improvements, design changes, failures, successes and experiments

It has been some time since my last post. During that time there have been various improvements, design changes, failures, successes and experiments on the electrics underneath the layout. I have still not quite finished, but I do have a working system again.

The original plan was to use Merg Servo4 kits to drive micro servos controlling points and permanent magnet uncouplers. A temporary switch box connected to the 25-way connector on the layout operated the individual points and uncouplers. This was going to be replaced by a different box with Merg CBus kits allowing push buttons to create events which would be used to switch one or more points to set a route. However, I found that the CBus modules would not drive the Servo4 inputs directly, and problems with sharing a single AC power supply burnt out a couple of CANbus circuits.

Meanwhile, developments and new ideas were happening within Merg. I decided to replace the three Servo4 kits with two CANservo2 modules (modified CANACC8 kits). This would mean the connection to a control panel would only need 4 wires (CAN Bus and power supply). A 12V DC power supply bus was also decided upon at this point, rather than the previously recommended 5V power supply.

Another initial design decision was to wire up the layout so that it could be easily switched between analogue DC train control to DCC by swapping a 35 way connector. Either a DCC or conventional controller could be plugged in. However, the new Merg DCC command station kit was small enough and cheap enough to build it into the layout. It also produces a regulated 12V DC supply that can be used by other CBus modules, and uses the CBus connection for attaching the matching Merg hand-held controllers. The capability to switch to analogue control was retained.

At this stage, another problem came to light. The power-on surge caused by the servos was lowering the power supply voltage too much for the control circuits to recover. I decided to add a second power supply bus at 9V DC just to supply the servos, separate from the CBus power supply bus. This has mostly resolved the problem, but there is still a small problem with servos twitching and moving on powering up the layout. This problem is still being investigated.

Still to do is replace the 12V and 9V power supply sockets, as the simple sockets fitted allow the plugs to drop out too easily. I have some latching XLR connectors to replace these. I have also not yet built a control panel. I can use the hand-held controller to create CBus events to select routes, operate individual points or uncouplers, and I can also connect a laptop to the layout, via a USB to CBus interface, and operate the layout using JMRI, so the control panel can wait. I also have to build signals, and fit some more servos to control them.

The first photo shows the underside of the layout with the protective hinged covers closed. The aluminium panel has the DCC command station attached behind it so that the power transistors can be bolted to it to act as a heatsink, if required. At each end of the layout are pairs of CBus 4-way RJ22 sockets for connecting hand-held controllers, PC interface and/or control panel.



The next photo shows one end of the layout with the hinged cover open. The CBus connectors and a CANservo2 module are attached to the lid while the now redundant Servo4 modules are attached under the baseboard along with the servos. The redundant 25-way connector is also visible. Just by the hinge can be seen two servo 'distribution' boards, each with its own 5V power regulator and plugs for up to four servos to connect to.



The other end of the layout shows the second CANservo2 module and the CANcmd DCC command unit attached to the cover, with another pair of CBus connectors. The DCC/Analogue switchover socket can also be seen.

A Case for DCC

In my last blog entry, I showed my recently completed Merg CAN-CMD CBus controlled DCC Command Station. The Merg kit includes the PCB and all the components to populate the PCB. For future layouts I will probably just mount the PCB directly to a baseboard and hard wire it in. However, this first one I wanted to keep as a portable and flexible unit.This meant fitting it into a case with suitable sockets, switches and Led indicators.


I found a suitable case on Ebay made from black plastic with aluminium end plates and adequate size to take the PCBs and wiring inside.Drilling, cutting and filing all the holes in the aluminium end plates took three evenings to complete. The aluminium plates were then cleaned, sprayed black and lettered with Letraset rub-down lettering, and finished with some clear spray laquer.



Inside the case is the CAN-CMD main circuit board and the CAN-TERM connector kit PCB with two RJ22 sockets. These can be used to plug in a CAN-USB computer interface, or the forthcoming CAN-CAB handheld controller, or to connect to a layout CBus as required.



The one panel has all the CBus related switches and connectors, and the two indicator LEDs. The green LED only lights up if the microcontroller program is running correctly. The Yellow LED lights up when in 'Mini-Booster' mode or flashes when programming locomotives or accessories decoders. The two RJ22 connectors previously mentioned are on this panel, along with two switches. One switches in a bus terminator resistor, required if this unit is at one end of a long Cbus, or used with just a CAN-CAB or CAN-USB. If this unit is connected to a layout CBus that already has terminators fitted then the inbuilt terminator can be switched out. The second switch allows this unit to supply 12V DC to power other CBus items, like the CAN-USB or CAN-CAB. Again, if connected to a layout Cbus that has a separate 12V DC supply, this can be switched out.



The other panel has a socket to connect the power supply, either 12V AC or 15V DC at up to 1 Amp.The screw terminals allow connection to either a programming track or a small layout if using 'Mini-Booster' mode. The mode of this output is controlled by the switch above. The 4-pin mini-Din socket will allow external DCC Boosters (another forthcoming Merg kit) to be attached if more than 1 Amp is required for a layout. The remaining switch controls 12V DC output the the external boosters if required.

A Bus for Freshwater

Not that sort of of bus - a layout control bus. DCC is really good for controlling trains, but is less suited for controlling points and signals and the like. A separate bus for operating accessories means that a short circuit on the track does not cause points and signals to change at random. The separate bus can also use systems that are more suited to train detection and route selection.

I initially joined Merg (Model Electronic Railway Group) in order to access their servo controller kits, for controlling points and signals. Having joined, I found out about their development of a layout control system based on the CBUS two-wire command bus. The CBUS protocol has been used in all new cars for a number of years, to reduce the complexity of the wiring loom, and increase the functionality. It is a fairly simple protocol, compared with TCP/IP as used by the Internet. The bus is used to join up various devices all over the car. It allows 'producer' devices (switches, or sensors for instance) to broadcast simple numbered 'event' messages over the bus. All the 'consumer' devices attached to the bus will see these 'event' messages, but certain devices will be setup to perform specific functions when specific events are seen. Thus a switch can broadcast an event which the windscreen wiper controller will act on to start the windscreen wiper motor. A rain sensor can be set up to broadcast the same event. It might also broadcast another event which would result in the headlight controller lighting the headlights. The CBUS is equally useful for controlling a layout. Control panel switches and train detectors can become 'producer' devices, and point motors, signal motors and mimic display panels can become 'consumers'. Because of the widespread use of CBUS in the automotive industry, the basic components required are readily available and low cost.

Last year, I purchased a couple of Merg kits, an eight input 'producer', and an eight output 'consumer'. I also picked up the experimenters kit, a small board with eight switches on that plugs onto the 'producer' kit, and a board with eight LEDs on that plugs into the 'consumer' kit. The Merg kits are designed to allow them to be 'programmed' using small switches that are part of the kits. The 'producer' can be told what events to broadcast for each switch operation, and the 'consumer' kit can be taught which events to listen for, and which LEDs to light or extinguish when the event is seen. The Merg kits were designed to use a 5VDC supply distributed from a power supply regulator on one of the kits, which required a 12-16V supply. I experimented with these modules, but did not get round to using them on Freshwater as deadlines approached, and a temporary 'traditional' control panel was built. I do intend to use CBUS eventually as it will allow simple route selection and some interlocking to be implemented.



The photo shows a 'producer' board on the left, with eight yellow switches on the experimenter board plugged on the end. On the right is a 'consumer' board, with eight red LEDs on the experimenter board plugged on its end. They are connected by the 2-wire bus (blue and white wires). The orange and black wires are the power supply lines. In the centre is a C-BUS connector board, and a power supply can plug into the lead coming down from the centre. I have modified these boards to run from a 12VDC supply instead of the 5VDC supply that the kits were originally designed for.

Over the last 12 months, more kits have become available, along with interfaces to a computer to simplify the programming of the modules. The computer interface also allows computer control of a layout, using suitable software like the freely available JMRI. The latest development from Merg is a DCC command unit and a hand-held controller. The CBUS is used for communication between the controller and the command unit. JMRI can also be used as a throttle connecting to the command unit via the CBUS.

So, to prepare for the DCC system, and use of the CBUS on Freshwater, I purchased the Merg kit for a CBUS to USB interface. This was initially built as per the instructions. It is designed to take a 5VDC supply. I therefore created a simple 5VDC regulator circuit on a small piece of veroboard, and mounted everything in a small black plastic case. A 4 way cable with an RJ22 type connector at the end that can plug into a Merg CBUS connector kit, comes from the box, connecting the two bus wires and the 12VDC supply into the box. A standard USB connector protrudes from the other end of the case.



Having a working USB interface, I set to building the DCC command station kit from Merg. This has been built as per its instructions. It is already designed to take an external 16VAC power supply, and can supply 12VDC to other devices on the bus.



The photo shows the USB interface box on the left, which connects to the USB port on a PC. It also plugs into the CBUS connector board and the bus then connects to the DCC command station board on the right, the red and black wires next to the bus wires have a socket for connecting the power supply. The red and black wires to the far right attach to the test track at the top of the photo. The white round object at the bottom right is a buzzer used as a short circuit warning. This setup now works, using a JMRI software throttle on the PC. I have also played with a Wi-throttle 'app' on an iPhone using a WiFi connection to the JMRI server on the PC.

Merg will very soon have a kit available for a hand held DCC controller that will plug directly into the CBUS connector board, and do away with the need for the USB interface and PC. Watch this space.

Bridging the Gap

Now I have taken on a new deadline for Freshwater, the 2mm Expo at Keighley, I am now motivated to get on with the scenics. First off, a bit of terra-forming. As I had some sheets of foam-board available, I thought I would use some to build up the contours. Most of the station area is flat, so it is only the river banks and the start of a small hillock behind the station that needed building up. When I have smoothed out the slopes, I intend to cover it with PVA soaked kitchen towel. I hope to avoid having to use much filler, as the board does twist and move a bit, and filler will probably crack and break up.

Only a small number of buildings are needed for the layout, so I want to avoid using kits (except for the ratio concrete platelayer's hut probably), and scratch build as much as I can. Starting with the basic civil engineering, I need a bridge over the tidal River Yar. I have not found any photos of the real bridge, so I need to freelance it. I would have liked to build a dainty little bridge with hand rails, but rail cleaning at exhibitions would probably destroy them. Therefore, I decided on a large girder type bridge, giving plenty of clearance for the tide to come in.

The main girder and end pillars were cut from a single piece of plasticard, then further layers of plasticard were added to build up the pier thickness. By using a single piece, the piers and girder will always be at right-angles to each other, and will not move when the bridge is fitted in place. Strips of thin plasticard have been added to complete the girder. In the photo, only the nearest girder is complete.



When the girders are complete and painted, they will be glued in place, and the abutments below the bridge will be completed in place. Brick paper will then be applied to finish off the abutments and piers. Hopefully, all will be complete next week. Then I can start on the platform. The original platform was brick edged, then it was extended using concrete panels, and then another extension was added with concrete pillars. Should be fun.

Ballast (A Disaster)

It must be the season for ballast laying. With all the track laid, wired up and painted, and a successful two days operation at the GJ Expo in Oxford we just needed an opportunity to have the layout set up for a few days to allow the ballast to be laid and for the glue to dry.



We followed the method used on previous layouts, applying the ballast dry, painstakingly moving around and removing it from sleepers and flangeways, then spraying water with a couple of drops of washing up liquid through an atomiser to make everything wet, then dripping watered down glue on it. There must be a less tedious way of doing it, but this works.



Previously I have used fine granite dust from the Mendips and PVA glue. This sets like concrete. This time I used Woodland Scenics finest grey ballast and Copydex. This combination should produce a more flexible result, better suited to my thin baseboard surface, and may reduce running noise (although I am not too bothered about that). I found the Tamiya disposable paint brushes very good for final removal of individual stray peices of ballast from the sleepers.



The photos show the job in progress. In the photo below you can see the white watered down glue just after application. It dries clear and matt. I expect it will take a few weeks to clean up the track and remove all obstructions from the flangeways, and a lot of glue disappeared down the holes into the point mechanisms below which will need some sorting out. It may be some time before proper operation is resumed.



(Footnote)
Well, 24 hours later, it all looked good, but as I tried to remove a stray piece of ballast from the inside of a rail, it pulled a long string of elastic glue with pieces of ballast in from between the sleepers. A light brushing with a toothbrush lifted lots of nasty elastic clumps of ballast. There was no way it would survive exhibition use. So, the bad areas were patched with fresh ballast, and the whole layout doused in watered down PVA. I am hoping the PVA will solidify everything rather than just form a crust on the surface, but I will find out tonight. If it fails, all the ballast will have to be removed, and we will have to start again. Oh dear :-(

Ian.

Another Servo problem solved

Not much progress on Freshwater for a few weeks because another problem arose with the servos used for points and uncoupling magnets. As I was adding more and more servos to the layout, I started getting problems switching on the power. On switch-on, the servos would move rapidly, hitting the physical limits of the mechanisms they are attached to, and carry on trying to drive past them. The current drawn by all the servos was collapsing the voltage from 16V AC down to about 3 volts. All this was happening before the PIC microcontrollers had time to initialise and bring the servos under control, and the voltage then dropped below the PIC operating voltage, so they stopped doing anything.

Consulting the Merg forums, I was advised to add some pull-up resistors to the servo signal lines. Apparently this stops the switch-on spike which sends the servos trying to reach their end limits long enough for the PIC microcontrollers to initialise and start sending sensible control signals to the servos. The pull-up resistors are 10k ohm, large enough not to affect normal operation. A change to the PIC software to speed up the initialisation process was also suggested, but has not been necessary. Having added the resistors, everything seems to be operating correctly again.

So, now I just have to build one more servo operated uncoupling magnet set and the electrics under the layout are done. Then I can start ballasting the track. Other jobs in the queue are:

- building a lighting gantry
- adding backscenes, and a transportation case
- replacing the temporary control switch box with a proper control panel (using CBUS kits to allow route setting)
- building a larger fiddle yard now the GJ challenge constraints are out of the way
- creating buildings and scenery

Ian Morgan
Hampshire

Magnetic uncouplers for Freshwater

Following the Expo, I can now get on with adding the uncoupling magnets. I had always intended using permanent magnets, following their successful use on Brunswick. I bought some small magnets from Merg, but they were nowhere near powerful enough to operate the DG couplers. Now I have purchased 50 'rare earth' magnets via Ebay. These are really powerful for their size (about 5mm diameter and 3mm long) and come with all sorts of warnings. 'Rare earth' magnets have a high iron content and would corrode very quickly if not protected by a special coating. Often this is nickel plating. It is therefore not practical to cut them, and you have to protect the plating from damage.

I planned to use some more servos, as used to operate the points, to move the magnets into position under the track, or away from the tracks when uncoupling was not required. The layout has several parallel tracks at various positions where I wanted uncoupling to take place, so I planned to have a number of magnets alligned to the parallel tracks, all operated by a single servo. I cut a length of paxolin sheet, and drilled it to take the magnets, which are glued in with epoxy. Working with the magnets is interesting, as they fly around the workbench attaching themselves to tools each time you get anywhere near them. Trying to get three magnets into their holes in the paxolin to glue them without them flying to each other was also quite fun.

I made a paxolin 'arm' which bolts to one of the servo attachments, and the bar with the magnets attaches to the arm, using bolts and a paxolin block with threaded holes in it. Because of al the tracks above where the servo needed to be, I cut a sheet of hardboard to attach the servo to, which bolted under the layout away from the tracks. The photos show how it works, I hope. One shows the magnets moved well away from the tracks, and the other two show the magnets in position hard against the underside of the layout surface, below the three parallel tracks there. You can also see the Merg Servo4 board that the servo plugs into. Now I just need to build two more.