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Robots

Robot collision detection

Collision detection works exactly the same for robots as it does for objects. The only significant difference is in how robots are initialized.

Robot joints are handled via ArticulationBodies. ArticulationBodies are very stable when used correctly but brittle when used incorrectly.

In Unity, if two objects with rigidbodies intersect each other, Unity will try to resolve the issue, sometimes with glitchy behavior. If an object with an ArticulationBody intersects with an object with a Rigibody, the build will likely crash. Be careful where you position your robots!

Some of the robots in TDW, such as ur5 and ur10, initially intersect with the floor. When collision detection is enabled (either by sending send_collisions or by initializing a CollisionManager), a robot must not be intersecting any objects or environment meshes such as the floor. If there are any intersections, the robot will severely glitch, or the build will crash, or both.

To resolve this, some robots have initial joint targets that are automatically set by the Robot add-on. These targets are stored in RobotRecord.targets:

from tdw.librarian import RobotLibrarian

lib = RobotLibrarian()
record = lib.get_record("ur5")
print(record.targets) # {'upper_arm_link': {'type': 'revolute', 'target': -5}}

To ensure that collision detection can be enabled, wait for the robot to reach its initial targets. Once this is done, you can initialize collision detection.

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.robot import Robot

c = Controller()
robot = Robot(name="ur5",
              position={"x": 1, "y": 0, "z": -2},
              rotation={"x": 0, "y": 0, "z": 0},
              robot_id=c.get_unique_id())
c.add_ons.append(robot)
c.communicate(TDWUtils.create_empty_room(12, 12))

while robot.joints_are_moving():
    c.communicate([])

# The robot has moved to its initial pose. Enable collision detection.
c.communicate({"$type": "send_collisions",
               "enter": True,
               "stay": False,
               "exit": False,
               "collision_types": ["obj", "env"]})
c.communicate({"$type": "terminate"})

We can check the robot's dynamic data to determine whether objects have collided with it:

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.robot import Robot
from tdw.add_ons.object_manager import ObjectManager

c = Controller()
robot = Robot(name="ur5",
              position={"x": 1, "y": 0, "z": -2},
              rotation={"x": 0, "y": 0, "z": 0},
              robot_id=c.get_unique_id())
c.add_ons.append(robot)
c.communicate(TDWUtils.create_empty_room(12, 12))

while robot.joints_are_moving():
    c.communicate([])

object_manager = ObjectManager(transforms=True, rigidbodies=True)
c.add_ons.append(object_manager)

object_id = c.get_unique_id()
c.communicate([c.get_add_object(model_name="iron_box",
                                position={"x": 1, "y": 10, "z": -2},
                                object_id=object_id),
               {"$type": "send_collisions",
                "enter": True,
                "stay": False,
                "exit": False,
                "collision_types": ["obj", "env"]}])

# Wait for the object to stop moving.
while not object_manager.rigidbodies[object_id].sleeping:
    c.communicate([])
    for collision in robot.dynamic.collisions_with_objects:
        joint_id = collision[0]
        print("Collision between iron_box and " + robot.static.joints[joint_id].name)
c.communicate({"$type": "terminate"})

Output:

Collision between iron_box and shoulder_link
Collision between iron_box and upper_arm_link
Collision between iron_box and ur5(Clone)

Next: Select a robot

Return to the README

Example controllers:

Python API:

Command API: