Subject:
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A review of 8539 (Manas)
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Newsgroups:
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lugnet.org.ca.vlc
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Date:
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Mon, 30 Jul 2001 04:21:35 GMT
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Viewed:
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1347 times
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These things work with the RCX! Up to three units (6 motors total)will
work! Wow!!!
Here's the RCX code!
http://news.lugnet.com/robotics/?n=15832
Dean
---8<---
I received the new 8539 (Manas) in the mail yesterday.
I have not built the models.
But I have taken the receiver unit to pieces and decoded the IR
messaging scheme ;)
The transmitters transmit short messages of two bytes encoded as
8 bit + odd parity. The transmissions use 76kHz modulated IR at
a baud rate of 4800.
I have a picture of the insides, but I cannot figure out how to upload
to brickshelf. (Any hints would be appreciated! - I have a username
but when I login there are no upload buttons or hints.)
Lego have sadly gone back to the cheap battery operated toy type
motors so there's none of the amazing technic motor efficiency of
either the technic or micro-scout variety.
It is interesting that there are two power take-offs, one "through axle"
hole and "end axle" hole at each end of the unit. The two are
differently
geared so you can choose higher speed or higher torque.
The transmitter offers channels 1, 2 or 3 or "All". A little switch must
set on both the transmitter and the receiver to get correct operation.
Each channel is differentiated by both an address in the message and
by the rate at which messages are sent. The messages are very short
in comparison to the time between messages which helps minimize the
chances of a "collision". The receivers have error checking and simply
ignore bad messages. Each button press on the transmitter sends a
continuous stream of messages. When the last button is released, a
set of three "no buttons pressed" messages are transmitted before the
transmitter shuts down. If the no buttons pressed message is missed
by the receiver, it times out after about half a second and turns the
motors off anyhow.
The messages, which consist of two bytes are best thought of as four
four bit nibbles.
byte 1 - high nibble : byte 1 - low nibble : byte 2 - high nibble : byte
2
low nibble
These four nibbles are used as follows;
address : orange : yellow : check
The address nibble can be;
4 - all
5 - Ch. 1
6 - Ch. 2
7 - Ch. 3
The orange and yellow nibbles reflect the current button state;
0 - no button pressed
7 - forward button
F - reverse button
The check nibble contains a check digit;
Checkdigit = 0 - (address + yellow + orange)
Thus, for example;
50 74 is forward yellow button on channel 1
6F 0B is reverse orange button on channel 2
40 0C no buttons pressed on "All" channel
The message rates are as follows;
Ch. 1 - 19.6 Hz
Ch. 2 - 14.8 Hz
Ch. 3 - 11.6 Hz
"All" - 19.6 Hz
The most interesting part of the whole thing is that the IR receiver
looks
a lot like the
one in the RCX. Therefor, I decided to test it and was surprised to find
it
responded
to both 76kHz and 38kHz!
This means that it may be possible to send these two byte messages from
the RCX
to these dual motor units. This would be very very handy.
The secondary reason why I posted this message was to find out if
anybody knows
how to send 4800 baud bytes using nqc. I would like to check if these
units
can be
used as auxiliary motors! :)
As a matter of note, I have browsed through the parts delivered with the
"big bits" I've
already discussed and there are quite a few nice new smooth beams of
various lengths
and other little technic parts I haven't seen before. Jim Hughes has
some
work to do ;)
JB
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