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Good afternoon, everybody.
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Thank you very much for being here. There are so many other interesting talks, but you chose to come here.
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Oh, I'm Shashank Daté.
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This is my hobby, and I do it for fun and, unfortunately, some losses.
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I have lost a couple of drones and never got them back.
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Now, to get the energy flowing in this room, I want you all to participate.
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On the count of three, I want you all to read the next slide as loudly as you can so that the energy in this room goes up.
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Okay? Alright. One, two, three.
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Thank you! Now, if you have blessed me, I'll show you why that blessing is required.
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And here, pretty soon, these two should take off using my hello_edu.rb file.
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I have to do one little thing that I forgot.
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Give me just a second; I need to find the IP address of these two drones.
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When they booted, they received different IP addresses.
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The way I communicate with them is through a Wi-Fi router that I have set up here.
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My laptop is connected to them through that, so I'm going to scan for these devices.
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It shouldn't take more than a few seconds to detect their IP addresses.
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The last three digits are 102 and 103.
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If our energy is right, they're going to take off and land— not exactly in the same spot, but somewhere nearby.
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If they start drifting, I have drone catchers in the audience who will catch them.
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Okay? Let's see if it turns green. There you go.
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That’s like my teenage daughter who doesn’t listen to me. She has a knife.
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It will land in a few seconds; it has a default 15-second wait time.
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They behaved much better today than they have in the past.
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Okay, so now, these are a special class of drones called Tello drones.
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Tello is the type of drone that I've been programming.
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These are probably the cheapest programmable drones you can find at under $150 each.
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The first few that I lost were during tests to see how high they could fly, but then the wind came up and they were gone.
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Nonetheless, they are perfect for educational purposes.
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They introduce beginners to programming.
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For those of you who attended the previous talk, it mentioned a language called Logo, which taught kids to draw diagrams using turtles on a 2D plane.
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These drones represent a 3D version of that. You can move not only horizontally but also vertically.
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The purpose of these drones is to teach programming.
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While there are many simple concepts to grasp, there are also deeper constructs that more advanced programmers can benefit from.
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The type of drones I’m using are called Tello EDU type drones.
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They have progressed from SDK 1.0 to 2.0, which includes the EDU capabilities we just saw.
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This enables us to program swarms of drones.
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I didn't have the budget to buy the full EDU kit that comes with 20 drones and costs about $5,000.
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But I bought a couple and started experimenting.
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These kits come with official support for Python, Scratch, and Swift.
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I thought, 'Why not Ruby?' So, I took it on myself.
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I got it working in Ruby as well.
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These drones require concepts of network programming and concurrent communication.
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They also involve video streaming and related tasks.
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In terms of specs, these drones have an Intel Core i4 processor.
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They are very lightweight and come equipped with a camera.
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Believe it or not, they also have collision detection sensors.
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There are two flight modes available in the EDU that you just saw.
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There’s AP mode and Station mode.
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AP mode is the access point mode that comes by default when you pull it out of the box.
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In this mode, you can only control one drone directly from a single computer.
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A single computer cannot control multiple drones.
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I have never tried controlling multiple computers to manage one drone.
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In this mode, video streaming from the camera is possible.
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Then there is the swarm mode, also known as station mode, which is available in the second version of the Tello EDU drones.
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To communicate with the drones in swarm mode, some manual setup is required.
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With this mode, you use a router to communicate from your laptop to the drones.
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In the AP mode, the drone itself acts as the access point.
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It publishes its own SSID and password, which you must capture in your program.
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This is why switching between those two modes is challenging.
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These are the two modes of communication.
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Now, let's talk about the programming prerequisites to control these drones.
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First, you need UDP/IP communication between the drones.
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Second, you should have some form of concurrency because you'll be sending commands in one thread while receiving responses in another.
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You need to keep track of which command corresponds to which response.
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Sending one command and waiting for the response in the same thread doesn’t work.
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UDP is fast enough, and we'll see why.
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Lastly, video streaming is optional; I couldn't get it to work for Ruby.
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If you want to see real-time video, you need a suitable library in your programming language.
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In Ruby, there's a UDP socket class available in the standard library.
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I use that for communication.
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Ruby 2.x has fibers and threads, and there are also reactors.
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There are many ways to implement concurrency in Ruby.
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When it comes to video streaming, I was excited when I discovered Ruby OpenCV.
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I'll discuss this library a bit later.
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So what is UDP/IP?
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You must have heard of TCP/IP. UDP/IP is a sibling of TCP/IP.
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It’s based on IP sockets and uses datagrams and port numbers for communication.
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It is connectionless, meaning there is no need for handshaking.
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You send a command and forget about it.
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No buffering of datagrams occurs at either end.
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While it is fast and meant for real-time communication, there is no guarantee of message delivery.
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Also, commands might return in different orders.
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Programmers need to keep this in mind when using this protocol.
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You witnessed an example of this today.
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One drone took the command to land while the other ignored it due to a packet loss.
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That's the drawback of UDP; however, speed takes precedence.
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In Ruby, if you wanted to see an example, this is a basic UDP socket implementation.
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You require the socket library of Ruby, set up a host and a port,
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and then prepare a message to be sent to that object.
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You create a new socket, binding it to the host and port, then send the message.
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Afterward, you’ll wait for the data to arrive.
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In this example, it's not threaded; it's waiting for data to return.
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Since it's essentially sending data to itself, it’s highly reliable.
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Printing the data reveals the output received.
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In summary, the first prerequisite for using UDP/IP is satisfied by Ruby.
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In terms of concurrency, Ruby offers fibers.
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Fibers handle cooperative concurrency, meaning the programmer must control the flow.
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Threads provide preemptive concurrency, meaning the programmer has no control over thread switching.
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Reactors come next, which are still in the experimental phase.
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Ruby might soon include them as a core part of the language.
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I wanted to highlight a library called Ruby OpenCV for video streaming.
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This library wraps the OpenCV C++ library for video processing.
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Unfortunately, I faced difficulties compiling it since it has been stagnant for eight years.
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Indeed, I couldn't get OpenCV running properly on my Mac.
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Because of this, we won't see a video streaming demo today.
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Now, concerning mruby, by default it has only fibers; there are no threads.
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To enable socket communication, you need to compile mruby with the socket gem.
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This core gem comes with the mruby installation.
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If it's not present in Ruby, it's not likely to be in mruby either.
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As of now, I haven't seen attempts to integrate video processing or streaming into mruby.
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For those unfamiliar with mruby, it’s a lightweight implementation of Ruby.
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The 'm' stands for Embedded Ruby, Modular Ruby, or Minimalistic Ruby.
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It's a proper subset of Ruby; anything you can do in mruby can also be done in Ruby, but the reverse isn't true.
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In terms of deployment architectures, mruby can be deployed in more spots and environments than Ruby.
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A key advantage of mruby lies in its ability to compile your code into a single executable.
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This reduces dependencies on the operating system library.
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Typical use cases include bare metal programming.
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There might not even be an operating system or file system available.
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For memory-constrained devices, I previously attempted to program point-of-sale systems using mruby.
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However, it's likely still bulkier than what those devices actually require.
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With progress made since my last attempt, it may now be more feasible.
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The latest stable version of mruby (3.0) can launch an app within 100 KB of RAM.
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The devices I had back then required less than 64 KB of RAM, so I'm skeptical.
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Nevertheless, progress is ongoing, and this is one of Mats's favorite projects.
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You'll see regular commits coming into mruby.
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Game engines and other applications could also see enhancements.
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Now, moving towards the implementation, you notice one line that is different: there is no require.
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Why no require? It's because mruby does not assume the existence of a file system.
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The require statement requires files to exist from a specified path.
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So, you'll have to recompile the interpreter with the core gem.
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There's a build configuration script in mruby.
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If you add an extra line in the build configuration file to compile with mruby, make sure to clean up previous builds.
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Once you clean the previous version, you can compile it with the socket layer.
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Once compiled, you’ll be able to run the example.
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What if you want to convert this program into a single executable?
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This process is slightly convoluted, so let's break it down.
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You can compile your example.rb code into a bytecode using the mrbc command.
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This bytecode can then be distributed to anyone who has mruby installed.
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They won’t see the original source code, just the bytecode.
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If you want to go further and ensure the person doesn't need mruby installed,
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you’ll need some C programming.
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It’s a two-step process.
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First, use mrbc to generate a symbol table, which is a data structure for the bytecode.
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You can assign a name to that table for easy reference.
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This is important for structuring your code.
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In the next step, you'll write boilerplate code and include the emitted file.
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Then you open the VM (virtual machine), which is standard for compiling any mrbc code.
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Use the generated symbol table in the C file to execute your code.
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You can compile it using your regular C compiler, and this creates a usable binary file.
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That binary file can then be distributed without needing mruby installed on the user's machine.
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So, this is the process to create a native binary.
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For this talk, my three focus areas were Tello drones, actors and fibers, and mruby.
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I opted to go deeper into mruby since that's my favorite.
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Now, how do we get these drones to fly? Are they still on?
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I should have turned them off earlier.
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One observation I've made regarding the battery life is that the reported flight time is around 15 minutes.
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However, I've never experienced a full 15 minutes on a single charge.
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I usually only get about five minutes of flight time.
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It’s vital to manage your battery effectively.
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So, let's see how much time we have left.
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I have a project on GitHub for Tello, where I’ve written the same code in Ruby, mruby, and Crystal.
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A friend contributed code in Elixir as well.
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Remember, those two concurrency prerequisites are essential to control these drones.
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If you have a favorite programming language not included in the project, please submit a pull request.
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Today, we're going to focus on the GitHub project where I've curated Ruby files for this conference.
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The code we saw running was hello_edu.rb, which we'll review.
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This all started because of a gentleman named Tom Black.
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In a previous RubyConf, he conducted a five-minute lightning talk showing off these drones.
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I got excited by his demonstration. Though he used an earlier version without swarm capabilities.
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I collaborated with him to create the second version of the gem.
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My pull request is still pending, but I am confident he will merge it once he sees the quality of the code.
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If you visit that GitHub repo, you'll find a gem that allows you to set up a local Tello server.
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This way, you don’t even need an actual Tello to test your client code.
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Tom has put a lot of effort into this gem, and I'm grateful to him.
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Now, let’s focus on the code we will be modifying today.
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Since I'm not on the public Wi-Fi, I'm on a Wi-Fi that isn’t connected to the internet.
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So I won’t be able to drive the drones right now.
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I'll show you the code, which is not production-quality code; it's more like a hello world example.
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I used global variables, which isn't a good practice.
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This code is specifically designed for two drones.
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So, to communicate with the two drones, I’ll use methods for sending commands.
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All my work was done on a Raspberry Pi equipped with a camera.
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As soon as the drones take off, the camera starts recording.
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If something goes wrong, I will at least have the video evidence.
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Thankfully, everything has worked so far.
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Here’s the command structure I used.
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This if statement will handle the response from the drones.
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I send commands to set the Tello into command mode.
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Now I will check the battery level since certain maneuvers are only possible with higher battery values.
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For take-off and landing, you don't need much power.
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Now, I will attempt to take off.
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We’re going to do some live testing with the drones.
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Let’s hope there’s enough battery for the drones to perform the tasks.
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While they boot up, I'll try to get them to flip.
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Let’s see how that works out!
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One of these drones will flip while the other will shift left.
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Let’s give that a shot.
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I’m hoping everything goes as planned.
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They should be up and flying now!
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Alright, I have about five more minutes. Should we keep going?
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Let’s try to do two flips this time!
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They should perform their flips now.
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If there aren’t any errors in the console, they will return together.
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Okay, here we go.
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Now they should perform their flips!
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And they're off!
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I just want to do one more thing, and then we can switch to Q&A.
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This time, one drone will rotate clockwise while the other will rotate counterclockwise.
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Let’s see if that works.
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Okay, let me clear up some space here.
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Can you all read the size of the text?
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Let’s get ready!
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The drones should begin their rotations!
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Here we go!
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If everything goes well, they should execute flawlessly.
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There you go! Thank you very much!
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That’s it, everyone! They’ve been on their best behavior today.
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I have about three minutes for questions.
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As you can see, it’s really straightforward.
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Please submit pull requests (PRs) for the code in the GitHub repository.
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If you do submit a PR, please ensure it follows the model created by my friend.
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I’m going to switch over to the public internet now.
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In my codebase, I have contributions in other languages like Crystal, Elixir, and more.
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Just last week, a friend submitted a PR that included detailed instructions.
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He provided examples of how to install and use it, which is great!
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I would love if PRs maintained a similar level of detail.
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Thank you very much for your attention!
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Any further questions? Let's give that a try!
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I have only one minute left.
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So let's proceed to try that!
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It is possible, let’s explore this option.
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I’m going to navigate to my Tello gem folder.
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I believe rake builds it.
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I might have the Tello gem and the EDU gem installed.
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So let’s see if that works.
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This is like an interactive mode, similar to IRB.
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Unfortunately, I’m encountering a permission error.
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The Tello gem allows for interactive commands, but I need to remember how to start.
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You must first issue a command to initiate the Tello, followed by others like takeoff.
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Alright, I’m almost out of time.
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If you want, we can try this outside and capture live interactions.
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You’re welcome to join and test things out!
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Thank you once again!
