Locomotion control Tutorial: The Robot Position

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NAOqi Motion - Overview | API | robot position Tutorial


Introduction

This tutorial explains how to use the robotPosition and getFootSteps API. Both these API will help you to have a better control on the walk algorithm.

Note

The tutorial is written in Python.

Download

You can download the robot position example here: almotion_robotPosition.py

If the matplotlib module is found, it will be used for plotting data: http://matplotlib.sourceforge.net/ .

For python-related troubleshooting, see: Python SDK - Installation Guide .

Code review

In this section we describe each important piece of code of the example.

NAOqi tools

First, we import some external modules:
  • config: custom module with helper functions
  • motion: constant definitions such as SPACE.
  • math: the standard python mathematic library useful for cos, sinus ...
  • almath: an optimized mathematic toolbox for robotics. For further details, see: libalmath API reference .
  • pylab: matplotlib useful for plotting data ( http://matplotlib.sourceforge.net/ ).

             
              #! /usr/bin/env python
# -*- encoding: UTF-8 -*-

"""Example: Robot Position - Small example"""

import qi
import argparse
import sys
import time
import math
import almath
try:
    import pylab as pyl
    PLOT_ALLOW = True
except ImportError:
    print "Matplotlib not found. this example will not plot data"
    PLOT_ALLOW = False


def main(session):
    """
    Robot Position - Small example to know how to deal
        with robotPosition and getFootSteps
    """
    # Get the services ALMotion & ALRobotPosture.

    motion_service = session.service("ALMotion")
    posture_service = session.service("ALRobotPosture")

    # Wake up robot
    motion_service.wakeUp()

    # Send robot to Stand Init
    posture_service.goToPosture("StandInit", 0.5)

    # Initialize the move
    motion_service.moveInit()

    # end init, begin experiment

    # First call of move API
    # Use _async=True argument to not be blocking here.
    motion_service.moveTo(0.3, 0.0, 0.5, _async=True)

    # wait that the move process start running
    time.sleep(0.1)

    # get robotPosition and nextRobotPosition
    useSensors = False
    robotPosition     = almath.Pose2D(motion_service.getRobotPosition(useSensors))
    nextRobotPosition = almath.Pose2D(motion_service.getNextRobotPosition())

    # get the first foot steps vector
    # (footPosition, unChangeable and changeable steps)

    footSteps1 = []
    try:
        footSteps1 = motion_service.getFootSteps()
    except Exception, errorMsg:
        print str(errorMsg)
        PLOT_ALLOW = False

    # Second call of move API
    motion_service.moveTo(0.3, 0.0, -0.5, _async=True)

    # get the second foot steps vector
    footSteps2 = []
    try:
        footSteps2 = motion_service.getFootSteps()
    except Exception, errorMsg:
        print str(errorMsg)
        PLOT_ALLOW = False

    # end experiment, begin compute

    # here we wait until the move process is over
    motion_service.waitUntilMoveIsFinished()
    # then we get the final robot position
    robotPositionFinal = almath.Pose2D(motion_service.getRobotPosition(False))

    # compute robot Move with the second call of move API
    # so between nextRobotPosition and robotPositionFinal
    robotMove = almath.pose2DInverse(nextRobotPosition)*robotPositionFinal
    print "Robot Move:", robotMove

    # Go to rest position
    motion_service.rest()

    # end compute, begin plot

    if PLOT_ALLOW:
        #################
        # Plot the data #
        #################
        pyl.figure()
        printRobotPosition(robotPosition, 'black')
        printRobotPosition(nextRobotPosition, 'blue')
        printFootSteps(footSteps1, 'green', 'red')

        pyl.figure()
        printRobotPosition(robotPosition, 'black')
        printRobotPosition(nextRobotPosition, 'blue')
        printFootSteps(footSteps2, 'blue', 'orange')

        pyl.show()

        # end plot

def printRobotPosition(pos, color):
    """ Function for plotting a robot position
        :param pos: an almath Pose2D
        :param color: the color of the robot
    """

    robotWidth = 0.01
    pyl.plot(pos.x, pos.y, color=color, marker='o', markersize=10)
    pyl.plot([pos.x, pos.x + robotWidth*math.cos(pos.theta)],
             [pos.y, pos.y + robotWidth*math.sin(pos.theta)],
             color=color,
             linewidth = 4)


def printFootSteps(footSteps, colorLeft, colorRight):
    """ Function for plotting the result of a getFootSteps
        :param footSteps: the result of a getFootSteps API call
        :param colorLeft: the color for left foot steps
        :param colorRight: the color for right foot steps
    """

    if len(footSteps[0]) == 2:
        posLeft  = footSteps[0][0]
        posRight = footSteps[0][1]

        if posLeft != posRight:
            leftPose2D = almath.Pose2D(posLeft[0], posLeft[1], posLeft[2])
            printLeftFootStep(leftPose2D, colorLeft, 3)
            rightPose2D = almath.Pose2D(posRight[0], posRight[1], posRight[2])
            printRightFootStep(rightPose2D, colorRight, 3)

    if len(footSteps[1]) >= 1:
        for i in range(len(footSteps[1])):
            name = footSteps[1][i][0]
            pos = footSteps[1][i][2]
            tmpPose2D = almath.Pose2D(pos[0], pos[1], pos[2])

            if name == 'LLeg':
                leftPose2D = rightPose2D * tmpPose2D
                printLeftFootStep(leftPose2D, colorLeft, 3)
            else:
                rightPose2D = leftPose2D * tmpPose2D
                printRightFootStep(rightPose2D, colorRight, 3)

    if len(footSteps[2]) >= 1:
        for i in range(len(footSteps[2])):
            name = footSteps[2][i][0]
            pos = footSteps[2][i][2]
            tmpPose2D = almath.Pose2D(pos[0], pos[1], pos[2])

            if name == 'LLeg':
                leftPose2D = rightPose2D * tmpPose2D
                printLeftFootStep(leftPose2D, colorLeft, 1)
            else:
                rightPose2D = leftPose2D * tmpPose2D
                printRightFootStep(rightPose2D, colorRight, 1)

    pyl.axis('equal')


def printLeftFootStep(footPose, color, size):
    """ Function for plotting a LEFT foot step
       :param footPose: an almath Pose2D
       :param color: the color for the foot step
       :param size: the size of the line
    """

    lFootBoxFL = footPose * almath.Pose2D( 0.110,  0.050, 0.0)
    lFootBoxFR = footPose * almath.Pose2D( 0.110, -0.038, 0.0)
    lFootBoxRR = footPose * almath.Pose2D(-0.047, -0.038, 0.0)
    lFootBoxRL = footPose * almath.Pose2D(-0.047,  0.050, 0.0)

    pyl.plot(footPose.x, footPose.y, color=color, marker='o', markersize=size*2)
    pyl.plot( [lFootBoxFL.x, lFootBoxFR.x, lFootBoxRR.x, lFootBoxRL.x, lFootBoxFL.x],
              [lFootBoxFL.y, lFootBoxFR.y, lFootBoxRR.y, lFootBoxRL.y, lFootBoxFL.y],
              color = color,
              linewidth = size)


def printRightFootStep(footPose, color, size):
    """ Function for plotting a RIGHT foot step
        :param footPose: an almath Pose2D
        :param color: the color for the foot step
        :param size: the size of the line
    """

    rFootBoxFL = footPose * almath.Pose2D( 0.110,  0.038, 0.0)
    rFootBoxFR = footPose * almath.Pose2D( 0.110, -0.050, 0.0)
    rFootBoxRR = footPose * almath.Pose2D(-0.047, -0.050, 0.0)
    rFootBoxRL = footPose * almath.Pose2D(-0.047,  0.038, 0.0)

    pyl.plot(footPose.x, footPose.y, color=color, marker='o', markersize=size*2)
    pyl.plot( [rFootBoxFL.x, rFootBoxFR.x, rFootBoxRR.x, rFootBoxRL.x, rFootBoxFL.x],
              [rFootBoxFL.y, rFootBoxFR.y, rFootBoxRR.y, rFootBoxRL.y, rFootBoxFL.y],
              color = color,
              linewidth = size)


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("--ip", type=str, default="127.0.0.1",
                        help="Robot IP address. On robot or Local Naoqi: use '127.0.0.1'.")
    parser.add_argument("--port", type=int, default=9559,
                        help="Naoqi port number")

    args = parser.parse_args()
    session = qi.Session()
    try:
        session.connect("tcp://" + args.ip + ":" + str(args.port))
    except RuntimeError:
        print ("Can't connect to Naoqi at ip \"" + args.ip + "\" on port " + str(args.port) +".\n"
               "Please check your script arguments. Run with -h option for help.")
        sys.exit(1)
    main(session)

             
            

Initialization of the robot

Then, the proxy to ALMotion module is created. This proxy is needed to call the ALMotion API. Set stiffness into the joint and execute a PoseInit.


             
              def main(session):
    """
    Robot Position - Small example to know how to deal
        with robotPosition and getFootSteps
    """
    # Get the services ALMotion & ALRobotPosture.

    motion_service = session.service("ALMotion")
    posture_service = session.service("ALRobotPosture")

    # Wake up robot
    motion_service.wakeUp()

    # Send robot to Stand Init
    posture_service.goToPosture("StandInit", 0.5)

    # Initialize the move
    motion_service.moveInit()


             
            

The experiment

We send a first walk command and, few seconds later, a second one.

We can see the difference between unchangeable and changeable foot steps. The second walk command is executed after the unchangeable foot generated by the first walk command.


             
              
    # First call of move API
    # Use _async=True argument to not be blocking here.
    motion_service.moveTo(0.3, 0.0, 0.5, _async=True)

    # wait that the move process start running
    time.sleep(0.1)

    # get robotPosition and nextRobotPosition
    useSensors = False
    robotPosition     = almath.Pose2D(motion_service.getRobotPosition(useSensors))
    nextRobotPosition = almath.Pose2D(motion_service.getNextRobotPosition())

    # get the first foot steps vector
    # (footPosition, unChangeable and changeable steps)

    footSteps1 = []
    try:
        footSteps1 = motion_service.getFootSteps()
    except Exception, errorMsg:
        print str(errorMsg)
        PLOT_ALLOW = False

    # Second call of move API
    motion_service.moveTo(0.3, 0.0, -0.5, _async=True)

    # get the second foot steps vector
    footSteps2 = []
    try:
        footSteps2 = motion_service.getFootSteps()
    except Exception, errorMsg:
        print str(errorMsg)
        PLOT_ALLOW = False


             
            

Compute robot move

Here, using walk API, we compute the move made by the robot. The goal is to find the value of the second walk command.

The robot begins the second walk command after the first command unchangeable foot step. In this case the robot position is the result of nextRobotPosition.

Then, we wait the end of the walk process (waitUntilMoveIsFinished) and we get the final robot position.

The distance is equivalent to:

(nextRobotPosition)^{-1}*robotPositionFinal .

And the result should be [0.3, 0.0, -0.5]


             
              
    # here we wait until the move process is over
    motion_service.waitUntilMoveIsFinished()
    # then we get the final robot position
    robotPositionFinal = almath.Pose2D(motion_service.getRobotPosition(False))

    # compute robot Move with the second call of move API
    # so between nextRobotPosition and robotPositionFinal
    robotMove = almath.pose2DInverse(nextRobotPosition)*robotPositionFinal
    print "Robot Move:", robotMove

    # Go to rest position
    motion_service.rest()