Asynchronous Multi-Body Framework (AMBF)

Author: Adnan Munawar ([email protected])

Contributors:

1. Melody Su (Email: --)

Wiki:

Please checkout the Wiki for indepth details about AMBF, it's components, examples and concepts.

Description:

This multi-body framework offers real-time dynamic simulation of multi-bodies (robots, free bodies and multi-link puzzles) coupled with real-time haptic interaction via several haptic devices (CHAI-3D) (including dVRK Manipulators and Razer Hydras). It also provides a python client for training NN and RL Agents on real-time data with simulation in the loop. This framework is built around several external tools that include an extended version of CHAI-3D (developed along-side AMBF), BULLET-Physics, Open-GL, GLFW, yaml-cpp, pyyaml and Eigen to name a few. Each external library has it's own license that can be found in the corresponding subfolder.

Usage:

Building:

To build the framework (Linux and Mac-OS):

cd ~
git clone https://github.com/WPI-AIM/ambf.git
cd ambf && mkdir build
cd build
cmake ..
make

On Linux systems, please source the correct folder to achieve system wide availability of AMBF ROS modules. While in the build folder, you can run:

source ./devel/setup.bash

You can also permanently add the install location in your .bashrc with the following command:

echo "source ~/ambf/build/devel/setup.bash" >> ~/.bashrc

Running the Simulator:

Having succesfully completed the steps above running is Simulator is easy. Depending on what OS you're using simply follow the commands below:

cd ~/ambf/bin/<os>
./ambf_simulator

Launching Specific Multibodies:

The -l command line argument can be used to launch a specific multibody at launch. The multibodies are defined in ambf_models/descriptions/launch.yaml and are commented with indices for ease of identification. As a default behaviour, launching the simulator without the -l command line argument loads the first multi-body defined in the launch.yaml. To launch a specific multi-body you can use the -l flag with the integer index of the multi-body as follows:

cd ~/ambf/bin/<os>
./ambf_simulator -l 4

This command will launch the 4th body defined in the launch.yaml file. To launch multiple multi-bodies, you can use a comma separated list (without spaces in between) of integers indices e.g../ambf_simulator -l 1,6,10. This in turn would load the multi-bodies defined at 1, 6 and the 10th index in the launch.yaml file.

Note:

The AMBF Simulator uses the yaml file located in ambf/ambf_models/descriptions/launch.yaml to load robot/multi-body models, haptic device end-effectors and the world. You can see the contents of this file by launching it in your favourite text editor. For an initial overview, the most important thing is the field multibody configs:. The uncommented config file(s) will be launced at startup. Multiple config files can be launched at the same time by uncommenting them. You can play around with a few config files to see how they work.

Interacting with the Robots/Multi-Bodies in the Simulator:

There are multiple way of interacting with the bodies in simulator. If you are using Linux, the provided Python client offers a convenient user interface and robust API.

Easy to Use Python Client

For full feature set of the AMBF Simulator, it is advised that you install it on Linux (Ubuntu) 16, 17 or 18. Other variants might be supported but have not yet been tested.

The AMBF Python Client

This simplest way to interact with simulated bodies, robots/multi-bodies, kinematic and visual objects in the AMBF simulator is by using the high-speed Asynchronous Communication that is implemented via ROS-topics in the AMBF Framework Library. One can use either C++ or Python for this purpose. For ease of interaction we provide a convenient Python Client which can be used as follows:

Start the AMBF Simulator with your choice of Multi-Body config file that (set in the multi bodies field in the ambf_models/launch.yaml file).

In your python application

# Import the Client from ambf_comm package
# You might have to do: pip install gym
from ambf_client import Client
import time

# Create a instance of the client
_client = Client()

# Connect the client which in turn creates callable objects from ROS topics
# and initiates a shared pool of threads for bidrectional communication 
_client.connect()

# You can print the names of objects found
print(_client.get_obj_names())

# Lets say from the list of printed names, we want to get the 
# handle to an object names "Torus"
torus_obj = _client.get_obj_handle('Torus')

# Now you can use the torus_obj to set and get its position, rotation,
# Pose etc. If the object has joints, you can also control them
# in either position control mode or open loop effort mode. You can even mix and
# match the joints commands 
torus_obj.set_pos(0, 0, 0) # Set the XYZ Pos in obj's World frame
torus_obj.set_rpy(1.5, 0.7, .0) # Set the Fixed RPY in World frame
time.sleep(5) # Sleep for a while to see the effect of the command before moving on

# Other methods to control the obj position include
# torus_obj.set_pose(pose_cmd) # Where pose_cmd is of type Geometry_msgs/Pose
# torus_obj.set_rot(quaterion) # Where quaternion is a list in the order of [qx, qy, qz, qw]
# Finally all the position control params can be controlled in a single method call
# torus_obj.pose_command(px, py, pz, roll, pitch, yaw, *jnt_cmds)

# We can just as easily get the pose information of the obj
cur_pos = torus_obj.get_pos() # xyx position in World frame
cur_rot = torus_obj.get_rot() # Quaternion in World frame
cur_rpy = torus_obj.get_rpy() # Fixed RPY in World frame

# Similarly you can directly control the wrench acting on the obj by
# The key difference is that it's the user's job to update the forces
# and torques in a loop otherwise the wrench in cleared after an internal
# watchdog timer expires if a new command is not set. This is for safety
# reasons where a user shouldn't set a wrench and then forget about it.
for i in range(0, 5000):
    torus_obj.set_force(5, -5, 10) # Set the force in the World frame
    torus_obj.set_torque(0, 0, 0.8) # Set the torque in the World frame
    time.sleep(0.001) # Sleep for a while to see the effect of the command before moving on

# Similar to the pose_command, one can assign the force in a single method call
# torus_obj.wrench_command(fx, fy, fz, nx, ny, nz) in the World frame

# We can get the number of children and joints connected to this body as
num_joints = torus_obj.get_num_joints() # Get the number of joints of this object
children_names = torus_obj.get_children_names() # Get a list of children names belonging to this obj

print(num_joints)
print(children_names)

# If the obj has some joints, we can control them as follows
if num_joints > 1:
    torus_obj.set_joint_pos(0, 0.5) # The the joints at idx 0 to 0.5 Radian
    torus_obj.set_joint_effort(1, 5) # Set the effort of joint at idx 1 to 5 Nm
    time.sleep(2) # Sleep for a while to see the effect of the command before moving on


# Lastly to cleanup
_client.clean_up()

The AMBF Controller Client

See here for more information.