Golf GTI shakedown

Faced with the possibility of 600 miles through England and France with five people in a car to accompany my parents on holiday, I decided to buy my own car.

Not wanting to take an easy option, I bought a 1985 Volkswagen Golf GTI Convertible. This replaced my previous but younger 1990 Nissan Sunny 1.4 LS, which was a remarkably reliable and well handling car if not particularly sporty.

This Golf is in good mechanical condition for a car of its age, and its chassis has been sealed well and is free of rust. I bought it from a private seller in Stockport and immediately took it to a garage for a check over. We fitted a new clutch, timing and alternator belt, and had both rear wheel brake cylinders replaced and the tyres re-sealed. This service cost almost as much as the car cost me in the first place, but I was expecting that.

The first run out was to Wales for a camping weekend. The fuel delivery problem became apparent during this run. It started kangarooing and cutting out while driving through the centre of Manchester, but with a good battery to keep starting it, it managed to get out without any serious problems. Once on the motorway it had no problems.

The Mk1 Golf GTI uses a Bosch K-Jectonic fuel injection system, which is an entirely mechanical multipoint but non-direct petrol injector system. A fuel pump under the driver's seat pumps fuel at injection pressure (I think) into an adjacent accumulator to cope with peak demands, which then feeds up to a fuel distributor in the engine compartment. The problem manifests as an infrequent but sometimes severe lack of power, often enough to stall the engine. My own experience from driving it makes me think there are large air pockets in the fuel, but I have been very wrong about diagnoses in the past. I think it's likely this problems does occur while driving on the motorway but is not noticed in the momentum at those times.

The fuel problem had been declared by the previous owner when he sold it to me, and he had done a lot of work to try and resolve it - fitting a new fuel pump, fuel distributor and injectors amongst other things but these evidently hadn't fixed it. Mk1s often suffer from rusted fuel filler tubes, and while this had been replaced on mine, there is a strong possibility of rust in the fuel tank contaminating or blocking the other systems. Just before leaving for France, I replaced the fuel and air filters as I had no evidence of their being recently changed. The old fuel filter did emit ominously brown fuel at the tank side when removed. I hoped the new filter would permit more fuel through and solve the problem.

As well as this, I replaced the fixed offside mirror which was deflecting under motorway winds with a decent one with remote cable controls. This would be especially important when driving in France. I also replaced the original cigarette lighter socket with a modern one which would accept an accessory plug without falling out, and correctly connected the passenger door lock so it could be locked and unlocked from the inside.

Unfortunately, at nearly the last minute I also noticed the reversing lights were not working. I had lighting problems with my old Nissan and patch wired them, but reverse lights are a bit tricky because UK law (as I understand it) requires that they can only be activated when reverse gear is engaged - a switch on the dashboard won't cut it. After a while prodding at a rather inaccessible switch unit on the gearbox, I decided to fix a microswitch to the gear lever housing in the cabin. I used Polymorph, a low melting point thermoplastic to construct a solid structure for the switch around the gear lever. I would recommend keeping a pot of this stuff around for emergency repairs to any engineer.

With that fixed, I set off for the Latitude festival. The fuel problem appeared once again while picking up a friend from Manchester, but after that there were no problems. Me and the Golf proceeded on to Saint-Barthelemy in Brittany and back, the only problem being an embarrassing incident while loading onto the return ferry. Near the top of the loading ramp, it cut out and would not restart for more than a few seconds, and this required us to raise the ramp and push it into position on the car deck. After sitting idle for 10 hours on the deck, it restarted with no problems and proceeded to drive back to Bolton via Hertfordshire without any further issues.

The fuel problem will be an interesting one to debug. A full inspection of the tank and the fuel lines will be the next project. One of the rear wheel cylinders also appears to be leaking again, but hopefully this will be fixed under guarantee.

"FabLab" opening in Manchester

Some vague details have appeared in the press of a 'FabLab' opening in Manchester later this year. It sounds like a low-volume, general manufacturing plant. I'm imagining some CAM and 3D printers. This could be very exciting if it goes ahead.

News article: http://opensource.sys-con.com/node/940106

The main backers seem to be manufacturinginstitute.co.uk although there aren't many more details on there yet.

Electric pressure gauges

Earlier this year I made a load average meter out of an old ammeter. But I've decided I want to use some even older technology, so I've been refitting some pneumatic pressure gauges so I can display information with them.

I got a load of old gauges from Empire Exchange, the little Mancunian goldmine that supplied the ammeter. Opening these reveals an arc-shaped copper pipe which deforms when inflated, driving a lever and gear which moves the needle. Now, ideally, I would control these using a computer-controlled variable pressure pneumatic source, but I don't have pneumatic mains in my house (not at 140 bar, anyway), so I've had to go for an electro-mechanical solution. It's a shame to cut the proper workings out of them, but I don't think they would have gotten any better life in their present form.

A servo motor is the obvious choice to get a controlled rotational movement. However, most servos only have a range of 180°. I need a range of 270° to use this meter properly. You can get servos with a greater than 180° range but they are quite rare, especially in the small sizes I need to fit into the gauge's body.

In order to get the 270° range I've used a rudimentary belt drive. I made a pulley for the gauge's output shaft by clamping the shaft into a dremel and using it as a lathe to turn down a larger plastic pulley to the right diameter.

The servo's output shaft is about 5.6mm diameter, so I made a pulley as close to 4.2mm as I could get it for a 1:1.5 enlargement. The pulley I made is rather rough, but no-one will see it in the finished product.

I've attached the servo to the gauge body with Araldite, and used polyester sewing thread as a belt, with two turns around both pulleys. The belt is tied to the servo motor's horn and fixed with glue at that point. Ideally, it would also be tied to the output shaft, but the tiny scale of the components make this kind of engineering impossible for me.

A real engineer would use a toothed belt or a gear drive for this - or make their own servo motor. But for a few hours' engineering in my kitchen, I'm happy with this solution.

I've tested this with a remote control system and it works very well. The biggest concern is slippage of the belt, but the exercise I've given it so far shows that it's actually perfectly repeatable - it doesn't slip at all.

The next steps are to replace the scale backplate with something like a 'load average' or 'spare memory' scale, and to rig up a servo motor driver so I can control it from a PC. Servos are very easily to control, just needing a PWM signal - a little easier than pneumatic signals in this day.

If you want to know why I bother to do this, you are probably not my target audience. :)

Opening a WRT150N

Only a tiny number of people will be interested in this, but I recently had to open the case of a Linksys WRT150N router and found a few questions on the web asking how to do so. Doing this voids your warranty, of course.

First of all, find a T10 security torx driver. These are like standard Torx bits with a hole in the middle.

Start by flipping the router over and levering up the silver panel at the rear of the router. I'm calling the rear the side which the antennae are attached to. The rear half of this panel will pop out of the body, but the front is attached with hooks which will break if you try to lever up the front half first. Once the rear half is free, the front half will slide off easily.

This will expose four security torx screws. Remove these.


Now you can remove the top and side panels. Pull one of the side panels and its side of the top panel away from the router at the same time. The hooks which hold the side panels on should pop open one at a time without damaging anything.



Repeat this with the other side panel. You should now have a completely disassembled WRT150N, so you can get at the serial port connections you want to attach to.

Tea-making with gas and electricity

B3ta recently asked whether it was cheaper to make a cup of tea using an electric kettle or a gas one. My gut feeling on this was that gas was cheaper, because gas is a lot cheaper than electricity per unit energy. I've done an experiment to see which is actually better.


Starting with gas, I put a mugful of water in a steel saucepan and heated it over a low flame. I can measure the amount of gas used using my gas meter. I've completely shut off my central heating boiler, including the pilot light, so no other gas is used during the experiment.

This took 0.0092 cubic metres of gas to bring it to the boil. I'm calculating the energy and cost based on my last gas bill, which explains how to convert from cubic metres to kWh - ultimately by multiplying by 11.0786. So I've used 0.102 kWh. I pay 2.88p per kWh for gas. USwitch.com reckons I could get gas for 2.86p from another supplier, so I'll use that. That makes a total of 0.29p.

Next I set up an electric kettle with a plug-in power meter. I've got to use half a litre of water to cover the element and make up the 'minimum' mark on the kettle, which is slightly more than the mugful I boiled in the saucepan. To boil this took 0.06kWh. The cheapest electricity I could find on USwitch was 11.21p/kWh, so this cost me 0.67p. Even given the inaccurate measurements in this experiment, gas is the clear winner.

But what if I've got friends round? I did a test with a large teapot full of water as well. This time, the saucepan took .281kWh for 0.82p, and the kettle took .140kwH for 1.57p. Still nearly double the price of the gas option.

Boiling speed is another factor - the gas saucepan takes a lot longer to boil than the electric kettle. I did some more experiments, using the gas turned up higher than I normally would. I expected this would waste gas, because a lot of heat escape round the side of the saucepan. However, it was barely any extra. There's probably a 'sweet spot' for the gas flow - too high would waste gas, and too low would take so long to boil that heat gets a chance to escape from the saucepan. Still, I couldn't get it as quick as the kettle. The kettle isn't a fast boil one - it's about 2.2kW. Even so, in all the experiments I measured time for, the kettle is twice as quick. So for the extra third of a penny it costs to boil the electric kettle, and the convenience of having an automatic off switch, I may well stick with that for the time being.

You'll notice that the kettle uses less energy despite costing more. Does this mean the kettle is more efficient? Not necessarily. The kettle is more efficient in itself than the stove and saucepan, but a lot of the electricity comes from gas in the first place. About 36% of our electricity comes from gas-fired power stations, and the best stations are about 58% efficient. Another 37% comes from coal, but I haven't found efficiency figures for those yet. If our electricity came entirely from gas, the kettle would use about the same amount of energy as the stove. To do a fair comparison you would also need to know how efficient the national electricity grid is, and how much energy is used in pumping gas around the country.

http://www.berr.gov.uk/files/file39569.pdf
http://www.the-eic.com/News/Archive/2006/Nov/Article2799.htm

The data in full:

Fuel	Quantity	Speed	Time (s)	Volume of gas	kWh	cost/kWh (p)	Cost (p)
Gas	1 cup	slow		0.0092	0.102	2.86	0.29
Gas	1 cup	fast	192	0.0100	0.111	2.86	0.32
Gas	1 teapot	slow	1376	0.0254	0.281	2.86	0.8
Gas	1 teapot	fast	506	0.0258	0.286	2.86	0.82
Electric	1 cup	n/a			0.060	11.21	0.67
Electric	1 teapot	n/a	213		0.140	11.21	1.57

The by-products of potato juice

Today I have mostly been performing silly experiments in the kitchen. I like potato pancakes, but they are problematic to make because the moisture has to be removed from the potatoes before frying them. This usually involves dirtying a clean cloth, or trying to squeeze the moisture out by hand which doesn't work well. I've also tried using a ricer on raw grated potato which is quite effective.

I had a brainwave today - realising that I already had a device which does this job, namely a juicer. I pushed three potatoes through the juicer, and kept the pulp that normally gets discarded. Mixed with some chopped onion and seasoning, this makes really good, fine potato pancakes. I wasn't brave enough to try drinking the potato juice.

An earlier experiment to try separating freshly brewed coffee from its grounds using the juicer didn't work so well. It just tastes like soil.

12 volt mains

If you like gadgets as much as me you probably have a large number of AC adaptors with power bricks cluttering your house up. A lot of these have different output voltages, but I have quite a few that deliver 12 volts, or claim to. Is it possible to replace some of these with a single transformer to simplify the wiring and increase efficiency?

The experiments I've done so far suggest that the first part is quite possible, but surprisingly, I couldn't run my appliances as efficiently with a single power supply than with individual bricks.

The appliances I used for this were my Netgear ADSL Wifi router, my 20" LCD TV, and my mini-itx based server computer.

The first step was to give each a common connector. I split the cable on each and attached a PC drive power connector on each side. Drive power connectors are cheap, meant specifically for 12V and can be plugged straight into an ATX power supply.

Having done that I reconnected them to their original power supplies and switched them all on, checking the power consumption for each. Measured at the mains socket with a plug-in power meter, I got: PC on idle: 28W. TV: 50W. and the router: 7W. Total 85W. Incidentally, if you repeat this experiment, it might be better to plug all those into a power strip and plug that into the power meter, in case the meter has some non-linear error.

Using the first attempt - an "L&W" 250W power supply used 48W just to run the router and PC - obviously less efficient. The TV wouldn't work properly at all - I got sound but no picture. A quick check revealed that the 12V output of this power supply was actually only raising 11.05V unloaded - which presumably is not enough to power the TV properly. The PSU also used 12W without any load at all.

I tried again with an older Opus PSU which had the same problem powering the TV. It also used 8W unloaded.

Next was a Morex PSU, only a 200W model for a micro-ATX system but this was evidently of better quality and managed to get the TV running. However, just the TV and PC drew 92W from the mains - over the limit before the router was connected. It also drew 11W when idle.

The last test was my bench PSU. This is a bit of a beast, rated at 40A continuous, but given its higher cost I thought it might stand a chance of being more efficient. No such luck though - with all three appliances it drew 110W, consuming 18W unloaded.

So, while it might make the wiring neater if done properly, I've yet to find a power supply which will do the job more efficiently than using individual power blocks.

I suspect that computer PSUs are not the best choice for this job, as they are probably geared towards delivering a very stable smooth 5V and 12V rather than efficiency. The power bricks are not, so far as I can tell, very stable in their output voltage, probably relying on further conditioning inside the appliance.

As usual, I wouldn't recommend anyone else trying this for themselves - running things on too low a voltage could damage them, and not all PSUs output the voltage they claim - the router's power brick, for example, delivers 16V when unloaded.