Tuesday, December 21, 2010

Lego Head Tracking Robot

Do you have a lego mindstorm NXT?

Do you want to play videogames using optical motion tracking?
This the idea I just had yesterday when playing with my robots.

What you need:
  • 3 lego nxt light sensors
  • 3 lego nxt cables
  • lego nxt core
  • a webcam which doesn’t have an IR optical filter OR a nintendo wiimote
  • a floppy disk
  • free-track software for windows
How it works:
the lego light sensors emits light in the visible and infra red spectrum
this 3 beams are captured by your camera
the coordinates of the 3 dots are used by the software free-track to estimate the player position
the head position is used in the game to look around

How to build it:
I used a 3 point cap model: build a triangle structure as in figure 1. I did it in such a way that you can attach it to a sport cap.
If your camera has ann IR filter you are in big trouble but you can still remove it as described here.
If you have a camera without an IR filter you are very lucky: open a floppy disk and remove the magnetic disk. Cut it and pose it in front of the camera lens as in figure 2.

Measure the distances as in figure 3 and insert them in the free-track configuration.
The Free-Track configuration can be downloaded from Free-Track configuration to use with Lego Head Tracker.
Write a simple program for the lego nxt that switches on and off the sensors when the user hold down the contact sensor. The simple program in NXT-G can be downloaded from Lego Nxt program
You can also use RoboRealm to track them:
The RoboRealm configuration file is Robo Realm script file.
And now enjoy your game!

If you are lazy to make one you can buy one from my website:
To find other distributors go here:

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