[Question] is there any examples for using mobile manipulators ? about orbit HOT 8 OPEN

@nikepupu I had the same question, I have a mobile manipulator (differential), and I modified the configuration file for my robot, but couldn't find any examples for differential base robots. Were you able to find something? Thanks

from orbit.

yes, I am able to get my robot to work through modifying the Franka example in the code base. However, I need to modify the USD file quite a lot to get it to work. Somehow there are some issues with joints when changing URDF to USD.

from orbit.

That's amazing, what mobile robot are you using? Also, is it holonomic or differential? Thanks

from orbit.

It's a ridgeback with 2 UR5s

from orbit.

Oh okay, that's a holonomic drive. I doubt if orbit supports differential or Ackerman drive for now, will have to dig more into documentation I guess. Thanks for the response though!

from orbit.

I don't think orbit or isaac sim really has the concept of holonomic drive or differential drive. It's actually implemented through two prismatic joint in x and y direction and a revolute joint in x-y plane for holonomic drive. It not really simulating a wheel rotating. I don't really think the simulator is complex enough to handle actually wheel movement for a very complicated base. For differential, you need to come up with different constraints or equivalents.

from orbit.

Yes you are right. I suppose with prismatic x, y and revolute z we can model almost every holonomic drives but won't be the same for differential. Well that solves my problem. I have a mobile manipulator to I'm not sure if I'll be able to use underlying or it's feature even after modelling the constraints. Thanks though for the clarification!

from orbit.

Not sure if this helps, but I was able to get the Nvidia Carter robot working with differential control commanding wheel velocities independently by simply remapping the dofs:

from omni.isaac.orbit.robots.mobile_manipulator import MobileManipulatorCfg
from omni.isaac.orbit.actuators.group import ActuatorControlCfg, ActuatorGroupCfg
from omni.isaac.orbit.actuators.model import ImplicitActuatorCfg

ROBOT_USD = "robot_usd_path"

ROBOT_CFG = MobileManipulatorCfg(
    meta_info=MobileManipulatorCfg.MetaInfoCfg(
        usd_path=ROBOT_USD,
        base_num_dof=2,
        tool_num_dof=0,
        arm_num_dof=0,
    ),
    init_state=MobileManipulatorCfg.InitialStateCfg(
        dof_pos={
            'left_wheel': 0.0,
            'right_wheel': 0.0,
        },
        dof_vel={
            'left_wheel': 0.0,
            'right_wheel': 0.0,
        },
    ),
    ee_info=MobileManipulatorCfg.EndEffectorFrameCfg(
        body_name="chassis_link", pos_offset=(0.0, 0.0, 0.1034), rot_offset=(1.0, 0.0, 0.0, 0.0)
    ),
    actuator_groups={
        "base": ActuatorGroupCfg(
            dof_names=["left_wheel", "right_wheel"],
            model_cfg=ImplicitActuatorCfg(velocity_limit=100.0, torque_limit=1000.0),
            control_cfg=ActuatorControlCfg(
                command_types=["v_abs"], 
                stiffness={".*": 0.0}, 
                damping={".*": 1e5}),
        ),
    },
)

The robot can then be operated using:

...

actions = torch.tensor([[left_vel, right_vel] for _ in range(robot.count)], device=robot.device)
robot.apply_action(actions)

...

from orbit.