This Notebook will show you the basics of working with the PyCRAM BulletWorld.
First we need to import and create a BulletWorld.
from pycram.bullet_world import BulletWorld
from pycram.pose import Pose
world = BulletWorld()
Unknown tag "material" in /robot[@name='plane']/link[@name='planeLink']/collision[1] Unknown tag "contact" in /robot[@name='plane']/link[@name='planeLink'] Unknown tag "material" in /robot[@name='plane']/link[@name='planeLink']/collision[1] Unknown tag "contact" in /robot[@name='plane']/link[@name='planeLink']
This new window is the BulletWorld, PyCRAMs internal physics simulation. You can use the mouse to move the camera around:
At the moment the BulletWorld only contains a floor, this is spawned by default when creating the BulletWorld. Furthermore, the gravity is set to 9.8 m^2, which is the same gravitation as the one on earth.
To close the BulletWorld again please use the exit method since it will also terminate threads running in the background
world.exit()
To spawn new things in the BulletWorld we need to import the Object class and create and instance of it.
from pycram.bullet_world import Object
milk = Object("milk", "milk", "milk.stl", pose=Pose([0, 0, 1]))
As you can see this spawns a milk floating in the air. What we did here was create a new Object which has the name "milk" as well as the type "milk", is spawned from the file "milk.stl" and is at the position [0, 0, 1].
The first three of these parameters are required while the position is optional. As you can see it was sufficent to only specify the filename for PyCRAM to spawn the milk mesh. When only providing a filename PyCRAM will search in its resource directory for a matching file and use it.
For a complete list of all parameters that can be used to crate an Object please check the documentation.
Since the Object is spawned we can now interact with it. First we want to move it around and change it's orientation
milk.set_position(Pose([1, 1, 1]))
milk.set_orientation(Pose(orientation=[1,0, 0, 1]))
milk.set_pose(Pose([0, 0, 1], [0, 0, 0, 1]))
In the same sense as setting the position or orientation you can also get the position and orientation.
print(f"Position: \n{milk.get_position()}")
print(f"Orientation: \n{milk.get_orientation()}")
print(f"Pose: \n{milk.get_pose()}")
Position:
x: 0.0
y: 0.0
z: 1.0
Orientation:
x: 0.0
y: 0.0
z: 0.0
w: 1.0
Pose:
header:
seq: 0
stamp:
secs: 1690203002
nsecs: 93374252
frame_id: "map"
pose:
position:
x: 0.0
y: 0.0
z: 1.0
orientation:
x: 0.0
y: 0.0
z: 0.0
w: 1.0
You can attach Objects to each other simply by calling the attach method on one of them and providing the other as parameter. Since attachments are bi-directional it doesn't matter on which Object you call the method.
First we neeed another Object
cereal = Object("cereal", "cereal", "breakfast_cereal.stl", pose=Pose([1, 0, 1]))
milk.attach(cereal)
Now since they are attached to each other, if we move one of them the other will move in conjunction.
milk.set_position(Pose([1,1,1]))
In the same way the Object can also be detached, just call the detach method on one of the two attached Objects.
cereal.detach(milk)
Objects spawned from mesh files do not have links or joints, but if you spawn things from a URDF like a robot they will have a lot of links and joints. Every Object has two dictionaries as attributes namley links and joints which contain every link or joint as key and a unique id, used by PyBullet, as value.
We will see this at the example of the PR2
pr2 = Object("pr2", "pr2", "pr2.urdf")
print(pr2.links)
{'base_link': 0, 'base_bellow_link': 1, 'base_laser_link': 2, 'fl_caster_rotation_link': 3, 'fl_caster_l_wheel_link': 4, 'fl_caster_r_wheel_link': 5, 'fr_caster_rotation_link': 6, 'fr_caster_l_wheel_link': 7, 'fr_caster_r_wheel_link': 8, 'bl_caster_rotation_link': 9, 'bl_caster_l_wheel_link': 10, 'bl_caster_r_wheel_link': 11, 'br_caster_rotation_link': 12, 'br_caster_l_wheel_link': 13, 'br_caster_r_wheel_link': 14, 'torso_lift_link': 15, 'l_torso_lift_side_plate_link': 16, 'r_torso_lift_side_plate_link': 17, 'imu_link': 18, 'head_pan_link': 19, 'head_tilt_link': 20, 'head_plate_frame': 21, 'sensor_mount_link': 22, 'high_def_frame': 23, 'high_def_optical_frame': 24, 'double_stereo_link': 25, 'wide_stereo_link': 26, 'wide_stereo_optical_frame': 27, 'wide_stereo_l_stereo_camera_frame': 28, 'wide_stereo_l_stereo_camera_optical_frame': 29, 'wide_stereo_r_stereo_camera_frame': 30, 'wide_stereo_r_stereo_camera_optical_frame': 31, 'narrow_stereo_link': 32, 'narrow_stereo_optical_frame': 33, 'narrow_stereo_l_stereo_camera_frame': 34, 'narrow_stereo_l_stereo_camera_optical_frame': 35, 'narrow_stereo_r_stereo_camera_frame': 36, 'narrow_stereo_r_stereo_camera_optical_frame': 37, 'projector_wg6802418_frame': 38, 'projector_wg6802418_child_frame': 39, 'laser_tilt_mount_link': 40, 'laser_tilt_link': 41, 'r_shoulder_pan_link': 42, 'r_shoulder_lift_link': 43, 'r_upper_arm_roll_link': 44, 'r_upper_arm_link': 45, 'r_elbow_flex_link': 46, 'r_forearm_roll_link': 47, 'r_forearm_link': 48, 'r_wrist_flex_link': 49, 'r_wrist_roll_link': 50, 'r_gripper_palm_link': 51, 'r_gripper_led_frame': 52, 'r_gripper_motor_accelerometer_link': 53, 'r_gripper_tool_frame': 54, 'r_gripper_motor_slider_link': 55, 'r_gripper_motor_screw_link': 56, 'r_gripper_l_finger_link': 57, 'r_gripper_l_finger_tip_link': 58, 'r_gripper_r_finger_link': 59, 'r_gripper_r_finger_tip_link': 60, 'r_gripper_l_finger_tip_frame': 61, 'r_forearm_cam_frame': 62, 'r_forearm_cam_optical_frame': 63, 'l_shoulder_pan_link': 64, 'l_shoulder_lift_link': 65, 'l_upper_arm_roll_link': 66, 'l_upper_arm_link': 67, 'l_elbow_flex_link': 68, 'l_forearm_roll_link': 69, 'l_forearm_link': 70, 'l_wrist_flex_link': 71, 'l_wrist_roll_link': 72, 'l_gripper_palm_link': 73, 'l_gripper_led_frame': 74, 'l_gripper_motor_accelerometer_link': 75, 'l_gripper_tool_frame': 76, 'l_gripper_motor_slider_link': 77, 'l_gripper_motor_screw_link': 78, 'l_gripper_l_finger_link': 79, 'l_gripper_l_finger_tip_link': 80, 'l_gripper_r_finger_link': 81, 'l_gripper_r_finger_tip_link': 82, 'l_gripper_l_finger_tip_frame': 83, 'l_forearm_cam_frame': 84, 'l_forearm_cam_optical_frame': 85, 'torso_lift_motor_screw_link': 86, 'base_footprint': -1}
Unknown attribute "type" in /robot[@name='pr2']/link[@name='base_laser_link'] Unknown attribute "type" in /robot[@name='pr2']/link[@name='wide_stereo_optical_frame'] Unknown attribute "type" in /robot[@name='pr2']/link[@name='narrow_stereo_optical_frame'] Unknown attribute "type" in /robot[@name='pr2']/link[@name='laser_tilt_link'] Unknown attribute "type" in /robot[@name='pr2']/link[@name='base_laser_link'] Unknown attribute "type" in /robot[@name='pr2']/link[@name='wide_stereo_optical_frame'] Unknown attribute "type" in /robot[@name='pr2']/link[@name='narrow_stereo_optical_frame'] Unknown attribute "type" in /robot[@name='pr2']/link[@name='laser_tilt_link']
For links there are similar methods available as for the pose. However, you can only get the position and orientation of a link.
print(f"Position: \n{pr2.get_link_position('torso_lift_link')}")
print(f"Orientation: \n{pr2.get_link_orientation('torso_lift_link')}")
print(f"Pose: \n{pr2.get_link_pose('torso_lift_link')}")
Position:
x: -0.05000000447034836
y: 0.0
z: 0.7906750440597534
Orientation:
x: 0.0
y: 0.0
z: 0.0
w: 1.0
Pose:
header:
seq: 0
stamp:
secs: 1690203043
nsecs: 303540229
frame_id: "map"
pose:
position:
x: -0.05000000447034836
y: 0.0
z: 0.7906750440597534
orientation:
x: 0.0
y: 0.0
z: 0.0
w: 1.0
Methods available for joints are:
get_joint_stateset_joint_stateget_joint_limitsWe will see how these methods work at the example of the torso_lift_joint
print(f"Joint limits: {pr2.get_joint_limits('torso_lift_joint')}")
print(f"Current Joint state: {pr2.get_joint_state('torso_lift_joint')}")
pr2.set_joint_state("torso_lift_joint", 0.2)
print(f"New Joint state: {pr2.get_joint_state('torso_lift_joint')}")
Joint limits: (0.0, 0.33) Current Joint state: 0.0 New Joint state: 0.2
There are a few methods that don't fit any category but could be helpful anyways. The first two are get_color and set_color, as the name implies they can be used to get or set the color for specific links or the whole Object.
print(f"Pr2 forearm color: {pr2.get_color('r_forearm_link')}")
Pr2 forearm color: (0.699999988079071, 0.699999988079071, 0.699999988079071, 1.0)
pr2.set_color([1, 0, 0], "r_forearm_link")
Lastly, there is get_AABB AABB stands for axis aligned bounding box. This method returns two points in world coordinates which span a rectangle representing the AABB.
pr2.get_AABB()
((-0.0015000000000000005, -0.0015000000000000005, 0.06949999999999999), (0.0015000000000000005, 0.0015000000000000005, 0.0725))