Robot Overview
This documentation is currently in beta. Please proceed carefully, and if you run into issues or need additional information, reach out to Hello Robot directly for support.
System Check
Run a full hardware and software check to confirm the system is ready:
stretch_system_checkIf all checks pass, your robot is ready to go. Use stretch_about to print robot identity and configuration, and stretch_params to inspect all robot parameters.
Homing
If your robot needs to be homed, the system check will tell you. The homing procedure takes approximately 30 seconds and finds the zero position of all joints. It must be run once every time the robot is powered on:
To home the robot:
stretch_robot_home--# insert video of robot homing
The robot will beep when finished. The motors will remember their homing state while the robot remains powered on — using the runstop, backdriving the robot, or restarting the NUC will not require rehoming. Powering the robot down completely will require homing again on the next boot.
To stow the robot to its compact travel pose:
stretch_robot_stow--# insert video of robot stowing
Runstop
The physical runstop button on the side of the robot's head immediately cuts power to all motors. The stretch_runstop tool lets you toggle the runstop programmatically from the terminal.
--# we already mentioned this in quick start should we point to it?
Monitoring
To monitor all robot devices, sensors, and activity in real time, including joint states, battery, and subsystem status:
This tool provides a unified live dashboard of the robot's state.
--# this tool exists in stretch_production_tools_ii, worth it to port to stretch4_body
Motors and Joints
--# add videos for each
Omnibase
Stretch 4 has a triangular omnibase, consisting of three holonomic closed-loop stepper motors each driving one wheel. Wheel numbering increases counter-clockwise, with wheel 0 to the left of the forward direction. This is consistent with the ROS frame convention where X+ is forward and Y+ is to the left, forming a right-handed coordinate frame.
The omnibase supports full planar motion — forward, sideways, diagonal, and rotation in place, all simultaneously. It also supports guarded contact sensitivity, which can be calibrated and tuned per use case.
To jog the base:
Lift
The lift provides vertical translation of the arm, reaching up to 47 inches high and all the way down to the ground. It is driven by a closed-loop stepper motor through a low gear-ratio belt drive, providing smooth and precise motion.
Arm
The arm comprises 4 telescoping links set on rollers, extending 21.6 inches beyond the base footprint and retracting to stow within it. Its proprietary drivetrain is driven by a stepper motor with closed-loop control and current sensing, enabling contact detection during motion. In combination, the lift, arm, and mobile base provide three orthogonal axes of motion — a Cartesian system for end-effector placement.
Contact Sensitivity (Guarded Contact)
Stretch's lift, arm, and omnibase joints have a contact detection system called Guarded Contact. This safety feature limits the forces Stretch can apply to a person or its environment, and can be tuned for your application.
Guarded Contact uses current sensing to detect when actuator effort exceeds a user-specified threshold during motion. When triggered, the safety controller halts the joint until a new movement command is received.
Feetech Motors
The wrist and gripper joints use Feetech servo motors, controlled over a TTL serial bus. To monitor Feetech motor status:
Feetech Errors and Reset
Feetech motors can enter an error state from over-force or over-temperature events. When in this state, the motor becomes backdrivable, stops responding to commands, and the LED on the motor body blinks red.
Powering the robot down completely will clear this error. Note: rebooting only the NUC will NOT clear it, as the Feetech motors remain powered. A faster way to clear the error:
This reboots all Feetech motors and resets their error status. You will need to re-run homing after doing this since the wrist_yaw and gripper joints lose their homed positions.
Head Cameras
Stretch 4 has a Luxonis OAK-FFC-3P camera module mounted in the head with three cameras:
Left
Fish-eye wide angle
1920×1200
30
Right
Fish-eye wide angle
1920×1200
30
Center
High-resolution color
4032×3040
10
The left and right cameras are fish-eye wide-angle cameras providing a broad environmental field of view. The center camera is a high-resolution color camera. All three are angled to maximize combined visual coverage in every frame.
To display any combination of camera feeds and open them in rerun or opencv :
use either --rerun or --opencv (not both) in conjunction with the choice of camera combination.
use the flag -h to see all options
Emulated RGBD from Head Cameras
The head cameras can be fused with the head Hesai lidars to produce RGBD (color + depth) point clouds. To visualize this:
Camera Focus and Calibration
Camera focus is adjusted and intrinsics are calibrated using the factory calibration pipeline. After calibration, cross-calibration between cameras and lidars is also performed during the bringup process to align all sensor modalities spatially.
Dexterous Wrist
Stretch 4 has a three degree-of-freedom wrist with yaw, pitch, and roll actuation — all driven by Feetech actuators.
Wrist Yaw
310°
range_deg: [-65, 245]
Wrist Pitch
310°
range_deg: [-65, 245] — effective range reduced by self-collision limits
Wrist Roll
310°
range_deg: [-65, 245]
To jog individual wrist joints:
To home all wrist joints:
Individual axis homing is also available with stretch_wrist_yaw_home, stretch_wrist_pitch_home, and stretch_wrist_roll_home.
Gripper
The compliant gripper is a robust single-degree-of-freedom end-effector. A Feetech actuator drives the center of the spring mechanism, which causes the outer fingers to flex and provide a grasping force.
Gripper Cameras
Stretch 4 has two OAK-D-SR (Short Range) cameras mounted at the gripper, providing stereo depth for in-hand manipulation tasks. These are detected as a separate Luxonis device from the head cameras (2-sensor device vs. the 3-sensor head device).
Sensors
Stretch 4 includes the following sensors:
Hesai JT128 3D LiDAR × 2 (Left and Right, mounted on the head)
Luxonis OAK-FFC-3P Camera Module (Head: 3-camera array) + OAK-D-SR (Gripper: stereo pair)
Speaker (mounted at the bottom of the head)
Pixart J3 Line Sensor Array (base, floor-facing)
Hesai JT128 3D LiDAR (Head)
Stretch 4 has two Hesai JT128 3D LiDAR units mounted on the head — a left lidar and a right lidar — providing full 3D point cloud coverage of the environment. These are used for mapping, navigation, and RGBD fusion with the head cameras.
Each lidar communicates over Ethernet. The NUC holds a single network profile with two IP addresses to communicate with both lidars and the Jetson simultaneously:
Left lidar
192.168.1.202
Hesai JT128 left
Right lidar
192.168.1.201
Hesai JT128 right
NUC (Lidar subnet)
192.168.1.2
Onboard computer — lidar communications
NUC (Jetson subnet)
192.168.1.100
Onboard computer — Jetson communications
Jetson
192.168.1.101
AI co-processor
Speaker and Microphone
The robot has a speaker and noise-cancelling microphone mounted at the bottom of the head, allowing Stretch to communicate from across a room. To test audio output:
Line Sensor Array
Stretch 4 includes a floor-facing GreatScott GS2 line sensor array on the base. This array continuously scans the floor in front of the robot and uses an on-robot model to classify the surface as floor or obstacle, enabling low-latency hazard detection independent of the lidar.
The line sensor runs in a dedicated background worker process at approximately 30 Hz, and its output is used by the omnibase to automatically limit velocity when an obstacle is detected in the direction of travel. To visualize the line sensor:
LED Eyes and Lightbar
The robot head has two LED eye displays. These support a set of built-in animations including idle glow, blinking, directional gaze, rainbow spin, alert, and happy states:
The head also has a programmable RGB LED lightbar. The lightbar can be triggered and tested via stretch_power_periph_jog.
NVIDIA Jetson (AI Co-processor)
Stretch 4 includes an NVIDIA Jetson Orin module as a dedicated AI co-processor, directly connected to the NUC via Ethernet.
Software Environment
The Jetson runs with:
OS: Ubuntu 22.04 + JetPack 6.1
Custom Docker container with: ROS 2 Jazzy, PyTorch, CUDA (cu129), Zenoh, Ultralytics, and OpenCV Bridge for NVIDIA Jetson
Accessibility
The NVIDIA Jetson boots up automatically whenever the robot is powered on. Passwordless SSH is pre-configured, so you can seamlessly access the Jetson from the NUC using the following command:
Note: If the Jetson fails to boot, you can manually power it on from the NUC using stretch_power_periph_jog -d. To forcefully power it off from the NUC, use stretch_power_periph_jog -c)
Internet Connectivity
To enable system updates and software package installations, there is a Wi-Fi dongle attached directly to the Jetson processor. You can connect the Jetson's Wi-Fi dongle to your local internet using the command line interface (CLI).
Once logged into the Jetson via SSH, use the nmcli network manager to connect to your Wi-Fi network:
Once connected, you can verify internet access by pinging an external server:
GPU Offloading
The Jetson communicates with the NUC via Zenoh for ROS 2 topic bridging. This enables offloading compute-heavy tasks such as YOLO object detection or pose estimation to the Jetson's GPU, while the NUC handles robot control. The Jetson subscribes to image topics published by the NUC and returns inference results.
Software Architecture
Stretch 4 uses a client/server architecture in stretch4_body:
stretch_body_serverruns a 100 Hz control loop on the NUC, managing all hardware stateApplication code connects via
RobotClientto issue commandsA C++ transport backend handles non-blocking USB communication to all motor controllers in parallel
The 100 Hz control loop follows this sequence every tick:
Pull status from all devices
Update sentries (safety watchdogs)
Ingest commands from the Robot Client
Run active controllers and behaviors
Compute safe motion limits
Push safe commands to motor controllers
To launch the body server:
Gamepad Teleoperation
Stretch 4 ships with an Xbox controller and supports two control mappings:
1. Joint Space (default)
Direct joint-level control of the robot. All controls are summarized below:
Base Controls
Left Stick
Translate base (XY)
LB / RB
Rotate base
Hold LB + RB, Right Stick
Analog base rotation
RT + Left Stick
Straight-line base movement
Arm Controls
Right Stick
Wrist Pitch (Y) and Yaw (X)
D-Pad Up / Down
Lift up / down
D-Pad Left / Right
Arm retract / extend
A / B Buttons
Close / Open gripper
RT + LB / RB
Wrist Roll
Modifiers
LT
Precision mode (reduce speed)
2. Flying Gripper IK
IK-based Cartesian control of the gripper. Point the gripper toward your target with the Right Stick, then move toward it with the Left Stick:
Left Stick
Move toward target (translation)
Right Stick
Point gripper at target (orientation)
D-Pad Up / Down
Lift up / down
D-Pad Left / Right
Wrist Roll
A / B Buttons
Close / Open gripper
LT
Precision mode (reduce speed)
Special Functions
Y Button (tap)
Cycle control mapping (Joint Space ↔ Flying Gripper IK)
RT + A (tap)
Cycle motion speed profile (Slow / Medium / Fast)
RT + B (tap)
Cycle contact sensitivity profile
Start Button (tap, unhomed)
Home the robot
Start Button (tap, homed)
Switch gripper handedness (without motion)
Start Button (hold 3s, homed)
Switch gripper handedness (with motion)
RT + Select (tap)
Announce current settings (handedness, speed, sensitivity, mapping)
RT + Select (hold 2s)
Stow the robot
X Button (hold 0.5s)
Execute custom function command
To launch gamepad teleoperation:
Developer I/O
Stretch 4 contains additional ports connected to the onboard NUC that can be used for accessories:
Trunk: 1× USB-A 3.0 ports, 2x USB-A 2.0 ports, 1× Ethernet port, 1× HDMI port.
Head (top): 1× USB-A 2.0 port, 1x USC-C Port
End-of-arm: 1× USB-A 2.0 port
Wrist: Quick-connect mechanism for tool attachment.
There are also threaded mounting points on the head to add additional sensors.
Key Tools Reference
stretch_body_server
Start / stop / release the 100 Hz robot control server
stretch_robot_home
Home all robot joints
stretch_robot_stow
Stow the robot to its compact travel pose
stretch_runstop
Toggle the runstop programmatically
stretch_system_check
Full hardware and software system check
stretch_about
Print robot identity and configuration
stretch_params
Print all robot parameters
stretch_battery_check
Check battery state of charge
stretch_status
Live robot status display
stretch_joint_viz
Joint state visualization
stretch_collision_viz
Visualize self-collision safety margins
stretch_gamepad_teleop
Launch Xbox gamepad teleoperation
stretch_puppet_teleop
Launch puppet (backdriving) teleoperation
stretch_omni_base_jog
Jog the omnibase
stretch_lift_jog
Jog the lift
stretch_arm_jog
Jog the arm
stretch_arm_home
Home the arm
stretch_lift_home
Home the lift
stretch_gripper_jog
Jog the gripper
stretch_gripper_home
Home the gripper
stretch_dex_wrist_jog
Jog dex wrist joints
stretch_dex_wrist_home
Home all dex wrist joints
stretch_feetech_reboot
Reboot Feetech motors and clear errors
stretch_feetech_monitor
Monitor Feetech motor status
stretch_camera_show
Live camera feed viewer (configurable)
stretch_rgbd_show
Emulated RGBD from head cameras + lidar
stretch_line_sensor_viz_3d
3D visualization of line sensor data
stretch_power_periph_jog
Manually control power periph (Jetson, fans, lidar, etc.)
stretch_eoa_power
Toggle end-of-arm power
stretch_eye_animations
Run LED eye animations
stretch_audio_test
Test speaker output
stretch_pose_play
Play back recorded robot poses
stretch_pose_record
Record robot poses
stretch_pose_edit
Edit recorded pose files
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