{"id":2220,"date":"2016-03-17T16:25:18","date_gmt":"2016-03-17T08:25:18","guid":{"rendered":"https:\/\/gergely.imreh.net\/blog\/?p=2220"},"modified":"2016-03-17T16:25:20","modified_gmt":"2016-03-17T08:25:20","slug":"scratch-robot-itch","status":"publish","type":"post","link":"https:\/\/gergely.imreh.net\/blog\/2016\/03\/scratch-robot-itch\/","title":{"rendered":"Scratch Your Robot Itch"},"content":{"rendered":"

Recently I’ve been experimenting with the Scratch programming language<\/a>, created by the Lifelong Kindergarten Group at MIT. It’s a fun environment that uses visual programming: drag-and-drop pieces of code blocks, and control objects on a stage, and the stage itself. It has quite a bit more depth to it, than the expression “visual programming language” implies, with it’s internal messaging system, multitasking, and event-driven approach. While it was originally aimed at creating interactive graphics and animations (see this TEDx talk by Prof. Mitch Resnick<\/a>\u00a0on the background), it is now evolving into new territories with the Scratch Experimental Extensions<\/a>.<\/p>\n

<\/p>\n

The Experimental Extensions define a smallish API<\/a>, which can be used to create custom programming blocks to be used in Scratch. All it needs is a Javascript file (currently) hosted on Github with a few pre-defined code blocks to unlock any sort of functionality. This creates a possibility to easily tap into any kind of web API or interface any hardware that can be addressed somehow through Javascript. There are a large number of examples<\/a>\u00a0already, and I wanted to see how easy or hard it is to create such an extension for a robot that happened to be around here at VIA<\/a>.<\/p>\n

The Robot<\/h2>\n

Some of the engineers at VIA have built a small robot using bits and pieces found in the lab: a dual-core ARM-based engineering sample control board, smart battery from another project, some wheels from a commercial robot (Rovio’s 3-wheel system a few years back), and I think some office supplies.<\/p>\n

\"Hacked-together<\/a>
Hacked-together robot from the lab<\/figcaption><\/figure>\n

The robot’s operating system creates an access point (with the Wi-Fi USB stick on the upper right of the picture), and hosts a webpage that can be used to control the movements<\/strong> (back\/forth\/left\/right), as well as streaming video<\/strong> (or more precisely Motion JPEG<\/a>) from the camera in the front (lower left, the little black square on top of the white sticky pad).\u00a0Besides the control board, there’s some voltage converter and battery-control circuits, off-the-shelf pieces by the look of them, with minor modifications (such as an LED to see when the battery is out of power).<\/p>\n

It is as hacky as it gets, but all that is needed to have some fun.<\/p>\n

Controlling Through Scratch<\/h2>\n

While the built in webpage to control the robot is very handy, and can be used from any device that has a browser (computer, smartphone, I guess could even control it from a Kindle<\/a>), it has it’s limitation: I need to click on buttons to get things done, and nothing can be really automated. Still, the underlying API is a good start to do more interesting things.<\/p>\n

The API is very hacky too, and that’s just fine like that. Looking at the built in webpage, I could see that there are a handful of GET requests<\/a>\u00a0to a specific URL to move_forward<\/span>\u00a0, or turn_left<\/span>\u00a0 or stop<\/span>\u00a0. That’s straightforward enough, and it does not take more than a couple of minutes to cook up a proof of concept Python script using requests<\/a> to try these endpoints.<\/p>\n

Once that worked, I followed the Scratch Extension documentation<\/a>\u00a0and some of the examples linked from the site to creating a Javascript module to implement these movement commands.<\/p>\n

\"Scratch<\/a>
Example Scratch script to control the robot, samba moves included (click for full size)<\/figcaption><\/figure>\n

It didn’t take too many iterations to add the blocks like “move forward for X seconds” and so on for the other movements. I’ve created a basic project to show how these work, where the robot moves following the directional arrows: forward\/backward, and turning with left\/right. Figured out that 0.5 turning is about 45\u00b0, so the arrow in the screen can sort of follow the direction of the robot in the physical world. For good measure I’ve also added a complex block of “samba” steps (I’m sorry, haven’t been doing samba for years, but that’s what it reminds me of), which is triggered by pressing “s” on the keyboard. Here’s a demo of the robot controlled through Scratch:<\/p>\n