Integrating V-REP with RoboComp as an external simulator and as an in-the-loop simulator

July 22, 2019

Goals:

### Convert scene files of RoboComp written in XML to .ttt scene file types supported in V-REP

• The scene files (like simpleworld.xml) of RoboComp are in .xml format, so, our goal is to convert these xml file to the filetype supported by V-REP.
• V-REP supports binary file format with .ttt extension.
• Advances:
  • Asked the concerned question in V-REP forum: XML/text to .ttt(binary files) supported by V-REP. The following are the methods suggested to convert existing xml files into ttt file:
    • V-REPs SDF plugin can be used in some way, since, V-REP can import SDF files (which are basically XML files conforming to the SDF specification) via the SDF plugin.
    • We can write some simple XML importer via an add-on function. With the help of an add-on function that ships with V-REP: vrepAddOnFunc_minimalisticImporter.lua Then we can use a Lua XML parser (preferably a pure-Lua, such as SLAXML for instance).

Validation test of the V-REP integration

### The idea is to use the Lego EV3 as the target robot in V-REP, a simple 2mx2m planar space with walls and a line drawn on the floor so it can follow it.

• For the testing, we required V-REP model of Lego EV3 robot. We found two model files for the Lego EV3 robot:
  • LEGO_EV3_GROUP
  • LEGO_EV3_MERGE
• Using the LEGO_EV3_MERGE model file, the following scene hierarchy was created in the V-REP scene:
  • 
• And, the following is the sped up demo of the Lego EV3 robot being controlled by controller to follow a line on the floor:
  • 

Documentation

### To guide the developers on how to use V-REP Remote API to control the behaviour of the scene:

• Advances:
  • Here, is the basic introduction to V-REP, and a tutorial on V-REP Remote API:
    • https://github.com/nikhil3456/V-REP/blob/documentation/tutorial/V-REP_API.md

Create a controller using RoboComp bridge components to control a EV3_Lego

• The component has a DifferentialRobot interface (see DifferentialRobot.idsl on robocomp interfaces). The component also has all of the necessary methods to implement the interface successfully.

• For testing, the EV3_LEGO robot is used with the following V-REP model-types:

  1. LEGO_EV3_GROUP
  2. LEGO_EV3_MERGE

• The following are the components that makes up the model:

  __COMPONENTS = {
          'robot': 'LEGO_EV3',
          'camera': 'Camara',
          'camera_bumper': 'Camara_bumper',
          'camera_sonar': 'Camara_sonar',
          'sensor_color_LR': 'Sensor_Color_LR',
          'sensor_color_RC': 'Sensor_Color_RC',
          'sonar': 'Sonar',
          'bumper': 'Bumper',
          'motor_b': 'Motor_B',
          'motor_c': 'Motor_C',
          'slider': 'Slider_SF',
          'giroscope': 'Giroscopio'
      }
  

  • The robot has two motors named “Motor_B”, and “Motor_C” which are used to control the movement(rotation and translation). And, it also has two sensors for sensing the surroundings.

• The V-REP scene act as a Server and the corresponding client logic is implemented in vrep_client_controller.py. This is the code snippet to initialize the client in robocomp component to connect to V-REP server:

  class VRepClientController:
  def __init__(self, host, port):
      self.host = host
      self.port = port
      self.client_id = -1
      self.console_id = -1
      self.debug = False
  
      self.connect()
  
      if not self.is_connected():
          if self.debug:
              err_print(prefix="COMPONENT CREATION",
                        message=["CANNOT CONNECT TO REMOTE API"])
          raise Exception("CANNOT CONNECT TO REMOTE API")
  

• remote_demo.ttt is the V-REP scene file for testing the robot.

• EV3_LEGO_controller is the python file containing the functions used to control the robot.

• The compute function in specificworker.py has the logic for the robot to follow a line in the scene. This file basically calls the function in the file EV3_LEGO_controller to control the robot.

Nikhil Bansal