Various and Random

Bench for RSPB Flatford

2011-06-24T12:20:00.000-07:00

I am a volunteer for the RSPB in south Suffolk and north Essex. Usually this involves site maintenance in large woods or on fields which are breeding areas for estuarial birds. But, this year has had an unusual project; making a wildlife friendly garden at Flatford.

The Flatford garden sits alongside the National Trust property at Flatford which is world-famous as the scene of the Haywain and several other Constable paintings.

One thing a garden which will get lots of visitors needs are benches. So, wanting something a little different, I produced this bench in the RSPB workshop using off-cuts of chestnut from other parts of the garden project (the chestnut is local, felled as coppicing to maintain a wood, so about as sustainable as it gets). The shape of the bench does not dictate how you sit on it, you can choose any direction of view. Some of the ideas came from a bench made by Trannon for a museum, though with many modifications to suit outdoor use and the locally available timber.

If the bench proves successful in the garden, I'll make a few more. The 2nd version will have some changes to the seat shape, though will keep the octagonal theme.

YADCV ( Yet another DCC Coupler Video )

2011-06-23T09:40:00.001-07:00

I've done another DCC coupler design, in a Farish class 14 diesel. This one is a commission installation for another modeller (like certain famous motor cars, if you have to ask the price, you can't afford it!)

This time the coils are within the N scale NEM coupler pockets, and the DG couplers are on the loco body. This makes maintenance very much simpler as the fragile parts are well protected and the mechanical parts are slightly modified standard aftermarket couplers. The couplers are "handed" to match the stock on the layout in question where DG loops are only fitted at one end of the stock. So, the loco has a normal loop at one end which can be lifted, and a "lifter" at the other which lifts the loop from a wagon off the loco coupler.

I'll post some drawings at some point, but a bit of video to illustrate how it all works. The loco is a Farish Class 14 diesel, with the wheels turned down and re-gauged to run on 2mm Finescale track. Chip is a CT DCX75.

Blogger's video feature seems to be broken, so I've had to put it on YouTube

The train on line 1 is running itself....

2010-11-14T12:19:00.001-08:00

A long time since the last posting, but here is a train one...

For the Warley show this year, I will have a demonstration on DCC and 2mm scale topics. This will include some basic issues, such as how to fit decoders in limited space, and some more advanced topics, such as train detection, interlocking, and automation.

The advanced topics are illustrated with a simple track arrangement which can be run automatically or manually. A fairly rough video is shown below (bring back the old version of Windows Movie Editor, it was easier than the current one !).

The automated shunting sequence includes careful buffing up to the train, and if the loco running has lights, these are switched on/off at appropriate times.

The train detection is through MERG DTC-8 detectors which register current in a track section. Those feed their output to a HDL LocoIO board, which places the information on a LocoNet network. From the network, information is picked up by other LocoIO boards (displays status on LEDs, etc), and via a computer interface, to JMRI. The LocoIO boards also provide input from the manual lever frame, and output to LED signals at the trackside and servo motor drivers to move turnouts.

JMRI provides the interlocking for the signals rules, an on-screen duplicate of the lever frame, and the automation scripts which send instructions to run trains, change signals and turnouts, alter functions on trains, etc.. The scripts respond to the state of the track detectors. JMRI can track a named train around the system, so it is known which train is in which section.

Train movement comes from a Digitrax Zephyr command station, which relays instructions from LocoNet to the track. It also offers the manual running controller.

A second manual handset, a Uhlenbrock Fred, provides a hand-held controller.

And, if any visitors turn up with an iPhone with the WiThrottle Application loaded, they are welcome to connect it into the system and drive the trains on their iPhone.

Skiing; Skarheimen 2010

2010-04-11T09:31:00.001-07:00

(With apologies to those looking for model railways; fair chance the next posting will be on model making...)

A hut-to hut tour through Skarheimen, March 2010. Weather mixed, good some days (hence pictures!), poor others.

Arriving at the first hut, staffed.

Start of long day climbing a 1750m peak.

Peak appears through light cloud...

Further up, peak is immediately above skiiers, still nearly 2hrs until the top. One to right heavily corniced.

View from the top; lake is around 800m below, mountain in far distance perhaps 70km away.

Unstaffed hut; home for two nights.

Staffed hut under spectacular rock edge. But weather not good !

Journey's end, the road in the valley with a bus stop !

Skiing; Kvitavatn 2010

2010-04-11T09:19:00.000-07:00

Early February 2010, possibly the best weather I have ever had skiing in mountains; whole week of sunshine, good visibility and only one windy day. Long days of up to 25km and 1000m of climbing - no ski lifts if you want to get into the wilderness !

Using six outputs on Zimo MX620

2010-01-27T12:47:00.000-08:00

I have a 2mm scale Class 24 diesel, fitted with a Zimo MX620. I wish to use all six of the outputs on the chip to drive various features; independent lights, working couplings, and I might use the last output for a cab light.

The standard Farish 24 comes with a circuit board for a six-pin (2 function) decoder, and took up all the top of the chassis. This has the lights paired front and back. So the board was replaced. I'll post a sketch of those new boards later, their main feature is a 2.2Kohm resistor on each function output to control the current to the LED lights at each end.

The Zimo MX620 has six function outputs. Four are normal 12v full current, and two are "logic level". Two of the normal outputs are on the wiring harness (or pins), and all the others are on solder pads at the other end of the chip (along with a "ground" or 0v, and another 12v (or blue) pad). The outputs Fo3 and F04 are enabled by a CV change; they have a lot of capabilities; Susi sound data output, Servo driver or normal function output.

The logic outputs are about 5v, and could drive a very small current LED. But, the wiring of the lamps in the class 24 make it difficult to connect; they are wired for a common positive supply.
So, it was necessary to make F03 and F04 drive a normal output. This can be done several ways, but this simple transistor circuit does the job nicely:

The only additions to the normal connection to a function output is the transistor, the 50Kohm resistor, and the connection back to the Ground Pad on the decoder.

In my case, I used the track pickup (decoder red wire) to provide the positive supply. I had to attach wires to the solder pads for ground and the Function output.

I built the circuit twice; once with big parts and using long leads from loco to a test board. The second circuit (used in the loco for real) is a few square mm of 0.3mm PCB with surface mount resistors, and transistor laying on its side with legs cut very short. Check all the resistances, etc. before hooking up to the decoder !

Skiing in Dedham Vale

2009-12-20T06:34:00.000-08:00

Dedham Vale is perhaps best know for the paintings of John Constable (Haywain, etc). Its a few minutes from my home, and for the first time ever I've been able to ski on the meadows leading down to the Stour. This meadow is on the north bank, Dedham church is visible in the background of the first picture. Sorry that the pictures are a bit blurry, there is only so much that a camera on a cellphone can do.

Couplings on 0-6-0T

2009-11-24T02:17:00.001-08:00

This loco belongs to the East Anglian Scalefour group and is used on Coldfair Green.

I have fitted DCC controlled AJ couplings to the loco using my etched parts.

I built up the couplings as complete units on a piece of printed circuit board. This was then fitted to the loco using the chassis mounting screws. Wires from the board went up to the loco, via some small PCB plug/sockets which allow the couplings to be electrically removed.

Coupling in closed (normal) position. Some parts temporarily held with "whitetac", araldite (or similar) will be used when happy that no further adjustments are required.

Coupling in open position, with magnet clearly visible on bottom of flap.

Close-up of front of loco, counterweight is visible below buffer beam, but fairly unobtrusive. Loco now requires cosmetic 3-link or screw coupling elements to be hung alongside AJ wire.

Yes, I am bending AJ hooks the "wrong" way. I have started experimenting with Vincent de Bode's method which puts the double section downwards (the downwards part still pulls the train load). Vincent's method offers the possibility of finer wire (the train load is no longer taken by the 180 degree bend) which in turn means the wire can be shorter for the same degree of springiness. It also means that the lower tail of a coupling cannot catch on a burr (there is no cut at the lower edge). The "Vincent bends" are compatible with conventional couplers, so its possible to mix and match between different types. Its too early for me to tell whether I will swap over wholesale to Vincent's method, but it shows promise.

Etched brackets for DCC controlled AJ's

2009-09-17T05:25:00.000-07:00

I've just taken delivery of a sheet of etched bits for the DCC Alex Jackson couplings. There was a fair bit of interest in them at Scaleforum, and I will be ordering a batch of coils in mid October.

If anyone would like to experiment with these, get in touch. There are pictures of the prototype etches in a small 4mm scale 0-4-0 posted earlier. There is some video of the 2mm version in action, and a list of CV values on the 2mm Scale Association website.

One etch per coupling (more if you are creative with the parts).
Prices £2 each, 6 for £10, 12 for £20 (UK post free), 20 for £30 (UK post free). Small orders post is £0.50 in the UK.

The etch picture shows the components;
top left - box to hold coil for rotating Alex Jackson (and similar rotation designs). Approx 4mm cube with "ear" for rotating shaft above.
bottom row - three different flap sizes
top right - base for DG coupling (2mm/N)
centre right - tongue for DG coupling
centre top - alternative brackets to box for coil (for very tight places).

Folded up box with simple flap (no counterweight).

Folded up DG version.

Snape diorama for Scaleforum

2009-09-13T09:33:00.000-07:00

Scaleforum, an annual exhibition of 4mm scale models, is held on the last weekend of September.

The picture shows a diorama with some of the buildings from Snape Maltings (buildings and painting by Richard Kimberling) which will be used to illustrate my DCC controlled Alex Jackson couplings.

The diorama shows only a small section of a much larger building, set into a temporary roadway.

2mm Scale Alex Jackson's

2009-09-06T10:22:00.000-07:00

The Alex Jackson coupling is well known in 4mm scale, but less common in other scales.

Jim Watt is the main user in 2mm scale, and he sent me a few for testing with my 2mm loco with DCC controlled couplings. The couplings are very small and unobtrusive, here are a couple of photos of them fitted to a 21T mineral wagon. Since taking the pictures, I've noticed some clown has knocked the corner of the buffer beam from the wagon, so more repairs will be required. The buffer heads are my own steel turnings.

ABC Stopping/Slowing

2009-06-20T11:12:00.001-07:00

( Post updated 19th July with some clues on how BM2 works. Updated 21st Sept with CT Sound chip information).
Lenz and Zimo DCC chips (* below) support an automated stopping method called ABC (assymetric braking control). This allows a very simple trackside circuit to cause a train to slow to a stop. The train can be reversed away from the stop signal. There are differences in how each company has implemented ABC.

I've got interested in ABC for two uses. Firstly, an automatic shuttling railbus which can be set to run from fiddleyard to platform, and back again on a timed sequence using features within the Lenz Gold chip. This automation requires nothing more than two ABC stopping modules. Secondly, using ABC to protect the end of the running area for a small demonstration track. The ABC module will make it impossible for a visitor to drive a locomotive into the buffers or off the end of the track.

Both decoder makers offer an option of constant braking distance. This means a train will always stop in the same place regardless of approach speed, which means it will stop ahead of a signal.

Lenz's version of ABC has two modes, stopping and slowing. They sell modules (BM1 for stopping and BM2 for slowing) to trigger the effect, though they seem quite expensive. The stop module (BM1) is well documented as an array of diodes, and a DIY one is trivial to construct. The exact number of diodes seems to vary between different websites. My experiments have suggested six (diagram on left) are required for a reliable stop with a Lenz Gold.

I have been unable to find details of the slowing module. An email sent to me indicated that the BM2 works by sending the assymmetric signal on alternate cycles of the DCC signal. This would make a home-brew BM2 somewhat more complicated than the home-brew BM1. (I have tried a four diode matrix, and that seemed to cause my solitary Lenz decoder to slow correctly, but it might be an artifact I'm seeing, rather than correct operation given the comments of my email correspondant).

A "slow approach" could be deployed at a caution (distant) signal, and a "stop" ahead of a stop signal. A simple on/off switch is used to disable the stopping or slowing module.

Lenz' implementation of constant braking distance is a bit limiting.

Firstly, its an all or nothing setting, so it can be quite awkward to manually drive a locomotive with constant braking distance enabled as stops will always take the same (long) distance from the place the throttle moves to zero (!). Judicious use of F4 to turn on the shunting mode (disables acceleration and constant distance braking) can give some manual control. One can use Ops-mode programming to turn constant distance braking on and off, but is a pain in the neck to keep doing that. The net result is a loco has to be set for constant-distance stopping combined with automatic running.
Secondly, the manner of stopping seems to be an initial decelleration at the programmed decelleration rate (CV4) followed by a creeping crawl up to the stop line. If the speed is too high for the stopping distance, the loco decellerates following CV4 until it reaches the distance and then stops dead from whatever speed it was doing. Not nice in either case.

Lenz do have a unique useful "shuttle" feature which can be used to automate a railcar, multiple unit or push-pull train. There are a few minor glitches in the Lenz implementation, notably the "direction" of the locomotive can be reversed depending when manual control is taken back. But it does work and its a very low cost of building an automatic shuttle. Use of Ops-Mode CV changes to turn the shuttle on and off is recommended if the locomotive is to also be used manually.

Zimo doesn't offer a "slow approach" mode for ABC (they do have their own HLU system, which I think is considerably more powerful, but I think only supported on Zimo command stations), but in all other respects has far more user-settings which allow detailed customisation.
Zimo allows the voltage assymetry to be set in a CV, this allows a grid of only four diodes to trigger a "stop", which means the track voltage drop is lower. This does mean that if Lenz and Zimo chips are mixed, there can be a problem in Zimo chips slowing noticeably on crossing the braking zone margins.

Zimo also have a much better implementation of "constant braking distance".

Firstly, the user can set "constant braking" for only automatic stops (ie. ABC stops) leaving throttle stops at the rates specified in CV4. (There is an option for all stops to be constant distance).

Secondly, the deceleration is done far more effectively; the train drives at its initial speed until the decoder decides it is time to slow to reach the stopping point. The visual effect is far better, it looks as if the train driver has chosen the right time to apply the brakes depending on approach speed. Alternatively, a Zimo can be set to decellerate smoothly using a rate calculated from the speed when the loco enters the stopping zone. This mimics a driver applying gentle braking from a low speed or harder braking from higher speeds.

So, that's my quick summary of ABC Braking experiments. I'd like some more details of the inner workings of the BM2 if they are available.

(*) 21st September. For another project, I've been experimenting with a CT Elektronik SL75 sound chip. This tiny chip has Lenz ABC braking support, and it works on my test rig (6 diodes, diode sensitivity set to 15 in the CT CV's). I am editing the JMRI file for this chip, so this detail should appear along with a large number of other changes. I haven't found ABC to work in other small CT chips, such as the DCX74 or DCX75.

L&Y 0-4-0 Electric Nearing Completion

2009-06-19T11:01:00.000-07:00

Progress continues on the L&Y battery electric, hopefully nearly done apart from lining (which was a bit over-the-top full-on swirly bits on the prototype!).

Firstly, some sprung buffers. The photo shows an original whitemetal casting (rear), and a bored out casting (middle) and a couple of steel heads and a buffer spring. All done on a lathe, the castings were bored after making a split collar to hold the casting in a collet. The spring is 36SWG phos-bronze, wound around a 1mm dia drill bit. The fat end of the buffer is 2.4mm dia. The buffers don't yet show the cross-drilling (0.35mm) in the thin tails (0.8mm dia) for the locking pin which fits behind the buffer beam. There is one pin for each end of the loco, which goes across the buffer beam, and through the shanks of both buffers.

Secondly further video of the loco uncoupling with the DCC controlled AJ's. As shown on earlier blogs, this is the first 4mm loco built with the couplings in mind, which was a lot easier and neater than retro-fitting. Chip is a Zimo MX620, activating F3 causes the entire "backup, uncouple, pull away, stop" routine. There is still some more electronics to add; a bank of capacitors to provide power over dirty track, and I've started to consider lamps fed by fibre optic.

Decoder Comparison; TCS vs Lenz

2009-05-21T03:02:00.000-07:00

Lets begin with the prices. Its an unfair comparison. A TCS MC2 costs under £20. A Lenz Gold plus USP module costs nearly £70. So, those with a restricted budget, stop reading now.

I have a 4mm scale railbus, its an Airfix kit with a Branchlines mechanism and interior. A Mashima motor drives one axle, the other has simple compensation. Wiper pickups on the top of the wheels. For a while this has run with the TCS chip; its seemed adequate for the job, but there have been shortcomings.

The biggest problem is not down to the chip, its the light weight four wheeled vehicle. The pickup can be erratic on all but the cleanest track. So, as an occaisional use vehicle on an exhibition layout, its a problem if it stalls on the crossing into the platform ! The TCS chip does exaggerate this problem to an extent; once power is lost, the chip restarts from speed zero, doing all the acceleration again. The TCS chip control is OK, the motor runs a little noisily, but its OK. The start speed is a little on the high side, but again, its OK.

So, why replace a £20 chip with a pair of devices costing £70 ?

One way round a pickup problem is a UPS capacitor to store power when there is a break in power to keep the chip alive. The store need only last for a tiny fraction of a second to overcome a microscopic bit of dirt. Zimo have solder pads for this and instructions on how to add the cheap components, some other chips can be end-user "hacked" to add a capacitor (your warranty is void when you start soldering bits onto most chips!). Lenz have a fairly expensive solution in the UPS module which fits Gold chips. It contains far more capacitance for the volume than is possible with the Zimo method.

The Railcar has potential to be used as an automatic train. If the layout operator wants a rest, or there are questions from a visitor, a train which shuttles into the platform, waits, then departs is very useful. DMUs and Railcars are ideal for this service. The Lenz Gold and Silver chips support automatic shuttles using ABC braking modules. ABC braking is very simple - four or five diodes per brake section - so a shuttle could be created on a layout for the price of a couple of on/off switches and about 20p worth of diodes, and the shuttle won't break anything else on the layout.

So, for both UPS and Shuttle features, the Gold is the chip for this particular loco.

Having fitted the Gold, the changes are significant.

The motor in the loco does run more quietly, though the slowest speed isn't massively better than the TCS chip (and its nowhere near the slow speed which CT and Zimo can achieve). I have tried various of the Lenz motor options (though there isn't any documentation to explain what they do, so changes are blind), and have gone back to the defaults as the best option.

The UPS module is the biggest improvement. I had expected this from my experience of similar units in Zimo equipped locos. Its now pretty much impossible to stall this locomotive.

The automation is taking a while to setup; the basics are fine - ABC plus Shuttle behaviour. Distance related stopping does what it is supposed to do, though it doesn't appear to be as well implemented as that on Zimo chips.

Getting the distance related stopping to stop smoothly seems to need tweaking of the decelleration (CV4) and possibly a custom speed curve, otherwise the loco decellerates quite rapidly (following CV4?) and then inches along to the stopping point. The Zimo method where the loco maintains its running speed until it needs to decellerate to the stopping point seems so much better (or optionally the Zimo can work out a braking curve depending on the approach speed). There may be a few CV's I haven't understood, but, in part, that must be the weak Lenz documentation compared to that from Zimo.

So, overall, for this locomotive, the Lenz Gold + UPS does the trick. Compared to other methods of building an automated shuttle train, the Gold/Silver features are quite cheap. The UPS is moderately pricey, but its the only way for a Gold. But, if not requiring the shuttle feature and only needing ABC braking, then I think a Zimo is a better chip than the Lenz; the low speed control is better, the distance braking control is much easier to understand and setup, the UPS capacitor is £1 or so, rather than £36. etc..

Latest 4mm Developments and ScaleFour North 2009

2009-04-14T01:38:00.000-07:00

At ScaleFour North in early April, I showed a few of my most recent developments.

To begin with, the "Coronation" has had its "up/down" coupler replaced with a rotating version. This has several new developments;
The rotation is in the opposite direction to previous designs. This works because the pivot point is below the deep buffer beam, so the coupling swings clear of the matching coupling on a wagon.
The pivot and flaps are from my test etch of parts; they have been modified further to fit the tight space, notably at the rear of the loco where brake rods interfere with the obvious positioning.
The coils are from Plantraco as discussed in earlier posts.

The chip in this loco is a CT DCX75, the coils are wired in series to the white function output. (The slow process of decyphering the behaviour of CT chips moves on; it seems that the white output is reliable for this operation, but the yellow still erratic. If the chip has firmware above v66, then both wires work correctly, though with different values for the CV's. The JMRI files are being updated again. ).

Secondly, I built a "demonstration frame" to show the etched bits and coil, these two photos might help illustrate where I am heading with etched components:

2mm 04 progress and more CT decoder issues

2009-03-24T04:32:00.000-07:00

Firstly the 2mm scale 04, mentioned before in the blog. This is a Farish model, which has 2mm scale wheels fitted to it (modified 2mm Scale Association castings and I have a lathe!). It finally has the coupler fitted to the front and it works nicely.

I did encounter a couple of problems along the way, one magnetic and one software.

The magnetic problem is quite simple - the Farish motor is in the bonnet, so near the front of the loco there is some magnetic field from the motor. This proved enough to just cause the magnet in the coupler to "stick" in the open position. The eventual solution was a larger counterweight on the shaft. Video below shows operation, and the counterweight. The filling of the big gap in the bufferbeam is not yet complete.

The software problems were a bit more fraught, its yet another undocumented feature/bug in CT decoders. Without getting too far into CV numbers, it revolves around CV152 and CV153 in decoders with version 56 (DCX74) or 59 (DCX75) firmware (might be other numbers below 59 as well). In theory those CV's specify the output wire to activate during an uncoupling sequence. A value of "2" works correctly for the white wire. The documentation (German language versions) say its a "bitwise" allocation, so in theory "4" would work for the yellow wire.

Yellow does not respond to a value of "4". However, a value of "1" does work for Yellow, but with a minor glitch.... If the loco is set for Yellow at one end, and White at the other, then the sequence to operate White will also cause Yellow to momentarily activate whiles the loco changes direction. Its not a massive issue, but it might cause some systems to disconnect unintentionally whilst operating the uncoupler at the other end of the loco.

In the end, I rewired the loco so that both coils are in series, rather than independent function outputs. With the rotating action, the "wrong" end will uncouple and re-couple, so there is no disadvantage from operating both together, and arguably a little bit of wiring simplification.

Further bench testing has shown that a version 66 decoder (DCX74) has yet another change to CV152/153, which looks like a bug fix. The values are now "White=1" and "Yellow=2" (logical!) and the behaviour is correct at both ends. For testing, I use a home made decoder tester, which is a collection of LEDs and resistors connected to a small screw terminal block. The decoder motor and function leads can be connected to these, the decoder red/black go via crocodial clips to the command station/programmer. In my case a Sprog which is driven from my computer using JMRI. Using JMRI its quick to flip between different CV settings and observe the results.

So, to the recommendation for anyone else trying this stuff; if using a CT decoder, check how CV152/153 works in advance for your firmware. If in doubt, use the White output wire.

I'd like to see reports from others using the CT decoder and CV152/153; what happens with your decoder, what is its version number. It will help with development of the JMRI decoder definition files.

Plantraco Coils in L&Y 0-4-0 loco

2009-03-03T13:47:00.000-08:00

The pictures in this post illustrate the use of the commercial Plantraco coils inside a scalefour L&Y electric loco (another High Level kit). I've used two slightly different arrangements, partly because of interior clearance issues, and partly to try out the options.

The first shows the coil mounted on a cylinder. This proved to be fairly troublesome to make, and I probably won't repeat the exercise.

The second shows a more normal "hinged flap" arrangement, similar to that on my 2mm scale Class 04. This was much simpler to build, and is the basis of a prototype etched component. The "nose" sticking out is a piece of lead which ensures the flap falls when the current is turned off, and the horizontal wire at the top limits rotation to 90 degrees.

The loco isn't finished yet; lots of details to add, and I want to make sprung buffers and other extras which require work on the lathe. So video in operation will be a while coming. But it does all work, the couplers are wired in series to a single function output of a Zimo MX620 chip. The chip is in a paper sleeve below the motor. Both couplers rotate 90 degrees, which is far more than I need to release an Alex Jackson. The Alex Jackson's will be fitted onto the outputs of the mechanisms with a bit of fine bore tube.

Zimo "stay alive" capacitors

2009-01-30T04:33:00.000-08:00

Zimo offer the option of adding "stay alive" capacitors to their chips, which will keep the chip alive when the loco is not connected to the track. This can be a bit of dirt or similar getting in the way. Its a cheaper DIY equivalent to the Lenz "UPS" add-on for Lenz Gold decoders. Lenz use "superCaps" which have massive capacitance and can keep a loco running for several seconds, but superCaps are expensive and need extra circuits to work on 12v.

I have a Simplex in 7mm scale, from an old Impetus kit. Its rigid underframe, 4 wheels, very short wheelbase. As its rigid, there is a fair chance only three wheels are on the track at any moment in time, so its a bit sensitive to tiny bits of dirt.

As there is lots of space inside, I have tried a 4700uF capacitor connected to the Zimo MX63, with the additional diode, resistors and choke recommended by Zimo. This seems to keep the wheels running for about 1/4 of a second before the chip decides there is insufficient power for the motor. The chip stays alive for about 12 seconds before the capacitor has discharged through a resistor. This is a massive improvement in practical running - if a loco has bad pickup for 1/4 second its not going to run at all. It will sail over turnouts where it previously would stutter or stall. Obviously 1/4 second doesn't allow silly stunts, such as running along a workbench, but practical considerations suggest that is an easy way to break a loco !

4700uF is a big lump for anything other than 7mm scale. In smaller stuff, I've tried 100uF and 220uF capacitors and it does help even if its only keeping things alive for tiny amounts of time.

Commercially wound coils for DCC controlled couplings

2009-01-10T09:33:00.000-08:00

The biggest drawback with the DCC controlled couplings I've been experimenting with is the need to wind coils. Its time consuming and difficult work (I need a close up TV camera and it takes over an hour of continuous concentration to wind a single coil at the lathe). So, the hunt has been on for ready to use coils.

( Fanfare....)

Plantraco Microflight of Canada sell a "Nano Actuator Kit", which is a 3.8mm dia coil and a couple of tiny magnets. Not only does this save winding ones own, but it comes with a few neat side-effect benefits. When I enquired, it was 10 coils minimum for shipping to the UK, but I recommend checking before ordering.

The coil is 75 ohm and designed for 4.2v. So, two in series is 150ohm and nominally 8.4v. Bench tests suggest they are fine with two in series driven from the 12v of a standard DCC function output for durations of up to 5 seconds (I think they'd be fine for longer, just not tried). Alternatively, they also seem fine on half-wave (using a track pickup for the positive supply rather than blue wire). Compared to my home-wound coils which all needed current limiting resistors, this is a big benefit; no longer need to find space to hide a resistor.

If really worried a 56ohm or 68ohm resistor in series with a pair of coils would bring the current back down to within the maker's specification.

Having an internal diameter of 3mm, they will slide fit over brass tube of 3mm dia (the tube needed a tiny amount taking off with abrasive paper), this makes mounting easy, and also the construction of a hinge pivot quite simple, see the diagram below.

The brass tube is cross-drilled to take the shaft (0.35mm dia), and then the "ears" carefully filed to shape. The shaft is inserted, and fixed to the screwhead (solder/glue to choice), and then the magnet glued to the back of the screwhead (if the screw is steel, the magnet self-sticks!). Finally, the coil is slid into position - ideally a bit further towards the pivot that the diagram shows.

In deciding the shape of the "screwhead" part, give thought to whatever counterweight is necessary to return the coupling to its rest position - a piece of 2mm square bar with a slit might be a better shape in some cases, in others the counterweight needs to be away from the shaft movement.

Coronation class with vertical movement DCC controlled AJ's

2008-12-31T07:05:00.000-08:00

The latest from the retrofitting workshop; a High Level Coronation class 0-4-0ST with vertical movement AJ's.

I fitted vertical movement rather than the rotary used in the Armstrong and the 2mm scale 04 because of various space constraints. Primarily, the relatively low footplate height, plus existing underframe components would have made a "through buffer beam" rotating coupling difficult to fit. In addition, I wanted to try out a vertical (normal) movement AJ.

The plan with the vertical movement had been to use the iron core of the coil to hold a permenant magnet in the "closed" position, and energising the coil would repell the magnet to the "open" position.

The main lessons :-

magnetic attraction back to rest is possible, but didn't quite work in this case due to lack of clearance around an existing brake shaft on the model. The iron core in the coil is too far from the magnets on the flap to pull the coupling back to rest, hence the need to add a counterweight (swings in space near gearbox).

the power required to pull an AJ down vertically is quite large, there is considerable drag as the tail of the coupling disengages due to the horizontal spring strength in the couplings. So, a more powerful mechanism is required than rotating. This required bigger magnets, and thus created the clearance problems in the first point above.

operationally the movement is better than rotation. The loco can be programmed to backup and uncouple, but does not need to have "move forward" in the programmed sequence. Therefore the movement is more prototypical, giving the crew time to disconnect the coupling before pulling away.

The DCC chip is a CT Elektronik DCX75, mounted in the bottom of the boiler underneath the motor. The coil is about 35ohms, and a further 33ohm series resistor is used to limit the current to the coil. The coil is wired to "half wave" (ie. to a track pickup rather than decoder blue), the DCX75 does not have a blue wire. Movement control is via various CV's which CT provide for couplings, the JMRI definitions file for this is available from me (and in time will be in a future JMRI release).

I am likely to rebuild this coupling in a few weeks with a further modification; a hollow electromagnet will allow the fixed magnet to move within the core of the coil, this should mean more power with a smaller fixed magnet. It will also make the magnetic "return to rest" more likely to work as the fixed magnet will be nearer the iron component.

Smaller (!) DCC controlled couplers

2008-12-06T10:41:00.000-08:00

I've had the 4mm scale loco with DCC controlled AJ couplings since the spring. But my aim has always been at "really small". 2mm scale "small". So, the last few months have seen various ideas tried, rejected, tried again.
The latest is for a 2mm scale Farish 04. Its a standard N item which has had the coupling pocket removed from the plastic keeper plate, plus 2mm finescale wheels (yes I know the spoke pattern is wrong for an 04!).

Picture shows coil on bench held on bit of bluetac. The coil wires are 45swg (0.07mm dia), or about the same as hair. The scale behind is a 1mm divisions.

The movie below shows it in operation. I will turn down the movement both forwards and backwards for real operations (various DCC CV settings) as they are currently a bit too large.

The chip driving the 04 is a CT DCX74. The DCX74 and DCX75 both support movement and coupling control from a single function press. It is intended for Krois uncouplers and I am exploiting the control here. The manuals from CT are fairly cryptic, but I think I have untangled most of the uncoupler issues. (The Zimo MX63 and MX620 are a bit larger, and also have functions for Krois couplers, though fractionally different in the way they operate. The Zimo documentation is a lot easier to follow). For those using JMRI (Decoder Pro), I have put my revised decoder file for the CT DCX chips in the JMRIUsers Yahoo group files area, when its had some more testing, I'll submit it for a future JMRI release.

I can see scope for a slightly larger version of this design (parts easier to handle!), with the frame and swing arm etched in nickel silver for 4mm use. I have a sketch design for the parts, and they should work with either a rotating AJ (like my earlier Armstrong Diesel) or the standard "pivoting" AJ with the pivot perpendicular to the coupling axis. I need to talk to someone who can put the etch bits on the side of a test-sheet, plus try out a few more electromagnet coil size options.

DCC Wagon Coupler finished

2008-10-05T09:08:00.000-07:00

Video of the finished wagon, right way up !

Goofy blows a decoder

2008-10-02T02:48:00.000-07:00

It had to happen, though its taken a while. But I blew up a DCC decoder yesterday.

I hard-wired the wagon with AJ couplings, and tested with a multimeter. All seemed fine. So I pushed some connectors onto the wheels and the decoder malfunctioned. Much prodding with multimeter and the DCC programmer followed, but the chip was dead.

Head scratching for several hours followed, until I realised a potential short circuit route; if the suspension of the wagon is compressed on one side only, a wheel rim can touch a W-iron. The W-iron base is used to solder the AJ wire. The AJ wire is pushed by the operating cam, and the operating cam is connected to the function output. BANG!!. The answer, by touching the wheel against the W-iron I could have put track current onto a function output wire.

Lessons learned:
a) Should have put the blue common onto the "dangerously exposed" bits of the mechanism, rather than the function output. Better still, should have wired it without a blue, but used half-wave back to the track (red/black) as in a NEM651 socketed decoder. (Check decoder supports this wiring before doing it!).
b) Should insulate EVERYTHING so it cannot short.
c) When fitting AJ couplings, should ensure that the coupling is not directly soldered to a metal W-iron, otherwise a short can go the length of a train. Same must apply to metal buffers attached to metal underframes.

Changes to the test wagon:
1) Lots of insulation added; the operating cam for the uncoupler is now rubber coated, the cam bracket has insulating tape between it and the W-iron. Insulating tape added where memory wire might short against W-iron it crosses. Plasticard added to prevent AJ wire shorting across.
2) Checking whether chip will support half-wave wiring (ie. don't use blue, instead connect to either red or black).

And finally, I will be sending the FL2 back for exchange under TCS' very generous Goof-Proof replacement scheme. (Replacement received in 48 Hours, fitted into wagon, all now working well done Bromsgrove Models for the prompt service)

(signed) Goofy.

Wagon uncoupler and TCS Decoder Documentation Shortcomings

2008-09-30T08:56:00.000-07:00

The under wagon uncoupler now works. Essentially a piece of "reversing" memory wire pulls a cam which in turn deflects the Alex Jackson wire downwards.

The memory wire comes from MERG, and is different to the more common one-way wire available from other UK sources. "Reversing" wire does not require a big spring to return it to normal length, it returns to length when the heat & current is removed. Thus, only the lightest of spring action is needed to keep the wire reasonably straight. In my case that spring is the Alex Jackson wire.

(click picture for enlargement)
A = cam which pivots in bracket glued to wagon floor.
B = actuating arm of cam, fitted with insulating sleeve (shrink wrap). This presses down on the Alex Jackson coupling, and opens the coupling on the right of wagon.
C = Crimp tag around memory wire. Memory wire is just visible leaving crimp heading towards (D)
D = bolt and washer into soldered nut. Memory wire is looped around this and pulled almost taught before bolt is pinched tight.
E = Phos-bronze wiper pickup onto wheel behind brake gear, all four wheels have similar pickups.
F = bus point for "red" side of wagon pickups. Matching bus on opposite side for "black".

The above photo was taken after blowing up the first DCC chip due to a short circuit, and thus has more insulation than the version in the video below. I also plan to change the wiring of the function output; I will move the output (purple) wire to the series resistor (56 ohm, 0.5W, behind bottom right wheel. 0.5W is under-spec, the circuit dumps 2W through it and it gets HOT, but for intermittant use it should be OK). I will try using a half-wave supply from one of the track buses rather than the blue full-wave supply, this might mean changing the series resistor value.

The video below shows the test wagon working on the bench. The chip is still remote from the wagon (hence no track and some crocodial clips showing). Also, sorry for the slightly shakey camera, my tripod was put away when decorating and I haven't dug it out again!

BUT, there is always a bug somewhere. And this case its TCS decoders. I have a FL2, bought because of the "momentary action" described in their instruction manuals (set a CV for momentary action, and another for the duration of up to 4 seconds). That CV does not work !! Further, digging deep through the manuals on the TCS website, I eventually found http://www.tcsdcc.com/pdf/CVguide.pdf which says that CV62 is no longer supported ! So, a feature described in their main decoder manuals isn't there any more. Email exchange with TCS confirmed that the function has been withdrawn on decoders and they haven't updated the online manuals. GRRRRR!!! I needed the time limit to prevent the current limiting resistor from burning out (its running way over current specification, but a larger one has a space problem in fitting below the wagon). Work around for me is probably to map the output onto Function Button 2, which is non-latching on my Digitrax throttles.

I will inspect Zimo and CT decoders to see whether I can get one at a not too high price which has a function output with a time control (both do have such features, but a £30 loco decoder seems a bit excessive for a 4-wheeled wagon with only one uncoupler !!). The alternative is DIY decoders, either the MERG version, or those developed by Paul Harman.

NCE command station wierdness

2008-09-28T00:19:00.000-07:00

I ran my Armstrong loco with DCC controlled uncouplers on an NCE PowerCab at Scaleforum. This is a different command station to the ones I have at home (Sprog, Bachmann EZ and Digitrax Zephyr).

Under the NCE, the behaviour was slightly odd; on most occaisions (but not quite all!) the loco would not stop at the end of the uncoupling sequence, but carried on driving along the track at constant low speed. The only way I found to stop it was the "Stop" key on the NCE, then turn off the uncoupler function. On getting home, I checked the loco on my Zephyr, and it behaved normally, so I conclude its something about the NCE and Zimo chip pairing.

I'd appreciate an explanation as to why this happened.

Also, having played with the NCE, I am correct in deciding that it's not the right controller for me, too big/heavy in the hand, too many buttons (well grouped compared to many, but its still far too many for driving a train), the number keys are badly arranged so I routinely hit "6" when aiming for "5" (have they never seen the square plan of calculators/keyboards!). I can see why its a popular command station and I will still leave it on my list of suggestions to others looking for a DCC starter system, but the standard recommendation of "try several different systems before buying" applies !

CT chip vagaries solved

2008-08-12T06:46:00.000-07:00

In an earlier posting I made mention of some problems with CV values in CT Elektronik DCX74 chips. I've now got much further towards a solution. The main lessons being:

check carefully which decoder files are used in DecoderPro, some of the CT files are for very old versions of the chips which have different CV layouts. Using those can make a newer chip go haywire.
the mapping of half-speed mode to a function key isn't well documented for the DCX74. It is in the DCX75 (German) manual, and there are DecoderPro files available on their JMRI users Yahoo group. With luck the files will find their way to a release version of JMRI/DecoderPro in due course.
the movement behaviour for uncoupling is different to that by Zimo. Loco movement seems to be triggered on "function off" rather than "function on". I haven't found a setting which will trigger the operation of a coil at the correct place in the operating sequence. Consequently, I think it will end up as a two function uncoupling sequence; the first to "open" the coupler, the second to move the locomotive. ( Update, December 2008 ; I have now deciphered the CT movement behaviour, and it does all the tricks ! See the 2mm scale 04 elsewhere in the blog. I have updated the JMRI/DecoderPro definitions file to make this considerably less cryptic. ).

Sensibly priced close up photography.

2008-08-12T04:14:00.000-07:00

Taking closeups does not require expensive kit, just a bit of thought.

These two pictures are of a 2mm scale wagon with 3 link chain couplers. To give an idea of scale, the wheels are 6mm diameter, the track gauge 9.42mm.

Camera is a Canon A710is, which is a typical Canon compact camera. The additional "magic" bits are:

Lighting box from Jessops; essentially a foldup white fabric box with a blue curved backcloth. Bright lamps are placed outside the box, and the fabric ensures a uniform light within the box.
Closeup lens. Canon accessory lens holder for A-series camera (about £17 from Canon). x4 screw-in closeup filter (about £4 from 7-day-shop). I also have a x2 filter lens. These allow the camera to focus closely whilst on maximum zoom and stood back over 30cm from the models. In turn, this means there is minimal barrel distortion caused by having the camera in "macro" mode a couple of cm from the subject.
Tripod to hold camera.
Camera setup: Manually set the whitebalance. Set film type to slowest available (typically 80 ISA). Set aperture to minimum, and let camera choose speed. Focus manually (at least check where any auto focus is locking!). Use timer-release option on camera to avoid any shake. If not sure about exposure, its worth trying with +/- a small amount of "EV" compensation.

Auto coupler now complete

2008-06-18T03:54:00.000-07:00

I received my upgraded (version 7) MX620's today, and fitted one back into the Armstrong shunter. It works !

Press the function key allocated to "uncouple" and the loco backs up enough to take up the slack, the coupler activates, and loco drives forward to clear train before coupler releases. Total movement is perhaps 1.5 sleepers, all at a slow crawl.

See earlier posting for pictures underneath and description of mechanical components.

There is scope for fiddling with the uncoupling movement time, speed, and the general speed table and acceleration parameters. These all influence the exact speed and distance moved. But priorities are 2mm models for the annual Expo at the end of June.

The video below shows the loco come to a stop under normal throttle control, then the function key is pressed which causes the loco to back-up, uncouple, and pull clear. This is an improved video, with better lighting and some closeups

(Next back to why the 2mm scale CT DCX 74's sometimes loose half-speed mode, and why one of them is reading back wierd values in its primary CV table. The alternative CV option is proving the way out, but this bug is wierd...).

Zimo mx620 upgraded

2008-05-15T11:20:00.001-07:00

Earlier in the blog I mentioned that the Zimo MX620 has a small bug in CV116; the shuffle back and pull away after uncoupling feature. This week Zimo emailed me to say there is a new release of software to Version 7, and this fixes the bug.

You need a MXDECUP programming box to upgrade the Zimo decoder chips; either purchase or find a dealer who has the box and can do the upgrade for you.

I'll report back when my chip has been upgraded.

Pictures of DCC AJ Coupling

2008-04-08T11:37:00.000-07:00

In an earlier blog entry, I described the DCC Alex Jackson Coupling which I have been developing.

I've now taken some pictures of the first version, and present them here with some annotations. Clicking the pictures should cause them to appear much larger.

The first photograph is labelled to show the main elements.

(A) is the Alex Jackson coupling, formed from 0.010 guitar string.
(B) is a nickel silver u-shaped bracket which forms the support for the pivoting wire (A).
(C) is a steel counterweight. 2mm diameter, with a 12BA thread at one end. The thread is cross-drilled 0.3mm below the brass nut. When installed, the nut is wound down to clamp the counterweight onto the AJ wire (A). I have a better design for the counterweight which will be much easier to install than this first version.
(D) is the electromagnet coil, squeezed in behind a gearwheel which drives the locomotive jackshaft.

Because the locomotive is upside-down, the counterweight (C) falls to one side under gravity. When the right way up, it hangs vertically downwards.

This second photograph shows the same elements from the other side. The wires from the coil can be seen running over the jackshaft axle before heading inside the locomotive. There is a small piece of PCB mounted below the motor where the coupling wires are connected to the DCC chip wires.

The third picture has a propelling pencil holding the counter-weight approximately vertically. This shows the (approximate) rest position of the system if the loco was the correct way up.

The final picture shows the counterweight pulled over by the electromagnet. The counterweight strikes the side of the coil, not the iron core; this avoids it "sticking" when the electromagnet is turned off. An alternative to avoid "stick" is to cover one of the moving parts with something non-magnetic, such as a tiny piece of brass, thin paper, or even blob of glue.

There is massive scope to improve the engineering; the pivot would benefit from an etched design, the counterweight can be made much easier to install, and the coil pole pieces could be designed to deliver a more effective magnetic field. Even the use of Blu-Tac to fix the coil in place should be avoided in later version !

The locomotive is a High Level kit of a small Armstrong 0-4-0 diesel shunter (original at Shildon museum). Prior to fitting the couplings, it was assembled according to the instructions, with P4 wheels, simple beam compensation on one axle. The next loco to have a similar coupling fitted will be built up with the coupling in mind; its a lot easier to design space for parts before assembly !

Photographs taken with a Canon Powershot A710, with addition of a x4 and x2 close-up lenses fitted to a Canon accessory lense holder. The camera is on tripod, and taken with timer release. Its a pretty cheap setup for closeup work.

Ski Pictures from Norway 2008

2008-04-08T01:13:00.001-07:00

Photographs from Geilo, Norway, Feb/March 2008.

Nigel's Photos

Sarah's Photos

There were also photos from Chris and Janet, though they require site registrations/invitations, so consult your personal email if you were on the trip.

4mm Scale Digital Alex Jackson (AJ) coupling

2008-04-07T05:55:00.000-07:00

As a break from 2mm scale modelling, I make some items to Scalefour standards. A while back, I started looking at DCC control of model trains and started to think of the control options a chip inside a model might offer.

One such is digitally controlled couplers; a function button on the controller can activate the uncoupler. This is not particularly new; European makers have offered such uncouplers for years on HO trainset models. The only real challenge is to make the system work with the uncouplers in common use in UK finescale model making.

My initial idea came from seeing the latest version of the 2mm scale Electra coupler. This is a small rotary acting coupling whose origins dates back to the 1970's. Its somewhat simpler to make than a 2mm scale Alex Jackson (AJ). There is a similarity in the coupling action of the AJ and Electra, and, as I have 8 times the volume inside a 4mm scale model, I decided to experimented digitally controlled uncouplers in 4mm scale as a route to 2mm scale operation.

The main shank of the coupler is a standard AJ. It rotates in two small holes arranged behind the buffer beam. A steel bar weight is fitted to the coupler shank, and ensures the correct coupler rest position. A home made electromagnet coil can attract the steel weight away from vertical, rotating the coupling head to the "uncouple" position.

The electromagnet is made from 45SWG enamelled wire (from the Scientific Wire Company), wound onto a ~1mm iron core. The core is a piece of garden wire with the green plastic coating removed. I have found that approximately 12m of wire works well (around 50 ohm resistance), though the exact amount will depend on the available space. There are various aspects of coil and magnetic field design which need experimentation in the future, such as turning one end of the core round to be near the opposite pole, or fitting a metal disc to one end of the coil.

Winding was done on my lathe in lowest back-gear, using a close-up TV camera to watch the wire was laying down tight against preceeding turns. Temporary end-cheeks from PTFE rod controls the length of the wound core. Care in winding makes a huge difference to final coil diameter - sloppy windings have lots of air spaces which make the coil bigger. My early coils were secured with occaisional dabs of super-glue, though I'll change to shellac for future ones. The PTFE end-cheeks are carefully pulled away once the coil is complete.

DCC control uses a function output from the chip. Both Zimo and CT Elektronik chips have support for uncouplers within their firmware, with CV values to set the time for the full power applied to the electromagnet (to initiate the pull) and then a lower power to hold the coupler open. Zimo have a function which can, optionally, back the loco up a few scale inches, uncouple, then drive away about a scale foot (though not yet working on the MX620, the manual is wrong on CV116, Zimo promise a fix during spring/summer 2008). I would expect that almost any maker's chip would work using their normal function outputs (lights, fans, etc).

Due to the rotary action, if the loco is not driven away and the coupler closed (magnet off), the train remains coupled. One function key can operate both uncouplers simultaneously. This simplifies the selection of function key on the DCC control panel. Selection of which function key is down to chip programming and individual choice; one or two handset makers suggest F3, but other makers use F3 for "half speed" mode. At the moment I am using F1.

With two coils (two couplings) in series on a single function wire, I measure about 90mA at full power from a Zimo chip, well within the 300mA limit for function output of the smallest Zimo (MX620). Its also just within the limit for the tiny CT DCX74/75 (100mA), though I've not yet tried these chips with the uncoupler; I would be tempted to slightly increase the resistance (small resistor in series) in the circuit with a CT to drop the current a little.

The more current through a given coil, the stronger the magnetic field. On a bench test, I found my coils were getting rather warm with 20 seconds at 150mA, but could not detect any heating at 100mA.

There is a video of its operation on the Google Video site and now duplicated on YouTube

The loco fitted with the digitally controlled AJ will work alongside conventional under-baseboard magnets. The loco acts as any other loco with a fixed coupling, and the wagon uncouples in the conventional manner.

It would be possible to put the uncoupler under rolling stock, though the cost of fitting a function decoder (a DCC chip which can respond to function commands but lacks motor control) under every wagon could get quite high, and having to address a wagon before uncoupling would be tedious on most DCC systems. I can conceive of ways of making it very easy to operate with minic diagrams, though the computer complexity and price of assembling such a system would be very high. There is a half-way house where some key items of stock could have an uncoupler fitted; brake vans, vehicles in trains which are regularly split, etc.

Having retro-fitted the coupler to an existing locomotive, I think it would be a lot easier to design the coupler components when building rather than afterwards. My next loco will be done that way round; design the coupling components before building. It should result in better shape of magnetic field and a smaller air gap for the moving part to move across, that means less current (or smaller coil) to operate. I'm still thinking about the 2mm scale version !

Comments welcome, pictures and drawings will follow when I have some time to add them.