Arm Component

A robotic arm is a serial chain of joints and links, with a fixed end and an end effector end. Joints may rotate, translate, or both, while a link is a rigid connector between joints.

In simple terms, an arm has two ends: one fixed in place, and one with a device you can position.

When controlling an arm component, you can place the end effector at arbitrary cartesian positions relative to the base of the arm. You can do this by calling the MoveToPosition method to move the end effector to specified cartesian coordinates, or by controlling the joint positions directly with the MoveToJointPositions method.

When controlling an arm with viam-server, the following features are implemented for you:

Linear motion planning
Self-collision prevention
Obstacle avoidance

Motion planning with your arm’s built-in software

Each arm model is supported with a driver that is compatible with the software API that the model’s manufacturer supports. While some arm models build inverse kinematics into their software, many do not.

Most of the arm drivers for the Viam RDK bypass any onboard inverse kinematics, and use Viam’s motion service instead.
This driver handles turning the arm on and off, querying the arm for its current joint position, sending requests for the arm to move to a specified set of joint positions, and engaging brakes as needed, if supported.

Arm drivers are also paired, in the RDK, with JSON files that describe the kinematics parameters of each arm.

When you configure a supported arm model to connect to viam-server, the Arm driver will load and parse the kinematics file for the Viam RDK’s frame system service to use.
The frame system will allow you to easily calculate where any part of your robot is relative to any other part, other robot, or piece of the environment.
All arms have a Home position, which corresponds to setting all joint angles to 0.
When an arm is moved with a move_to_position call, the movement will follow a straight line, and not deviate from the start or end orientations more than the start and orientations differ from one another
If there is no way for the arm to move to the desired location in a straight line, or if it would self-collide or collide with an obstacle that was passed in as something to avoid, then the move_to_position call will fail.

Configuration

For configuration information, click on one of the supported arm models:

Model	Description
`fake`	A model used for testing, with no physical hardware.
`xArm6`	UFACTORY xArm 6
`xArm7`	UFACTORY xArm 7
`xArmLite`	UFACTORY Lite 6
`yahboom-dofbot`	Yahboom DOFBOT
`ur5e`	Universal Robots UR5e

Follow this guide to implement your custom arm as a modular resource.

Control your arm with Viam’s client SDK libraries

To get started using Viam’s SDKs to connect to and control your robot, go to your robot’s page on the Viam app, navigate to the Code sample tab, select your preferred programming language, and copy the sample code generated.

Location secret

By default, the sample code does not include your robot location secret. We strongly recommend that you add your location secret as an environment variable and import this variable into your development environment as needed.

To show your robot’s location secret in the sample code, toggle Include secret on the Code sample tab. You can also see your location secret on the locations page.

Caution

Do not share your location secret, part secret, or robot address publicly. Sharing this information could compromise your system security by allowing unauthorized access to your robot, or to the computer running your robot.

When executed, this sample code will create a connection to your robot as a client. Then control your robot programmatically by adding API method calls as shown in the following examples.

These examples assume you have an arm called "my_arm" configured as a component of your robot. If your arm has a different name, change the name in the code.

Be sure to import the arm package for the SDK you are using:

Python
Go

from viam.components.arm import Arm
# To use move_to_position:
from viam.proto.common import Pose
# To use move_to_joint_positions:
from viam.proto.component.arm import JointPositions

import (
  "go.viam.com/rdk/components/arm"
  // To use MoveToPosition:
  "go.viam.com/rdk/referenceframe"
  "go.viam.com/rdk/spatialmath"
  // To use MoveToJointPositions ("armapi" name optional, but necessary if importing other packages called "v1"):
  armapi "go.viam.com/api/component/arm/v1"
)

API

The arm component supports the following methods:

Method Name	Description
`GetEndPosition`	Get the current position of the arm as a Pose.
`MoveToPosition`	Move the end of the arm to the desired Pose.
`MoveToJointPositions`	Move each joint on the arm to the desired position.
`JointPositions`	Get the current position of each joint on the arm.
`Stop`	Stop the arm from moving.
`IsMoving`	Get if the arm is currently moving.
`GetKinematics`	Get the kinematics information associated with the arm.
`DoCommand`	Send or receive model-specific commands.

GetEndPosition

Get the current position of the arm as a Pose.

Python
Go

Parameters:

extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

(Pose): A representation of the arm’s current position as a 6 DOF (six degrees of freedom) pose. The Pose is composed of values for location and orientation with respect to the origin. Location is expressed as distance, which is represented by x, y, and z coordinate values. Orientation is expressed as an orientation vector, which is represented by o_x, o_y, o_z, and theta values.

For more information, see the Python SDK Docs.

my_arm = Arm.from_robot(robot=robot, name="my_arm")

# Get the end position of the arm as a Pose.
pos = await my_arm.get_end_position()

Parameters:

ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
extra (map[string]interface{}): Extra options to pass to the underlying RPC call. Returns:
(error): An error, if one occurred.
(spatialmath.Pose): A representation of the arm’s current position as a 6 DOF (six degrees of freedom) pose. The Pose is composed of values for location and orientation with respect to the origin. Location is expressed as distance, which is represented by x, y, and z coordinate values. Orientation is expressed as an orientation vector, which is represented by o_x, o_y, o_z, and theta values.

For more information, see the Go SDK Docs.

myArm, err := arm.FromRobot(robot, "my_arm")

// Get the end position of the arm as a Pose.
err, pos := myArm.EndPosition(context.Background(), nil)

MoveToPosition

Move the end of the arm to the desired Pose, relative to the base of the arm.

Python
Go

Parameters:

pose (Pose): A representation of the arm’s current position as a 6 DOF (six degrees of freedom) pose. The Pose is composed of values for location and orientation with respect to the origin. Location is expressed as distance, which is represented by x, y, and z coordinate values. Orientation is expressed as an orientation vector, which is represented by o_x, o_y, o_z, and theta values.
extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

None

For more information, see the Python SDK Docs.

my_arm = Arm.from_robot(robot=robot, name="my_arm")

# Create a Pose for the arm.
examplePose = Pose(x=5, y=5, z=5, o_x=5, o_y=5, o_z=5, theta=20)

# Move your arm to the Pose.
await my_arm.move_to_position(pose=examplePose)

Parameters:

ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
Pose (spatialmath.Pose): A representation of the arm’s current position as a 6 DOF (six degrees of freedom) pose. The Pose is composed of values for location and orientation with respect to the origin. Location is expressed as distance, which is represented by x, y, and z coordinate values. Orientation is expressed as an orientation vector, which is represented by o_x, o_y, o_z, and theta values.
extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

(error): An error, if one occurred.

For more information, see the Go SDK Docs.

myArm, err := arm.FromRobot(robot, "my_arm")

// Create a Pose for the arm.
examplePose = []float64{x: 5, y: 5, z: 5, o_x: 5, o_y: 5, o_z: 5, theta:20}

// Move your arm to the Pose.
err := myArm.MoveToPosition(context.Background(), pose: examplePose, nil)

MoveToJointPositions

Move each joint on the arm to the position specified in positions.

Caution

Collision checks are not enabled when doing direct joint control with MoveToJointPositions().

Python
Go

Parameters:

positions (JointPositions): The desired position of each joint of the arm at the end of movement. JointPositions can have one attribute, values, a list of joint positions with rotational values (degrees) and translational values (mm).
extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

None

For more information, see the Python SDK Docs

my_arm = Arm.from_robot(robot=robot, name="my_arm")

# Declare a list of values with your desired rotational value for each joint on
# the arm.
degrees = [0.0, 45.0, 0.0, 0.0, 0.0]

# Declare a new JointPositions with these values.
jointPos = arm.move_to_joint_positions(
    JointPositions(values=[0.0, 45.0, 0.0, 0.0, 0.0]))

# Move each joint of the arm to the position these values specify.
await my_arm.move_to_joint_positions(positions=jointPos)

Parameters:

ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
positions (JointPositions): The desired position of each joint of the arm at the end of movement. JointPositions can have one attribute, values, a list of joint positions with rotational values (degrees) and translational values (mm).
extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

(error): An error, if one occurred.

For more information, see the Go SDK Docs.

myArm, err := arm.FromRobot(robot, "my_arm")

// Declare an array of values with your desired rotational value for each joint on the arm.
degrees := []float64{4.0, 5.0, 6.0}

// Declare a new JointPositions with these values.
jointPos := componentpb.JointPositions{degrees}

// Move each joint of the arm to the position these values specify.
err := myArm.MoveToJointPositions(context.Background(), jointPos, nil)

JointPositions

Get the current position of each joint on the arm.

Python
Go

Parameters:

extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

(JointPositions): The position of each joint of the arm. JointPositions can have one attribute, values, a list of joint positions with rotational values (degrees) and translational values (mm).

For more information, see the Python SDK Docs

my_arm = Arm.from_robot(robot=robot, name="my_arm")

# Get the current position of each joint on the arm as JointPositions.
pos = await my_arm.get_joint_positions()

Parameters:

ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

(error): An error, if one occurred.
(JointPositions): The desired position of each joint of the arm at the end of movement. JointPositions can have one attribute, values, a list of joint positions with rotational values (degrees) and translational values (mm).

For more information, see the Go SDK Docs.

my_arm, err := arm.FromRobot(robot, "my_arm")

// Get the current position of each joint on the arm as JointPositions.
pos, err := my_arm.JointPositions(context.Background(), nil)

Stop

Stop all motion of the arm.

Python
Go

Parameters:

extra (Optional[Dict[str, Any]]): Extra options to pass to the underlying RPC call.
timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

None

For more information, see the Python SDK Docs.

my_arm = Arm.from_robot(robot=robot, name="my_arm")

# Stop all motion of the arm. It is assumed that the arm stops immediately.
await my_arm.stop()

Parameters:

ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
extra (map[string]interface{}): Extra options to pass to the underlying RPC call.

Returns:

(error): An error, if one occurred.

For more information, see the Go SDK Docs.

myArm, err := arm.FromRobot(robot, "my_arm")

// Stop all motion of the arm. It is assumed that the arm stops immediately.
err := myArm.Stop(context.Background(), nil)

GetKinematics

Note

This method is not yet available with the Viam Go SDK.

Get the kinematics information associated with the arm as the format and byte contents of the kinematics file.

Python

Parameters:

timeout (Optional[float]): An option to set how long to wait (in seconds) before calling a time-out and closing the underlying RPC call.

Returns:

(Tuple[KinematicsFileFormat.ValueType, bytes): A tuple containing the format of the arm’s .URDF or .json kinematics file and the byte contents of the file.

For more information, see the Python SDK Docs.

my_arm = Arm.from_robot(robot=robot, name="my_arm")

# Get the kinematics information associated with the arm.
kinematics = await my_arm.get_kinematics()

# Get the format of the kinematics file.
k_file = kinematics[0]

# Get the byte contents of the file.
k_bytes = kinematics[1]

IsMoving

Get if the arm is currently moving.

Python
Go

Parameters:

None

Returns:

(bool): If it is true or false that the arm is currently moving.

For more information, see the Python SDK Docs.

my_arm = Arm.from_robot(robot=robot, name="my_arm")

# Stop all motion of the arm. It is assumed that the arm stops immediately.
await my_arm.stop()

# Print if the arm is currently moving.
print(my_arm.is_moving())

Parameters:

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

Returns:

(bool): If it is true or false that the arm is currently moving.
(error): An error, if one occurred.

For more information, see the Go SDK Docs.

myArm, err := arm.FromRobot(robot, "my_arm")

// Stop all motion of the arm. It is assumed that the arm stops immediately.
myArm.Stop(context.Background(), nil)

// Log if the arm is currently moving.
is_moving, err := myArm.IsMoving(context.Background())
logger.Info(is_moving)

DoCommand

Execute model-specific commands that are not otherwise defined by the component API. For built-in models, model-specific commands are covered with each model’s documentation. If you are implementing your own arm and add features that have no built-in API method, you can access them with DoCommand.

Python
Go

Parameters:

command (Dict[str, Any]): The command to execute.

Returns:

(Dict[str, Any]): Result of the executed command.

my_arm = Arm.from_robot(robot, "my_arm")

command = {"cmd": "test", "data1": 500}
result = my_arm.do(command)

For more information, see the Python SDK Docs.

Parameters:

ctx (Context): A Context carries a deadline, a cancellation signal, and other values across API boundaries.
cmd (map[string]interface{}): The command to execute.

Returns:

(map[string]interface{}): Result of the executed command.
(error) : An error, if one occurred.

myArm, err := arm.FromRobot(robot, "my_arm")

command := map[string]interface{}{"cmd": "test", "data1": 500}
result, err := myArm.DoCommand(context.Background(), command)

For more information, see the Go SDK Docs.