Object Command Payload

afObject Command Message

ObjectCmd Payload	Description
header	The ROS message header includes seq_number, time_stamp and frame_id. frame_id not used for now
pose	The pose command (position and orientation) in Parent frame
wrench	The wrench command (force and torque) for this body in World Frame
enable_position_controller	Boolean to inform which command to consider 1 for pose Command & 0 for wrench Command
joint_cmds	An array of joint commands for children joints
position_controller_mask	A mask to inform if the joint command is a Position Control Target or Effort Command

Types of Controllers:

The ObjectCmd has two distinct control fields. One being the afBody's Cartesian Pose Control using pose, wrench and enable_position_control payload fields and the other being the joint control of connected bodies using the joint_cmds and position_control_mask payload fileds.

Body's Pose Control

The payload fields (pose, wrench and enable_position_control) are designed to control the body in either Cartesian Wrench Control Mode or Cartesian Position Control Mode. The pose and wrench fields serve to control the equivalent pose or wrench of the object whose topic is being published to. The selection between pose and wrench command depends on the flag enable_position_control. When this flag is 0 (default), wrench command is considered while pose command is considered for when it's 1. The controller gains for pose command are set directly in the bodies AMBF Description File. The wrench field does not require any controller gains.

Connected Bodies Joint Control

The payload fields (joint_cmds and position_control_mask) are designed to control the children joints of the relevant afBody. The joints_cmds array is set in the order of the joint_names* from the corresponding ObjectState message of the Object a user is trying to control. One can echo the joint_names* in the ObjectState message to see what joints a body has (if any) and what order are they are stored. The size of the joint commands array depends on the number of joints, however, it's not required to fill in all the joints. For example, if the user intends to control the first 2 of the listed 10 joints, just setting the first two elements in the array should yield the desired result. Similarly, the position_controller_mask can be set to 1's for the joints that require position control, and 0 for open loop effort. Similar to afBody's Pose control, the controller gains for the joints positions are set directly in the AMBF description file.

If one wants to directly control the pose or wrench of any child Object, it can be accomplished by utilizing the corresponding objects' afObjectCmd (just like in the last section)

joint_names:*

Only the root bodies of a connected tree of bodies are set to publish the children_names, joint_names, joint_positions. This can be easily changed by either setting the the last three fields in the afObjectCmd message or by modifying the corresponding AMBF Description file. Here is a simple example of an afBody data block where the fileds publish_children_names, *pubish_joint_names and publish_joint_positions have been added and set to true:

BODY WristPlatform:
  name: WristPlatform
  mesh: WristPlatform.STL
  mass: 0.4
  collision margin: 0.001
  scale: 1.0
  publish children names: True
  publish joint names: True
  publish joint positions: True
  location:
    orientation: {p: -0.0, r: -0.0, y: -3.136}
    position: {x: -0.136, y: 0.002, z: -0.319}
  inertial offset:
    orientation: {p: 0, r: 0, y: 0}
    position: {x: 0.0, y: -0.055, z: -0.054}
  friction: {rolling: 0.01, static: 0.5}
  damping: {angular: 0.9, linear: 0.9}
  restitution: 0
  collision groups: [0]
  color components:
    ambient: {level: 1.0}
    diffuse: {b: 0.4576, g: 0.3377, r: 0.0488}
    specular: {b: 1.0, g: 1.0, r: 1.0}
    transparency: 1.0

You can do this for any afBody before launching the simulator.