Backends

The Toolbox supports a number of backends to display a robot animation or to control a physical robot.

Available backends

By default, only the PyPlot backend is included in the Toolbox install. The others require additional installation steps.

PyPlot (matplotlib)

This backend displays the robot as a noodle using matplotlib graphics. matplotlib is the most ubiquitous graphics library for Python and runs on all platforms.

>>> import roboticstoolbox as rtb
>>> p560 = rtb.models.DH.Puma560()
>>> qt = rtb.tools.trajectory.jtraj(p560.qz, p560.qr, 50)
>>> p560.plot(qt.q)

Options exist to:

• attach a velocity or force ellipsoid,
• display link frames and joint axes,
• save the animation to a file as an animated GIF

VPython

This backend displays the robot in 3D in a browser window using JavaScript and VPython. At the moment it only works with models defined using DH notation and requires STL meshes.

>>> import roboticstoolbox as rtb
>>> p560 = rtb.models.DH.Puma560()
>>> env = p560.plot(qt.q, backend='vpython')

If you wish to record the scene, it is recommended to slow the robot down and record in a slow rate. Trying to record in high fps can lag and jumble the resulting video.

>>> env.record_start(5)  # Record at 5 fps
>>> for q in qt.q:
>>>     time.sleep(1/5)
>>>     env.step(puma, q=q)
>>> env.record_stop('vpython_video.mp4', save_fps=25)  # Save the resulting file at 25 fps

Swift

Swift displays in a web browser table using three.js. At the moment it only works with models defined using URDF and can use STL or Collada meshes.

>>> import roboticstoolbox as rtb
>>> p560 = rtb.models.URDF.Puma560()
>>> qt = rtb.tools.trajectory.jtraj(p560.qz, p560.qr, 50)
>>> p560.plot(qt.q)

TODO ADD CODE EXAMPLE AND IMAGE/ANIMATION

Using the backend

The simplest way is using plot with a backend option as shown above. The alternative is to create a backend environment

from roboticstoolbox.backends.BACKEND import BACKEND
env = BACKEND()

# where BACKEND is PyPlot, VPython or Swift

env.launch()  # start the backend
env.add(robot)  # add a robot to the backend

for ...:
    robot.q = some value
    env.step()

Installation

Follow the instructions on the Swift home page.

CopelliaSim (nee VREP)

CopelliaSim is a mature and capable cross-platform robot simulation environment with a free licence to use for education.

TODO ADD CODE EXAMPLE AND IMAGE/ANIMATION

Installation

ADD DETAILS FOR COPSIM, CONFIGURATION

Backend API

The backend supports a simple API defined in backends/Connector.py

• launch() launch the external program with an empty or specific scene as defined by args

• step(dt) requests the external program to make a time step of defined time updating the state of the environment, including all robots, as defined by the robot's actions.

• id = add(object) adds an object to the external environment. If object is a robot, it must be of an appropriate class. This adds the object to a list of which will act upon the step() method being called. This method returns the id of the object.

• remove(id) removes the specified object from the external environment.

• reset() triggers the external program to reset to the original state defined by launch

• restart() request the external program to close and relaunch to the state defined by launch

• close() requests that the external program to gracefully close

• hold() requests that the external program stays open, will prevent Python from exiting the script. Is blocking

• getframe() return a PIL image for current frame if possible

TODO

• tidy up objects that can be added, they should have a common superclass with abstract methods that addables must have
• teach panel, this is still an underscore function.
• getframe method. Can we make this work for VPython and Swift? We have too many different ways of recording movies, need to unify