Robot Head Mark 2

Around 3 months ago I started a new robot project. I decided that I wanted to build another robot head that could sit on a desktop. I had a few goals in mind when starting the project. I wanted to 3D print the parts and try out some finishing techniques on the parts. Nothing too fancy, just sand them smooth and paint, to see how good a finish I could achieve. I also wanted the robot to be low-cost and simple. I mean really simple, just two servos and a couple of sensors. This was very intentional. I want to expand on the work of my previous project, the desktop robot head and arm, by concentrating on the software. I found I was too often dealing with mechanical issues or limitations and these were an all to welcome distraction from the software. I like making things and having something physical to show for the hard work, whilst I find that with software there isn’t always that sense of satisfaction of having created something. However, the software is where the robot really comes to life and I need to get better and more focused at writing it and implementing the ideas that I have. To that end I wanted a simple robot with very little to go wrong that can serve as a platform to develop some interesting functions. This project will hopefully pull together a lot of the work from previous projects into one robot, and I intend to craft the software with care. I want to squeeze as much functionality out of this simple robot platform as possible. I also wanted to take the opportunity of a new project to switch from using TKinter for the GUI to using wxPython.

I started the process by designing the robot in FreeCad. I did more design work on this than in previous projects and really spent my time on the modelling. I even put the parts together into an assembly to help decide on the colour scheme. I have started another youtube series following the design and build of the robot. Part 1 is below.

This video shows the design and printing of the robot and at the end of it I had a pile of 3D printed parts ready for finishing. The design is a simple pan/tilt robot head, with a camera and a sonar sensor mounted in the head. I want to build on my previous work with point clouds so I wanted a sonar mounted on the head. I don’t think I will end up creating point clouds with this robot but I will likely use the techniques to come up with a different way to represent the environment. However, I didn’t want the sonar sensor looking like the robots ‘eyes’ as they often do, so I tried something new with this project. I printed a mesh to mount in front of the sonar and, combined with a piece of filter fabric, made a cover for the sensor. Later testing would reveal if this was successful or not.  The only other feature of the head was the robots actual ‘eye’. In place of the TFT screen used in the last project I opted for an RGB LED in a custom enclosure that would furnish the robot with a single colour changing eye that it can use to attract interest or convey emotions.

Part 2 shows the finishing of the 3D printed parts.

This involved a lot of sanding and priming before finally painting the parts. I was overall really pleased with the finished parts. It become clear from this process that the quality of the final finish is directly proportional to the amount of finishing work put in. I also took away a few other lessons from this process when designing the parts for finishing. Sharp corners and deep recesses are difficult to sand and remove all of the build lines without removing too much material. Smooth, rounded surfaces or large flat surfaces are easier to sand and look good when painted.

Part 3 of the video series documents the assembly of the robot.

With the robot assembled I was able to do some testing. I decided to use an Arduino Nano for this project, in-keeping with the minimalist and simplicity goals of the project. I knocked up a bread board circuit for testing and set about testing the RGB LED eye and the sonar sensor. Good news was that the sonar still seemed to function just fine from behind its cover, and the RGB LED worked as expected.

I initially connected the RGB LED to digital outputs, thinking that the few colours that this yields would suffice. I subsequently decided to use PWM outputs, so that a wider range of colours could be generated. Given that the robot was so simple, I thought this was a reasonable extravagance.

Part 4 shows testing of the RGB connected to PWM outputs and the first test of the servos.

This video also represents my first simple programs written using wxPython. So far, I like it. The GUI’s look better than their TKinter counterparts and overall it is not much more complex, if at all. I created a couple of test programs, one that sends commands via serial to set R,G and B values for the LEDs and another that sends servo positions. Code for the Arduino has also been written to receive these commands and set the RGB outputs and servo positions accordingly. I can also send get commands to the Arduino and it will return values as appropriate.

This brings us almost up to date on this project. There will be a new video soon, so be sure to subscribe to my youtube channel. I have been working on embedding OpenCV images and MatPlotLib plots in wxPython windows, as well as making a more permanent circuit for the robots electronics.

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Point clouds using the robot arm

Several months ago I posted the final video (Part 8) in the series looking at the build of a Desktop robot head and arm.  I say final video as, for the time being, I have shelved this project and have moved on to something else. I learnt a lot from this project and I will likely revisit it at some point in the future.

The video above takes you through the process of using the robot arm, along with the model described in the previous post, to build a point cloud representation of the robots surroundings. I added feedback to the final servo in the robot arm assembly, the sonar tilt servo, and I was then able to calculate the position and orientation of the sonar mounted on the end of the robot arm. Using the sonar reading, I could then apply the same technique used to calculate the robot joint positions to find the x,y and z coordinates of the object that the sonar was detecting. This position could then be stored as a point. I programmed the robot arm to move to a series of positions and record a measurement from the sonar sensor as a point which was added to a large array. This array could then be plotted as a 3D plot in the matplotlib window in the GUI.  I pushed this as far as I could and ended up with a point cloud of several thousand points. At this point my PC was struggling to display the points and allow the plot to be rotated or zoomed smoothly. The gathering of the data for the largest point cloud I created took somewhere in the region of 30-40 minutes.

The point cloud experiment was interesting as it showed that the position of objects could be estimated and stored as positions in an array. One of the reasons that I moved on from this project was that I wanted to revisit previous work of combining a distance sensor with a camera. I would like to be able to capture an image, extract one or more objects of interest from the image and measure a distance to the object. This information can them be stored in some form. Similar to the way the point cloud represents distance points, I would like to build up a cloud of objects and their positions that the robot can later use to reference what it is currently seeing.

I will be back very soon with another post as I have made good progress with the next project that I will be sharing here.

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jimsickstee

Hi, I'm Jim. Read what I write and I'll write more to read.