Robots and Systems
home  >  BARG index

Previous BARG Newsletter #3/4 pages 14 - 20 -- Polaroid Ultrasonic Ranging System - Richard Moyle

BARG Newsletter Issue 3/4, Spring/Summer 1985 p21 - 28 -- Zero 2 review, Letters, Index
Zero 2 Robot - reviewed by R E Moyle
Zero 2 is a new machine from Intergalactlc Robots Ltd, and combines robot features with the ability to act as a turtle or a buggy. IGR claim it as the first true robot costing less than 100.

In fact, it is a robot base with two wheels, pen lift, line followers, horn and LED indicators, each individually programmable. The machine comes complete with software, power supply, umbilical cable and a connector for the chosen computer. Apart from the software and connector, the machine is standard, irrespective of the computer for which it is sold. This means that any Zero 2 can run on any computer supporting an RS232-type port or any programmable parallel port. IGR can supply a general-purpose connector to fit most RS232 ports.

The robot weighs about 2 lb and is about 7" long by 6" wide. The body is 3.5" tall, with a support for the umbilical sticking out of the top. There are two drive wheels mounted towards the rear, with a slide support at the front instead of a third wheel. The wheels are driven by stepper motors, and the geometry is arranged so that one step of the motors converts to 0.5 mm at the wheel rim. If the motors move in the same direction the robot travels 0.5 mm per step. When they move in opposite directions the robot rotates through 0.5 degree per step. The software provided doubles this to give a resolution of 1 mn and 1 degree per step, with correction for any mechanical tolerance and an overall accuracy of 0.5 mm/degree. A third stepper motor is provided which is connected to a pen-lift cam for turtle applications. This can be removed, and the motor connected to an arm or gripper. There are pads on the circuit board for connection to a fourth motor or relays for further development. Zero 2's shell is of transparent plastic and the working parts can be seen through it, a useful aspect in education. The rear of the shell is open, with a re-entrant design giving access to the pen slide. Fitting a pen or other device is simple. The point of the pen is arranged to be directly between the wheels, and is regarded as the "centre" of the machine In turtle mode.

The base is fitted with a small speaker which is connected to a horn circuit in the standard model. An add-on board promised for the near future wilI contain a speech synthesiser and sound generator using the speaker. The horn has two tones, each of which can be enabled independently. At the front of Zero 2 is the board containing the 6402 UART for the two-way RS232, the drive circuits, two LEDs and the line follower. The LEDS, one green, one red, are individually controlled, and sit at the front in Boeing 747 style bulges in the shell. The line follower consists of two infra-red transmitters with three phototransistors mounted through the base of the robot. The transistors are positioned to detect a line about 5 mm wide. The line may be black on white (normal mode) or white on black (inverted mode), the choice being selected In software. The black has to be black to infra-red, which unfortunately is not the case with several kinds of felt-tip pen ink.

Also on the board is an expansion connector. IGR has promised several add-on boards to be released in the next few months which plug in here. There is room for two additional boards without discarding the shell. Above the UART, and poking through the top of the shell is the umbilical connector. This is similar to the new telephone sockets, and the serial connector on the Sinclair QL. There are 5 connections taken through the umbilical to the adaptor which fits to the computer. Inside the connector is the RS232 connection proper, and the power supply board providing 5 and 9 volts for the robot from the separate power

Barg Newsletter lssue 3/4 - Page 21

supply. A wire support "halo" is fitted to the top of Zero 2 to minimise the problems of the umbilical getting in the way. One of the promised add-ons is a two-way infra-red link which will replace the umbilical. The mobile end wlll sit on top of the robot, located in the halo sockets. Another expansion board will contain 8 bump sensors and 4 hole detectors.

Zero 2 can be operated directly from machine code or any higher-level language supporting byte i/o. The codes required to step the motors or operate the other devices are given in the Zero 2 manual, and a simple Microsoft BASIC programme to drive the robot forward 4n steps is:

    10 width lprint 255
    20 for i=1 to n
    30   lprint chr$(5);chr$(0);chr$(10);chr$(15);
    40  next i
    50 end
Line 10 prevents BASIC sending automatic crlf characters at line-end. Lprint sends characters to the printer instead of the screen. Obviously Zero Z would have to be connected instead of the printer, and the baud rate set up correctly.

If you try this approach, one thing will be immediately apparent: it is very slow. IGR supply a machine-code driver (ZeroDrive) with the Spectrum version, and shortly for most other common home computers. The purpose of the driver is to increase the speed of the machine, and also to provide a command structure which will remain consistent whichever computer or language is used for programming.

ZeroDrive provides a large number of routines which can be split into several classes. These include movement, pen control, horn/LED control, line-following, status. Each command is called in the same way. A small area of memory is set aside for passing data to and from the machine code routines. The locations are kept in the same place for any one computer, irrespective of the version of ZeroDrive in use. In this way, if a new version becomes available, to handle the Speech board for example, existing programmes will not need to be altered. In the Spectrum, these "letter-boxes" are at locations 64958 to 64999. All calls to the machine code are made by placing the command number in the location called "routine", and up to three arguments in "arg1" to "arg3". A subroutine call is made to "usrcall", which jumps to a routine decoding the routine number and performs the required command. Returned values are placed in arg1 to arg3 and any error code is returned in "error". Arguments greater than 255 are split between arg1 and arg2, with the least significant byte in arg1. Other locations in the interface area hold the version number and various default values.

Movement commands are provided to move and rotate, and to drive each wheel individually. Distances are translated by Zerodrive to steps for each motor, to allow for the current scale factor and any errors in the step size. A FORWARD 100 comand with a SCALE of 1 will cause the robot to move forward 1OO mm +-0.5 mm. With the sensors turned on, Zero 2 checks each sensor before each step and stops with an error code if any is non-zero. It also stops if there is a significant problem with the RS232 link. In the event of an interruption the number of steps remaining can be reported back to the control programme, as can the state of the sensors, and appropriate action taken. If required, a CONTINU command can be given to carry on with the rest of the move. The sensors can be switched off to speed up movement in turtle mode. The sensors can still be read, but are not interrogated each step. The speed of the robot can be varied

Barg Newsletter lssue 3/4 - Page 22

with the ST.SPD command. The ST.SCAL command sets the number of millimetres maved for each unit in a forward /backward comnand. This allows a design to be created on a small scale then demonstrated, say, 10 or 20 times larger.

The pen can be moved fully up or down, or one step at a time. Like the drive motors, the speed of the pen can be changed, with the ST.SPP commnd. Horn/LED control is by way of the ST.HORH and ST.LEDS commands.

The Line-follower, and other sensors if fitted, are controlled by the SETSENS command. This sets the sensor on or off, and in the case of the line follower determines whether it is in normal or invert mode, and which detectors are to operate.

The status commands are really functions and get information back from the robot. It is this ability which causes IGR to regard Zero Z as a real robot and not just a turtle. LINE, HOLE and BUMP return the condition of each sensor, " while SENSR shows which sensors are currently switched on. Similar functions are used to return the current horn or LEDs state, current scale, drive or pen speed.

There are also miscellaneous commands which allow direct access to the robot control lines, so fancy commands can be sent direct to the motors for apparently simultaneous actions.

High Level Programing
ZeroDrive can be called directly from other machine-code programmes, or by high level languages which allow machine code calls. The cassette supplied with Zero 2 holds various programmes In addition to ZeroDrive. The Spectrum tape holds several procedure files which can be used immediately from Sinclair Logo. Using Zero 2 with this programme is very easy, as direct links are built in already to the main Logo graphics commands. The BBC version will have similar links to Logotron Logo. The tape procedures provide additional Logo commands which are directly related to the equivalent machine-code call. They handle the messy business of putting the correct values into the correct locations and passing control to and from ZeroDrive. The same file can also be used from BASIC, and the tape holds subroutines to provide similar BASIC commands. Finally, the tape also has a machine code programme which allows Zero 2 to learn a routine from keyboard or Joystick and then repeat the same sequence again and again.

Zero 2 seems to be a lot of machine for the price of 99.95 complete and including VAT, at about half the price of any comparable machine. The provision of add-on boards later in the year wili bring it well within our definition of robots, and even now will give any serious robot enthusiast a good base to work from. Most of the work involved in getting something moving has been completed, allowing you to concentrate on making it do something meaningful. Suggestions for use have varied from plant watering in a greenhouse, playing the organ and amusing the cat (all have been done) to controlling a full size fork-lift truck (not yet. but. .. )

You may have detected a certain bias, so perhaps I had better come clean. David designed the beast, and I wrote the Z80 code and Logo/BASIC Interface. Nevertheless, we are sure you will find that Zero 2 is a good introduction to Robotics and a lot of fun.

Barg Newsletter lssue 3/4 - Page 23


Thank you for sending Newsletters one and two, which I found informative and amusing (a quality definitely in the newsletter's favour).

Although I am a member of the Group, I feel somewhat isolated, and would very much like to know if you have details of any robotics group within reasonable proximity to myself, or can provide the address of any other members of the Group who live in my area, whom I could contact.

On the point of contact between members: it might be an idea to set up a database of numbers' names, addresses and telephone numbers, and divide them into 'local areas', corresponding to areas of the country.

Whenever a new member joins the Group, names, addresses and telephone numbers of other members within his local area could automatically be sent to him with his first newsletter. His own details could be added to the data-base to be used in the same way. Established members could receive the information with their next newsletter.

This could be done on the understanding that such use of the above information could be made without notifying the member, and that this would be the only use to which it would be put. A statement to that effect could be made upon application for membership (I can't remember if such a statement was on my application form). The provision of information concerning the location of other 'local members' would surely enhance the aim of BARG - contact.

I was going to write to you after receiving the first newsletter, but somehow didn't get around to it. I was going to ask you for tips on motor suppression - what do I find in the second newsletter - tips on that very subject. I am thinking of obtaining a Spectrum computer from a friend at a bargain price (not wishing to experiment on my larger 'established system'), and have been wondering about robot interfaces for the machine - you have anticipated me again by announcing an article on the very subject, to be seen in the third newsletter. What can I say?

I found the book review to be very interesting, and would like to suggest that members interested in casting robot components in aluminium should read 'The Backyard Foundry' by B.Terry Aspin (1978). This book provides all the information you are likely to need, covering basic principles and moving on to detail construction of small furnaces, listing suppliers of materials etc.

Whilst I am looking up some of the books reviewed in the last newsletter, I shall now seek further information on motor suppression and control, having been inspired by your comments. By the way, how about an index for newsletters?

NOTE: If any member has copies of - 'Practical Robotics' magazine that he no longer has a use for, could he please let me know how much he wants for them? I would like any issue except Sept/Oct 1984 and Nov/Oec 1984 (I have these).

Just in case anyone doesn't yet know, 'Practical Robotics' has been discontinued. I made a real nuisance of myself at the newsagents before I found out. In desperation I wrote to the publishers for an 'official' confirmation. Here's what they said; 'I am sorry to inform you that 'Practical Robotics' has ceased publication from the Nov/Dec 1984 Issue'. Obviously not enough interest to make it popular.

Barg Newsletter lssue 3/4 - Page 24

I have had some pleasant experiences as far as shopping for professionally made components is concerned. Replacement parts/repair shops for domestic vacuum cleaners and washing machines have proved to be a gold mine when needing sealed ball-races and bearings. Plastic bellows sections can also be had In these shops, being intended for air outlets In tumble driers. Various gaskets etc are also available.

On one occasion, I was in need of a sealed ball-race. I had an extremely large one salvaged from a motorcycle. I needed an extremely small one. I took the big one to the domestic appliance shop and explained what I needed. At first I was told that none were In stock. The proprietor happened to enquire what I needed it for, when I told him 'For a robot' he became very interested, and rummaged in the stock room, returning with a box of assorted ball-races, tipped them on the counter and helped me search for the one I needed. I ended up buying two or three, and getting them at a discount. I have since returned to the shop for further components, becoming known to the proprietor. As they say, it pays to shop around.

Yours sincerely,

Thankyou for the compliments. I hope you find the port interface article is what you need. We are working on your suggestion about member lists, and hope to provide more informatlon next issue. Thanks also for the index idea - see below.

I have some information regarding robotics study at a formal level.

Barnsley College of Technology will, starting In September, be running a course entitled "Robotics and Automation Literacy course (Open Tech)'. The course is open to anyone with an interest in the control of robots in the field of automation. In particular it is valuable to teachers, engineers, training officers, managers, sales representatives, maintenance personnel etc. No formal entry qualifications are required, and the course is conducted on an "open learning" basis. All practical sessions will be held at Barnsley College of Technology in a specially equipped robotics and automation centre, at times to suit the Students convenience.

The course is a new one, and never been done before, so perhaps an explanation would be wise.

This aims to extend training opportunities available to adults. The programme will help employers and individuals to train, retrain and update skills and knowledge at all levels. Its special focus is to overcome barriers which many adults face in entering or rejoining education and training. It does this through the use of open learning - learning designed for individuals to use at a time, place and pace to suit themselves.

The open tech ort robotics and automation literacy programe consists of 92 sessions of theoretical and practical work, each session requiring approx two hours of study. A session consists of an individual booklet which contains all the necessary data to enable the student to attain the aims specified for that

Barg Newsletter lssue 3/4 - Page 25

session. The course is divided into 6 areas of study;
Area Study   Subject
S    30 hrs  Supporting subjects, including elementary physics and maths
E    20 hrs  Electronics. Analogue & digital devices, logic circuits
C    28 hrs  Computers. Computer & Robot programming
R    46 hrs  Robotics. Drive systems, robot geometry, sensors, end-effectors, control
A    38 hrs  Applications. The Industrial environment application criteria,
             computer aided design & manufacture
T    20 hrs  Social and economic aspects. Effects on people and society,
             robots and education, economic aspects

Students will select an appropriate combination of sessions after consultation with a tutor. The distribution of all course material will be handled by the College. The programme may be joined at any time during the year.

The cost to the student will be 6.00 per session, the fees to include the cost of all printed material, the necessary tutor support and the use of equipment where appropriate.

Each student will be assigned a tutor to whom all problems can be referred at any stage of the course. The tutor will organise practical sessions, and give help when necessary on the use of equipment. All practical sessions will be held at the College, Tutor support for theoretical sessions may be made by means of personal visits, letter or telephone.

A College certificate will be issued to all students who have participated in the course, detailing titles of the sessions studied. Discussions are also taking place with 3 national examination body, with a view to awarding a certificate on satisfactory completion if the course ( City & Guilds).

To enable the student to gain a more detailed insight into each session, a booklet is available which details the aims of each session and identifies whether it is theoretical or practical. This is available on request

Further information about the course can be obtained from;-

     J.B.Longstaff or J.B.Ismay (course tutors) at the College.
     Barnsley College of Technology
     Church Street
     South Yorkshire S70 2AN Barnsley 299191
     J B Longstaff extension 266
     J B Ismay extension 223
After seeing the course advertised, I arranged to attend a short introductory meeting at the College. This was very interesting. After meeting the tutor, we were shown the session booklets extremely well produced and detailed from what

Barg Newsletter lssue 3/4 - Page 26

I saw. Then we were shown the robotics and automation centre. This is intended to be used by no more than two people simultaneously, enabling a very personalised environment to be established. The tutor would be hovering somewhere nearby - just In case you needed help.

The Equipment you get to use is very impressive. We were shown the "Armdroid" robot arm, two types of "Smartarm" - all under control from a BBC computer.

Additionally, you get to use the "Colne Robotic Vision System", and a test-bed on which you have to design, build and operate a simulated factory environment. This involves building and programming a robot system that Is capable of recognising objects, sorting them, and using pick and place techniques to load the items as required. This task forms the "Grand Finale" of the course. It embodies all that you will have learned in previous sessions, including sensing, processing, mechanics of robots etc. All in all, can you go wrong at 6.00?

At the meeting, we were told that funding MAY be available, but as the course is a new one, this would probably involve a test-case situation. I have made enquiries at the local Education Authority offices, but have been told that they are unsure if they can help, as the course is new to them - they will have to check further but as they can see initially, funding is probably not going to be available.

If anyone is interested in the course, check with the local technical college, because the course is apparently nationally available. If anyone pursues the funding line of enquiry, perhaps they will have better luck by using some local scheme, or similar. It's worth a try - let me know.

yours sincerely,


The next Newsletter should be in October, and we hope to bring you the first of a series of articles on building small mobiles, maze theory and elementary mechanics. Anyone feel in need of articles on elementary electronics, machine-code programming, or A. I.? Anyone feel up to writing articles on elementary electronics, machlne-code programing, A. I. ?

Barg Newsletter lssue 3/4 - Page 27

Issue 1    ZYLATRON a home-built robot                     RM
           Polaroid ultrasonic ranging system -	part 1     RM
           Robot Intelligence                              AD
           Dibley Tests competition                        AD
           Walking Machine competition                     RM

Issue 2    Motors                                          DB
           Ace/Hebot control programme                     CF
           Books review                                    DB

Issue 3/4  Robots for all?                                 DB
           AARGH Spectrum port interface board             PL
           Polaroid Ultrasonic ranging system - part 2     RM
           ZERO 2 Robot review                             RM
           Robotics Course                                 RH letter

Barg Newsletter lssue 3/4 - Page 28