I started building this little rover to test
ball caster. While I was the first to demonstrate the use
of NXT ball as a caster, Brian design is far superior to mine...
Then I got my wireless camera and used the rover to remotely
explore my house. It can either be remote controlled using my
NXT joystick (or any
other Bluetooth remote control program, see bottom
of this page), or wander by itself, using the ultrasonic
sensor to avoid obstacles.
Side view of the rover.
Bottom view. The white beam in the
middle transmit movement from right motor to ultrasonic
sensor assembly. Thanks to this linkage, the sensor
sweeps from left to right. This increase obstacle
detection field width, and minimize the chance of
being in a sensor "blind incidence" (as
you probably noticed, a flat wall approached at
45° may remain undetected).
Detail of the ball caster, also shows
the linkage between motor and ultrasonic sensor.
Close-up on the camera and on battery
holder. I tried to power the camera from the NXT
third motor output, but voltage was too low as I
use NiMH batteries. It might have worked with alkaline
The tiny camera itself. I epoxy-glued
it to a L-shape beam for easy integration with my
LEGO models. The transmission frequency is 1.2GHz
that should not interfere with the 2.5GHz of NXT
Bluetooth. The range is similar to Bluetooth (about
10m in my house).
The camera next to the receiver.
This is a purely analog device, providing video
and audio connectors to be connected directly to
a TV set. If you want to get the video on your computer,
you will need to add a video digitizer.
shot from the rover (Divx5, 4Mb). Quality is correct
for something I bought for about 30 Euro on eBay.
A few simple NXT-G programs I have written for the rover:
program allows the rover to wander around your
room, avoiding obstacles thanks to the ultrasonic
sensor. If something is too close, the rover backs
up while turning randomly left or right. Simple
program enable the rover to be remotely controlled
by my NXT
joystick through Bluetooth link. When you press
the trigger button, the rover plays an R2D2 sound...
(place this sound file
in your C:\Program Files\LEGO Software\LEGO MINDSTORMS
The NXT joystick must be running the "Joystick"
program is similar to the previous one, but
constantly sends ultrasonic sensor distance to the
NXT joystick. Unfortunately, changing direction
of the Bluetooth link takes time, and the rover
is much less responsive with this program (and harder
The NXT joystick must be running the "Joystick-bidi"