Valiant Turtle: Retro Restoration Part 1

Back in the 1980s, many schools in the UK had BBC Micro computers as part of the BBC’s computer literacy project. One of the major strengths of the BBC at the time was its expandability, it had many different expansion ports.

The expansion possibilities meant that many addons were made for it, particularly for educational purposes. Around this time one popular computer language was Logo, which is a language to draw vector graphics. Not just on screen but drawn on paper too.

This led to one popular type of expansion for the BBC (and other 8bit machines at the time), known as a “Turtle” or “Roamer”.

There were several kinds around, but by far the cutest, and the one I used as a child in primary school, was a Valiant Turtle. This is a battery powered turtle which communicates via infrared. On the computer side there is a module to connect to the computer which provides the infrared signal, and driver software to use it with Logo.

My Turtle

I recently acquired a Valiant Turtle which was in need of restoring. I intend to use this as part of a small course I’m putting together to teach local children in the same ways we were taught in the 80s.

In general it appears to be in good physical condition, but it will need a bit of a clean. Someone appears to have added “Left” and “Right” stickers to the front feet, my guess is because it might not be obvious to a child which is right and left when the turtle is facing you.

The most common issue that I expect to find is corrosion in the battery compartment. I also need to acquire a communication module to talk to the turtle.

Inspection

Flipping the turtle over, we can see two black covers with screws in them, these are the battery compartments. I knew before opening it to expect 10x NiCad batteries. Of course, 40 year old NiCads will not be in a healthy physical condition, but being sealed in means that any damage shouldn’t extend outside this area.

The screws to the battery door are corroded, which doesn’t fill me with a lot of hope. Also of note is the ball bearing front roller that has rusted and doesn’t move as easily as it should.

Let’s remove those screws…

Luckily, the batteries have been removed, but unfortunately it was a little late. The bottom plates are looking pretty corroded, but the springs aren’t looking too bad, I can probably clean those up.

As expected, it takes 10 AA batteries, 6 in one side, 4 in the other. It might not be obvious, but the plates are keyed on one edge, so they will only cover one hole and will only go on the right way around.

Corrosion Cleanup

I attempted to remove the corrosion on the bottom plates, but even after using chemicals and abrasion, this is the best I could get them.

Whilst that is an improvement, it is not good enough. I’m going to need to replace these contacts.

To get to the springs we need to take the whole thing apart, the lid comes off with a few screws on the bottom, then 3 more screws remove the PCB. Finally there are two plate covers that are similar to the bottom ones.

From here I can clean the springs. These had very little corrosion on, my guess is the corrosive material dripped downwards, a quick brushing with a brass brush got rid of the small bits of corrosion on the springs.

As for the contacts on the bottom plates, I snapped them off and you can see that the corrosion was pretty bad underneath too.

I was then able to use two-part epoxy glue with new contacts. These are not quite the same, but the spacing is the same and given the springs on the other side, I think they will be good enough. I was careful to figure out what would be positive and negative on the batteries when gluing them on.

As the screws for the battery compartment had also been hit with corrosion, after much searching I managed to find identical ones. These are No.8 5/8″ (4.2x16mm) pozi pan head blunt self taping screws. Every other screw of the same size had the wrong thread.

Now to test the battery pack. I found these nice coloured AA NiMH batteries for about half price, it is shame you won’t see the colours inside of it.

I screwed the top plates back on, inserted the batteries and screwed the bottom plates on. With a multimeter I checked the voltage was around 12v.

Unfortunately the post for one of the battery doors that accepts the screw has cracked badly, The battery door won’t fully close due to this which means the wheels won’t touch the ground. This will need fixing.

In the mean time I did a power-on test, the eyes are glowing, which is a good sign. I’ve also cleaned it a little bit whilst I was awaiting parts to arrive.

Oh Balls!

As mentioned, the front roller ball on the turtle had corroded and it was quite pitted, it was very difficult to turn. The ball is a 3/4″ ball bearing and I managed to find replacements on Amazon. But first, I had to get the old ball out. There is no way to push it out, it has to be a pull action. The first thing I tried was a powerful fishing magnet, but whilst it gripped well, it let go before the ball popped out.

I then had another idea. I got some Mylar tape and stuck it to the ball, I then rolled the ball around so I could tug on both ends of the tape, the ball suddenly popped out with ease.

I then cleaned the socket and popped in the replacement. This one moves much more freely.

Next Steps

Now that we have power there is a clear path going forward. The battery door needs to be repaired, I have a plan for that. I also need to test that all the motors function correctly.