Concepts in ROS and CAD design

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 Previously on this page ……

  • We saw how to use Xserver to export gui from wsl and how to open wsl in vscode.
  • We installed ROS on wsl / windows and hope you have gone through beginner tutorials on ROS wiki page.
  • I have suggested some points in previous post as well you may encounter some errors and how to solve them.

Concepts in ROS:

  • Nodes: scripts that handle the operation under ROS master, they can publish data on one or more topic or can subscribe to a topic to get the published data . Also they can be service provider i.e. nodes can have sever-client communication .

  • ROS Master: It is like a CPU in pc, it registers nodes, keep track of which topics are published ,which node is subscribed to which topic ,which node is publishing on which topic, basically master is monitor of software nothing can kept hidden form it.

  • Topic: rostopic is topic on which nodes talk to each other😂, just kidding , rostopic is way by which nodes communicate with each other, as there can be many node publishing different data and if there wouldn't concept of topics then every thing would be mess!! 

  • Message: messages are the format in which data is published and received they are also important as much as the rostopics are, you can customize them according to your need.

  • Package: rospackage is set of folders which contains your launch, scripts, message, service, urdf etc. folders along with two most important files namely cmakelist and packge.xml these two file help ros to understand that this is a package and what are its dependencies.

  • Service file: These files are used by server node to provide service to client node.

  •  Action file: These files are used by action server and client, to know more about action server and difference between action and normal sever, visit the roswiki page.

  • Co-ordinate frame: it is co-ordinate system in which a part or robot itself exists, every part of robot has its own co-ordinate system, which help us to know how much the part is rotated or translated w.r.t the global frame. 

  • Transforms(TF): One of the important package used in ros to keep track of robot  state, to more about it click here.

  • URDF: urdf stands for unified robot description format, it is one of the file format in which robot can be described in detail, there are many other file format I want you to explore them.

  • Plugins: these are set of codes used as part of main urdf file so that simulator can understand what to simulate.

CAD design of robot...….

  • In above section we had brief look at concepts and terms used in ros and now its time to get to practical.
  • Hope you have installed Fusion 360 and got little bit familiar with it, explored it and the tools provided by software.
  • Its always a good convention to make a folder for your project in which you save your cad files and also, to keep version track save it on cloud, which s by default, we will later download these to our system.
  • first lets sketch and extrude parts of our robot one by one:
  1. Wheels: draw a circle of specific diameter , its up to you how big wheel you want, I took diameter as 80mm and extruded it by 40mm, also if you want you can use tools like fillet and chamfer to it also if you want to create patterns on surface you can, also make sure to add material to it, you are free to do any thing after all its your design😅, here is my design:
  2. Base: make a new file and again start a sketch, draw rectangle or square again its your choice, my design has dimension 200*200 and extrude of 5mm, I have also added material to it but so get perfect mass and moment of inertia values in urdf here is mine one:

  3. Now similarly make different parts like shaft, motor, arm, gripper and feel free to design more components and explore the software, I am keeping the design as simple as possible, but you can explore more.
  4. I will be sharing these cad files and other files on GitHub.
  5. Now its time to add urdf exporter to the software, there is plugin known as fusion2urdf exporter download it and install it by following the process on GitHub page, If any error occurs feel free to comment am there to solve the problem. 
  6. Now its enough for this blog I know this was  more technical but we will do more exciting things from next one.

 Upcoming...…

  • In next one we will assemble different parts we made in this blog.
  • We will take note of some important things while assembling the robot.
  • We will see what type of files are generated by the exporter and we will understand it in detail in upcoming blogs
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