[chbot] Introduction & Lego NXT stuff

Richard Jones rjtp at ihug.co.nz
Sat Aug 23 04:58:48 BST 2008

Hi Charles,

Welcome to our list, many thanks for your post and for your and Timothys
presentations on Wednesday evening.

I'm sure that a number of us would be very interested in knowing more about
your Java port to NXT and how to find the NXT schematics and consider how
to make new or cheaper NXT sensors. If you are putting your hand up to do
say a one hour presentation I'm in.

Our groups diverse age range, range of interests and stages of development
makes an in depth technical presentation a little hard going for the casual
new recruit. So a little differentiation may be in order.

Several folks have suggested starting meetings earlier, say 6.30pm. Some
have asked for them more often. And lately we don't seem to run out of
things to say between 7.30 and 9.30.

Maybe its time to consider special interest group meetings targeting more
in depth treatment of topics that have a robotics connection. Alternatively
we could just have very long meetings with timed sections such as: 

6.30-7.30 demos and presentations from those who need to leave early.
7.30-8.30 formal presentations
8.30-9.30 social chat

Thoughts anyone? Looks a bit like a marathon!

Richard Jones  

On Thu, 21 Aug 2008 11:02:37 +1200, "Charles Manning"
<cdhmanning at gmail.com> wrote:
> Hi
> I am Charles Manning. I live near Whitecliffs (about 70km inland from
> Christchurch).
> I am the "dad" refered to at the August 20th meeting. I have been
> in robotics for quite a few years and for a time I worked at Trimble
> Navigation designing and programming tractor guidance and steering
> systems.
> That's basically turning a tractor into a big, big, robot! We use gyros,
> accelerometers and GPS as the input sensors. Obviously these systems have
> to
> be very reliable because crashing one can cause a lot of damage.
> The first time I turned on a new system I was testing I had connected the
> motor the wrong way around and crashed into a ditch and had to get towed
> out!
> We have both Lego RCX and NXT robots. One of the things that really
> frustrates me about most robot programming languages (Basic etc) is that
> these don't structure the code well. That made me very interested in Java
> and the Lejos project in particular: http://lejos.sourceforge.net/
> I contacted the Lejos programmers but they had not yet done a port to NXT
> so
> I decided to start the effort because I had a lot of experience with the
> microcontroller used in the NXT. Here's a picture of an NXT with the
> plastics off:: http://users.actrix.co.nz/manningc/lejos_nxt.jpg
> As you can see there's a ribbon cable out the side that is connected to
> the
> debugger unit used to load in test code.
> All the low level code is written in C and assembler. It needs to be very
> fast to get everything done. The NXT processes up to about 50,000
> interrupts
> per second. This low-level code then runs a very tight Java VM allowing
> people to write Java code for the robot.
> The Java code compiles to classes. When you download a new program you
> just
> download the classes that are not already on the system. Since most
> programs
> share the same base classes (eg. motor control) this means that you can
> normally stuff a lot of classes into the robot.
> Java is a very well structured language and this has lead to lots of
> modules
> being written including quite sophisticated things like behaviour based
> handlers.
> Lego published the circuit diagrams for the NXT which makes it a lot
> easier
> for people to  make their own sensors. I will maybe run people through
> to do this.
> Charles

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