Continuous Joint Control in While Loop

[JaeYoungLee79]

Only use python not ROS

Summary

Operation flow is : Input value of end-tip position --> Inverse Kinematics --> Calculated Target Joint Value --> Joint Control as continuously

Status

I'm coding above the flow and It works as well based on "[01-move_angular_and_cartesian.py]". Problem is that once running. I have four XYZ position sets. it is rectangular points. I already control the position of end-tip in Cartesian space by using "03-twist_command.py" example. Based on "While Loop", a change amount of each X,Y,Z inputs to Twist Command. It woking well to tracking the pixel value of video capture as my another application coding. In case of Joint Level, the example of "01-move_angular_and_cartesian.py"

Code Flow

Maximum allowed waiting time during actions (in seconds)

TIMEOUT_DURATION = 100

#Calculated Target joint value of First Position 
#And Joint value input to as below

joint_angle = action.reach_joint_angles.joint_angles.joint_angles.add()

print("Executing action")
base.ExecuteAction(action)
# It wokring well. And Second joint value input to as below

joint_angle = action.reach_joint_angles.joint_angles.joint_angles.add()

print("Executing action")
base.ExecuteAction(action)
# It is not working.

[JaeYoungLee79]

Question

It connection time is enough to operation as my just thinking. Is possible that continuous joint value control in real-time? (as like the twist command example) The example of waypoint trajectory already has the joint value of each point. I try : Each loop step --> calculate Joint values --> Throw value for Joint control command

Thanks for reading. Best Regards

[JaeYoungLee79]

As I look insdie API manual Below It can operate at "While Loop" API

• ChangeJointSpeeds.md
• ChangeTwist.md
• ChangeWrench.md

I can't looking "Angle Control" I want to control changes of angle value.

Anybody this experiences?

Thanks Best Regards

[felixmaisonneuve]

Hi @JaeYoungLee79,

I am not sure I fully understand what you want to do, so I will explain why what you are doing is not working and hopefully it will help you.

First, when you create your reach_joint_angle with your and create the joint_angles in a loop like this

    for joint_id in range(actuator_count.count):
        joint_angle = action.reach_joint_angles.joint_angles.joint_angles.add()
        joint_angle.joint_identifier = joint_id
        joint_angle.value = 0

Your action.reach_joint_angles.joint_angles.joint_angles is initially empty, so you need to add your joint angles with .add(). In you loop, it will look something like this (I will assume a 7DOF arm, so range(actuator_count.count) = [0..7])

action.reach_joint_angles.joint_angles.joint_angles = [] # initially, then you add {joint_id, 0} in each loop
action.reach_joint_angles.joint_angles.joint_angles = [{0, 0}] # after the first loop
action.reach_joint_angles.joint_angles.joint_angles = [{0, 0}, {1, 0}] # after the second loop
action.reach_joint_angles.joint_angles.joint_angles = [{0, 0}, {1, 0}, {2, 0}] # after the third loop
...
action.reach_joint_angles.joint_angles.joint_angles = [{0, 0}, {1, 0}, {2, 0}, {3, 0}, {4, 0}, {5, 0}, {6, 0}] # after the whole for loop

You finish with 7 JointAngle in your action.reach_joint_angles.joint_angles.joint_angles. If you .add another JointAngle, you would end up with more JointAngle in your action then the number of joints on your arm and it won't work. If you want to send another reach_joint_angles Action using the same object you created, you will want to edit the current values with something like this

    for joint_id in range(actuator_count.count):
        joint_angle = action.reach_joint_angles.joint_angles.joint_angles[joint_id] # instead of .add
        # joint_angle.joint_identifier = joint_id # not needed since it is already at the correct ID
        joint_angle.value = 0 # you can change the value here

I could help you more if you sent maybe a small sample of your code so I could better understand what you are trying to do and why it is not working

Best, Felix

[JaeYoungLee79]

Thanks for answer! It solved!