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Published © MIT

Lego Script3r

Teach kids how to write using Lego Mindstorms and Amazon Alexa

AdvancedFull instructions provided20 hours1,140
Lego Script3r

Things used in this project

Hardware components

Mindstorms EV3 Programming Brick / Kit
LEGO Mindstorms EV3 Programming Brick / Kit
×1
LEGO Technic Rough Terrain Crane 42082 Building Kit
×1
LEGO Technic Compact Crawler Crane 42097 Building Kit
×1
Amazon Echo
Amazon Alexa Amazon Echo
×1
Black marker pen
×1
wireless adapter
optional
×1
Micro SDHC card
for installing ev3dev
×1

Software apps and online services

ev3dev
Alexa Skills Kit
Amazon Alexa Alexa Skills Kit
Alexa Gadgets Toolkit
Amazon Alexa Alexa Gadgets Toolkit
VS Code
Microsoft VS Code

Story

Read more

Schematics

X Arm

Build instructions for the X arm

Y arm

Build instructions for the Y arm

Motor

Build instructions for motors

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Code

script3r.py

Python
The main code for the EV3 brick
#!/usr/bin/env python3
import os
import logging
import json
import threading
import xml.etree.ElementTree as ET
from time import sleep
from math import cos, sin, pi, acos, asin, sqrt, atan
from sys import stderr, stdout
import traceback


from ev3dev2.motor import LargeMotor, MediumMotor, OUTPUT_A, OUTPUT_D, OUTPUT_B
from ev3dev2.sound import Sound
from ev3dev2.led import Leds

from agt import AlexaGadget

MAX_ROTATION_X = 16
MAX_ROTATION_Y = 16
MAX_SPEED_X = 80
MAX_SPEED_Y = 80
POSITION_PEN = 130

# set logger to display on both EV3 Brick and console
logging.basicConfig(level=logging.INFO, stream=stdout,
                    format='%(message)s')
logging.getLogger().addHandler(logging.StreamHandler(stderr))
logger = logging.getLogger(__name__)


class Printer(object):

    def __init__(self):
        self.motor_x = LargeMotor(OUTPUT_A)
        self.motor_y = LargeMotor(OUTPUT_D)
        self.motor_pen = MediumMotor(OUTPUT_B)
        self._pen_down = False
        self.solver = Solver()

    def x(self):
        return -self.motor_x.position / (MAX_ROTATION_X * self.motor_x.count_per_rot)

    def y(self):
        return self.motor_y.position / (MAX_ROTATION_Y * self.motor_y.count_per_rot)

    def reset(self):
        self.motor_x.on_to_position(speed=80, position=0, block=False)
        self.motor_y.on_to_position(speed=80, position=0, block=False)
        self.motor_x.wait_until_not_moving()
        self.motor_y.wait_until_not_moving()
        self.pen_up()

    def move_wh(self, w, h, speed_x=MAX_SPEED_X, speed_y=MAX_SPEED_Y):
        self.motor_x.on_for_rotations(
            speed=speed_x, rotations=-w * MAX_ROTATION_X, block=False)
        self.motor_y.on_for_rotations(
            speed=speed_y, rotations=h * MAX_ROTATION_Y, block=False)
        self.motor_x.wait_until_not_moving()
        self.motor_y.wait_until_not_moving()

    def pen_down(self):
        if not self._pen_down:
            self.motor_pen.on_for_degrees(
                speed=25, degrees=POSITION_PEN, brake=True)
            self.motor_pen.wait_until_not_moving()
        self._pen_down = True

    def pen_up(self):
        if self._pen_down:
            self.motor_pen.on_for_degrees(
                speed=25, degrees=-POSITION_PEN, brake=True)
            self.motor_pen.wait_until_not_moving()
        self._pen_down = False

    def draw_arc(self, rad_x, rad_y, large, sweep, sx, sy, ex, ey):
        h, k, start, end = self.solver.solve_ellipse(
            (sx, sy), (ex, ey), rad_x, rad_y, large, sweep)
        print('The solution is:', h, k, start*180/pi, "->", end*180/pi)

        if start < 0:
            start += 2*pi
        if start < 0:
            end += 2*pi
        angle = start
        angle_to_do = 0

        if sweep:
            cclock = 1
            angle_to_do = end - start
        else:
            cclock = -1
            angle_to_do = start-end

        if angle_to_do < 0:
            angle_to_do += 2*pi

        print('doing:', angle_to_do*180/pi)

        step = 0
        angle_done = 0
        integral_error_x = 0
        integral_error_y = 0
        integral_weight = 0.15
        while angle_done < angle_to_do:
            dx = -sin(angle) * rad_x * cclock - \
                integral_error_x * integral_weight
            dy = cos(angle) * rad_y * cclock - \
                integral_error_y * integral_weight
            magnitude = sqrt(dx**2 + dy**2)
            speed_x = (dx/magnitude) * MAX_SPEED_X
            speed_y = (dy/magnitude) * MAX_SPEED_Y
            self.motor_x.on(speed=-speed_x)
            self.motor_y.on(speed=speed_y)
            sleep(0.1)

            old_angle = angle
            angle = self.solver.solve_angle(
                cx=h, cy=k, a=rad_x, b=rad_y, px=self.x(), py=self.y())
            step_angle = abs(angle-old_angle)

            if(step_angle > pi):
                step_angle = 2*pi - step_angle

            angle_done += step_angle

            x_sol = cos(angle) * rad_x + h
            y_sol = sin(angle) * rad_y + k
            integral_error_x += (self.x()-x_sol)
            integral_error_y += (self.y()-y_sol)

            step += 1
            if(step > 1000):
                break

        self.motor_x.stop()
        self.motor_y.stop()

    def draw_line(self, from_x, from_y, to_x, to_y, pen=True):
        self.move_wh(from_x - self.x(), from_y - self.y())
        if pen:
            self.pen_down()
        x = self.x()
        y = self.y()
        if (to_x-x) < 0.00001 and (to_x-x) > -0.00001:
            self.move_wh(0, to_y-y)
        else:
            m = abs((to_y-y)/(to_x-x))
            speed_x = 1
            speed_y = m * speed_x
            magnitude = sqrt(speed_x**2 + speed_y**2)
            speed_x = (speed_x/magnitude) * MAX_SPEED_X
            speed_y = (speed_y/magnitude) * MAX_SPEED_Y
            self.move_wh(to_x-x, to_y-y,
                         speed_x=speed_x, speed_y=speed_y)

        if pen:
            self.pen_up()

    def draw_svg_path(self, path, width, height):
        path_list = path.split(" ")
        index = 0
        m_x = 0
        m_y = 0
        while index < len(path_list):
            current = path_list[index]
            if current == 'M':
                x = float(path_list[index+1]) / width
                y = float(path_list[index+2]) / height
                m_x = x
                m_y = y
                self.move_wh(x-self.x(), y-self.y())
                index += 3
                self.pen_down()
            elif current == 'L':
                x = float(path_list[index+1]) / width
                y = float(path_list[index+2]) / height
                m_x = x
                m_y = y
                self.draw_line(m_x, m_y, x, y, pen=False)
                index += 3
            elif current == 'A':
                rad_x = float(path_list[index+1]) / width
                rad_y = float(path_list[index+2]) / height
                large = int(path_list[index+4])
                sweep = int(path_list[index+5])
                dx = float(path_list[index+6]) / width
                dy = float(path_list[index+7]) / width
                index += 8
                self.draw_arc(rad_x, rad_y, large, sweep, m_x, m_y, dx, dy)
                m_x = dx
                m_y = dy
            else:
                index += 1
        self.pen_up()


class Solver(object):

    def solve_angle(self, cx, cy, a, b, px, py):
        if px-cx:
            theta = atan(((py-cy)*a)/((px-cx)*b))
            if px-cx < 0:
                # quadrand 2 and 3
                theta = theta + pi
        else:
            if py-cy < 0:
                theta = -pi/2
            else:
                theta = pi/2
        return theta

    def solve_ellipse(self, p1, p2, a, b, large, sweep):
        x1 = p1[0]
        y1 = p1[1]
        x2 = p2[0]
        y2 = p2[1]

        m = -2*(b**2)*x1 + 2*(b**2)*x2
        n = -2*(a**2)*y1 + 2*(a**2)*y2
        q = -(b**2)*x1**2 - (a**2)*(y1**2) + (b**2)*(x2**2) + (a**2)*(y2**2)

        if n < -0.00001 or n > 0.00001:
            aa = b**2 + (a**2)*(m**2)/(n**2)
            bb = -2*(b**2)*x1 - (2*q*(a**2)*m)/(n**2) + (2*(a**2)*y1*m)/n
            cc = ((a**2)*(q**2))/(n**2) - (2*(a**2)*y1*q)/n + \
                (b**2)*(x1**2) + (a**2)*(y1**2) - (a**2)*(b**2)

            if bb**2 - 4*aa*cc < -0.00001 or bb**2 - 4*aa*cc > 0.00001:
                h1 = (-bb + sqrt(bb**2 - 4*aa*cc))/(2*aa)
                h2 = (-bb - sqrt(bb**2 - 4*aa*cc))/(2*aa)
            else:
                h1 = h2 = (-bb)/(2*aa)

            k1 = (q - m * h1)/n
            k2 = (q - m * h2)/n
        else:
            aa = a**2
            bb = -2*a**2*y1
            if m < -0.0001 or m > 0.0001:
                cc = b**2*q**2/m**2 - 2*b**2*x1*q/m + b**2*x1**2 + a**2*y1**2 - a**2*b**2

                h1 = q/m
                h2 = q/m
                if bb**2 - 4*aa*cc < -0.00001 or bb**2 - 4*aa*cc > 0.00001:
                    k1 = (-bb + sqrt(bb**2 - 4*aa*cc))/(2*aa)
                    k2 = (-bb - sqrt(bb**2 - 4*aa*cc))/(2*aa)
                else:
                    k1 = k2 = (-bb)/(2*aa)
            else:
                h1 = h2 = x1
                k1 = k2 = (-bb)/(2*aa)

        h = "h"
        k = "k"
        if h1 != h2 or k1 != k2:
            results = [
                {h: h1, k: k1},
                {h: h2, k: k2}
            ]
        else:
            results = [{h: h1, k: k1}]

        results_len = len(results)
        for result in results:
            theta1 = 0
            theta2 = 0
            if p1[0]-result[h]:
                theta1 = atan(((p1[1]-result[k])*a)/((p1[0]-result[h])*b))
                if p1[0]-result[h] < 0:
                    # quadrand 2 and 3
                    theta1 = theta1 + pi
            else:
                if p1[1]-result[k] < 0:
                    theta1 = -pi/2
                else:
                    theta1 = pi/2

            if p2[0]-result[h]:
                theta2 = atan(((p2[1]-result[k])*a)/((p2[0]-result[h])*b))
                if p2[0]-result[h] < 0:
                    # quadrand 2 and 3
                    theta2 = theta2 + pi
            else:
                if p2[1]-result[k] < 0:
                    theta2 = -pi/2
                else:
                    theta2 = pi/2

            if results_len == 1:
                return result[h], result[k], theta1, theta2

            angle = theta2 - theta1
            if angle < 0:
                angle += 2 * pi
            if angle >= 2*pi:
                angle -= 2 * pi

            if large == 0:
                if sweep:
                    if angle <= pi:
                        return result[h], result[k], theta1, theta2
                else:
                    if angle >= pi:
                        return result[h], result[k], theta1, theta2
            else:
                if sweep:
                    if angle >= pi:
                        return result[h], result[k], theta1, theta2
                else:
                    if angle <= pi:
                        return result[h], result[k], theta1, theta2

        return None


class MindstormsGadget(AlexaGadget):
    """
    An Mindstorms gadget that will react to the Alexa wake word.
    """

    def __init__(self):
        """
        Performs Alexa Gadget initialization routines and ev3dev resource allocation.
        """
        super().__init__()

        self.leds = Leds()
        self.sound = Sound()
        self._waiting_for_speech = False
        self.lock = threading.Lock()
        self.printer = Printer()

    def on_connected(self, device_addr):
        """
        Gadget connected to the paired Echo device.
        :param device_addr: the address of the device we connected to
        """
        self.leds.set_color("LEFT", "GREEN")
        self.leds.set_color("RIGHT", "GREEN")
        logger.info("{} connected to Echo device".format(self.friendly_name))

    def on_disconnected(self, device_addr):
        """
        Gadget disconnected from the paired Echo device.
        :param device_addr: the address of the device we disconnected from
        """
        self.leds.set_color("LEFT", "BLACK")
        self.leds.set_color("RIGHT", "BLACK")
        logger.info("{} disconnected from Echo device".format(
            self.friendly_name))

    def on_custom_mindstorms_gadget_learn(self, directive):
        """
        Handles the Custom.Mindstorms.Gadget control directive.
        :param directive: the custom directive with the matching namespace and name
        """
        try:
            payload = json.loads(directive.payload.decode("utf-8"))
            print("Payload: {}".format(payload), file=stderr)
            self._waiting_for_speech = True
            threading.Thread(target=self.draw_letter, args=(
                payload["letter"], True), daemon=True).start()
        except KeyError:
            print("Missing expected parameters: {}".format(
                directive), file=stderr)

    def on_custom_mindstorms_gadget_guess(self, directive):
        """
        Handles the Custom.Mindstorms.Gadget control directive.
        :param directive: the custom directive with the matching namespace and name
        """
        try:
            payload = json.loads(directive.payload.decode("utf-8"))
            print("Payload: {}".format(payload), file=stderr)
            self._waiting_for_speech = True
            threading.Thread(target=self.draw_letter, args=(
                payload["letter"], False), daemon=True).start()
        except KeyError:
            print("Missing expected parameters: {}".format(
                directive), file=stderr)

    def on_alexa_gadget_speechdata_speechmarks(self, directive):
        """
        Alexa.Gadget.SpeechData Speechmarks directive received.
        For more info, visit:
            https://developer.amazon.com/docs/alexa-gadgets-toolkit/alexa-gadget-speechdata-interface.html#Speechmarks-directive
        :param directive: Protocol Buffer Message that was send by Echo device.
        """
        try:
            if self._waiting_for_speech:
                if directive.payload.speechmarksData[-1].value == 'sil':
                    # sleep until time
                    print('received silence', file=stderr)
                    # sleep(
                    #     int(directive.payload.speechmarksData[-1].startOffsetInMilliSeconds)/1000)
                    self._waiting_for_speech = False

        except KeyError:
            print("Missing expected parameters: {}".format(
                directive), file=stderr)

    def draw_letter(self, letter, speak):
        print('drawing letter ', letter, file=stderr)
        while self._waiting_for_speech:
            sleep(0.1)
        file = "svg/"+letter+".svg"
        tree = ET.parse(file)
        root = tree.getroot()
        width = int(root.attrib["width"])
        height = int(root.attrib["height"])
        self.lock.acquire()
        try:
            for child in root:
                if child.tag == '{http://www.w3.org/2000/svg}path':
                    for pos_title in child:
                        if pos_title.tag == '{http://www.w3.org/2000/svg}title':
                            if speak:
                                self._waiting_for_speech = True
                                self.send_custom_event(
                                    'Custom.Mindstorms.Gadget', 'speak', {'txt': pos_title.text})
                                while self._waiting_for_speech:
                                    sleep(0.1)
                    self.printer.draw_svg_path(
                        child.attrib["d"], width, height)
                elif child.tag == '{http://www.w3.org/2000/svg}line':
                    for pos_title in child:
                        if pos_title.tag == '{http://www.w3.org/2000/svg}title':
                            if speak:
                                self._waiting_for_speech = True
                                self.send_custom_event(
                                    'Custom.Mindstorms.Gadget', 'speak', {'txt': pos_title.text})
                                while self._waiting_for_speech:
                                    sleep(0.1)
                    self.printer.draw_line(
                        float(child.attrib["x1"])/width,
                        float(child.attrib["y1"])/height,
                        float(child.attrib["x2"])/width,
                        float(child.attrib["y2"])/height)
        except Exception as e:
            print(e, file=stderr)
            traceback.print_exc(file=stderr)
        self.printer.reset()
        self.lock.release()
        self.send_custom_event(
            'Custom.Mindstorms.Gadget', 'done', {})


if __name__ == '__main__':

    gadget = MindstormsGadget()

    # Set LCD font and turn off blinking LEDs
    os.system('setfont Lat7-Terminus12x6')
    gadget.leds.set_color("LEFT", "BLACK")
    gadget.leds.set_color("RIGHT", "BLACK")

    # Startup sequence
    # gadget.sound.play_song((('C4', 'e'), ('D4', 'e'), ('E5', 'q')))
    gadget.leds.set_color("LEFT", "GREEN")
    gadget.leds.set_color("RIGHT", "GREEN")

    # Gadget main entry point
    gadget.main()

    # Shutdown sequence
    # gadget.sound.play_song((('E5', 'e'), ('C4', 'e')))
    gadget.leds.set_color("LEFT", "BLACK")
    gadget.leds.set_color("RIGHT", "BLACK")

script3r.ini

Textile
ini file for scrip3r.py file
[GadgetSettings]
amazonId = YOUR_ID
alexaGadgetSecret = YOUR_SECRET

[GadgetCapabilities]
Custom.Mindstorms.Gadget = 1.0
Alexa.Gadget.SpeechData = 1.0 - viseme

Zip with SVG files

SVG
unzip it in the main source directory
No preview (download only).

model.json

JSON
Model for Alexa Skill
{
    "interactionModel": {
        "languageModel": {
            "invocationName": "lego scripter",
            "intents": [
                {
                    "name": "AMAZON.CancelIntent",
                    "samples": []
                },
                {
                    "name": "AMAZON.HelpIntent",
                    "samples": []
                },
                {
                    "name": "AMAZON.StopIntent",
                    "samples": []
                },
                {
                    "name": "AMAZON.NavigateHomeIntent",
                    "samples": []
                },
                {
                    "name": "LearnIntent",
                    "slots": [
                        {
                            "name": "Letter",
                            "type": "Letter",
                            "samples": [
                                "letter {Letter}",
                                "{Letter}"
                            ]
                        }
                    ],
                    "samples": [
                        "draw a letter {Letter}",
                        "write a letter {Letter}",
                        "write letter {Letter}",
                        "write {Letter}",
                        "learn letter {Letter}",
                        "draw letter {Letter}",
                        "draw {Letter}",
                        "learn {Letter}"
                    ]
                },
                {
                    "name": "PlayGameIntent",
                    "slots": [],
                    "samples": [
                        "Quiz",
                        "Let's play a game",
                        "Play a game"
                    ]
                },
                {
                    "name": "PlayGameAnswerIntent",
                    "slots": [
                        {
                            "name": "Letter",
                            "type": "Letter",
                            "samples": [
                                "Answer is {Letter}",
                                "Answer is letter {Letter}",
                                "{Letter}",
                                "Letter {Letter}"
                            ]
                        }
                    ],
                    "samples": [
                        "{Letter}",
                        "Answer is {Letter}",
                        "Answer is letter {Letter}",
                        "Letter {Letter}"
                    ]
                }
            ],
            "types": [
                {
                    "name": "Letter",
                    "values": [
                        {
                            "name": {
                                "value": "Z"
                            }
                        },
                        {
                            "name": {
                                "value": "Y"
                            }
                        },
                        {
                            "name": {
                                "value": "X"
                            }
                        },
                        {
                            "name": {
                                "value": "W"
                            }
                        },
                        {
                            "name": {
                                "value": "V"
                            }
                        },
                        {
                            "name": {
                                "value": "U"
                            }
                        },
                        {
                            "name": {
                                "value": "T"
                            }
                        },
                        {
                            "name": {
                                "value": "S"
                            }
                        },
                        {
                            "name": {
                                "value": "R"
                            }
                        },
                        {
                            "name": {
                                "value": "Q"
                            }
                        },
                        {
                            "name": {
                                "value": "P"
                            }
                        },
                        {
                            "name": {
                                "value": "O"
                            }
                        },
                        {
                            "name": {
                                "value": "N"
                            }
                        },
                        {
                            "name": {
                                "value": "M"
                            }
                        },
                        {
                            "name": {
                                "value": "L"
                            }
                        },
                        {
                            "name": {
                                "value": "K"
                            }
                        },
                        {
                            "name": {
                                "value": "J"
                            }
                        },
                        {
                            "name": {
                                "value": "I"
                            }
                        },
                        {
                            "name": {
                                "value": "H"
                            }
                        },
                        {
                            "name": {
                                "value": "G"
                            }
                        },
                        {
                            "name": {
                                "value": "F"
                            }
                        },
                        {
                            "name": {
                                "value": "E"
                            }
                        },
                        {
                            "name": {
                                "value": "D"
                            }
                        },
                        {
                            "name": {
                                "value": "C"
                            }
                        },
                        {
                            "name": {
                                "value": "B"
                            }
                        },
                        {
                            "name": {
                                "value": "A"
                            }
                        }
                    ]
                }
            ]
        },
        "dialog": {
            "intents": [
                {
                    "name": "LearnIntent",
                    "confirmationRequired": false,
                    "prompts": {},
                    "slots": [
                        {
                            "name": "Letter",
                            "type": "Letter",
                            "confirmationRequired": false,
                            "elicitationRequired": true,
                            "prompts": {
                                "elicitation": "Elicit.Slot.1207405175159.184443735393"
                            }
                        }
                    ]
                },
                {
                    "name": "PlayGameAnswerIntent",
                    "confirmationRequired": false,
                    "prompts": {},
                    "slots": [
                        {
                            "name": "Letter",
                            "type": "Letter",
                            "confirmationRequired": false,
                            "elicitationRequired": true,
                            "prompts": {
                                "elicitation": "Elicit.Slot.551051320616.1560203168942"
                            }
                        }
                    ]
                }
            ],
            "delegationStrategy": "ALWAYS"
        },
        "prompts": [
            {
                "id": "Elicit.Slot.1207405175159.184443735393",
                "variations": [
                    {
                        "type": "PlainText",
                        "value": "What letter should it be?"
                    }
                ]
            },
            {
                "id": "Elicit.Slot.551051320616.1560203168942",
                "variations": [
                    {
                        "type": "PlainText",
                        "value": "What letter did you say?"
                    }
                ]
            }
        ]
    }
}

index.js

JavaScript
Main part of the Alexa Skill code. Copy to the "Code" section of the skill in Alexa developer console
const Alexa = require('ask-sdk-core');
const Util = require('./util');

// The namespace of the custom directive to be sent by this skill
const NAMESPACE = 'Custom.Mindstorms.Gadget';
const NAME_LEARN = 'learn'
const NAME_GUESS = 'guess'

const LaunchRequestHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'LaunchRequest';
    },
    handle: async function (handlerInput) {

        let request = handlerInput.requestEnvelope;
        let { apiEndpoint, apiAccessToken } = request.context.System;
        let apiResponse = await Util.getConnectedEndpoints(apiEndpoint, apiAccessToken);
        if ((apiResponse.endpoints || []).length === 0) {
            return handlerInput.responseBuilder
                .speak(`I couldn't find an EV3 Brick connected to this Echo device. Please check to make sure your EV3 Brick is connected, and try again.`)
                .getResponse();
        }

        // Store the gadget endpointId to be used in this skill session
        let endpointId = apiResponse.endpoints[0].endpointId || [];
        Util.putSessionAttribute(handlerInput, 'endpointId', endpointId);

        // Set skill duration to 2 minutes (4 30-seconds interval)
        Util.putSessionAttribute(handlerInput, 'duration', 4);
        // Set the token to track the event handler
        const token = handlerInput.requestEnvelope.request.requestId;
        Util.putSessionAttribute(handlerInput, 'token', token);

        return handlerInput.responseBuilder
            .speak("Welcome to Lego Scripter. I can teach you how to write the letters of the " +
                "alphabet or we can play a game. What should it be?")
            .withShouldEndSession(false)
            .addDirective(buildStartEventHandler(token, 30000, {}))
            .getResponse();
    }
};
// The request interceptor is used for request handling testing and debugging.
// It will simply log the request in raw json format before any processing is performed.
const RequestInterceptor = {
    process(handlerInput) {
        let { attributesManager, requestEnvelope } = handlerInput;
        let sessionAttributes = attributesManager.getSessionAttributes();

        // Log the request for debug purposes.
        console.log(`=====Request==${JSON.stringify(requestEnvelope)}`);
        console.log(`=========SessionAttributes==${JSON.stringify(sessionAttributes, null, 2)}`);
    }
};

// Generic error handling to capture any syntax or routing errors. If you receive an error
// stating the request handler chain is not found, you have not implemented a handler for
// the intent being invoked or included it in the skill builder below.
const ErrorHandler = {
    canHandle() {
        return true;
    },
    handle(handlerInput, error) {
        console.log(`~~~~ Error handled: ${error.stack}`);
        const speakOutput = `Sorry, I had trouble doing what you asked. Please try again.`;

        return handlerInput.responseBuilder
            .speak(speakOutput)
            .getResponse();
    }
};

const HelpIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && Alexa.getIntentName(handlerInput.requestEnvelope) === 'AMAZON.HelpIntent';
    },
    handle(handlerInput) {
        const speakOutput = 'I can draw a letter for your or we can play a game! How can I help?';
        return handlerInput.responseBuilder
            .speak(speakOutput)
            .withShouldEndSession(false)
            .getResponse();
    }
};
const CancelAndStopIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && (Alexa.getIntentName(handlerInput.requestEnvelope) === 'AMAZON.CancelIntent'
                || Alexa.getIntentName(handlerInput.requestEnvelope) === 'AMAZON.StopIntent');
    },
    handle(handlerInput) {
        return handlerInput.responseBuilder
            .addDirective(buildStopEventHandlerDirective(handlerInput))
            .speak('Goodbye!')
            .withShouldEndSession(true)
            .getResponse();
    }
};
const SessionEndedRequestHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'SessionEndedRequest';
    },
    handle(handlerInput) {
        // Any cleanup logic goes here.
        return handlerInput.responseBuilder
            .addDirective(buildStopEventHandlerDirective(handlerInput))
            .getResponse();
    }
};

const LearnIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && Alexa.getIntentName(handlerInput.requestEnvelope) === 'LearnIntent';
    },
    handle: function (handlerInput) {

        let letter = Alexa.getSlotValue(handlerInput.requestEnvelope, 'Letter');
        letter = letter.charAt(0).toUpperCase();
        letter = letter.toUpperCase();
        const attributesManager = handlerInput.attributesManager;
        let endpointId = attributesManager.getSessionAttributes().endpointId || [];

        // Set skill duration to 2 minutes (4 30-seconds interval)
        Util.putSessionAttribute(handlerInput, 'duration', 4);

        let directive = Util.build(endpointId, NAMESPACE, NAME_LEARN,
            {
                letter: letter
            });
        Util.putSessionAttribute(handlerInput, 'mode', 'learn');

        console.log(directive);

        return handlerInput.responseBuilder
            .speak(`Let me draw letter ${letter} for you.`)
            .addDirective(directive)
            .getResponse();
    }
};

const EventsReceivedRequestHandler = {
    // Checks for a valid token and endpoint.
    canHandle(handlerInput) {
        let { request } = handlerInput.requestEnvelope;
        console.log('Request type: ' + Alexa.getRequestType(handlerInput.requestEnvelope));
        if (request.type !== 'CustomInterfaceController.EventsReceived') return false;

        const attributesManager = handlerInput.attributesManager;
        let sessionAttributes = attributesManager.getSessionAttributes();
        let customEvent = request.events[0];

        // if (sessionAttributes.token !== request.token) {
        //     console.log("Event token doesn't match. Ignoring this event");
        //     return false;
        // }

        // Validate endpoint
        let requestEndpoint = customEvent.endpoint.endpointId;
        if (requestEndpoint !== sessionAttributes.endpointId) {
            console.log("Event endpoint id doesn't match. Ignoring this event");
            return false;
        }
        return true;
    },
    handle(handlerInput) {

        console.log("== Received Custom Event ==");
        let customEvent = handlerInput.requestEnvelope.request.events[0];
        let payload = customEvent.payload;
        let name = customEvent.header.name;

        const token = handlerInput.requestEnvelope.request.requestId;
        Util.putSessionAttribute(handlerInput, 'token', token);

        console.log(customEvent)

        if (name === 'speak') {
            return handlerInput.responseBuilder
                .speak(payload.txt)
                .getResponse();
        }

        if (name === 'done') {
            let mode = handlerInput.attributesManager.getSessionAttributes().mode || 'learn';
            if (mode === 'learn') {
                return handlerInput.responseBuilder
                    .speak('Done. What to do next?')
                    .addDirective(buildStopEventHandlerDirective(handlerInput))
                    .withShouldEndSession(false)
                    .getResponse();
            } else if (mode === 'guess') {
                return handlerInput.responseBuilder
                    .speak('What letter is this?')
                    .addDirective(buildStopEventHandlerDirective(handlerInput))
                    .withShouldEndSession(false)
                    .getResponse();
            }
        }

        return handlerInput.responseBuilder
            .speak('unknown event')
            .getResponse();
    }
};
const ExpiredRequestHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'CustomInterfaceController.Expired'
    },
    handle(handlerInput) {
        console.log("== Custom Event Expiration Input ==");

        const attributesManager = handlerInput.attributesManager;

        let token = handlerInput.attributesManager.getSessionAttributes().token || '';

        let duration = attributesManager.getSessionAttributes().duration || 0;
        if (duration > 0) {
            Util.putSessionAttribute(handlerInput, 'duration', --duration);
            // Extends skill session
            return handlerInput.responseBuilder
                .addDirective(buildStartEventHandler(token, 30000, {}))
                .getResponse();
        }
        else {
            // End skill session
            return handlerInput.responseBuilder
                .withShouldEndSession(true)
                .getResponse();
        }
    }
};

const PlayGameIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && Alexa.getIntentName(handlerInput.requestEnvelope) === 'PlayGameIntent';
    },
    handle(handlerInput) {
        const attributesManager = handlerInput.attributesManager;
        let endpointId = attributesManager.getSessionAttributes().endpointId || [];

        // Set skill duration to 2 minutes (4 30-seconds interval)
        Util.putSessionAttribute(handlerInput, 'duration', 4);

        const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXTZ";
        var rnum = Math.floor(Math.random() * alphabet.length);
        let letter = alphabet[rnum]
        let directive = Util.build(endpointId, NAMESPACE, NAME_GUESS,
            {
                letter: letter
            });

        console.log(directive);

        Util.putSessionAttribute(handlerInput, 'mode', 'guess');
        Util.putSessionAttribute(handlerInput, 'letter', letter);

        return handlerInput.responseBuilder
            .speak(`I will draw a letter and you have to guess which one.`)
            .addDirective(directive)
            .getResponse();
    }
};

const PlayGameAnswerIntentHandler = {
    canHandle(handlerInput) {
        return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest'
            && Alexa.getIntentName(handlerInput.requestEnvelope) === 'PlayGameAnswerIntent';
    },
    handle(handlerInput) {
        let mode = handlerInput.attributesManager.getSessionAttributes().mode || 'learn';
        let answer = Alexa.getSlotValue(handlerInput.requestEnvelope, 'Letter');
        answer = answer.charAt(0).toUpperCase();
        answer = answer.toUpperCase();

        if (mode === 'guess') {
            let letter = handlerInput.attributesManager.getSessionAttributes().letter || '';
            if (letter === answer) {
                return handlerInput.responseBuilder
                    .speak(`Correct! What should we do next?`)
                    .withShouldEndSession(false)
                    .getResponse();
            } else {
                return handlerInput.responseBuilder
                    .speak(`Incorrect! Try again.`)
                    .withShouldEndSession(false)
                    .getResponse();
            }
        }

        return handlerInput.responseBuilder
            .speak(`How can I help?`)
            .withShouldEndSession(false)
            .getResponse();
    }
};

// The SkillBuilder acts as the entry point for your skill, routing all request and response
// payloads to the handlers above. Make sure any new handlers or interceptors you've
// defined are included below. The order matters - they're processed top to bottom.
exports.handler = Alexa.SkillBuilders.custom()
    .addRequestHandlers(
        LaunchRequestHandler,
        LearnIntentHandler,
        PlayGameIntentHandler,
        PlayGameAnswerIntentHandler,
        EventsReceivedRequestHandler,
        ExpiredRequestHandler,
        HelpIntentHandler,
        CancelAndStopIntentHandler,
        SessionEndedRequestHandler,
    )
    .addRequestInterceptors(RequestInterceptor)
    .addErrorHandlers(
        ErrorHandler,
    )
    .lambda();

function buildStartEventHandler(token, timeout = 30000, payload) {
    return {
        type: "CustomInterfaceController.StartEventHandler",
        token: token,
        expiration: {
            durationInMilliseconds: timeout,
            expirationPayload: payload
        }
    };
}

function buildStopEventHandlerDirective(handlerInput) {
    let token = handlerInput.attributesManager.getSessionAttributes().token || '';
    return {
        "type": "CustomInterfaceController.StopEventHandler",
        "token": token
    }
}

util.js

JavaScript
Utils file for Alexa Skill. Copy to the "Code" section of the skill in Alexa developer console
/*
 * Copyright 2019 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * You may not use this file except in compliance with the terms and conditions 
 * set forth in the accompanying LICENSE.TXT file.
 *
 * THESE MATERIALS ARE PROVIDED ON AN "AS IS" BASIS. AMAZON SPECIFICALLY DISCLAIMS, WITH 
 * RESPECT TO THESE MATERIALS, ALL WARRANTIES, EXPRESS, IMPLIED, OR STATUTORY, INCLUDING 
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.
*/

'use strict';

const Https = require('https');

/**
 * Build a custom directive payload to the gadget with the specified endpointId
 * @param {string} endpointId - the gadget endpoint Id
 * @param {string} namespace - the namespace of the skill
 * @param {string} name - the name of the skill within the scope of this namespace
 * @param {object} payload - the payload data
 * @see {@link https://developer.amazon.com/docs/alexa-gadgets-toolkit/send-gadget-custom-directive-from-skill.html#respond}
 */
exports.build = function (endpointId, namespace, name, payload) {
    // Construct the custom directive that needs to be sent
    // Gadget should declare the capabilities in the discovery response to
    // receive the directives under the following namespace.
    return {
        type: 'CustomInterfaceController.SendDirective',
        header: {
            name: name,
            namespace: namespace
        },
        endpoint: {
            endpointId: endpointId
        },
        payload
    };
};

/**
 * A convenience routine to add the a key-value pair to the session attribute.
 * @param handlerInput - the context from Alexa Service
 * @param key - the key to be added
 * @param value - the value be added
 */
exports.putSessionAttribute = function (handlerInput, key, value) {
    const attributesManager = handlerInput.attributesManager;
    let sessionAttributes = attributesManager.getSessionAttributes();
    sessionAttributes[key] = value;
    attributesManager.setSessionAttributes(sessionAttributes);
};

/**
 * To get a list of all the gadgets that meet these conditions,
 * Call the Endpoint Enumeration API with the apiEndpoint and apiAccessToken to
 * retrieve the list of all connected gadgets.
 *
 * @param {string} apiEndpoint - the Endpoint API url
 * @param {string} apiAccessToken  - the token from the session object in the Alexa request
 * @see {@link https://developer.amazon.com/docs/alexa-gadgets-toolkit/send-gadget-custom-directive-from-skill.html#call-endpoint-enumeration-api}
 */
exports.getConnectedEndpoints = function (apiEndpoint, apiAccessToken) {

    // The preceding https:// need to be stripped off before making the call
    apiEndpoint = (apiEndpoint || '').replace('https://', '');
    return new Promise(((resolve, reject) => {

        const options = {
            host: apiEndpoint,
            path: '/v1/endpoints',
            method: 'GET',
            headers: {
                'Content-Type': 'application/json',
                'Authorization': 'Bearer ' + apiAccessToken
            }
        };

        const request = Https.request(options, (response) => {
            response.setEncoding('utf8');
            let returnData = '';
            response.on('data', (chunk) => {
                returnData += chunk;
            });

            response.on('end', () => {
                resolve(JSON.parse(returnData));
            });

            response.on('error', (error) => {
                reject(error);
            });
        });
        request.end();
    }));
};

package.json

JSON
Copy to the "Code" section of the skill in Alexa developer console
{
  "name": "script3r",
  "version": "1.0.0",
  "description": "Learn the alphabet with Lego Mindstorms and Alexa",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Andrei Ciobanu",
  "license": "ISC",
  "dependencies": {
    "ask-sdk-core": "^2.6.0",
    "ask-sdk-model": "^1.18.0",
    "aws-sdk": "^2.326.0",
    "request": "^2.81.0"
  }
}

Printer Simulation

Python
This little program simulates the printer movement. It will output the result in an image
from math import copysign, cos, sin, acos, asin, pi, sqrt, atan
from random import random
from sys import stderr
from PIL import Image, ImageDraw
import xml.etree.ElementTree as ET

MAX_ROTATION_X = 16
MAX_ROTATION_Y = 16

MAX_SPEED_X = 80
MAX_SPEED_Y = 80
DEGREES_PEN = 10

INTEGRAL_WEIGHT = 0.05

IMG_SIZE = 1000


class Motor(object):
    def __init__(self):
        self._count_per_rot = 360
        self._position = 0

    @property
    def count_per_rot(self):
        return self._count_per_rot

    @property
    def position(self):
        return self._position

    def reset(self):
        self._position = 0

    def on_for_rotations(self, speed, rotations, block=False):
        self._position += rotations * \
            self._count_per_rot * copysign(1, speed)

    def on_for_seconds(self, speed, seconds, block=False):
        # +- 5% erro
        error = 1+(random()-0.5)/10
        self._position += (speed/100) * seconds * 1050 * error

    def on_for_degrees(self, speed, degrees, block=False):
        self._position += (degrees/360) * \
            self._count_per_rot * copysign(1, speed)

    def wait_until_not_moving(self):
        return

    def stop(self):
        return


class PrinterSimulation(object):
    def __init__(self):
        self.solver = Solver()
        self.motor_x = Motor()
        self.motor_y = Motor()
        self.motor_pen = Motor()
        self._pen_down = False

        self.image = Image.new('RGBA', (IMG_SIZE, IMG_SIZE))
        self.image_draw = ImageDraw.Draw(self.image)

    def record_position(self):
        return (self.x() * IMG_SIZE, self.y() * IMG_SIZE)

    def draw(self, old_position):
        self.image_draw.line(
            [old_position, (self.x()*IMG_SIZE, self.y()*IMG_SIZE)], width=10)

    def reset(self):
        self.motor_x.reset()
        self.motor_y.reset()
        self.pen_up()
        self.image.save('run.png', "PNG")

    def x(self):
        return -self.motor_x.position / (MAX_ROTATION_X * self.motor_x.count_per_rot)

    def y(self):
        return self.motor_y.position / (MAX_ROTATION_Y * self.motor_y.count_per_rot)

    def move_wh(self, w, h, speed_x=MAX_SPEED_X, speed_y=MAX_SPEED_Y):
        old_position = self.record_position()
        self.motor_x.on_for_rotations(
            speed=speed_x, rotations=-w * MAX_ROTATION_X, block=False)
        self.motor_y.on_for_rotations(
            speed=speed_y, rotations=h * MAX_ROTATION_Y, block=False)
        self.motor_x.wait_until_not_moving()
        self.motor_y.wait_until_not_moving()
        if self._pen_down:
            self.draw(old_position)

    def pen_down(self):
        if not self._pen_down:
            self.motor_pen.on_for_degrees(speed=10, degrees=DEGREES_PEN)
        self._pen_down = True

    def pen_up(self):
        if self._pen_down:
            self.motor_pen.on_for_degrees(speed=10, degrees=-DEGREES_PEN)
        self._pen_down = False

    def draw_arc(self, rad_x, rad_y, large, sweep, sx, sy, ex, ey):
        h, k, start, end = self.solver.solve_ellipse(
            (sx, sy), (ex, ey), rad_x, rad_y, large, sweep)
        print('The solution is:', h, k, start*180/pi, "->", end*180/pi)

        if start < 0:
            start += 2*pi
        if start < 0:
            end += 2*pi
        angle = start
        angle_to_do = 0

        if sweep:
            cclock = 1
            angle_to_do = end - start
        else:
            cclock = -1
            angle_to_do = start-end

        if angle_to_do < 0:
            angle_to_do += 2*pi

        print('doing:', angle_to_do*180/pi)

        step = 0
        angle_done = 0
        integral_error_x = 0
        integral_error_y = 0

        while angle_done < angle_to_do:
            dx = -sin(angle) * rad_x * cclock - \
                integral_error_x * INTEGRAL_WEIGHT
            dy = cos(angle) * rad_y * cclock - \
                integral_error_y * INTEGRAL_WEIGHT
            magnitude = sqrt(dx**2 + dy**2)
            speed_x = (dx/magnitude) * MAX_SPEED_X
            speed_y = (dy/magnitude) * MAX_SPEED_Y
            old_position = self.record_position()
            self.motor_x.on_for_seconds(speed=-speed_x, seconds=0.1)
            self.motor_y.on_for_seconds(speed=speed_y, seconds=0.1)
            if self._pen_down:
                self.draw(old_position)

            old_angle = angle
            angle = self.solver.solve_angle(
                cx=h, cy=k, a=rad_x, b=rad_y, px=self.x(), py=self.y())
            step_angle = abs(angle-old_angle)

            if(step_angle > pi):
                step_angle = 2*pi - step_angle

            angle_done += step_angle

            x_sol = cos(angle) * rad_x + h
            y_sol = sin(angle) * rad_y + k
            integral_error_x += (self.x()-x_sol)
            integral_error_y += (self.y()-y_sol)

            step += 1
            if(step > 1000):
                break

        self.motor_x.stop()
        self.motor_y.stop()

    def draw_line(self, from_x, from_y, to_x, to_y, pen=True):
        self.move_wh(from_x - self.x(), from_y - self.y())
        if pen:
            self.pen_down()
        if (to_x-self.x()) < 0.000001 and (to_x-self.x()) > -0.000001:
            self.move_wh(0, to_y-self.y())
        else:
            m = abs((to_y-self.y())/(to_x-self.x()))
            speed_x = 1
            speed_y = m * speed_x
            magnitude = sqrt(speed_x**2 + speed_y**2)
            speed_x = (speed_x/magnitude) * MAX_SPEED_X
            speed_y = (speed_y/magnitude) * MAX_SPEED_Y
            print(to_x-self.x(), to_y-self.y(), speed_x, speed_y)
            self.move_wh(to_x-self.x(), to_y-self.y(),
                         speed_x=speed_x, speed_y=speed_y)

        if pen:
            self.pen_up()

    def draw_svg_path(self, path, width, height):
        path_list = path.split(" ")
        index = 0
        m_x = 0
        m_y = 0
        while index < len(path_list):
            current = path_list[index]
            if current == 'M':
                x = float(path_list[index+1]) / width
                y = float(path_list[index+2]) / height
                m_x = x
                m_y = y
                self.move_wh(x-self.x(), y-self.y())
                index += 3
                self.pen_down()
            elif current == 'L':
                x = float(path_list[index+1]) / width
                y = float(path_list[index+2]) / height
                m_x = x
                m_y = y
                self.draw_line(m_x, m_y, x, y, pen=False)
                index += 3
            elif current == 'A':
                rad_x = float(path_list[index+1]) / width
                rad_y = float(path_list[index+2]) / height
                large = int(path_list[index+4])
                sweep = int(path_list[index+5])
                dx = float(path_list[index+6]) / width
                dy = float(path_list[index+7]) / width
                index += 8
                self.draw_arc(rad_x, rad_y, large, sweep, m_x, m_y, dx, dy)
                m_x = dx
                m_y = dy
            else:
                index += 1
        self.pen_up()

    def draw_svg(self, file):
        tree = ET.parse(file)
        root = tree.getroot()
        width = int(root.attrib["width"])
        height = int(root.attrib["height"])
        for child in root:
            if child.tag == '{http://www.w3.org/2000/svg}path':
                for pos_title in child:
                    if pos_title.tag == '{http://www.w3.org/2000/svg}title':
                        print(pos_title.text, file=stderr)
                self.draw_svg_path(child.attrib["d"], width, height)
            elif child.tag == '{http://www.w3.org/2000/svg}line':
                for pos_title in child:
                    if pos_title.tag == '{http://www.w3.org/2000/svg}title':
                        print(pos_title.text, file=stderr)
                self.draw_line(
                    float(child.attrib["x1"])/width,
                    float(child.attrib["y1"])/height,
                    float(child.attrib["x2"])/width,
                    float(child.attrib["y2"])/height)


class Solver(object):

    def solve_angle(self, cx, cy, a, b, px, py):
        if px-cx:
            theta = atan(((py-cy)*a)/((px-cx)*b))
            if px-cx < 0:
                # quadrand 2 and 3
                theta = theta + pi
        else:
            if py-cy < 0:
                theta = -pi/2
            else:
                theta = pi/2
        return theta

    def solve_ellipse(self, p1, p2, a, b, large, sweep):
        x1 = p1[0]
        y1 = p1[1]
        x2 = p2[0]
        y2 = p2[1]

        m = -2*(b**2)*x1 + 2*(b**2)*x2
        n = -2*(a**2)*y1 + 2*(a**2)*y2
        q = -(b**2)*x1**2 - (a**2)*(y1**2) + (b**2)*(x2**2) + (a**2)*(y2**2)

        if n < -0.000001 or n > 0.000001:
            aa = b**2 + (a**2)*(m**2)/(n**2)
            bb = -2*(b**2)*x1 - (2*q*(a**2)*m)/(n**2) + (2*(a**2)*y1*m)/n
            cc = ((a**2)*(q**2))/(n**2) - (2*(a**2)*y1*q)/n + \
                (b**2)*(x1**2) + (a**2)*(y1**2) - (a**2)*(b**2)

            if bb**2 - 4*aa*cc < -0.000001 or bb**2 - 4*aa*cc > 0.000001:
                h1 = (-bb + sqrt(bb**2 - 4*aa*cc))/(2*aa)
                h2 = (-bb - sqrt(bb**2 - 4*aa*cc))/(2*aa)
            else:
                h1 = h2 = (-bb)/(2*aa)

            k1 = (q - m * h1)/n
            k2 = (q - m * h2)/n
        else:
            aa = a**2
            bb = -2*a**2*y1
            if m < -0.000001 or m > 0.000001:
                cc = b**2*q**2/m**2 - 2*b**2*x1*q/m + b**2*x1**2 + a**2*y1**2 - a**2*b**2

                h1 = q/m
                h2 = q/m
                if bb**2 - 4*aa*cc < -0.000001 or bb**2 - 4*aa*cc > 0.000001:
                    k1 = (-bb + sqrt(bb**2 - 4*aa*cc))/(2*aa)
                    k2 = (-bb - sqrt(bb**2 - 4*aa*cc))/(2*aa)
                else:
                    k1 = k2 = (-bb)/(2*aa)
            else:
                h1 = h2 = x1
                k1 = k2 = (-bb)/(2*aa)

        h = "h"
        k = "k"
        if h1 != h2 or k1 != k2:
            results = [
                {h: h1, k: k1},
                {h: h2, k: k2}
            ]
        else:
            results = [{h: h1, k: k1}]

        results_len = len(results)
        for result in results:
            theta1 = 0
            theta2 = 0
            if p1[0]-result[h]:
                theta1 = atan(((p1[1]-result[k])*a)/((p1[0]-result[h])*b))
                if p1[0]-result[h] < 0:
                    # quadrand 2 and 3
                    theta1 = theta1 + pi
            else:
                if p1[1]-result[k] < 0:
                    theta1 = -pi/2
                else:
                    theta1 = pi/2

            if p2[0]-result[h]:
                theta2 = atan(((p2[1]-result[k])*a)/((p2[0]-result[h])*b))
                if p2[0]-result[h] < 0:
                    # quadrand 2 and 3
                    theta2 = theta2 + pi
            else:
                if p2[1]-result[k] < 0:
                    theta2 = -pi/2
                else:
                    theta2 = pi/2

            if results_len == 1:
                return result[h], result[k], theta1, theta2

            angle = theta2 - theta1
            if angle < 0:
                angle += 2 * pi
            if angle >= 2*pi:
                angle -= 2 * pi

            if large == 0:
                if sweep:
                    if angle <= pi:
                        return result[h], result[k], theta1, theta2
                else:
                    if angle >= pi:
                        return result[h], result[k], theta1, theta2
            else:
                if sweep:
                    if angle >= pi:
                        return result[h], result[k], theta1, theta2
                else:
                    if angle <= pi:
                        return result[h], result[k], theta1, theta2

        return None


printer = PrinterSimulation()
printer.draw_svg("B.svg")
printer.reset()

B.svg

SVG
This is the representation of letter B in SVG format
<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
    <rect width="100" height="100" fill="beige"></rect>
    <line x1="30" x2="30" y1="10" y2="90" stroke="black" >
        <title>Start at the top and go down to the bottom</title>
    </line>
    <path d="M 30 10 A 35 20 0 1 1 30 50" fill="black" fill-opacity="0.1" stroke="black">
        <title>Go back to the top and draw a curved line to the middle</title>
    </path>
    <path d="M 30 50 A 40 20 0 1 1 30 90" fill="black" fill-opacity="0.1" stroke="black">
        <title>Then draw a curved line to the bottom</title>
    </path>
</svg>

Draw letter B using EV3

Python
Draw letter B using the real printer
#!/usr/bin/python3

from ev3dev2.motor import LargeMotor, MediumMotor, OUTPUT_A, OUTPUT_D, OUTPUT_B
from time import sleep
from math import cos, sin, pi, acos, asin, sqrt, atan
import xml.etree.ElementTree as ET
from sys import stderr
import traceback

MAX_ROTATION_X = 16
MAX_ROTATION_Y = 16
MAX_SPEED_X = 80
MAX_SPEED_Y = 80
POSITION_PEN = 115


class Printer(object):
    def __init__(self):
        self._pen_down = False
        self.motor_x = LargeMotor(OUTPUT_A)
        self.motor_y = LargeMotor(OUTPUT_D)
        self.motor_pen = MediumMotor(OUTPUT_B)
        self.solver = Solver()

    def x(self):
        return -self.motor_x.position / (MAX_ROTATION_X * self.motor_x.count_per_rot)

    def y(self):
        return self.motor_y.position / (MAX_ROTATION_Y * self.motor_y.count_per_rot)

    def reset(self):
        self.motor_x.on_to_position(speed=80, position=0, block=False)
        self.motor_y.on_to_position(speed=80, position=0, block=False)
        self.motor_x.wait_until_not_moving()
        self.motor_y.wait_until_not_moving()
        self.pen_up()

    def move_wh(self, w, h, speed_x=MAX_SPEED_X, speed_y=MAX_SPEED_Y):
        self.motor_x.on_for_rotations(
            speed=speed_x, rotations=-w * MAX_ROTATION_X, block=False)
        self.motor_y.on_for_rotations(
            speed=speed_y, rotations=h * MAX_ROTATION_Y, block=False)
        self.motor_x.wait_until_not_moving()
        self.motor_y.wait_until_not_moving()

    def pen_down(self):
        if not self._pen_down:
            self.motor_pen.on_for_degrees(
                speed=10, degrees=POSITION_PEN, brake=True, block=True)
        self._pen_down = True

    def pen_up(self):
        if self._pen_down:
            self.motor_pen.on_for_degrees(
                speed=10, degrees=-POSITION_PEN, brake=True, block=True)
        self._pen_down = False

    def draw_arc(self, rad_x, rad_y, large, sweep, sx, sy, ex, ey):
        h, k, start, end = self.solver.solve_ellipse(
            (sx, sy), (ex, ey), rad_x, rad_y, large, sweep)
        print('The solution is:', h, k, start*180/pi, "->", end*180/pi)

        if start < 0:
            start += 2*pi
        if start < 0:
            end += 2*pi
        angle = start
        angle_to_do = 0

        if sweep:
            cclock = 1
            angle_to_do = end - start
        else:
            cclock = -1
            angle_to_do = start-end

        if angle_to_do < 0:
            angle_to_do += 2*pi

        print('doing:', angle_to_do*180/pi)

        step = 0
        angle_done = 0
        integral_error_x = 0
        integral_error_y = 0
        integral_weight = 0.15
        while angle_done < angle_to_do:
            dx = -sin(angle) * rad_x * cclock - \
                integral_error_x * integral_weight
            dy = cos(angle) * rad_y * cclock - \
                integral_error_y * integral_weight
            magnitude = sqrt(dx**2 + dy**2)
            speed_x = (dx/magnitude) * MAX_SPEED_X
            speed_y = (dy/magnitude) * MAX_SPEED_Y
            self.motor_x.on(speed=-speed_x)
            self.motor_y.on(speed=speed_y)
            sleep(0.1)

            old_angle = angle
            angle = self.solver.solve_angle(
                cx=h, cy=k, a=rad_x, b=rad_y, px=self.x(), py=self.y())
            step_angle = abs(angle-old_angle)

            if(step_angle > pi):
                step_angle = 2*pi - step_angle

            angle_done += step_angle

            print('Step', angle*180/pi, 'done:',
                  step_angle*180/pi, 'total:', angle_done*180/pi)

            x_sol = cos(angle) * rad_x + h
            y_sol = sin(angle) * rad_y + k
            integral_error_x += (self.x()-x_sol)
            integral_error_y += (self.y()-y_sol)

            step += 1
            if(step > 1000):
                break

        self.motor_x.stop()
        self.motor_y.stop()

    def draw_line(self, from_x, from_y, to_x, to_y, pen=True):
        self.move_wh(from_x - self.x(), from_y - self.y())
        if pen:
            self.pen_down()
        if (to_x-self.x()) < 0.000001 and (to_x-self.x()) > -0.000001:
            self.move_wh(0, to_y-self.y())
        else:
            m = abs((to_y-self.y())/(to_x-self.x()))
            speed_x = 1
            speed_y = m * speed_x
            magnitude = sqrt(speed_x**2 + speed_y**2)
            speed_x = (speed_x/magnitude) * MAX_SPEED_X
            speed_y = (speed_y/magnitude) * MAX_SPEED_Y
            print(to_x-self.x(), to_y-self.y(), speed_x, speed_y)
            self.move_wh(to_x-self.x(), to_y-self.y(),
                         speed_x=speed_x, speed_y=speed_y)

        if pen:
            self.pen_up()

    def draw_svg_path(self, path, width, height):
        path_list = path.split(" ")
        index = 0
        m_x = 0
        m_y = 0
        while index < len(path_list):
            current = path_list[index]
            if current == 'M':
                x = float(path_list[index+1]) / width
                y = float(path_list[index+2]) / height
                m_x = x
                m_y = y
                self.move_wh(x-self.x(), y-self.y())
                index += 3
                self.pen_down()
            elif current == 'L':
                x = float(path_list[index+1]) / width
                y = float(path_list[index+2]) / height
                m_x = x
                m_y = y
                self.draw_line(m_x, m_y, x, y, pen=False)
                index += 3
            elif current == 'A':
                rad_x = float(path_list[index+1]) / width
                rad_y = float(path_list[index+2]) / height
                large = int(path_list[index+4])
                sweep = int(path_list[index+5])
                dx = float(path_list[index+6]) / width
                dy = float(path_list[index+7]) / width
                index += 8
                self.draw_arc(rad_x, rad_y, large, sweep, m_x, m_y, dx, dy)
                m_x = dx
                m_y = dy
            else:
                index += 1
        self.pen_up()

    def draw_svg(self, file):
        tree = ET.parse(file)
        root = tree.getroot()
        width = int(root.attrib["width"])
        height = int(root.attrib["height"])
        for child in root:
            if child.tag == '{http://www.w3.org/2000/svg}path':
                for pos_title in child:
                    if pos_title.tag == '{http://www.w3.org/2000/svg}title':
                        print(pos_title.text, file=stderr)
                self.draw_svg_path(child.attrib["d"], width, height)
            elif child.tag == '{http://www.w3.org/2000/svg}line':
                for pos_title in child:
                    if pos_title.tag == '{http://www.w3.org/2000/svg}title':
                        print(pos_title.text, file=stderr)
                self.draw_line(
                    float(child.attrib["x1"])/width,
                    float(child.attrib["y1"])/height,
                    float(child.attrib["x2"])/width,
                    float(child.attrib["y2"])/height)


class Solver(object):

    def solve_angle(self, cx, cy, a, b, px, py):
        if px-cx:
            theta = atan(((py-cy)*a)/((px-cx)*b))
            if px-cx < 0:
                # quadrand 2 and 3
                theta = theta + pi
        else:
            if py-cy < 0:
                theta = -pi/2
            else:
                theta = pi/2
        return theta

    def solve_ellipse(self, p1, p2, a, b, large, sweep):
        x1 = p1[0]
        y1 = p1[1]
        x2 = p2[0]
        y2 = p2[1]

        m = -2*(b**2)*x1 + 2*(b**2)*x2
        n = -2*(a**2)*y1 + 2*(a**2)*y2
        q = -(b**2)*x1**2 - (a**2)*(y1**2) + (b**2)*(x2**2) + (a**2)*(y2**2)

        if n < -0.000001 or n > 0.000001:
            aa = b**2 + (a**2)*(m**2)/(n**2)
            bb = -2*(b**2)*x1 - (2*q*(a**2)*m)/(n**2) + (2*(a**2)*y1*m)/n
            cc = ((a**2)*(q**2))/(n**2) - (2*(a**2)*y1*q)/n + \
                (b**2)*(x1**2) + (a**2)*(y1**2) - (a**2)*(b**2)

            if bb**2 - 4*aa*cc < -0.000001 or bb**2 - 4*aa*cc > 0.000001:
                h1 = (-bb + sqrt(bb**2 - 4*aa*cc))/(2*aa)
                h2 = (-bb - sqrt(bb**2 - 4*aa*cc))/(2*aa)
            else:
                h1 = h2 = (-bb)/(2*aa)

            k1 = (q - m * h1)/n
            k2 = (q - m * h2)/n
        else:
            aa = a**2
            bb = -2*a**2*y1
            if m < -0.000001 or m > 0.000001:
                cc = b**2*q**2/m**2 - 2*b**2*x1*q/m + b**2*x1**2 + a**2*y1**2 - a**2*b**2

                h1 = q/m
                h2 = q/m
                if bb**2 - 4*aa*cc < -0.000001 or bb**2 - 4*aa*cc > 0.000001:
                    k1 = (-bb + sqrt(bb**2 - 4*aa*cc))/(2*aa)
                    k2 = (-bb - sqrt(bb**2 - 4*aa*cc))/(2*aa)
                else:
                    k1 = k2 = (-bb)/(2*aa)
            else:
                h1 = h2 = x1
                k1 = k2 = (-bb)/(2*aa)

        h = "h"
        k = "k"
        if h1 != h2 or k1 != k2:
            results = [
                {h: h1, k: k1},
                {h: h2, k: k2}
            ]
        else:
            results = [{h: h1, k: k1}]

        results_len = len(results)
        for result in results:
            theta1 = 0
            theta2 = 0
            if p1[0]-result[h]:
                theta1 = atan(((p1[1]-result[k])*a)/((p1[0]-result[h])*b))
                if p1[0]-result[h] < 0:
                    # quadrand 2 and 3
                    theta1 = theta1 + pi
            else:
                if p1[1]-result[k] < 0:
                    theta1 = -pi/2
                else:
                    theta1 = pi/2

            if p2[0]-result[h]:
                theta2 = atan(((p2[1]-result[k])*a)/((p2[0]-result[h])*b))
                if p2[0]-result[h] < 0:
                    # quadrand 2 and 3
                    theta2 = theta2 + pi
            else:
                if p2[1]-result[k] < 0:
                    theta2 = -pi/2
                else:
                    theta2 = pi/2

            if results_len == 1:
                return result[h], result[k], theta1, theta2

            angle = theta2 - theta1
            if angle < 0:
                angle += 2 * pi
            if angle >= 2*pi:
                angle -= 2 * pi

            if large == 0:
                if sweep:
                    if angle <= pi:
                        return result[h], result[k], theta1, theta2
                else:
                    if angle >= pi:
                        return result[h], result[k], theta1, theta2
            else:
                if sweep:
                    if angle >= pi:
                        return result[h], result[k], theta1, theta2
                else:
                    if angle <= pi:
                        return result[h], result[k], theta1, theta2

        return None


printer = Printer()

try:
    printer.draw_svg("S.svg")
except Exception as e:
    print(e, file=stderr)
    traceback.print_exc(file=stderr)
printer.reset()

# for i in range(0, 100):
#     printer.pen_down()
#     printer.pen_up()

# printer.move_wh(-0.0, 1)

# printer.motor_pen.on_for_degrees(speed=5, degrees=-10)  # - pen down

Credits

Andrei Ciobanu

Andrei Ciobanu

12 projects • 16 followers
Viorela Roxana Pop

Viorela Roxana Pop

1 project • 1 follower

Comments

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