E1 · Detect the fall
5 minRun the detector block and note how long the tumble took from 10° to 40°.
Done when: python3 kit/queda.py; echo "saída: $?" → queda detectada: inclinação passou de 40°, amortecimento enviado and saída: 0.
Lesson 5 · 15 min
When it falls: detect, damp, and get up
Every humanoid under test falls. What separates a prepared lab from a broken robot is what the software does in the first tenths of a second and what the people do afterward. In this lesson the simulated G1 really falls, and your IMU detector sends damping without trying to catch the tumble.
Start the lesson
In this lesson you will
- 1Why holding a pose with PD is not balance
- 2Tilt with a threshold: too early × too late
- 3Damp instead of locking the motors
- 4Getting up is a human procedure, after inspection
Goal: detect the G1's fall from the IMU tilt and send damping, without trying to get up on its own.
01From tilt to inspection
Click each step.
Click each block in the diagram to see what it does.
What the robot does on its own ends at damping. The rest is up to people.
02Three things the fall teaches
Click each one.
1. PD does not balance
In practice, in this lesson, the script holds the starting pose with the gains from the official example. Released from the elastic band, the simulator's G1 falls right after, with no push at all.
Standing up takes balance control: the manufacturer's (high level) or your own policy (courses 1 and 2).
2. Threshold
A low threshold fires on normal sway and stops the test for no reason. A threshold that is too high only acts once the robot is already on the floor, or never.
The "Common mistake" tab shows the 170° threshold: the robot fell and the detector never fired, with the motors stiff the whole time.
3. After
Stop the session, check on the people, log it with photos and the MCAP, do not power back on without an inspection, find the cause.
Only then does the robot go back to the gantry. This step goes into your deployment plan (lesson 8) as a stop condition.
03Release, fall, detect
The simulator holds the G1 on the elastic band with its feet on the ground and releases it at t = 3 s. The queda.py script holds the pose with PD, watches the tilt, and damps once it passes 40°.
Terminal · simulator + detector
F=${FTH:-$HOME/fth}; cd $F/operar && . $F/.venv/bin/activate
python3 kit/sim.py --s 12 --soltar-em 3 &
python3 kit/queda.py; echo "saída: $?"
waitExcerpt · kit/queda.py
incl = op.inclinacao(s.imu_state.quaternion)
incl_max = max(incl_max, incl)
t = t_ciclo - inicio
if t10 is None and incl > 10:
t10 = t
if caiu is None and incl > a.limite:
caiu = tTerminal · the common mistake: threshold too high
F=${FTH:-$HOME/fth}; cd $F/operar && . $F/.venv/bin/activate
python3 kit/sim.py --s 12 --soltar-em 3 > /dev/null &
python3 kit/queda.py --limite 170; echo "saída: $?"
waitExample from the repository
simulador: G1 29 motores · DDS domínio 1 em lo · 12 s · suspenso: não · elástico solta em t = 3 s segurando a pose inicial com PD · limiar de queda: 40° de inclinação do tronco queda detectada: inclinação passou de 40° (≈ 500 ms depois de passar de 10°) amortecimento enviado: kp=0, kd=2 em todos os motores (sem tentar levantar) no fim: inclinação acima de 40°: sim · motores amortecidos saída: 0 simulador: fim em t = 12.0 s · robô no chão
The fall takes about half a second to go from 10° to 40°. The detector acts in the middle of the tumble, and the robot ends up on the floor with the motors damped.
segurando a pose inicial com PD · limiar de queda: 170° de inclinação do tronco nenhuma queda detectada: o limiar de 170° nunca foi atingido · motores continuaram rígidos saída: 1
The robot fell all the same, but the threshold was never reached: no damping, motors stiff during the impact, code 1.
04Practice
Fall on purpose, in the simulator.
E2 · The wrong threshold
5 minRun the common-mistake block and write, in one line, what threshold you would use on your robot and why.
Done when: python3 kit/queda.py --limite 170; echo "saída: $?" → nenhuma queda detectada and saída: 1.
E3 · The post-fall step in the checklist
5 minIn your ~/fth/checklist.yaml, add the chosen threshold and who decides to power back on after a fall to item 8.
Done when: python3 operar/kit/conferir_checklist.py checklist.yaml still shows 12 itens, 0 em branco.
05Lesson quiz
The explanation appears after your answer.
Question 1 of 4
The script held the pose with PD and the G1 fell anyway. Why?skill
Correct
PD on each joint holds angles, not the center of mass over the feet. Standing up takes a balance controller or a trained policy.Not this one
PD on each joint holds angles, not the center of mass over the feet. Standing up takes a balance controller or a trained policy.Review: Three things the fall teachesQuestion 2 of 4
Why does the detector use the IMU and not the pelvis height?
Correct
In the simulator the height comes for free; on the real robot it doesn't. The detector has to use what exists in both: the IMU quaternion.Not this one
In the simulator the height comes for free; on the real robot it doesn't. The detector has to use what exists in both: the IMU quaternion.Review: From tilt to inspectionQuestion 3 of 4
Once a fall is detected, what does the kit send to the motors?
Correct
Damping lets the body settle instead of fighting the fall; it's what the high-level Damp() does. Getting up is a human procedure, after inspection.Not this one
Damping lets the body settle instead of fighting the fall; it's what the high-level Damp() does. Getting up is a human procedure, after inspection.Review: Release, fall, detectQuestion 4 of 4
With a 170° threshold, what happened?
Correct
The torso never reaches 170° of tilt lying on the floor. A threshold that's too high is the same as having no detector.Not this one
The torso never reaches 170° of tilt lying on the floor. A threshold that's too high is the same as having no detector.Review: Release, fall, detectQuiz complete
You got {a} of {n} right. Get them all right and the lesson is marked as completed.Choose an option. The explanation appears after your attempt.
06In three sentences
It fallsPD holding a pose does not balance: released, the G1 falls.
DetectsIMU tilt above the threshold → damping.
AfterStop, inspect, record; getting up is for the people.