This tutorial will explore coppelia sim and understand basic interactions using the ZeroMQ remote API

The tutorial was made on ubuntu 20.04

After studyuing this tutorial you will understand how to:

  • install Coppelia Simulator
  • add and manipulate basic shapes
  • add and manipulate joints
  • setup ZeroMQ remote api

  • interact with the simulator and simulation using the ZeroMQ API

    Note : The tutorial assumes you have a folder named coppelia in your home directory, so you should create it first $ mkdir ~/coppelia

Installing the simulator

  1. Visit the coppelia simulator website and go to downloads section. https://www.coppeliarobotics.com/downloads

  2. Download the edu version (since we are not using it for commercial purposes)

  3. Extract the downloaded folder and copy to desired location

    I am going to assume that we have renamed the extracted folder to CoppeliaSim and placed it at /home/<user>/coppelia/CoppeliaSim

  4. Test the installation by going to /home/<user>/coppelia/CoppeliaSim and running ./coppeliaSim

    Once the simulator starts up, you should see the following screen.

    The version of the simulator used here is 4.4.0 rev 0, if you are using another version , there could be slight differences.

  5. If you saw the screen, coppelia simualtor has successfully been installed on your system.
Start screen

Creating a simple robot

Before proceeding further, you should familiarize with the interface of the simuator so that you know what the terms being talked about are referring to. you can find the refrence in the User Interface section of https://www.coppeliarobotics.com/helpFiles/index.html

Now that the simulator is ready for use, we will create our own simple robot arm to explore and understand how robot/models are represented in CoppeliaSim.

Our robot is going to be a 1 DOF robot arm. It is going to consist of :

  • A tall cuboidal base
  • One cylindrical link attached to the base by a revolute joint.
  1. Go to Menu –> Add –> Primitive Shape –> Cubiod, set dimensions x = 0.1, y = 0.1 and z = 0.2, rename the shape to ‘robot_base’. you should see an object like this
Start screen

  1. Next , we will add a revolute joint. Go to Menu –> Add –> Joint –> Revolute and rename it to shoulder_joint. This will create a joint at the origin, to place the joint at our desired position (i.e top of the cuboid) we need to apply translation to the joint.

    • Select the joint from scene hierarchy
    • click on the translation button
  • A pop up window will appear, select the position tab and you should see options like this.

  • Keep the Relative to: option set to World and set value of Z to 0.25 so that the joint origin is slightly above the robot base

  • The default axis of rotation for the revolute joint in coppelia sim is the z-axis, so we do not need to modify orientation since the axis of rotation we want is along z as well.

This should give you a result like this.

Shoulder joint

  1. The next step is to add a link, select Cylinder from the Primitive Shapes and set value of x = 0.01 and z = 0.2. This will create a cylinder but you cannot see it at this point since it is inside the base. To place it properly , we need to apply some translations and rotations.

    • Select the cylinder from scene hierarchy
    • Select the translation button and go to position tab like before
    • Set y = 0.1 and z = 0.25
    • Close the window and click on the rotation button
Rotation button 
- Go to orientation tab, set `Aplha` = -90
Orientation window 
Now you should see the cylinder properly placed like this.
Shoulder link

  1. Now we have all the parts we need, but they exist as independent components and are not connected to each other. In this step we will create those connections that describe the structue of the robot.

    • Select the shoulder_joint from scene hierarchy , press ctrl and select robot_base.
    • From Menu –> Edit –> Make last selected object parent

    This makes shoulder_joint attached to robot_base

    • Select shoulder_link , press ctrl and select shoulder_joint
    • Select ‘Make last selected object parent’ from Edit

    Now the shoudler_link is attached to shoulder_joint and you have an overall structure like this.

  1. Once we have our structure, we need to tell the simulator how our shoulder_joint behaves.

    • Double click on the joint icon next to shoudler_joint in the scene hierarchy to open the object properties window.
- Selct `Dynamic Properties Dialog` to open the joint dynamics properties.

- Set `Control Mode` to velocity and set target velocity and torque to 0

- close the property windows.


The robot is now ready to be used.

Install ZeroMQ Remote API

We are going to use the ZeroMQ python remote API provided by CoppeliaSim.

  1. Set variable used by cmake to find CoppeliaSim

    export COPPELIASIM_ROOT_DIR=/home/<user>/coppelia/CoppeliaSim

  2. Follow instructions on https://github.com/CoppeliaRobotics/zmqRemoteApi to install the library.

Setup env to use the api from python

To keep things clean, we will create a python virtual environment to work in. If you dont have python3-venv installed yet, you should install it first.

  1. create a venv named coppelia_env $ python3 -m venv ~/copellia/coppelia_env

  2. Activate the env using $ source ~/coppelia/coppelia_env/bin/activate

  3. Follow instructions on https://www.coppeliarobotics.com/helpFiles/en/zmqRemoteApiOverview.htm to install required python modules.

Controlling the robot using the remote API from python

API Reference : https://www.coppeliarobotics.com/helpFiles/en/apiFunctions.htm


import sys
import time
# Add the path to  zmq python client to system paths
sys.path.append("~/coppelia/zmqRemoteApi/clients/python")

from zmqRemoteApi import RemoteAPIClient

client = RemoteAPIClient()

# Enable client stepping so that we can manually step through the simulation
client.setStepping(True)

# Get the simulation object
sim = client.getObject('sim')

# From the simulation get the handle for the shoulder joint
shoulder = sim.getObject('/robot_base/shoulder_joint')

# Check the state of the joint
jointPosition = sim.getJointPosition(shoulder)
jointVelocity = sim.getJointVelocity(shoulder)

# Set desired joint velocity
targetVelocity = 2  # deg/s
maxForce = 0.1 # Nm
sim.setJointTargetVelocity(shoulder, targetVelocity)
sim.setJointMaxForce(shoulder, maxForce)

# Simulation loop
# We will simulate 50 steps

sim.startSimulation()

for _ in range(50):
    # Run one simulation step
    client.step()
    time.sleep(0.1)
    print(sim.getJointPosition(shoulder))

sim.stopSimulation()