Finally three images of our visit. My father in front of the gib crane in J Samuel White's yard, a view across the Medina river of the same crane some 60 years previously, and a sunset from the headland garden of our cottage.
Wednesday, 21 February 2007
Isle of White
Finally three images of our visit. My father in front of the gib crane in J Samuel White's yard, a view across the Medina river of the same crane some 60 years previously, and a sunset from the headland garden of our cottage.
Wednesday, 14 February 2007
Controller Electronics
Due to being on-site all day I haven't had a chance to do any work on the point motor situation, so I thought I'd start on a discussion about the electronics for the controller.
Before we begin, please be aware of two things, firstly I am not an electronics engineer, nor even an electrician. All the information given here is self taught, and experience of 25 years working in industry, books are a wonderful thing and a helpful electrical expert can teach you many things (thanks Keith).
Secondly - electricity can KILL. Usually the statement given is 'mains voltages can kill', but a 12 volt car battery can deliver upwards of 40 amps, which is enough to weld steel! Believe me. I've seen an expert weld 5mm mild steel plates using a car battery, so beware!
OK, as to our controller, we need to do three things:
- Convert the mains AC electricity to a nominal 12V DC for the locomotive motor.
- Vary the output to the tracks from 0V to 12V with as much control as possible.
- Be able to change direction (polarity) of the tracks
In converting the 240V AC mains (or 110V in the US), to 12V DC (nominal) we need to either use a transformer or a switching power supply. You can build these yourself but there are so many cheap alternatives that a secondhand supply is an easy option. A used car battery charger, CB radio power supply, a printer or laptop power supply or even on old PC desktop power supply would do the trick.
The magic numbers you are looking for are an output of between 12V and 18V DC capable of supplying 1.5 Amps to 3 Amps (lower than 1 Amp will not be enough). Most PSU's used for in-car equipment run at 13.8V - ideal for our needs. For these circuits an output of 14 - 18 volts is best as will be seen.
The image below shows what would happen if we simply connected the PSU to the tracks. The only way to start and stop the loco would be to turn the PSU on and off. Also the loco would have two speeds, stopped and flat out! There is only one direction of travel since the positive and negative supplies are always connected to the same points on the motor. Not very good.
In order to alter the voltage to the tracks, and therefore the speed, we need to use a voltage divider. This is a very well known and common circuit. There is a mathematical formula for calculating voltage division, but lets forget that, in simple terms if you place a resistor between V1 and the positive side of the motor, and another between the positive side of the motor and earth, by varying the value of the resistors we can vary the positive voltage reaching the motor. If the two values of the resistors are equal, exactly half the voltage (6 volts) will reach the motor.
Obviously we don't want to keep physically changing the resistors, so we use a 'variable resistor' or potentiometer. There is one shown in the image below, these cost about £1.50 at time of writing. You need a 'linear potentiometer'.
As you can see, there are three connections.
Inside the 'POT' there is a track of resistor material, one end is connected to one of the outer connectors, the other end to the other outer connector. The central connector is joined to a 'wiper' which moves along the track. By turning the control knob, the resistances on each side of the wiper vary, thus the output at the central wiper changes due to voltage division. Simple.
These pots are used for volume controls, gain controls, all sorts of things and are very common.
In theory, any value (given in Ohms) will work because it is the relationship in percentages between the two resistances that we are interested in. However in practice the amount of control to the loco is affected by the value. This is because we are really only interested in the voltages between about 4 volts (at which the loco starts to move) and maximum.
Here is our circuit with the pot fitted in as a speed controller. Will this circuit work then? Well, yes and no. In theory it should work at least to control the speed, but in reality it would last only a few seconds. The reason for this is that the track in the pot is very thin. In order to change the voltage, the resistor must dissipate the difference as heat. The more current drawn by the motor (in Amps) the more heat will need to be dissipated (this value is given in Watts just like a light bulb). Most pots will only sink a very small amount of current and a loco motor will force it to overheat and break very quickly.
A well run in and smooth loco motor will draw around 250mA at start up dropping back to around 100mA whilst cruising. An old sticky or stubborn motor could draw around an Amp at start up, so our circuit must allow for around 1.5A normal running.
We need to 'boost' or amplify the output from the POT so that it is not destroyed. Enter the transistor. This acts as an amplifier, a switch and a gate valve all in one. Pictured below is a very common transistor, the 2N2222A. This is a 'small signal' transistor, which has very fast switching and good amplification. They are small and cost pennies.
The transistor has three connectors, the 'Base' which in our case acts as the control connector, the 'Collector' which takes the incoming current, and the 'Emitter' which gives the outgoing current.
The transistor will take 0.7v from the circuit to operate, we must allow for this 'Tax' in calculating the final output. As the potentiometer output voltage reaches 0.7v the transistor 'turns on' and starts to pass current from the collector to the emitter, as you can see from the diagram below, this bypasses the potentiometer and protects it from burning out.
As the voltage at the base of the transistor increases, so the output at the emitter increases, always 0.7v below the input voltage. So over all our 12V output will now only be 11.3V, additional transistors will add to this effectively dropping the final output, hence the requirement for a PSU between 14 and 18 Volts.
Here is the diagram with the 2N2222 fitted. So will this circuit work? Again yes and no. The 2N2222 is only capable of sinking around 800mA, and we need 1.5A. The reason for using this transistor is its good amplification, and fast switching.
What we are going to need for the final output stage is a power transistor capable of sinking more power.
As you can also see, there is still only one direction of travel, this will be dealt with right at the end.
So far the total cost of our circuit, if we allow for some hook up wire and a bit of strip board to build it on, has reached the grand total of £2.00
Next we shall add a power transistor, this is fed off the 2N2222 in the same way as the potentiometer fed the first transistor. This configuration is known as a ' Darlington Pair' and is one of the most common transistor circuits used in electronics.
In the new circuit diagram you can see the addition of a 2N3055 power transistor. The only reason I chose it was because I had taken one out of an old amplifier when I was designing my circuit. A better choice for our application could be a TIP 41a. These are cheaper, smaller and easier to fit than the 3055. Again they cost pennies.
You will need to use a small heat sink for the power transistor. Heat sinks are available for all power transistors, these range from a small flat plate of metal to huge elaborate finned contraptions. You only need a small one to help dissipate some of the heat. If you reclaim a transistor from an old, broken bit of gear, then the chances are that it will already have the heat sink attached.
Next - direction of travel. Reversing the polarity at the tracks is very simple. The outputs from the controller are wired through a Double Pole Double Throw (DPDT) switch. You only need a miniature toggle switch (about £1.00).
Here's one.
To incorporate it into our circuit, you wire the two outputs to the centre two connectors on the switch, wire two new outputs to one pair of end connections on the switch then wire a crossover between the four outer connectors. Trowing the switch now reverses the polarity.
The addition of a small value resistor ahead of the base of Q1 acts as a protection for both the track on the pot and the base on the transistor.
Here is the final diagram of the super simple controller. S1 and S2 are the DPDT switch.
So will this one work? Well yes and no.
I use one of these to carry out very basic running tests because it's so small and cheap. It is perfectly capable of driving a loco, and using a 10K pot it is fairly controllable. So whats wrong with it? Well there's no on off switch for a start, there's no overload cut out, there's no indicators as to whats going on and very slow speed running can be a little erratic. For the overload protection you could use a 1A fuse in the positive rail of the output from Q2. If you use a refittable type than you can just change it if it blows.
Fitting a SPST switch into the input from the PSU will give an on off switch. Fit an LED with a 1K resistor behind the switch and across the negative rail for an on off indicator.
Very slow running will always be an issue, one I'll discuss in the next post.
Bear in mind with this circuit the following when choosing the value of the pot:
12V electric motors, like all electric motors are designed to run at maximum torque and maximum power when fed with the recommended voltage. The motor designer will then build in some overload allowance such that our little loco motor will probably accept 15 - 16V before it starts to complain. The designer will also take into account that there needs to be some slower speed running so its a compromise.
If we say that at 16V the loco will be doing the equivalent of 125mph, then the vast majority of running is done at a speed nearer a third of that (around 5V) and shunting at even less (say 3V). The motor designer cannot possibly allow for that amount of variation and still have the motor run at full torque. Most locos need around 4V just to start moving, or the electronics in the controller need to give it a 'kick' start, then once on the move the speed can be turned down a bit.
Now, since the circuits transistors are taxing 1.4V before there is any output at the tracks, and the loco needs around 4V to start moving, the voltage divider has to be supplying 5.4V before anything happens. For a 12V system this means that the control knob is going to be at nearly half way before it start to move the train!
I tested loads of pots with values from 100 Ohms to 2 Mega Ohms (2 million Ohms). The higher the value the further I had to advance the control before the train moved, if the value was too low full speed was reached too early. I suggest you try values from 1K Ohms to about 20K Ohms for your pot. This range seems to give the best control over the 4 - 12V we want. You can bias the circuit with an additional resistor between the pot and the negative (earth) rail so that the pot begins to operate earlier. Experiment!
Next time, the capacitor discharge unit for the point motors, the overload protection circuit and simulated inertia and braking.
Tuesday, 13 February 2007
Problems
No post for yesterday, I was working on a customer order - hooray! Some small jobs have been creeping onto the books so things look OK for this month.
My Father's PC has died and despite all my efforts it would appear that the motherboard has given up the ghost. This is causing him some grief because, since my mother died 18 months ago, his PC has been a bit of a lifeline to the outside world. It seems that the hard drive data is intact so we should be able to get him back up and running again.
I went to price up a job to fit a replacement shower this evening, it would have been a straightforward job since it's an instantaneous electric one and the element had burnt out. However, on actually viewing the site I became far more concerned with the fact that there is an obvious leak, either in the water feed or the waste pipe system. The ceiling of the kitchen below has become so water logged that a section 4 feet by 4 feet in in danger of falling down!
I'll be on site tomorrow so we'll see how we get on.
The model railway has hit it's first major hold up. I've spent a lot of this week wiring up the electrics to the control box. In the images below you can see the wiring loom for the isolating sections and the point motor switches. Note that as yet there are no electronics for the controller installed. This is because I have 4 different prototype designs in the testing stage and I don't know which one will be fitted yet. In the meantime I am just using my loco testing controller for some running tests.
There are a number of possible solutions. I could dump the entire base boards and start over using 6mm MDF throughout, not a palatable idea. I could revise the mechanical linkage, possibly for a crank based system which would allow the motors more travel and more torque, I am still toying with this one. Or I could route out recesses for the 3 point motors that are suffering, thus reducing the length of the drive pin and eliminating the flexing. At the moment, the last is the most favourable but also the most messy to perform with all the under board clutter.
Mounting the motors above the baseboard and 'hiding' them would have been an option but the layout planning has not allowed for this. If anyone out there has been following this blog and is thinking of modelling in N Gauge, don't use a baseboard thicker than about 9mm if you are mounting the motors beneath the board.
The next railway post will include my resolution to this problem, and a discussion of the electronic systems.
Sunday, 11 February 2007
Railway Electrics and Electronics
Since I don't have the money for a computer controlled DCC system, I decided to use the tried and trusted methods for wiring up and controlling the layout ... with a few differences.
First and foremost I needed to convert the AC mains current to a usable DC supply. Rather than buy or build one I rummaged through the workshop and came up with an old HP power supply. This either came from an old printer or a laptop, but I remembered picking it up at a car boot sale for less than a fiver. It's output is 18V DC at 3 Amps. More than enough for such a small layout.
The image below shows the PSU installed under the station baseboard.
When using non DCC control for a layout there are a number of systems that need wiring. Firstly you need to be able to vary the output to the tracks in order to control the speed of the locos. Secondly you need to be able to isolate various track sections so that only the locomotive you are using starts to move. Any other locos on the track need to be kept stationary.
If, as in my case, you are using point motors to operate the points, these need a separate control system. I wanted push button operation for mine.
Finally there is the possibility of adding lighting and electronic signals, but I chose not to have these on such a simple layout.
When using non DCC, it is nice to have a good looking control panel, so after designing all the electrical systems on paper I set about making a control panel.
Below is a sheet of anodised aluminium I had left over from a customer job. I bought these on e-bay, just search for 'Aluminium Sheet'. A 2mm thick piece should cost no more than a few pounds.
In order to get around this problem a 'capacitor discharge unit is used to store up power from the PSU and then release it in a short, powerful burst when the button is pressed. With careful design, the circuit for this can also be used to ensure that once the charge has been sent to the point motor, if the button is held down inadvertently, no further charge reaches the coils until the button is released and the capacitor re-charged.
I set about designing and building the circuit. It is a very simple circuit and quite a few examples are available on the net. I simply used components 'reclaimed' from old devices. The capacitors were reclaimed from an old TV and the power transistor was from a huge number I had left over from another job. Almost any NPN power transistor would do. For example you could substitute a 3055 MOSFET from an old amplifier instead. I will publish all the circuit diagrams that I devised for the layout in another post.
Next came the wiring for the tracks. The wires were carried through holes in the baseboard and then through tie wraps to the controller box. Below shows the start of the wiring loom. I used red and black for the fixed feeds and brown and blue for the switched feeds (isolating sections).
The image below shows the wiring loom completed. the white wires are multi-core (six core alarm cable), that I had in the workshop. these will operate the point motors that require three cables each.
You can see the main PSU and the CDU under the board. The huge mass of coiled wires laying on the top of the baseboard will all have to be terminated in the control box! At this stage it is a good idea to ensure that all the cable ends have been clearly labeled.
Saturday, 10 February 2007
The Station
Before I could start this I had to alter one set of points. The reason for this, was that past experience of 'N Gauge' had shown that the very small locos have difficulty in negotiating certain types of points at low speed.
Peco produce two types of points, 'electrofrog' and 'insulfrog'. The latter have an insulated frog (the web area where the two tracks diverge). This simplifies the electrical installation, but it means that there is an electrically 'dead' area on the points. Below you can see an example of an 'insulfrog' point. The black plastic area at the diverging point is the frog, small locos sometimes lose electrical contact when passing over this area at low speed.
I had decided to use all 'electrofrog' points but I was one set short. So rather than spend around £10.00 on another set, I thought I would convert a set of 'insulfrog' points that were spare.
Below you can see the 'insulfrog' point at the bottom with the frog carfully cut out with a razor saw. Three of the sleepers have been removed as well. At the top of the photo are a set of points that I am trying to match. Note the all metal rails running throughout the point.
Below, I have cut out 3 new sleepers from paxolin copper-clad circuitboard material. I have made a small electrical break on each side to prevent a short circuit, though these are not really visible in the photo. The paxolin was then soldered to the outside of each outer rail.
The cost of the conversion in materials was zero, and it took about an hour from start to finish. Since the original points only cost me £3.00 at a swap-meet I think they are a bargain!
The station area board was then moved upstairs to my workshop. Below you can see the initial placement of the points to establish where the baseboard needed to be worked to fit the point motors.
What is more difficult to see are that some of the points will be operated directly by the point motors and some use a rod in tube method to connect the motors. This was done to hide the motor connectors under buildings in areas that were difficult to access.
The control box is in evidence in the bottom right hand corner ready to take the electrical connections. This and the other electronic bits will be described in the next installment.
Friday, 9 February 2007
Track Laying
I started in earnest on the fiddle yard. Below is the baseboard showing the frame used to raise the track level to match the corner unit.
Installing the track for the fiddle yard was relatively easy since all the runs come off points and there are no cross-overs. Work began from the throat end and the points were joined one after another, then the runs were simply joined off that.
The electrical plan had been designed in advance, so it was simply a metter of drilling some small holes to pass the feed wires and some 8mm holes to allow for the point changing motors to be installed beneath the board later. The electrically conducting joints were all soldered, and the insulated sections had feed wires added so that certain areas can be isolated using SPST switches.
The aluminium strips were left over from a job, and would have gone for scrap.
Next - the station section....
Model Railway
Here's the basic station layout on it's chipboard base, the chipboard was a mistake as shall be seen in a later post, but the basic elements are shown here. The simple track plan has been drawn out and the semi-constructed buildings are evident. Some slight re-arrangement took place before the final plan was arrived at.
Here's the fiddle yard board with the track design drawn up, again the MDF shelf that I used as the baseboard was a mistake, but it's done now.
The corner section built from 6mm MDF, if I ever do another layout this is what I will use for the baseboard material. Since the viaduct was to be curved, no kits were available, therefore it had to be 'scratchbuilt'. The first three pillars (made of cardboard) can be seen on the bed waiting for fitment.
The five pillars in place, the lower portions have been dressed with 'brick papers' and the arches are under construction, once all the glue had set these pillars became extremely strong.
The pillars have been dressed, the abutments added, and the archways installed. The parapet and approach walls will be added after the base has been built up into mountains. The back frame has also been added.
That's enough for this post, watch this space to see how progress goes.
Wednesday, 7 February 2007
Control Box
Monday, 5 February 2007
Some Work
I went there at 9.00am this morning to appraise the job and came away with an order to entirely replace the control box panel. Mostly to try and make it safe.
Below is a photo of the control box, and when I opened to door you can see why there might be a problem! Whoever did the original installation should be shot, if I had done work like this I would be utterly ashamed, and wouldn't expect any further work to come out of it.
Believe it or not, there is 240V AC of mains voltage 'live' in this box! No wonder there were 'a few problems', I'm surprised they haven't had a fire.
Saturday, 3 February 2007
Reviving a hobby
In my childhood, and my youth, I made and painted scale models and figures. This continued until I was in my late twenties by which time I had achieved a level of skill to exhibition / competition standards. The hobby fell by the wayside with only minor recurrances since then.
Anyway, for reasons that I am not really sure of, a friend of mine gave me three small metal 'fantasy' figures to paint. I dug around in the loft and found I had kept all of my old modelling tools and brushes, but I had no paints that I could find. So I added some model paints to my 'X-Mas' list and a few models just to see if I could still manage a reasonable level of success.
It certainly tought me that my eyesight has deteriorated somewhat! Below are some images of my first attempts to get my hand back in.
These are the three figures I was given to paint. Some kind of skeletal warriors. The one below was supplied with the set of paints I got for X-Mas.
In both cases the figures stand about an inch tall.
I talked it over with my wife and decided to try and utilise these skills to try and build a model railway. I wanted it to be a fixed model rather than a 'train set' and since money is priority I decided to scratch-build as much as I could, buy secondhand and make do and mend.
I will publish my progress on here as and when work progresses.