Motion Service

The Motion Service enables your robot to plan and move itself or its components relative to itself, other robots, and the world. The Motion Service:

  1. Gathers the current positions of the robot’s components as defined with the Frame System.
  2. Plans the necessary motions to move a component to a given destination while obeying any constraints you configure.

The Motion Service can:

  • use motion planning algorithms locally on your robot to plan coordinated motion across many components.
  • pass movement requests through to individual components which have implemented their own motion planning.

Configuration

You need to configure frames for your robot’s components with the Frame System. This defines the spatial context within which the Motion Service operates.

The Motion Service itself is enabled by default, so you do not need to do any extra configuration in the Viam app to enable it.

API

The Motion Service supports the following methods:

Method NameDescription
MoveMove multiple components in a coordinated way to achieve a desired motion.
MoveSingleComponentMove a single component “manually.”
GetPoseGet the current location and orientation of a component.

Move

The Move method is the primary way to move multiple components, or to move any object to any other location. Given a destination pose and a component to move to that destination, Move will:

  1. Construct a full kinematic chain from goal to destination including all movable components in between.
  2. Solve that chain to move the specified component frame to the destination while adhering to any constraints.
  3. Execute that movement to move the actual robot.
  4. Return whether or not this process succeeded.

The Motion Service takes the volumes associated with all configured robot components (local and remote) into account for each request to ensure that the robot does not collide with itself or other known objects.

Parameters:

  • component_name (ResourceName): Name of the piece of the robot that should arrive at the destination. Note that move moves the distal end of the component to the destination. For example, when moving a robotic arm, the piece that will arrive at the destination is the end effector attachment point, not the base of the arm.

  • destination (PoseInFrame): Describes where the component_name frame should be moved to. Can be any pose, from the perspective of any component whose location is configured as a frame.

    Note that the destination pose is relative to the distal end of the specified frame. This means that if the destination is the same as the component_name frame, for example an arm’s frame, then a pose of {X: 10, Y: 0, Z: 0} will move that arm’s end effector by 10 mm in the local X direction.

  • world_state (WorldState) (optional): Data structure specifying information about the world around the robot. Used to augment the motion solving process. world_state includes obstacles and transforms:

    • Obstacles: Geometries located at a pose relative to some frame. When solving a motion plan with movable frames that contain inherent geometries, the solved path is constrained such that none of those inherent geometries intersect with the obstacles. Important considerations:
      • If a motion begins with a component already in collision with an obstacle, collisions between that specific component and that obstacle will not be checked.
      • The Motion Service assumes that obstacles are static. If a worldstate geometry is physically attached to a part of the robot such that it will move with the robot, specify it with transforms.
      • Geometry locations are defined with respect to the origin of the specified frame. Their poses are relative to the origin of the specified frame. A geometry associated with the frame of an arm with a pose of {X: 0, Y: 0, Z: -10} will be interpreted as being 10mm below the base of the arm, not 10mm below the end effector. This is different from destination and component_name, where poses are relative to the distal end of a frame.
    • Transforms: A list of PoseInFrame messages that specify other transformations to temporarily add to the frame system at solve time. Transforms can be used to account for geometries that are attached to the robot but not configured as robot components. For example, you could use a transform to represent the volume of a marker held in your robot’s gripper. Transforms are not added to the config or carried into later processes.

  • constraints (Constraints) (optional): Pass in motion constraints. By default, motion is unconstrained with the exception of obstacle avoidance.

  • extra (Mapping[str, Any]) (optional): A generic struct, containing extra options to pass to the underlying RPC call.

Returns:

  • (bool): Whether the move was successful.

For more information, see the Python SDK Docs.

motion = MotionClient.from_robot(robot=robot, name="builtin")

# Assumes a gripper configured with name "my_gripper" on the robot
gripper_name = Gripper.get_resource_name("my_gripper")
my_frame = "my_gripper_offset"

goal_pose = Pose(x=0, y=0, z=300, o_x=0, o_y=0, o_z=1, theta=0)

# Move the gripper
moved = await motion.move(component_name=gripper_name, destination=PoseInFrame(reference_frame="myFrame", pose=goal_pose), world_state=worldState, constraints={}, extra={})

Parameters:

  • ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.

  • componentName (resource.Name): Name of the piece of the robot that should arrive at the destination. Note that Move moves the distal end of the component to the destination. For example, when moving a robotic arm, the piece that will arrive at the destination is the end effector attachment point, not the base of the arm.

  • destination (PoseInFrame): Describes where the component_name should end up. Can be any pose, from the perspective of any component whose location is configured as a frame.

    Note that the destination pose is relative to the distal end of the specified frame. This means that if the destination is the same as the component_name frame, for example an arm’s frame, then a pose of {X: 10, Y: 0, Z: 0} will move that arm’s end effector by 10 mm in the local X direction.

  • worldState (WorldState): Data structure specifying information about the world around the robot. Used to augment the motion solving process. worldState includes obstacles and transforms:

    • Obstacles: Geometries located at a pose relative to some frame. When solving a motion plan with movable frames that contain inherent geometries, the solved path is constrained such that none of those inherent geometries intersect with the obstacles. Important considerations:
      • If a motion begins with a component already in collision with an obstacle, collisions between that specific component and that obstacle will not be checked.
      • The Motion Service assumes that obstacles are static. If a worldstate geometry is physically attached to a part of the robot such that it will move with the robot, specify it with transforms.
      • Geometries are “part of” their frame, rather than at the distal end of the frame. Their poses are relative to the origin of the specified frame. A geometry associated with the frame of an arm with a pose of {X: 0, Y: 0, Z: -10} will be interpreted as being 10mm below the base of the arm, not 10mm below the end effector. This is different from destination and componentName, where poses are relative to the distal end of a frame.
    • Transforms: A list of PoseInFrame messages that specify other transformations to temporarily add to the frame system at solve time. Transforms can be used to account for geometries that are attached to the robot but not configured as robot components. For example, you could use a transform to represent the volume of a marker held in your robot’s gripper. Transforms are not added to the config or carried into later processes.

  • constraints (Constraints): Pass in optional motion constraints. By default, motion is unconstrained with the exception of obstacle avoidance.

  • extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

  • (bool): Whether the move was successful.
  • (error): An error, if one occurred.

For more information, see the Go SDK Docs.

 // Access the Motion Service
motionService, err := motion.FromRobot(robot, "builtin")
if err != nil {
  logger.Fatal(err)
}

// Assumes a gripper configured with name "my_gripper" on the robot
gripperName := Gripper.Named("my_gripper")
myFrame := "my_gripper_offset"

goalPose := PoseInFrame(0, 0, 300, 0, 0, 1, 0)

// Move the gripper
moved, err := motionService.Move(context.Background(), gripperName, goalPose, worldState, nil, nil)

MoveSingleComponent

The MoveSingleComponent method allows you to bypass Viam’s internal motion planning entirely, if desired, for a single component. It looks similar to Move above but may result in radically different behavior.

MoveSingleComponent translates the given destination into the frame of the specified component, and then calls MoveToPosition on that component to move it to the desired location. As of April 25, 2023, arms are the only component supported by MoveSingleComponent.

As the name of the method suggests, only the single component specified by component_name will actuate.

An example of when this may be useful is if you have implemented your own custom arm model, and wish to use your own motion planning for it. Implement MoveToPosition on that arm using whatever method you desire to plan motion to the specified pose, and then use MoveSingleComponent to pass the destination in the frame of any other robot component.

Parameters:

  • component_name (ResourceName): The name of the component to move. This component must support the move_to_position API call with a Pose. As of April 21, 2023, arm is the only component so supported.

  • destination (PoseInFrame): Describes where the component_name should end up. Can be any pose, from the perspective of any component whose location is configured as a frame. The destination will be converted into the frame of the component specified in component_name when passed to move_to_position.

  • world_state (WorldState) (optional): Not used. See note above.

  • extra (Mapping[str, Any]) (optional): A generic struct, containing extra options to pass to the underlying RPC call.

Returns:

  • (bool): Whether the move was successful.

For more information, see the Python SDK Docs.

motion = MotionClient.from_robot(robot=robot, name="builtin")

# Assumes an arm configured with name "my_arm" on the robot
my_frame = "my_arm_offset"

goal_pose = Pose(x=0, y=400, z=0, o_x=0, o_y=0, o_z=1, theta=0)

# Move the arm
moved = await motion.move_to_position(component_name=my_arm, destination=PoseInFrame(reference_frame="myFrame", pose=goal_pose), world_state=worldState, extra={})

Parameters:

  • ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.

  • componentName (resource.Name): The name of the component to move. This component must support the MoveToPosition API call with a Pose. As of April 21, 2023, arm is the only component so supported.

  • destination (PoseInFrame): Describes where the component_name should end up. Can be any pose, from the perspective of any component whose location is configured as a frame. The destination will be converted into the frame of the component specified in componentName when passed to MoveToPosition.

  • worldState (WorldState): Not used. See note above.

  • extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

  • (bool): Whether the move was successful.
  • (error): An error, if one occurred.

For more information, see the Go SDK Docs.

 // Access the Motion Service
motionService, err := motion.FromRobot(robot, "builtin")
if err != nil {
  logger.Fatal(err)
}

// Assumes an arm configured with name "my_arm" on the robot
myFrame := "my_arm_offset"

goalPose := PoseInFrame(0, 400, 0, 0, 0, 1, 0)

// Move the arm
moved, err := motionService.MoveSingleComponent(context.TODO(), goalPose, worldState, nil)

GetPose

GetPose gets the location and orientation of a component within the Frame System. The return type of this function is a PoseInFrame describing the pose of the specified component with respect to the specified destination frame. You can use the supplemental_transforms argument to augment the robot’s existing frame system with supplemental frames.

Parameters:

  • component_name (ResourceName): Name of the piece of the robot whose pose is returned.

  • destination_frame (str): The name of the frame with respect to which the component’s pose is reported.

  • supplemental_transforms (Optional[List[Transforms]]) (optional): A list of Transforms. A Transform represents an additional frame which is added to the robot’s frame system. It consists of the following fields:

    • pose_in_observer_frame: Provides the relationship between the frame being added and another frame.
    • physical_object: An optional Geometry can be added to the frame being added.
    • reference_frame: Specifies the name of the frame which will be added to the frame system.

    When supplemental_transforms are provided, a frame system is created within the context of the GetPose function. This new frame system builds off the robot’s frame system and incorporates the Transforms provided. If the result of adding the Transforms results in a disconnected frame system, an error is thrown.

  • extra (Mapping[str, Any]) (optional): A generic struct, containing extra options to pass to the underlying RPC call.

Returns:

For more information, see the Python SDK Docs.

The following code example gets the pose of the tip of a gripper named my_gripper which is attached to the end of an arm, in the “world” reference_frame:

from viam.components.gripper import Gripper
from viam.services.motion import MotionClient

# Assume that the connect function is written and will return a valid robot.
robot = await connect()

motion = MotionClient.from_robot(robot=robot, name="builtin")
gripperName = Gripper.get_resource_name("my_gripper")
gripperPoseInWorld = await robot.get_pose(component_name=gripperName, destination_frame="world")

For a more complicated example, take the same scenario and get the pose of the same gripper with respect to an object situated at a location (100, 200, 0) relative to the “world” frame:

from viam.components.gripper import Gripper
from viam.services.motion import MotionClient
from viam.proto.common import Transform, PoseInFrame, Pose

# Assume that the connect function is written and will return a valid robot.
robot = await connect()

motion = MotionClient.from_robot(robot=robot, name="builtin")
objectPose = Pose(x=100, y=200, z=0, o_x=0, o_y=0, o_z=1, theta=0)
objectPoseInFrame = PoseInFrame(reference_frame="world", pose=objectPose)
objectTransform = Transform(reference_frame="object", pose_in_observer_frame=objectPoseInFrame)
gripperName = Gripper.get_resource_name("my_gripper")
gripperPoseInObjectFrame = await motion.get_pose(
  component_name=gripperName,
  destination_frame="world",
  supplemental_transforms=objectTransform
)

Parameters:

  • ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.

  • componentName (resource.Name): Name of the piece of the robot whose pose is returned.

  • destinationFrame (string): The name of the frame with respect to which the component’s pose is reported.

  • supplementalTransforms (LinkInFrame): An optional list of Transforms. A Transform represents an additional frame which is added to the robot’s frame system. It consists of the following fields:

    • pose_in_observer_frame: Provides the relationship between the frame being added and another frame.
    • physical_object: An optional Geometry can be added to the frame being added.
    • reference_frame: Specifies the name of the frame which will be added to the frame system.

    When supplementalTransforms are provided, a frame system is created within the context of the GetPose function. This new frame system builds off the robot’s frame system and incorporates the Transforms provided. If the result of adding the Transforms results in a disconnected frame system, an error is thrown.

  • extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

For more information, see the Go SDK Docs.

import (
  "context"

  "github.com/edaniels/golog"
  "go.viam.com/rdk/components/gripper"
  "go.viam.com/rdk/referenceframe"
  "go.viam.com/rdk/services/motion"
)

// Insert code to connect to your robot.
// (see code sample tab of your robot's page in the Viam app)

// Assumes a gripper configured with name "my_gripper" on the robot
gripperName := Gripper.Named("my_gripper")
myFrame := "my_gripper_offset"

 // Access the Motion Service
motionService, err := motion.FromRobot(robot, "builtin")
if err != nil {
  logger.Fatal(err)
}

myArmMotionPose, err := motionService.GetPose(context.Background(), my_gripper, referenceframe.World, nil, nil)
if err != nil {
  logger.Fatal(err)
}
logger.Info("Position of myArm from the Motion Service:", myArmMotionPose.Pose().Point())
logger.Info("Orientation of myArm from the Motion Service:", myArmMotionPose.Pose().Orientation())

Next Steps

The following tutorials contain complete example code for interacting with a robot arm through the arm component API, and with the Motion Service API, respectively:

A robotic arm

Move a Robot Arm

Access and control one of the most fundamental systems in robotics: A robotic arm.

Plan Motion with an Arm

Use the Motion Service to move robot arms and other components.