Drive a Grizzly
================

.. warning::

	Grizzly is a discontinued platform.  Please see :doc:`Drive a Husky <Drive a Husky>` or
	:doc:`Drive a Warthog <Drive a Warthog>` for currently-supported platforms.

Updating the Virtual Machine
------------------------------
Open a terminal window (Ctrl + Alt + T), and enter the following:

.. parsed-literal::
	sudo apt-get update
	sudo apt-get install ros-melodic-grizzly-simulator
	sudo apt-get install ros-melodic-grizzly-desktop
	sudo apt-get install ros-melodic-grizzly-navigation


Running a Virtual Grizzly
--------------------------

Open a terminal window, and enter:

.. parsed-literal::
	roslaunch grizzly_gazebo grizzly_empty_world.launch

Open another terminal window, and enter:

.. parsed-literal::
	roslaunch grizzly_viz view_robot.launch

You should be given two windows, both showing a yellow, rugged robot (Grizzly!). The left one shown is Gazebo.
This is where we get a realistic simulation of our robot, including wheel slippage, skidding, and inertia.
We can add objects to this simulation, or even entire maps of real places.

.. image:: grizzlysim.png
	:scale: 75%


This window below is RViz. This tool allows us to see sensor data from a robot, and give it commands (in a future post). RViz is a more simplified simulation in the interest of speed.

.. image:: grizzlyviz.png
	:scale: 75%

We can now command the robot to go forwards. Open a terminal window, and copy the following:

.. parsed-literal::
	rostopic pub /cmd_vel geometry_msgs/Twist "linear:
		x: 0.5
		y: 0.0
		z: 0.0
	angular:
		x: 0.0
		y: 0.0
		z: 0.0"

In the above command, we publish to the cmd_vel topic, of topic type **geometry_msgs/Twist**.
The data we publish tells the simulated Grizzly to go forwards at 0.5m/s, without any rotation.
You should see your Grizzly move forwards. In the gazebo window, you might also notice simulated wheel slip, and skidding.