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Guardians as You Fall: Active Mode Transition for Safe Falling

Code for training and onboard deployment of "Guardians as You Fall: Active Mode Transition for Safe Falling". 2023icra

Code Base

This repository is based on legged_gym https://leggedrobotics.github.io/legged_gym/ and https://github.com/Alescontrela/AMP_for_hardware.git.

Installation

  1. Create a new python virtual env with python 3.6, 3.7 or 3.8 (3.8 recommended)
  2. Install pytorch 1.10 with cuda-11.3:
    • pip3 install torch==1.10.0+cu113 torchvision==0.11.1+cu113 tensorboard==2.8.0 pybullet==3.2.1 opencv-python==4.5.5.64 torchaudio==0.10.0+cu113 -f https://download.pytorch.org/whl/cu113/torch_stable.html
  3. Install Isaac Gym
    • Download and install Isaac Gym Preview 4 from https://developer.nvidia.com/isaac-gym
    • cd isaacgym/python && pip install -e .
    • Try running an example cd examples && python 1080_balls_of_solitude.py
    • For troubleshooting check docs isaacgym/docs/index.html)
  4. Install rsl_rl (PPO implementation)
    • Clone this repository.
    • cd Guardians_as_You_Fall/rsl_rl && pip install -e .
  5. Install legged_gym
    • cd ../ && pip install -e .

Code Structure

  1. Each environment is defined by an env file (*env_name*.py) and a config file (*env_name*_config.py). The config file contains two classes: one conatianing all the environment parameters (*env_name*Cfg) and one for the training parameters (*env_name*CfgPPo).
  2. Both env and config classes use inheritance.
  3. Each non-zero reward scale specified in cfg will add a function with a corresponding name to the list of elements which will be summed to get the total reward.
  4. Tasks must be registered using task_registry.register(name, EnvClass, EnvConfig, TrainConfig). This is done in envs/__init__.py, but can also be done from outside of this repository.

Framework

917_overview

  1. Working policy: the standing policy, trained with go1_stand.py.
  2. Transition controller: the policy for falling control, trained with curr.py or go1_fall_dr.py. curr.py provides mixed terrains, mixed tasks and training curriculum (optional). go1_fall_dr.py provides extra domain randomization for sim-to-real transfer.
  3. recovery controller, the policy for convert the quadrupedal from reversed mode to regular mode, trained with go1_recover.py.
  4. Planner: trained with selector.py, which is trained to select the appropriate low-level policy. Trained from demonstration.

The rl algorithm of each environment is defined in the corresponding _config.py files.

Usage

  1. Train:
    python issacgym_anymal/scripts/train.py --task=back --headless
    • To run on CPU add following arguments: --sim_device=cpu, --rl_device=cpu (sim on CPU and rl on GPU is possible).
    • To run headless (no rendering) add --headless.
    • Important: To improve performance, once the training starts press v to stop the rendering. You can then enable it later to check the progress.
    • The trained policy is saved in ./logs/<experiment_name>/<date_time>_<run_name>/model_<iteration>.pt. Where <experiment_name> and <run_name> are defined in the train config.
    • The following command line arguments override the values set in the config files:
    • --task TASK: Task name.
    • --resume: Resume training from a checkpoint
    • --experiment_name EXPERIMENT_NAME: Name of the experiment to run or load.
    • --run_name RUN_NAME: Name of the run.
    • --load_run LOAD_RUN: Name of the run to load when resume=True. If -1: will load the last run.
    • --checkpoint CHECKPOINT: Saved model checkpoint number. If -1: will load the last checkpoint.
    • --num_envs NUM_ENVS: Number of environments to create.
    • --seed SEED: Random seed.
    • --max_iterations MAX_ITERATIONS: Maximum number of training iterations.
  2. Play a trained policy:
    python ./legged_gym/scripts/play.py --task=back
    • By default the loaded policy is the last model of the last run of the experiment folder.
    • Other runs/model iteration can be selected by setting load_run and checkpoint in the train config.

Adding a new environment

The base environment legged_robot implements a rough terrain locomotion task. The corresponding cfg does not specify a robot asset (URDF/ MJCF) and no reward scales.

  1. Add a new folder to envs/ with '<your_env>_config.py, which inherit from an existing environment cfgs
  2. If adding a new robot:
    • Add the corresponding assets to resourses/.
    • In cfg set the asset path, define body names, default_joint_positions and PD gains. Specify the desired train_cfg and the name of the environment (python class).
    • In train_cfg set experiment_name and run_name
  3. (If needed) implement your environment in <your_env>.py, inherit from an existing environment, overwrite the desired functions and/or add your reward functions.
  4. Register your env in isaacgym_anymal/envs/__init__.py.
  5. Modify/Tune other parameters in your cfg, cfg_train as needed. To remove a reward set its scale to zero. Do not modify parameters of other envs!

Troubleshooting

  1. If you get the following error: ImportError: libpython3.8m.so.1.0: cannot open shared object file: No such file or directory, do: sudo apt install libpython3.8

Known Issues

  1. The function gym.set_*_tensor() or gym.set_*_tensor_indexed() can take effect only once in a simulation step. If multiple times of reset of joints or root states is needed, a solution is to record the indices of envs need to be reset in this step, reset all the environments recorded at the end of each step.

  2. The contact forces reported by net_contact_force_tensor are unreliable when simulating on GPU with a triangle mesh terrain. A workaround is to use force sensors, but the force are propagated through the sensors of consecutive bodies resulting in an undesireable behaviour. However, for a legged robot it is possible to add sensors to the feet/end effector only and get the expected results. When using the force sensors make sure to exclude gravity from trhe reported forces with sensor_options.enable_forward_dynamics_forces. Example:

    sensor_pose = gymapi.Transform()
    for name in feet_names:
        sensor_options = gymapi.ForceSensorProperties()
        sensor_options.enable_forward_dynamics_forces = False # for example gravity
        sensor_options.enable_constraint_solver_forces = True # for example contacts
        sensor_options.use_world_frame = True # report forces in world frame (easier to get vertical components)
        index = self.gym.find_asset_rigid_body_index(robot_asset, name)
        self.gym.create_asset_force_sensor(robot_asset, index, sensor_pose, sensor_options)
    (...)

    sensor_tensor = self.gym.acquire_force_sensor_tensor(self.sim)
    self.gym.refresh_force_sensor_tensor(self.sim)
    force_sensor_readings = gymtorch.wrap_tensor(sensor_tensor)
    self.sensor_forces = force_sensor_readings.view(self.num_envs, 4, 6)[..., :3]
    (...)

    self.gym.refresh_force_sensor_tensor(self.sim)
    contact = self.sensor_forces[:, :, 2] > 1.

Guidelines for Onboard Deployment

Connect user PC to onboard mini PC

  1. Set the user's PC IP to: 192.168.123.xxx, so that the user's PC and the onboard PC can be integrated into the same local network.
  2. Connect to one of the mini PC via ethernet or ssh. The recommendation is the Jetson NX: 192.168.123.15

Configure the Libtorch

The main tools being used are libtorch(C++ version of Pytorch) and other dependencies listed in https://github.com/unitreerobotics/unitree_legged_sdk. Ideally, the required environment is pre-installed. Check the version of pre-installed Pytorch. If the version is >=1.8.0, skip to Deploy a Custom Model. Otherwise, you need to manully install Libtorch on the mini PC. There are several choices:

  1. Download the source code of Libtorch to the mini PC and compile onboard. Downloading the official pre-built version is not feasible because all mini PCs are based on the ARM architecture.
  2. Download the pre-built PyTorch pip wheel installers for Jetson.https://forums.developer.nvidia.com/t/pytorch-for-jetson-version-1-11-now-available/72048
  3. Build a docker image containing the required libtorch and other dependencies, and install the docker on the mini PC. You may use the docker provided by https://github.com/Improbable-AI/walk-these-ways.git. Then mount the ~/unitree/unitree_legged_sdk/ directory into the docker by moving the directory inside ~/unitree/go1_gym/ and editting the ~/unitree/go1_gym/go1_gym_deploy/docker/Makefile as follows:
run:
	docker stop foxy_controller || true
	docker rm foxy_controller || true
	docker run -it \
		--env="DISPLAY" \
		--env="QT_X11_NO_MITSHM=1" \
		--volume="/tmp/.X11-unix:/tmp/.X11-unix:rw" \
		--env="XAUTHORITY=${XAUTH}" \
		--volume="${XAUTH}:${XAUTH}" \
		--volume="/home/unitree/go1_gym:/home/isaac/go1_gym" \   # this line mount the go1_gym directory into the docker
		--privileged \
		--runtime=nvidia \
		--net=host \
		--workdir="/home/isaac/go1_gym" \
		--name="foxy_controller" \
		jetson-model-deployment bash

Then enter the docker by cd ./go1_gym_deploy/docker && sudo make run .

Deploy a Custom Model

  1. cd unitree_legged_sdk
  2. Export a TorchScript model of your custom model. This could be accomplished in https://github.com/ykwang20/Guardians_as_You_Fall/blob/minimal/legged_gym/scripts/play.py by setting EXPORT_POLICY = True.
  3. Write your control source code source.cpp to receive sensor data （filter the data if needed), inference, and perform action.
  4. Edit the CMakeLists.txt:
cmake_minimum_required(VERSION 2.8.3)
project(unitree_legged_sdk)

find_package(Torch REQUIRED) #Add this line

# check arch and os
message("-- CMAKE_SYSTEM_PROCESSOR: ${CMAKE_SYSTEM_PROCESSOR}")
if("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "x86_64.*")
  set(ARCH amd64)
endif()
if("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "aarch64.*")
  set(ARCH arm64)
endif()

include_directories(include)
link_directories(lib/cpp/${ARCH})

option(PYTHON_BUILD "build python wrapper" OFF)
if(PYTHON_BUILD)
  add_subdirectory(python_wrapper)
endif()

set(EXTRA_LIBS -pthread libunitree_legged_sdk.a)
set(CMAKE_CXX_FLAGS "-O3 -fPIC")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TORCH_CXX_FLAGS}")
set(CMAKE_CXX_STANDARD 14)

add_executable(executable_name path/to/source.cpp)
target_link_libraries(executable_name ${TORCH_LIBRARIES} ${EXTRA_LIBS})     # to configure your source code
  1. Compile:
mkdir build
cd build
cmake .. -DCMAKE_PREFIX_PATH=$(python3 -c 'import torch;print(torch.utils.cmake_prefix_path)') # to locate libtorch
make
  1. Switch the robot to damping mode using remote controller. The command sequence is : L2+A, L2+B, L1+L2+START.
  2. Run the controller: cd build && sudo ./executable_name

Citation

@misc{wang2023guardians,
      title={Guardians as You Fall: Active Mode Transition for Safe Falling}, 
      author={Yikai Wang and Mengdi Xu and Guanya Shi and Ding Zhao},
      year={2023},
      eprint={2310.04828},
      archivePrefix={arXiv},
      primaryClass={cs.RO}
}