Arduino Lego Robot – Update 2

Eyes and Brainz

In the past few days I’ve been busy installing the brain of my Arduino Lego robot, namely the Raspberry Pi, and making a mount for the Raspberry Camera to allow it to pan and tilt. If you haven’t read the first entry of my robot blog, you can do so here.

The Raspberry Pi is running Gentoo Linux, my favourite Linux distro. Installation was straightforward using the wiki and cross-compiling the software on my Gentoo desktop. The Arduino is connected directly to the Raspberry via USB and communicates over serial. All my robot code is done in Python (except for C++ for the Arduino), but since I’m still working on that I’ll focus on the mechanical parts in this blog update.

At this point the robot is basically completed mechanically.

I’ve installed the Raspberry Pi on top of the robot with some strategically placed Lego beams and axles. It sits just clear of the Arduino and its shield underneath it. The power supply for the Raspberry is a mobile phone power pack slung underneath the robot with rubber bands. The Arduino uses a 9V battery which also powers the 2 servo motors for the camera mount. Lastly, the robot Lego motors are powered by a Lego 9V (actually 7,2V) power pack on the back.

Underside view showing the battery pack for the Raspberry Pi and the 2 Lego motors.

I’m communicating with the robot via WiFi from either my desktop PC or laptop. At this time I just connect the Raspberry to my router but I’ll probably make a hotspot on my laptop to be able to take the robot out into the field. Since communications never leave the LAN I don’t experience too much lag and can easily pilot the robot in real time.

Camera mount

For the camera mount I chose not to use Lego parts as it would become too bulky and I couldn’t really find a way to attach the servos to them without having to modify the Lego parts. Only the lower servo is attached to Lego, for the upper servo I made a simple frame from some spare metal and attached that to the servo plastic arms. The camera is attached to the upper servo with double-sided tape.

Due to the limitations of the servos the camera rotates only +/- 50 degrees from center (up and down). I think the servos are good up till +/- 70 degrees but I prefer to keep a margin not to damage them. As of now the camera is controlled from the PC with the arrow keys in 10 degree increments and a key to recenter it. It works well, but I’ll probably look into programming a more fluid movement, possibly using a gamepad.

Front View

My next task will be modifying the code to show the live video feed within Pygame instead of a separate VLC window, and generally modifying and cleaning up my code. Especially the networking part needs a good look through.

Whenever I have something new to show I’ll write the next entry, but expect it to be focused on the software not the hardware. Oh, and I’ll soon make a video of the robot in action!

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