A-750 Robotic Arm¶

Support for the A-750 robotic arm includes visualization, an adapter to talk to real hardware, and keyboard teleop blueprint.

Quick Start¶

Run the A-750 teleop stack in mock mode:

dimos run keyboard-teleop-a750

This launches:

Module	Role
`KeyboardTeleopModule`	Publishes routed spatial EEF twist intent from the keyboard UI
`ControlCoordinator`	Runs a 100 Hz coordinator loop and `EEFTwistTask`
`ManipulationModule`	Loads the A-750 robot model in Drake and serves Meshcat visualization

Open the Meshcat URL printed in the terminal, usually http://localhost:7000, to view the robot.

Real Hardware¶

The A-750 blueprint uses the mock adapter by default. Start by connecting the arm to your computer with a USB cable. On Linux, the device will likely appear as /dev/ttyACM0. You can also check /dev/serial/ for stable symlinks to connected serial devices.

Pro tip: run this in a separate terminal while plugging in the arm to verify that the OS detects it normally:

dmesg -w

If the device appears but dimOS gets a permission error when opening it, you may need to add yourself to the dialout group:

sudo usermod -aG dialout "$USER"

After changing groups, log out and back in again, or start a new login shell, before retrying.

To connect to a physical arm, set DEVICE_PATH when launching the blueprint:

DEVICE_PATH=/dev/ttyACM0 dimos run keyboard-teleop-a750

# setting --device-path is not currently supported
# dimos --device-path /dev/ttyACM0 run keyboard-teleop-a750

Robot Model¶

The robot model and hardware config are defined in dimos/robot/manipulators/a750/config.py. The runnable keyboard teleop stack is composed in dimos/robot/manipulators/a750/blueprints/teleop.py.

Field	Value
Arm joints	`joint1` through `joint6`
Arm DOF	6
Gripper joints	`finger`, `finger_mimic` in the URDF; exposed as `arm/finger` in coordinator hardware
Base link	`base_link`
End-effector link	`gripper_base`
Home joints	`[0, 0, -90 deg, 0, 0, 0]`
Drake model	Pinned `a750_rev1.urdf` from `https://github.com/adob/a750_description`
FK/EEF twist task model	Same pinned model, with `joint1` through `joint6` controlled by the IK solver

The runtime model and a750_description package root are resolved lazily through a Git-backed robot description source handle pinned to an immutable commit. Planning and FK/IK share this model. Both finger joint limits are adjusted to 0–0.06 m so the model accepts the zero-position gripper used at initialization. Keyboard teleop does not load the model directly.

Gripper¶

The blueprint configures a parallel-jaw gripper:

Parameter	Value
Type	`a750`
Open position	`0.06 m`
Close position	`0.02 m`
Collision exclusions	Imported from the A-750 MoveIt/SRDF collision pairs

The adapter reads and commands gripper position in meters using the a750_control Python binding.

Hardware Adapter¶

The adapter is registered as a750 in dimos/hardware/manipulators/a750/adapter.py.

It supports:

Method family	Status
Connect/disconnect	Uses `a750_control.Robot(device_path)`
Joint position reads	Reads `pos_rad` from joints 1-6
Joint velocity reads	Reads `vel_rads` from joints 1-6
Joint effort reads	Reads `torque_nm` from joints 1-6
Joint position commands	Sends six joint positions plus a velocity ratio
Enable/disable	Starts and stops the `a750_control` control loop
Gripper reads/commands	Reads and commands gripper position in meters
Cartesian hardware commands	Stubbed; Cartesian motion is handled through dimOS IK
Force/torque reads	Not currently implemented

The a750_control package starts a separate thread with real-time priority for its hardware control loop. That loop sends commands and reads back joint state at 1 kHz. The dimOS read_joint_positions, read_joint_velocities, and read_joint_efforts calls return the most recent data cached by that loop rather than synchronously querying the robot, so returned joint data may be up to 1 ms stale. The USB connection also adds roughly 1 ms of latency.

The adapter requires the optional manipulation dependency:

a750-control @ git+https://github.com/adob/a750_control.git@7153e271317e22b4aa55ac1186c0f0e4903e8f39

If a750_control is not installed, connect() records an error and returns False.

Control Path¶

The keyboard-teleop-a750 blueprint is defined in dimos/robot/manipulators/a750/blueprints/teleop.py.

KeyboardTeleopModule
  -> /coordinator_ee_twist_command TwistStamped
  -> ControlCoordinator EEFTwistTask
  -> A750Adapter or mock adapter
  -> /coordinator_joint_state JointState
  -> ManipulationModule Drake/Meshcat visualization

The coordinator runs at 100 Hz. The lower-level a750_control binding runs its hardware control loop at 1 kHz once the adapter is enabled.

Keyboard Controls¶

The A-750 teleop command uses the same keyboard controls as the other manipulator teleop blueprints:

Key	Action
W/S	+X/-X
A/D	+Y/-Y
Q/E	+Z/-Z
R/F	+Roll/-Roll
T/G	+Pitch/-Pitch
Y/H	+Yaw/-Yaw
ESC	Quit

Known Limitations¶

Joint limits are currently approximate: [-pi, pi] for each arm joint, with max velocity pi rad/s in the dimOS adapter.
EEF twist commands are integrated and solved by the dimOS coordinator task, not by a native Cartesian mode in the hardware adapter.
Force/torque data is not exposed yet.
Real hardware mode depends on the external a750_control package and a reachable serial device.