Robots and Linux, cool stuff.

I want to post some minor advances I've made on my robot without getting
into the seemingly never ending debate about micro-controllers vs PC type
systems. So, can we lay off the micro-controller vc PC debate for this
post?

Anyway, if you are using Linux on your robot, or may be tempted to try it,
here are some quick time-savers and potentially cool things:

First of all, my robot uses 802.11G wireless networking. Radio controlled
operation is just an extension of normal wireless networking.

The programs on my website: http://64.46.156.80/robot/  are command line
based utilities. Using ssh, a remote console, I can use the command line
utilities as if I was sitting using a keyboard and display on the robot
while my desktop machine or laptop.

Using the "ffmpeg" package included on most Linux distributions, I can
stream my QuickCam over the internet. Using any network aware viewer on
almost any machine, I can see the video output of the camera. It is
amazingly easy:
# This runs the video server
ffserver -f /usr/share/doc/ffmpeg-0.4.8/doc/ffserver.conf &
# This runs a program to read the quickcam and produce mpeg
# The "-an" parameter disables audio
ffmpeg -r 8 -an -vd /dev/video0 http://localhost:8090/feed1.ffm &

(Streaming seems unusable for navigation in that it is pretty slow, but I'm
looking for a better solution.)

Most Linux distributions, if you are unfamiliar with Linux, have a fairly
sophisticated startup which can be a bit daunting, but don't be too
freaked, look for the file: "rc.local", typically located in "/etc/rc.d."
Just add the commands you want to run at the bottom of this file. (The UNIX
purists will choke on this one, but it isn't all that "bad")

Since the robot does not have a keyboard or display, but it does have
speakers, I use the librsynth's "say" program, like this:
/usr/local/bin/say $(/usr/local/robot/robot diag)
The above line will execute "robot diag" and take its output and pass it to
"say" as a program command line argument, causing the robot to speak the
results.

One problem I ran into is that the synth is usually customized by the user,
so Mandrake (the version of Linux I am using) didn't set the output volume
at startup and for some reason it couldn't find the presets. (probably
because there was no "user."). So I added the program to set the sound up,
aumix, in rc.local BEFORE the commands that will be sent to "say."
/usr/bin/aumix aumix -v90 -w90 -c80

(You may need to install "aumix" on some distributions as it is not always
installed if you have a desktop like GNOME or KDE)


So, right now, I can drive the robot from a remote computer, view the camera
images, it reports its status at startup, and works pretty darn well.

One last thing, "nice." Since my motor control system runs as a process
under Linux, it sort of has to run at a fairly high priority, so use the
program "nice" to start it with a negative "nice" values, making the
program "less nice."