wiki:Tutorials

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Version 67 (modified by fma, 8 years ago) ( diff )
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Vocabulary
Tutorial 1
1. Settings
Tutorial 2
1. Settings
Tutorial 3
Conclusion

Tutorial

First, you need to know that Py4bot is just a framework, not a ready-to-use software. So it is up to you to write the application matching your robot. But don't worry, it is very easy.

The framework contains all base code to setup a working multi-legs robot. All we have to do is overwrite a few classes, and implement virtual methods. It means that you need to know how to code in Python, and what classes / methods are... If it is not the case, have a look here.

Before we dive into the tutorials, we need to install Py4bot, as described in the InstallationGuide. It is strongly suggested to install from git, so we can keep it up-to-date very easily.

Once it is done, we don't need to edit/modify the source code anymore; we will write our own code in a dedicated directory.

Vocabulary

First, lets define a few words. I tried to use commonly used vocabulary, and hope I did understand them correctly. Feel free to contact me if you find mistakes.

IK: Inverse Kinematic

Tutorial 1

Files for this tutorial are available in py4bot/examples/tutorial_1/. But don't just copy them here: write them from scratch, following the tutorial.

First, we create a new empty dir in our home dir:

$ mkdir tutorial_1
$ cd tutorial_1

All usefull classes are available from the api.py module. So, we just have to import things from here. Let's create a hexapod.py file to put our code, and import what we are going to use in this tutorial:

# -*- coding: utf-8 -*-

from py4bot.api import *

Now, let's create the robot! A multi-legs robot is mainly build from a body, and several legs.

We also need to create an actuator pool, which contains all legs joints actuators, in order to move them synchronized. In our example, actuators are standard servos, and we use the Veyron board, from DFRobot, to drive them:

import settings


class Hexapod(Robot):
    def _createBody(self):
        return Body(settings.LEGS_ORIGIN)

    def _createLegs(self):
        legs = {}
        legIk = {}
        for legIndex in settings.LEGS_INDEX:
            legs[legIndex] = Leg3Dof(legIndex, {'coxa': Coxa(), 'femur': Femur(), 'tibia': Tibia()}, settings.FEET_NEUTRAL[legIndex])
            legIk[legIndex] = Leg3DofIk(settings.LEGS_GEOMETRY[legIndex])

        return legs, legIk

    def _createActuatorPool(self):
        driver = Veyron()
        pool = ServoPool(driver)

        for leg in self._legs.values():

            # Create joints actuators
            num = settings.LEGS_SERVOS_MAPPING[leg.index]['coxa']
            servo = Servo(leg.coxa, num, **settings.SERVOS_CALIBRATION[num])
            pool.add(servo)

            num = settings.LEGS_SERVOS_MAPPING[leg.index]['femur']
            servo = Servo(leg.femur, num, **settings.SERVOS_CALIBRATION[num])
            pool.add(servo)

            num = settings.LEGS_SERVOS_MAPPING[leg.index]['tibia']
            servo = Servo(leg.tibia, num, **settings.SERVOS_CALIBRATION[num])
            pool.add(servo)

        return pool

As you can see, we just implemented 3 virtual methods, _createBody(), _createLegs() and _createActuatorPool().

Also note that we used some values from the settings.py module. This module is just a simple way to centralise the configuration of our hexapod. We will describe this module later.

To drive a robot, we need a remote control. In this tutorial, we are going to use an old gamepad, a Thrustmaster Firestorm Dual Analog 3. As I own such gamepad, I already added support in Py4bot:

class Gamepad(RemoteControl):
    def _createFrontend(self):
        return Thrustmaster(settings.THRUSTMASTER_PATH)

    def _buildComponents(self):
        self._addConfig("walk")
        self._addConfig("body")

        self._addComponent(Button, command=self.selectNextConfig, key="button_008", trigger="hold")
        self._addComponent(Button, command=self.selectPreviousConfig, key="button_009", trigger="hold")

        self._addComponent(Button, command=self.robot.incBodyPosition, key="button_004", mapper=MapperSetValue(dz=+5))
        self._addComponent(Button, command=self.robot.incBodyPosition, key="button_005", mapper=MapperSetValue(dz=-5))
        self._addComponent(Joystick, configs="walk", command=GaitSequencer().walk, keys=("analog_02", "analog_03", "analog_00"), mapper=MapperWalk())

        self._addComponent(Analog, configs="body", command=self.robot.setBodyExtraPosition, key="analog_00", mapper=MapperSetMultiply('yaw', coef=-15))
        self._addComponent(Analog, configs="body", command=self.robot.setBodyExtraPosition, key="analog_03", mapper=MapperSetMultiply('pitch', coef=-15))
        self._addComponent(Analog, configs="body", command=self.robot.setBodyExtraPosition, key="analog_02", mapper=MapperSetMultiply('roll', coef=15))

We won't deep into details, here; refer to the documentation for more informations about remote controls. This is an important part of the framework, and you can do very smart things, like having several configurations, using several remotes for the same robot...

Now, let's create our robot:

def main():
    def addGait(gaitClass, gaitName):
        gait = gaitClass(gaitName, settings.GAIT_LEGS_GROUPS[gaitName], settings.GAIT_PARAMS[gaitName])
        GaitManager().add(gait)

    addGait(GaitTripod, "tripod")
    addGait(GaitTetrapod, "tetrapod")
    addGait(GaitRiple, "riple")
    addGait(GaitWave, "metachronal")
    addGait(GaitWave, "wave")
    GaitManager().select("riple")

    robot = Hexapod()

    remote = Gamepad(robot)

    GaitSequencer().start()
    remote.start()

    robot.setBodyPosition(z=30)

    robot.mainLoop()

    remote.stop()
    remote.join()
    GaitSequencer().stop()
    GaitSequencer().join()


if __name__ == "__main__":
    main()

First, we add a few pre-defined gaits, in order to make it walk. Then, we create the robot itself, the remote control, and start all this little world!

Settings

Let's discuss about settings used in the previous part. See the user guide for the body/legs geometry conventions used.

LEGS_INDEX = ('RF', 'RM', 'RR', 'LR', 'LM', 'LF')

LEGS_INDEX contains the names used to define legs; they can be freely chosen, but these values must be used as keys for other params.

LEGS_GEOMETRY = {
    'RM': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'RF': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'LF': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'LM': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'LR': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'RR': {'coxa': 25, 'femur': 45, 'tibia': 65}
}

LEGS_GEOMETRY dict contains the lengths of the different parts of the legs, in mm.

LEGS_ORIGIN = {
    'RM': {'x':  50., 'y':   0., 'gamma0' :   0.},
    'RF': {'x':  35., 'y':  80., 'gamma0' :  30.},
    'LF': {'x': -35., 'y':  80., 'gamma0' : 150.},
    'LM': {'x': -50., 'y':   0., 'gamma0' : 180.},
    'LR': {'x': -35., 'y': -80., 'gamma0' : 210.},
    'RR': {'x':  35., 'y': -80., 'gamma0' : 330.},
}

LEGS_ORIGIN dict contains the positions and orientation of the origin of the legs: (x, y) defines the center of rotation of coxa joint, and gamma0 is the angle of the legs at neutral position.

FEET_NEUTRAL = {
    'RM': LEGS_GEOMETRY['RM']['coxa'] + LEGS_GEOMETRY['RM']['femur'],
    'RF': LEGS_GEOMETRY['RF']['coxa'] + LEGS_GEOMETRY['RF']['femur'],
    'LF': LEGS_GEOMETRY['LF']['coxa'] + LEGS_GEOMETRY['LF']['femur'],
    'LM': LEGS_GEOMETRY['LM']['coxa'] + LEGS_GEOMETRY['LM']['femur'],
    'LR': LEGS_GEOMETRY['LR']['coxa'] + LEGS_GEOMETRY['LR']['femur'],
    'RR': LEGS_GEOMETRY['RR']['coxa'] + LEGS_GEOMETRY['RR']['femur'],
}

FEET_NEUTRAL dict contains the feet neutral positions af all legs. This is just the distance from the legs origins, in the ground plane, along leg X axis.

LEGS_SERVOS_MAPPING = {
    'RF': {'coxa':  0, 'femur':  1, 'tibia':  2},
    'RM': {'coxa':  4, 'femur':  5, 'tibia':  6},
    'RR': {'coxa':  8, 'femur':  9, 'tibia': 10},
    'LR': {'coxa': 15, 'femur': 14, 'tibia': 13},
    'LM': {'coxa': 19, 'femur': 18, 'tibia': 17},
    'LF': {'coxa': 23, 'femur': 22, 'tibia': 21}
}

LEGS_SERVOS_MAPPING is a table to map all joints to actuators nums.

SERVOS_CALIBRATION = {
    0: {'offset': _90., 'pulse90': 1500, 'ratio': -1000/90.},  # coxa leg RF
    1: {'offset':  90., 'pulse90': 1500, 'ratio': -1000/90.},  # femur leg RF
    2: {'offset':   0., 'pulse90': 1500, 'ratio':  1000/90.},  # tibia leg RF

    4: {'offset': -90., 'pulse90': 1500, 'ratio': -1000/90.},  # coxa leg RM
    5: {'offset':  90., 'pulse90': 1500, 'ratio': -1000/90.},  # femur leg RM
    6: {'offset':   0., 'pulse90': 1500, 'ratio':  1000/90.},  # tibia leg RM

    8: {'offset': -90., 'pulse90': 1500, 'ratio': -1000/90.},  # coxa leg RR
    9: {'offset':  90., 'pulse90': 1500, 'ratio': -1000/90.},  # femur leg RR
    10: {'offset':  0., 'pulse90': 1500, 'ratio':  1000/90.},  # tibia leg RR

    15: {'offset': -90., 'pulse90': 1500, 'ratio': -1000/90.},  # coxa leg LR
    14: {'offset':  90., 'pulse90': 1500, 'ratio':  1000/90.},  # femur leg LR
    13: {'offset':   0., 'pulse90': 1500, 'ratio': -1000/90.},  # tibia leg LR

    19: {'offset': -90., 'pulse90': 1505, 'ratio': -1000/90.},  # coxa leg LM
    18: {'offset':  90., 'pulse90': 1500, 'ratio':  1000/90.},  # femur leg LM
    17: {'offset':   0., 'pulse90': 1500, 'ratio': -1000/90.},  # tibia leg LM

    23: {'offset': -90., 'pulse90': 1500, 'ratio': -1000/90.},  # coxa leg LF
    22: {'offset':  90., 'pulse90': 1500, 'ratio':  1000/90.},  # femur leg LF
    21: {'offset':   0., 'pulse90': 1500, 'ratio': -1000/90.},  # tibia leg LF
}

SERVOS_CALIBRATION contains some calibration:

offset is the angle between the servo reference and the real angle. See the FAQ for the real angles definition;
pulse90 is the pulse value for the neutral position of the servo, which is usually 90°;
ratio is the pulse width per degree.

Offsets may vary, depending how you mount the servos. Same, ratio sign may have to be inverted on one side, if you have a symetrical design; all angle are always computed using trigonometric direction (CCW).

See the user guide how to fine tune servos calibration.

Finally:

GAIT_LEGS_GROUPS = {
    'tripod':      (('RM', 'LF', 'LR'), ('RF', 'LM', 'RR')),
    'tetrapod':    (('RR', 'LM'), ('RF', 'LR'), ('RM', 'LF')),
    'riple':       (('RR',), ('LM',), ('RF',), ('LR',), ('RM',), ('LF',)),
    'metachronal': (('RR',), ('LM',), ('RF',), ('LR',), ('RM',), ('LF',)),
    'wave':        (('RR',), ('RM',), ('RF',), ('LR',), ('LM',), ('LF',))
}

GAIT_PARAMS = {
    'tripod': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 40.}, 'speed': {'min': 50., 'max': 200.}},
    'tetrapod': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 200.}},
    'riple': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 300.}},
    'metachronal': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 200.}},
    'wave': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 200.}},
}

GAIT_LEGS_GROUPS contains the legs grouped together and controlled at the same time during the gait usage.

Note that we need to define sequences, so don't forget the comma to define a tuple with a unique element.

GAIT_PARAMS contains some additional gaits params:

length is the distance (range) each leg will move for an entire cycle when the robot translate at full speed;
angle is the angle (range) each leg will turn for an entire cycle when the robot rotate at full speed;
height is the height (range) the leg will lift up;
speed is the speed (range).

These values must be adjusted for each robot, to avoid legs collisions.

THRUSTMASTER_PATH = "/dev/input/by-id/usb-Mega_World_Thrustmaster_dual_analog_3.2-event-joystick"

No need for further explanations.

Tutorial 2

Files for this tutorial are available in py4bot/examples/tutorial_2/

Here, we will see how to use the 3D simulation stuff.

As before, we create a new empty dir in our home dir:

$ mkdir tutorial_2
$ cd tutorial_2

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import math

import visual

from py4bot.api import *

import settings

Nothing fancy, here.

class Hexapod3D(Robot3D):
    def _createBody(self):
        return Body(settings.LEGS_ORIGIN)

    def _createLegs(self):
        legs = {}
        legIk = {}
        for legIndex in settings.LEGS_INDEX:
            legs[legIndex] = Leg3Dof(legIndex, {'coxa': Coxa(), 'femur': Femur(), 'tibia': Tibia()}, settings.FEET_NEUTRAL[legIndex])
            legIk[legIndex] = Leg3DofIk(settings.LEGS_GEOMETRY[legIndex])

        return legs, legIk

Same as before, except that we inherits from Robot3D, instead of Robot.

    def _createActuatorPool(self):
        driver = Driver3D()
        pool = ActuatorPool(driver)

        num = 0
        for leg in self._legs.values():

            # Create joints actuators
            coxa3D = Coxa3D(leg.coxa, num, settings.LEGS_GEOMETRY[leg.index]['coxa'])
            pool.add(coxa3D)
            num += 1

            femur3D = Femur3D(leg.femur, num, settings.LEGS_GEOMETRY[leg.index]['femur'])
            pool.add(femur3D)
            num += 1

            tibia3D = Tibia3D(leg.tibia, num, settings.LEGS_GEOMETRY[leg.index]['tibia'])
            pool.add(tibia3D)
            num += 1

            # Init 3D view
            coxa3D.frame = self._body3D
            femur3D.frame = coxa3D
            tibia3D.frame = femur3D

            coxa3D.pos = (settings.LEGS_ORIGIN[leg.index]['x'], 0, -settings.LEGS_ORIGIN[leg.index]['y'])
            femur3D.pos = (settings.LEGS_GEOMETRY[leg.index]['coxa'], 0, 0)
            tibia3D.pos = (settings.LEGS_GEOMETRY[leg.index]['femur'], 0, 0)

            coxa3D.rotate(angle=math.radians(settings.LEGS_ORIGIN[leg.index]['gamma0']), axis=(0, 1, 0))

        return pool

Here, we use specific 3D actuators: Coxa3D, Femur3D, Tibia3D; they all use the VPython library to represent themselves on the screen.

Note that we don't use a custom actuator mapping; nums are automatically incremented.

We also need to configure the hierarchy, and the relative positions of the actuators.

Note: this may change in the future; I'm working on a simpler way to do all this.

class Gamepad(RemoteControl):
    def _createFrontend(self):
        return Thrustmaster(settings.THRUSTMASTER_PATH)

    def _buildComponents(self):
        self._addConfig("walk")
        self._addConfig("body")

        self._addComponent(Button, command=self.selectNextConfig, key="button_008", trigger="hold")
        self._addComponent(Button, command=self.selectPreviousConfig, key="button_009", trigger="hold")

        self._addComponent(Button, command=self.robot.incBodyPosition, key="button_004", mapper=MapperSetValue(dz=+5))
        self._addComponent(Button, command=self.robot.incBodyPosition, key="button_005", mapper=MapperSetValue(dz=-5))
        self._addComponent(Joystick, configs="walk", command=GaitSequencer().walk, keys=("analog_02", "analog_03", "analog_00"), mapper=MapperWalk())

        self._addComponent(Analog, configs="body", command=self.robot.setBodyExtraPosition, key="analog_00", mapper=MapperSetMultiply('yaw', coef=-15))
        self._addComponent(Analog, configs="body", command=self.robot.setBodyExtraPosition, key="analog_03", mapper=MapperSetMultiply('pitch', coef=-15))
        self._addComponent(Analog, configs="body", command=self.robot.setBodyExtraPosition, key="analog_02", mapper=MapperSetMultiply('roll', coef=15))

Same as before...

def main():
    scene = visual.display(width=settings.SCENE_WIDTH, height=settings.SCENE_HEIGHT)
    ground = visual.box(axis=(0, 1, 0), pos=(0, 0, 0), length=0.1, height=500, width=500, color=visual.color.gray(0.75), opacity=0.5)

    def addGait(gaitClass, gaitName):
        gait = gaitClass(gaitName, settings.GAIT_LEGS_GROUPS[gaitName], settings.GAIT_PARAMS[gaitName])
        GaitManager().add(gait)

    addGait(GaitTripod, "tripod")
    addGait(GaitTetrapod, "tetrapod")
    addGait(GaitRiple, "riple")
    addGait(GaitWave, "metachronal")
    addGait(GaitWave, "wave")
    GaitManager().select("riple")

    robot = Hexapod3D()

    remote = Gamepad(robot)

    GaitSequencer().start()
    remote.start()

    robot.setBodyPosition(z=30)

    robot.mainLoop()

    remote.stop()
    remote.join()
    GaitSequencer().stop()
    GaitSequencer().join()

if __name__ == "__main__":
    main()

The only difference, here, is the scene size init, and the ground addition (optional).

Settings

# -*- coding: utf-8 -*-

from py4bot.common import config


# Legs index
LEGS_INDEX = ('RF', 'RM', 'RR', 'LR', 'LM', 'LF')

# Legs geometry
LEGS_GEOMETRY = {
    'RM': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'RF': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'LF': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'LM': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'LR': {'coxa': 25, 'femur': 45, 'tibia': 65},
    'RR': {'coxa': 25, 'femur': 45, 'tibia': 65}
}

# Legs origin
LEGS_ORIGIN = {
    'RM': {'x':  35., 'y':   0., 'gamma0' :   0.},
    'RF': {'x':  35., 'y':  65., 'gamma0' :  30.},
    'LF': {'x': -35., 'y':  65., 'gamma0' : 150.},
    'LM': {'x': -35., 'y':   0., 'gamma0' : 180.},
    'LR': {'x': -35., 'y': -65., 'gamma0' : 210.},
    'RR': {'x':  35., 'y': -65., 'gamma0' : 330.},
}

# Legs feet neutral position
FEET_NEUTRAL = {
    'RM': LEGS_GEOMETRY['RM']['coxa'] + LEGS_GEOMETRY['RM']['femur'],
    'RF': LEGS_GEOMETRY['RF']['coxa'] + LEGS_GEOMETRY['RF']['femur'],
    'LF': LEGS_GEOMETRY['LF']['coxa'] + LEGS_GEOMETRY['LF']['femur'],
    'LM': LEGS_GEOMETRY['LM']['coxa'] + LEGS_GEOMETRY['LM']['femur'],
    'LR': LEGS_GEOMETRY['LR']['coxa'] + LEGS_GEOMETRY['LR']['femur'],
    'RR': LEGS_GEOMETRY['RR']['coxa'] + LEGS_GEOMETRY['RR']['femur'],
}

# Gaits
GAIT_LEGS_GROUPS = {
    'tripod':      (('RM', 'LF', 'LR'), ('RF', 'LM', 'RR')),
    'tetrapod':    (('RR', 'LM'), ('RF', 'LR'), ('RM', 'LF')),
    'riple':       (('RR',), ('LM',), ('RF',), ('LR',), ('RM',), ('LF',)),
    'metachronal': (('RR',), ('LM',), ('RF',), ('LR',), ('RM',), ('LF',)),
    'wave':        (('RR',), ('RM',), ('RF',), ('LR',), ('LM',), ('LF',))
}

GAIT_PARAMS = {
    'tripod': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 40.}, 'speed': {'min': 50., 'max': 200.}},
    'tetrapod': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 200.}},
    'riple': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 300.}},
    'metachronal': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 200.}},
    'wave': {'length': {'min': 4., 'max': 40.}, 'angle': {'min': 2., 'max': 10.}, 'height': {'min': 10, 'max': 30.}, 'speed': {'min': 50., 'max': 200.}},
}

# Gamepad path
THRUSTMASTER_PATH = "/dev/input/by-id/usb-Mega_World_Thrustmaster_dual_analog_3.2-event-joystick"

# VPython scene default size
SCENE_WIDTH = 640
SCENE_HEIGHT = 480

We removed the servos mapping/calibration, as we don't need them anymore, and we just added the scene default size.

Tutorial 3

Files for this tutorial are available in py4bot/examples/tutorial_3/.

Here, we will see how to create a custom input frontend for a new gamepad.

Again, we create a new empty dir in our home dir:

$ mkdir tutorial_3
$ cd tutorial_3

TODO

Conclusion

Thanks for reading these tutorials! This is the first working dev. release; there are many additional things to do, and final implementation may change, according to feedback/suggestions I will get. But the core is there. Again, the goal of this framework is to provide a high level tool to build complete and powerfull applications to control multi-legs robots.

Have a look at py4bot/examples/cronos/, which contains the code for my 4DoF hexapod, and closely follows Py4bot devs.

Note: See TracWiki for help on using the wiki.

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Table of Contents

Tutorial

Vocabulary

Tutorial 1

Settings

Tutorial 2

Settings

Tutorial 3

Conclusion

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