Tutorial 1: Commands
Starting a MuJoCo simulated robot
In a terminal, call:
pam_mujoco tutorials_1_to_3
this will start an instance of pam_mujoco in a new terminal.
This instance does not start a simulated robot yet, as it works for a client process to configure it.
Introduction to commands
You may now run tutorial_1.py
python3 ./tutorial_1.py
Here some comments regarding the source code similar of the one of Tutorial 1.
# configuring pam_mujoco and getting an interface to it.
# More on handle somewhere below.
# In this specific case, this will configure pam_mujoco
# to start a pressure controlled robot
handle = get_handle()
# getting an o80 frontend to the pressured robot
# The frontend will allow to send pressures to the robot
# and/or read the robot's state
frontend = handle.frontends["robot"]
pressure = 20000
duration = 5 # seconds
# creating a command locally. The command is *not* sent to the robot yet.
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.QUEUE)
# sending the command to the robot, and waiting for its completion.
frontend.pulse_and_wait()
You should observe the pressures of all muscles raising to 20000 in 5 seconds.
Note that you can add more than one command at once:
# adding a first command
pressure = 12000
duration = 3 # seconds
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.QUEUE)
# adding a second command
pressure = 20000
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.QUEUE)
# sending both commands to the robot, and waiting for their completions.
print("sending commands to shared memory and waiting for completion ...")
frontend.pulse_and_wait()
print("... completed !")
In the program above, the method “pulse_and_wait” returns once both commands have been executed by the robot.
pressure = 15000
duration=10
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.QUEUE)
pressure = 20000
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.QUEUE)
# sending command to the robot, and returning immediately
frontend.pulse()
Above, we use the method “pulse” instead of “pulse_and_wait”. You may notice that the method returns immediately. “pulse” writes the command in the shared memory, and the robot executes it. But as the robot does this, you may create new commands.
For example, rerun the code above, and immediately execute:
pressure = 0
duration = 1
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.QUEUE)
frontend.pulse()
You may notice that the pressures of the muscles go to 15000, then 20000, and finally to 0 (or their minimal pressure value). While the robot was running the commands for setting the pressures to 15000 and 20000, it receives the supplementary command to set the pressures to 0. The mode o80.Mode.QUEUE commanded the command to go to pressure 0 to start only once the other commands have been achieved. On the contrary, if we had run:
pressure = 0
duration = 1
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.OVERWRITE)
frontend.pulse()
the mode o80.Mode.OVERWRITE has the command to go to pressure 0 replacing the previous command. Similarly:
pressure = 12000
duration = 10
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.QUEUE)
frontend.pulse()
time.sleep(5)
pressure = 0
duration = 1
frontend.add_command([pressure]*4,[pressure]*4,
o80.Duration_us.seconds(duration),
o80.Mode.OVERWRITE)
frontend.pulse()
the code above has the robot starting to go toward the pressures 12000, but after 5 seconds this is interrupted (o80.Mode.OVERWRITE used) and the pressures brutally (in 1 second) go to 0.
add_command overloads
Controlling only selected muscle(s)
All the commands applied so far targeted all muscles. It is possible to request the change of the pressure of only one muscle:
muscle=0
frontend.add_command(muscle,12000,o80.Duration_us.seconds(3),o80.Mode.OVERWRITE)
frontend.pulse()
The above will request a change in the pressure of the muscle indexed 0.
frontend.add_command(0,15000,o80.Duration_us.seconds(3),o80.Mode.OVERWRITE)
frontend.add_command(1,20000,o80.Duration_us.seconds(6),o80.Mode.OVERWRITE)
frontend.pulse()
Note that the command above will have the muscles 0 and 1 changing pressure at the same time. Because these two commands target 2 different muscles, the second command does not overwrite the first one.
Controlling a degree of freedom
dof=0
frontend.add_command(dof,20000,15000,o80.Duration_us.seconds(3),o80.Mode.OVERWRITE)
frontend.pulse()
The command above will have the pressures of the agonist and antagonist muscles of the degree of freedom indexed 0 reach the values 20000 and 15000 (respectively) in 3 seconds.
Controlling all muscles
agonists = [15000,16000,17000,18000]
antagonists = [18000,17000,16000,15000]
frontend.add_command(agonists,antagonists,o80.Duration_us.seconds(3),o80.Mode.OVERWRITE)
frontend.pulse()
This command will target all muscles, for example the target pressure values for the first degree of freedom will be (15000,18000).
Speed commands
All the commands so far have been duration command, i.e. the request to interpolate between the current desired pressure value to a target desired pressure value over a given duration. It is possible to also create speed command, i.e. requesting the desired pressures to achieve a target value at a certain velocity (in terms of unit of pressure per unit of time).
Here are examples of speed commands:
agonists = [15000,16000,17000,18000]
antagonists = [18000,17000,16000,15000]
frontend.add_command(dof,20000,15000,o80.Speed.per_second(300),o80.Mode.OVERWRITE)
dof=0
frontend.add_command(dof,20000,15000,o80.Speed.per_second(200),o80.Mode.QUEUE)
frontend.add_command(3,15000,o80.Speed.per_second(400),o80.Mode.OVERWRITE)
frontend.add_command(4,20000,o80.Speed.per_second(300),o80.Mode.OVERWRITE)
frontend.pulse()
Direct commands
It is possible to create commands that do not specify any duration or speed. Direct commands request the desired pressure to reach the target pressure as fast as possible. For example:
# creating a sinusoid trajectory
pressure = 15000
v = 0.
increment = 0.025
amplitude = 3000
dof=2
for _ in range(5000):
v+=increment
ago = pressure + int(amplitude*math.sin(v))
antago = pressure - int(amplitude*math.sin(v))
frontend.add_command(dof,
ago,antago,
o80.Mode.QUEUE)
# playing the trajectory
frontend.pulse_and_wait()
Similarly to duration and speed commands, direct commands may use o80.Mode.QUEUE or o80.Mode.OVERWRITE, and refers to specific muscles, degrees of freedom or full set of pressures
Iteration command
Iteration command are an advanced type of command covered later in this tutorial.
Introduction to handles
The tutorial above started with:
handle = get_handle()
The code for the get_handle function is similar to:
def get_handle():
mujoco_id = "tutorials_1_to_3"
robot_segment_id = "robot"
control = pam_mujoco.MujocoRobot.PRESSURE_CONTROL
robot = pam_mujoco.MujocoRobot(robot_segment_id,
control=control)
graphics=True
accelerated_time=False
handle = pam_mujoco.MujocoHandle(mujoco_id,
robot1=robot,
graphics=graphics,
accelerated_time=accelerated_time)
return handle
The code above requested to create an handle to the pam_mujoco process running on the mujoco_id “tutorials_1_3”, and configuring it:
to run a pressure controlled robot with segment_id “robot”
to show MuJoCo graphics
to run realtime (and not accelerated_time)
During the handle creation, the corresponding configuration is written in the shared memory, and the waiting pam_mujoco instance uses it to start.
The handle provides access to the corresponding o80 robot frontend, which will allow to send commands to the robot:
frontend = handle.frontends["robot"]
# "robot" is the robot_segment_id as set in the handle