.123.x subnet (example: 192.168.123.99) and the interface goes by name (enp3s0).
The base G1 costs US$ 13.5 thousand on the official page (read on 10/19/2026), but it has no secondary development: no SDK. To program as in this course, you need the EDU version, sold on request.
Resellers cited by the training research (Oct/2026): US$ 43.5 thousand to 73.9 thousand (reported; varies by version and reseller). The simulator costs nothing and speaks the same DDS.
A venv in ~/fth (the same one from course 0, if you took it), the simulator and SDK pinned to commits, and CycloneDDS 0.10.2 compiled: pip alone fails on aarch64 without the C library. You need python3.12 (with venv), git, cmake, and a C compiler.
F=${FTH:-$HOME/fth}; mkdir -p $F && cd $F
[ -d .venv ] || python3.12 -m venv .venv; . .venv/bin/activate
pip install -q mujoco==3.16.0 numpy pygame==2.6.1 mcap==1.6.0
[ -d operar ] || git clone -q --depth 1 https://github.com/inematds/formacao-fth-operar-v72 operar
[ -d unitree_mujoco ] || git clone -q --filter=blob:none --sparse https://github.com/unitreerobotics/unitree_mujoco
(cd unitree_mujoco && git sparse-checkout set simulate_python unitree_robots/g1 && git checkout -q 1eb6642)
[ -d unitree_sdk2_python ] || git clone -q https://github.com/unitreerobotics/unitree_sdk2_python
(cd unitree_sdk2_python && git checkout -q 814556d)
for r in unitree_mujoco unitree_sdk2_python; do git -C $r log -1 --format="$r %h (%ad)" --date=short; doneF=${FTH:-$HOME/fth}; cd $F && . .venv/bin/activate
[ -d cyclonedds ] || git clone -q --depth 1 -b 0.10.2 https://github.com/eclipse-cyclonedds/cyclonedds 2>/dev/null
cmake -S cyclonedds -B cyclonedds/build -DCMAKE_INSTALL_PREFIX=$F/cyclonedds/install -DBUILD_EXAMPLES=OFF > /dev/null 2>&1
cmake --build cyclonedds/build --target install -j 4 > /dev/null 2>&1 && echo "cyclonedds C 0.10.2 instalado em $F/cyclonedds/install"
export CYCLONEDDS_HOME=$F/cyclonedds/install
pip install -q cyclonedds==0.10.2 && pip install -q -e unitree_sdk2_python
python3 -c "from importlib.metadata import version as v; import unitree_sdk2py; print('cyclonedds', v('cyclonedds'), '· unitree_sdk2py', v('unitree_sdk2py'), '· mujoco', v('mujoco'))"unitree_mujoco 1eb6642 (2026-09-07) unitree_sdk2_python 814556d (2026-09-21)
cyclonedds C 0.10.2 instalado em ~/fth/cyclonedds/install cyclonedds 0.10.2 · unitree_sdk2py 1.0.1 · mujoco 3.16.0
The two commits and the three versions. The build takes a few minutes; the compiler warning is hidden in /dev/null.
kit/sim.py runs the unitree_mujoco bridge with no window, in the background, for 8 s; ler_estado.py is another process that only subscribes to rt/lowstate. The G1 hangs from the elastic band (the simulator's gantry).
F=${FTH:-$HOME/fth}; cd $F/operar && . $F/.venv/bin/activate
python3 kit/sim.py --s 8 --suspenso &
python3 kit/ler_estado.py; echo "saída: $?"
waitclass Estado:
"""Assina rt/lowstate e guarda a última mensagem e quantas chegaram."""
def __init__(self):
from unitree_sdk2py.core.channel import ChannelSubscriber
from unitree_sdk2py.idl.unitree_hg.msg.dds_ import LowState_
self.ultima, self.n, self.t_ultima = None, 0, 0.0
self.sub = ChannelSubscriber("rt/lowstate", LowState_)
self.sub.Init(self._chegou, 10)# Trecho de example/g1/low_level/g1_low_level_example.py (unitree_sdk2_python 814556d)
ChannelFactoryInitialize(0, sys.argv[1]) # domínio 0 + nome da placa ligada ao robô
self.msc = MotionSwitcherClient()
self.msc.SetTimeout(5.0)
self.msc.Init()
status, result = self.msc.CheckMode()
while result['name']: # libera o controle interno antes do baixo nível
self.msc.ReleaseMode()
status, result = self.msc.CheckMode()
time.sleep(1)simulador: G1 29 motores · DDS domínio 1 em lo · 8 s · suspenso: sim tópico: rt/lowstate · tipo: unitree_hg LowState_ IMU quatérnio (w, x, y, z): [1.0, 0.0, 0.1, 0.0] · tronco em pé (inclinação < 20°): sim junta 0 (left_hip_pitch): q = 0.0 rad · torque estimado = 0 N·m motores no pacote: 35 (o G1 de 29 GDL usa os índices 0 a 28) saída: 0 simulador: fim em t = 8.0 s · robô suspenso (pés fora do chão)
The packet has 35 motor slots; the 29-DoF G1 uses the first 29. Loose motors: zero torque.
ERRO: nenhuma mensagem em rt/lowstate em 10 s. O simulador está rodando? (kit/sim.py) saída: 1
No message in 10 s: the simulator is not running, or your program is on another domain or interface.
Bench ready and first message read.
Run the two setup blocks. If cmake complains, install cmake and a C compiler with your system's package manager and run the second block again.
Done when: the output shows cyclonedds 0.10.2 · unitree_sdk2py 1.0.1 · mujoco 3.16.0.
Run the simulator block with the reading and explain why the packet has 35 motors if the G1 has 29.
Done when: python3 kit/ler_estado.py; echo "saída: $?" (with sim.py running) → motores no pacote: 35 (o G1 de 29 GDL usa os índices 0 a 28) and saída: 0.
Run only ler_estado.py, without the simulator, and wait the 10 s.
Done when: ERRO: nenhuma mensagem em rt/lowstate em 10 s and saída: 1.
The explanation appears after your answer.
Question 1 of 4
ler_estado.py waited 10 s and then failed. What is the most likely cause?skill
Question 2 of 4
Which topic carries the G1's state (IMU and motors)?
Question 3 of 4
Before sending low-level commands to the real robot, what does the official example do?
Question 4 of 4
Why does the course compile CycloneDDS instead of just using pip?
Choose an option. The explanation appears after your attempt.