@ 25 November 2009
document history
For Maplin Magazine, typed by Colin, edited DB 13Jun06
ZEABO MICROROBOT David Buckley
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* May be used by any computer with RS 232 facility
* Stepper Motor controlled
* Designed to draw Logo graphics
* Half millimetre/half degree resolution
* Pen Colours easily changed
* Uses ordinary felt-tipped pens
* Built-in two-tone horn and LED indicators
* Built-in line follower
* Onboard bus connector for easy expansion with
plug-in speech board and obstacle detectors etc.
Concept
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What is ZEABO, is it a turtle - yes; is it a robot vehicle - yes;
is it even another buggy - yes. ZEABO is all of these and much more
besides - it is whatever you want it to be.
While the idea of electronically controlled robot vehicles is
by no means new it is only in the past few years with the widespread use
of microcomputers that it has become a practicality. One of the most
frequent questions asked about computer-controlled robot vehicles is :
"What can you do with it?". However, no one asks the same about a ball,
they have been around for such a long time that everyone knows.
ZEABO in its primary mode has a ready built function, that of
drawing Logo graphics, but it is also equipped with LED's to be turned
on and off, a two-tone horn that can be sounded and a line-follower.
Add-on boards provide speech, obstacle detection and hole sensing so that
it doesn't fall off the edge of the table.
Like a ball, what you actually do with ZEABO is up to you.
General Description
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ZEABO is 180mm long, 150mm wide and 90mm high with a transparent
Shell and Baseplate. This is a feature essential to Turtle Microrobots
used in Logo programming where viewing of partly completed patterns is
desirable.
The machine is driven by two Stepper-motors, each controlling a
wheel in half millimeter steps. The pen is raised or lowered by a third
Stepper-motor. These three motors and the pen lift mechanism are mounted on
a rigid aluminium framework, a 'Pelvis', which in turn is mounted on
the transparent baseplate. Towards the front of the baseplate there is a nylon
glider, or toe, to prevent ZEABO falling over. All the electronics are mounted
on a 4inch by 2 1/2inch PCB which in turn is fastened to the Pelvis. At the
top of the PCB is a socket, similar to a telephone connector socket but with
a different polarization, to take the power and control umbilical. All
the works are protected by the easily removable cover; in buggy mode leave
it off. The umbilical is held clear of the pen by the wire loop halo which
plugs in the top of the body.
To allow ZEABO to be independent off the make of computer used to
control it, the computer end of the umbilical plugs into a special box
which includes connectors for the serial ports of the Commodore 64, BBC-B,
Spectrum and a 25 way industry standard RS 232 D type connector for all
other computers including Amstrad, MSX-machines and the QL.
Mechanical Construction
-----------------------
Some of the parts such as motor drive bosses and rubber axle supports
are bonded together with adhesive and this is done in the factory so that
only a screwdriver is necessary to complete the assembly, instructions for
which are included with the kit.
Electronic Construction
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The PCB is very densely populated with components and consequently
has to be double-sided with fine tracks and many plated-through holes;
because of this it is supplied as a ready assembled and tested item onto
which plug the leads for the three motors and the speaker. ( Having the
circuitry ready built in this way should be seen as similar to buying an
integrated circuit as opposed to trying to make an equivalent circuit from
discrete components).
Circuit Description
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A 6402 UART is wired to accept and send serial data, 8 bits, parity disabled
2 stop bits at 4800 baud.
The received data is split into high and low nibbles as in Figure 4,
D7 is discarded and D4 D5 D6 are used to address a 3 to 8 line
analog decoder. The Data-Received output of the UART which goes high when
a received byte has been transferred to the output buffer and is stable,
is routed through the decoder to form the select clocks S0 to S7. Only
S0 to S2 are actually used and these enable the Drive Motor Latch, the
Pen Motor Latch and the Indicators Latch as appropriate. S0 is also used
to route the line follower output to the UART for transmission back to the
computer. The latches used have Q and not Q outputs and from the latches at
address 0 and 1 these are routed through Darlington drivers to control
the stepper motors. Two more Darlington drivers are used to switch the
LED's at address 2. The other two data bits at address 2 are used to
gate two oscillators, the outputs of each being routed to the speaker.
Circuit Expansion
-----------------
All the necessary signals and power are routed to a 16 pin
socket in the centre of the PCB to enable expansion boards to be simply
plugged on the front. For those boards which need a Ready line, such as
speech boards, D7 of the parallel data accepted by the UART is available;
it is intended that this line be wired so that any peripheral board can
pull it low.
Add - Ons
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One of the problems with umbilical-controlled vehicles is the umbilical
itself and one add-on that shortly will be available is an infra- red
communications link. For the vehicle end there will be a backpack containing
a rechargeable battery and an infra-red receiver/transmitter unit with
a complementary infra-red unit at the computer end.
Most animals have learned the value of audible communication and
while R2D2 may get away with squeaks, where humans are concerned speech is
much more understandable, hence another add-on board will be a programmable
speech system which will plug onto the Expansion Bus connector.
Two other add-on boards that will plug onto the main board will be
one for detecting obstacles in ZEABO's path and another for detecting holes
or edges of tables or simply a coloured border round ZEABO's territory to
prevent it straying.
5/
Programming ZEABO
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Figures 4, 5 and 6 give complete details for controlling ZEABO in its
basic form. This is easy to do even from BASIC but to follow a line or
detect obstacles bitwise comparison is needed and some versions of BASIC
do not support this. In these cases it is necessary to write a routine in
machine code. Such sets of routines are available for the Commodore, BBC
and Spectrum either to interface to Logo or to be called from BASIC.
Conclusion
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Robots are going to play an increasing role in all our lives in one
way or another and they are not going to get any simpler. In a few years'
time, I should not be surprised to see robots controlled by multiprocessor
systems with a couple of megabytes of RAM and gigabytes of storage on laser
disc. So now is the time to get into Robotics while robots are relatively
easy to understand and ZEABO is an excellent and affordable way to learn.
