Posts Tagged 'fix'

Bring Back the Big Trak!

For this one, there are two stories to this title…

1) Robotics in Schools Sucks! Bring Back The Big Trak!

I can remember when I was at primary school, one of the teachers sons brought in a “Big Trak”. For those who haven’t heard of Big Trak, let Peter explain!

This was great, and let people play with some programming basics. It was a time when teaching things like Logo was popular, based primarily on the Constructionist Learning work of people like Seymour Papert. I’ve managed to get hold of his “Mindstorms” book on Ebay, so am looking forward to reading it having had a great time reading a similar era book, “The Mighty Micro”.


After playing with Big Trak, I was pretty inspired and went away to built my own turtle. The result was a 2 motor wheeled block thing with a felt tip pen down a tube in the middle on a winch. This was to allow it to do “pen up” and “pen down” so it could draw on a big sheet of paper on the floor. And it had a big umbilical cord to a relay board I built for the BBC Micro our primary school had. And you’ve guessed it, I programmed a control program in our old favourite, BBC Basic! Awesome!

So, however many years later, I recently went in to a secondary school to help SETPoint run an activity day. It turned out I was teaching a class of around 30(!) about robots. The task was to build some kits, program them, and write a presentation. Having never seen the kits before in my life, or taught a full class, I have to say I was a little nervous/suprised when it became clear what I had signed up for!

Hex Walker IQ2 Board

It all went ok, but I have to say I was shocked by the kit being used. Everyone built a robot kit in groups of about 4, and these kits were pretty poor quality and obviously overused (partly to do with the cost of kitting out so many kits no doubt; there were 3 other classes!). They were basically fiddly gearboxes obviously intended for one-time assembly; they were un-reliable, had gears jamming, wires breaking off, broken parts, fell apart due to them being held together with a rubber-band assembly, etc. If ever you wanted an example of why good engineering pays off, you got it loud and clear from the frustration of the students.

The programmable controller also wasn’t intuatitive; there was no real sense of programming in a sequence of instructions, the motors had to be going while programming, it repeated the commands over and over so it was confusing what it was doing, and anytime you wanted to change it, everything was erased. It left all the students pretty confused and underwhelmed, and to add insult to injury, they had to dissassemble everything leaving many having felt they hadn’t achieved anything.

The shock and dissapointment for me was really that after 20 years, given all our advances in technology, we seemed to have gone backwards from Big Trak. There is no real excuse for such poor execution of teaching quite simple concepts. And it should be great fun!

2) Look What I Found! Bring Back The Big Trak!

Now this is pretty cool. Two weeks later, I’m helping run an after school club at a different place, and the head of D&T gives me a tour. They’ve got pretty cool stuff in some schools now; things like laser cutters! Anyway, whilst in the store room these places always have, enjoying the sawdust filled air, what do I spot on the shelf. Yes, that’ll be a Big Trak that will!

Obviously my exceitment must have been a little supprising to them, and it got better; I quickly found myself as the new owner! Thanks! I was warned it was broken, but where would the fun be otherwise!

On getting it home, I went to put some batteries in and was meet with big lumps of battery acid. This is some of the contacts, after I had knocked off a lot of it!

Big Trac Battery Damage

The acid had got everywhere, and after applying power directly, it was obviously dead. Time to get it apart. Here are the basic body components once i’d got the top off and all the circuit boards out:

Big Trac Case Parts

I replaced the main batteries with a 4AA battery pack. I needed to add a centre tap, as it turns out they use a split rail; this is so they can use half the number of transistors to get both directions! Soldering was really hard, and I had to clock up quite a temperature on the iron to get the old solder to melt. Anyway, the result was as follows…

It is somewhat alive! But only half the keyboard works, and perhaps more importantly, it doesn’t move! The reason i’m pushing it is to see if the movement sensor is working. There is a light/sensor pair spanning a cog with holes in it in one of the motor drives; after pushing it you can see it thinks it has got to the end of it’s sequence, so that confirms that bit is working!

Some more fudging got the power to the motors; the main powerswitch was totally corroded, so I just bypassed that.

In this demo, I had to be a bit selective about what keys to press as only half were working, but getting there! I think there is life in the Big Trak yet! More to come…


Bring Back The Beko!

Our washing machine, a “Beko WMA 641 W”, broke down; no bangs, no smells, no intermittent behaviour, just dead. Having checked the fuse, the socket, the fuse again, it was confirmed broken.

Predictably, it decided to do this after passing the 1 year old mark, so no warranty. And like many appliances, getting it repaired is the same sort of cost as buying a new one, so time to go shopping…

But that felt just a little like the wrong answer. I’m not sure whether it was the idea of having to go shopping, paying again, shifting heavy white goods, or it ending up in a landfill that prompted it, but I became determined not to be beaten so easily. So instead, time to get naked…

Naked Washing Machine

The machine came apart easily, and seemed very well designed. It was very quick to confirm power was getting to the control board and that full disassembly was needed. Top tip: I have always clustered groups of related screws when taking things apart to help when re-assembling, but I realised for the first time that putting these groups in line is really useful. Probably obvious, but I had never done it before. So re-assembly is just working backwards along the line.

The power of chronology should never be underestimated! Our brains seem very good at searching things by time. We may spend ages organising photos in to folders, but given instead a huge list of photos ordered simply by date, we’d probably find what we were after more quickly.

Anyway, the PCB is out…

Beko Controller PCB

The controller is made by a company called Invensys. Some searching uncovered that these boards are about £50, but after firing off a few emails to potential suppliers I was met with silence. Knowing power was getting to the board, its time to try and understand what is going on. Multimeter in hand, some patience and PCB probing…

Beko WMA641 Schematic

The thing that stumped me for a while was that what I thought was the logic DC power supply output seemed to be connected through to ground. Short circuit? It turns out after a little more head scratching that the power supply was designed to produce -5v; suddenly with that insight the whole world flips on its head and things start looking a little more sane.

Having uncovered what looked like a switch-mode power supply design, I attached the power again and investigated that. I wouldn’t recommend probing a live board hanging out of the front of an appliance, but it helped me confirm the problem; the rail wasn’t achieving the voltage it needed to power the logic.

It Works!

By replacing the BC556 used in the power supply, I was welcomed with the sight above. That’s the “Ready” led that is!

So after all that, a 7p transistor is what brings the Beko back! Lucky i’m not charging for my time, but also cost is not really the issue. If nothing else, it saved me the mind-numbing process of choosing a new machine, and another big white box from landfill!