The valiant turtle is a floor roving robot made by Valiant Technologies and was a popular education robot for teaching geometry and programming during the 1980s and 1990s. It was often used with the LOGO programming language.
It is possible to connect the turtle using either serial or 'parallel' connections from a microcomputer. Supported models (that I'm aware off) where the BBC Model B, RM Nimbus 186, Acorn Archimedes and modern 9-pin serial connection to a PC.
I have two turtles and one control system which came with a cable labelled 'Nimbus to Valiant Turtle'. The cable has a 5 pin DIN (to connect to the turtle's control unit) and an RJ11 to connect to the Nimbus. Obviously this was not terribly useful since I want to connect it to the BBC. Furthermore, I received no power supplies with the turtle or control unit.
The control unit
The control unit has 3 connectors; a 15 pin male D-sub parallel connector, a 5 pin female DIN serial connector and a 2 pin power supply socket.
The first trick is getting the unit powered up. The circuit board has a LM340TS voltage regulator IC, which means the unit requires a stable 5V input, tracing the power connection shows that the power socket is centre-positive (i.e. the middle pin of the PSU should be positive and the outer pin should be negative).
Since the controller requires a stable 5Vs, the input power should be slightly above this and can be supplied by an unregulated power supply. I used a 6V DC/500mA power supply (a simple 'wall wart' AC/DC converter). With this connected to the control system the red LED lights up and we are in business.
The control unit connectors
Since there are no serial cable diagrams available on the web I had to reverse engineer the cable from the control unit. By simply tracing the connections from the socket to the circuit board I was able to see that 3 of the connections went to diodes which were connected to earth and 2 of the pins went to a LM339 IC.
The LM339 IC is a 'Quad Differential Comparator' which (in English) means it is used to measure power. This clearly indicates that the two lines running to it are the Tx and Rx of the serial connector.
Firstly the control unit needs to be configured for the Valiant Mover software on a serial interface. There are 4 switches on the side of the unit which should be set as: 1-ON, 2-ON, 3-OFF and 4-OFF. Furthermore the two switches on the base of the turtle should be set to OFF.
Next I set up a test cable which interconnected through a solderless-breadboard and using the Valiant Mover software I tried out various configurations. When nothing worked, I linked the RTS and CTS lines from the BBC together, and the turtle jumped into life (a common serial issue with simple hardware).
The final cable configuration is shown in the diagram. There is no reason why this cable should not work for any other machine (of course you will need to change the style of connector for the computer).
The main chip on the controller circuit board is a Philips PCB 80C49 which is a programmable microcontroller. This is programmed with custom logic, so if you are looking to build your own board using the original components you are out of luck. This is a shame since there seem to be far more turtles available than control systems.
If you have an old turtle like mine then the chances are the battery pack has been there a long time and is probably badly corroded. Luckily the corrosion does not affect the plastic, although you will have to remove both of the battery connectors and replace them with new ones. To remove the batteries remove the covers on the top and the bottom of the machine (you will have to take the mainboard off first, make sure you note which connector goes where as the LED and pen motor both have the same connectors). Unsnap the battery connectors and tap the batteries from the bottom until they fall out.
To replace the batteries I used some NiMH 2500mAh AA cell rechargeable batteries (you need 10 in all), buy the ones ready with soldering tags. Simply connect them up like the old batteries, replace the battery connectors and reassemble.
The case should be properly cleaned and any battery 'goo' removed.
Similar to the control unit; the turtles mainboard is a microcontroller based board with IR receivers in the centre. When the turtle is switched to 'on' the red LED should light (and the turtle's eyes), when switched to 'charge' the yellow LED should light.
Stepper motors and wheels
The wheels are probably the most likely part of the turtle to be damaged, and the original design is not very strong. Unfortunately Valiant decided to glue in all the parts, so removal is vitually impossible without breaking one or more of the supporting pieces of plastic.
If you do break anything (or, as in my case, the wheels are already broken) you can reconstruct the wheel mounts using some small pieces of plastic and some epoxy glue. I used a couple of pieces of thin lego parts as can be seen in the picture.
There is a small screw on the side of each of the wheels (in the middle) these adjust the wheel's alignment. Be very careful not to over turn them, or you will break the wheel.
The stepper motors are held on by two nuts (the screw part is glued down since the screw head is inaccessible). You should remove the nuts and replace the washers with wider parts since the original washers are too small and can cause the plastic mounts to warp.
The stepper motor itself is a Sterling Instruments stepper motor with a step angle of 7 degrees and 30 minutes. I have included a picture of an original part.
Pen control motor
The pen control motor is a simple DC motor as shown in the picture. Nothing exciting here, but make sure it works.