7. Multibot Guide

November 2, 2023 · View on GitHub

7. Multibot Guide

The SimFramework supports the simulation of multiple robotic arms in a single scene. This can be used to simulate bimanual setups or multi-agent cooperation.

Please refer to the Multibot Demos for reference implementations.

7.1 Multibot Initializaton

A multibot scene can be intuitively initalized by simply creating multiple robots. Remember to initialize the robots with different base positions.

scene = sim_factory.create_scene()
robot = sim_factory.create_robot(scene)
robot2 = sim_factory.create_robot(scene, base_position=[2.0, 0.0, 0.0])

7.2 Multibot Movement Commands

By using the standard movement commands, e.g.

print(scene.time_stamp) # 0.0
robot.gotoJointPosition(des_q_1, duration=2)
print(scene.time_stamp) # 2.0
robot2.gotoJointPosition(des_q_2, duration=4)
print(scene.time_stamp) # 6.0

the movement commands will be executed sequentially.

You can use the new optional block=False argument to execute movements simultaneously. The movements do not require to be of the same duration.

print(scene.time_stamp) # 0.0
robot.gotoJointPosition(des_q_1, duration=2, block=False)
print(scene.time_stamp) # 0.0
robot2.gotoJointPosition(des_q_2, duration=4)
print(scene.time_stamp) # 4.0

Please keep in mind, that the blocking call will control the program execution regardless of duration.

robot.gotoJointPosition(des_q_1, duration=2, block=False)
robot2.gotoJointPosition(des_q_2, duration=4)

# This will wait for robot2 to finish its movement, as this was a blocking call.
robot.gotoJointPosition(des_q_3, duration=2)

7.3 Multibot Task Space Commands.

Multibot setups support Task Space (IK) Commands. Per default, we assume that the target cartesian position and orientation are in the global coordinate system, i.e. relative to the world origin / table.

The Simframework will convert it to a local coordinate in the robots specific coordinate system, relative to its base position and orientation.

By setting global_coord=False, this conversion will be skipped.

scene = sim_factory.create_scene()
robot_default = sim_factory.create_robot(scene)
robot_forward = sim_factory.create_robot(scene, base_position=[2.0, 0.0, 0.0])
### GLOBAL COORDS
# Moves to global [1, 0, 0] coords
robot_default.gotoCartesianPosition([1, 0, 0]) 

# Moves to global [1, 0, 0] coords
robot_forward.gotoCartesianPosition([1, 0, 0]) 

### LOCAL COORDS
# Moves to global [1, 0, 0] coords, i.e. [1,0,0] relative to the default base [0, 0, 0]
robot_default.gotoCartesianPosition([1, 0, 0], global_coord=False) 

# Moves to global [3, 0, 0] coords, i.e. [1, 0, 0] relative to its base [2, 0, 0]
robot_forward.gotoCartesianPosition([1, 0, 0], global_coord=False)

7.4 Pybullet: Inhand Camera freeze

Pybullet Camera rendering can sometimes freeze the whole program execution. This reliably happens in a MultiBot Context, but the issue is the p.getCameraImage() call. Therefore we suspect that the issue is caused by Pybullet itself and not our implementation.