Following on from my last post here are a couple of ‘posed’ photos with their prototype inspirations. Enjoy…….
Having finished the main station building my thoughts have now turned to the main goods shed. As with the station a reduction in space has of necessity meant a proportional reduction in the size of the goods shed while at the same time trying to preserve the feeling of the original. Tavistock had quite a sizeable goods shed with two tracks running through it. It was of a timber construction with a brick built office at one end and a wooden lean to office at the other end.
I used a plan of Chipping Campden shed from Ian Allan’s book on Great Western Branch Stations to get general dimensions and pictures of the original Tavistock structure to get a suitable representation. The model is constructed from card. Unfortunately the card I used for the main roof is a bit thin which resulted in some bowing which I managed to reduce to a degree by using internal bracing. Hopefully it doesn’t show too much.
The shed has now been installed and the water tower and Down starting signal as well. The water tower is a cut down version of a typical GWR conical tower. This was originally a 3mm Society kit and is recycled from an old layout of many years ago!
The final part of this end of the station will be a covered footbridge which sits between the station and the goods shed and connects the two platforms. This is the next project…..
The original Tavistock GWR station had an overall roof. My interpretation of the station for necessity of space involves a shortened building. There are no plans of the original station but looking at pictures in a very good article published in the Great Western Journal I could see comparisons with the buildings of Henley-on-Thames. They are in brick whereas Tavistock is in stone but the window and door sizes appear quite comparable. There are very good drawings of Henley in Paul Karau’s book on the subject.
The building Is constructed from card to which I stuck a brown manilla envelope turned inside out onto which I scribed the stone courses. This is a method I learnt from the late Peter Gentle-a superb building modeller. The brown paper gives a very good texture and takes watercolour very well. The stones are painted on using various shades of grey and brown
The outer wall of the train shed is constructed from a sandwich of Wills sheets and planked plasticard with the windows made up from thin card and set into openings cut in the sheets.
The overall roof is made from mounting board with plastruct girders and trusses soldered up from 0.7mm brass rod on a marked out jig. The outer surface is covered with corrugated plasticard. The whole roof is detachable to allow access to the inside of the shed.
I think it portrays an atmosphere of the original building.
In lockdown again but there still seems to be multiple jobs to keep me away from the modelling room!
However, there has been some progress. The track has all been ballasted and painted, the platform basics are in place and I have started on the station building and overall roof.
Initially the track and cork base was airbrushed with a mixture of grey and earth colour. I use the Vallejo paints which are already thinned for spraying.
The ballast is then added dry and gently brushed into place. I use Attwood Aggregates ex fine ballast which is produced local to me.
The ballast was then fixed in place using a PVA based laminate floor polish. I originally found out about this method from a thread on the Scalefour forum. The original polish was Johnson Klear but this is no longer available. However I found an equivalent from B&Q made by Stickatack.
Using a pipette the polish is dribbled along the edge of the ballast and immediately is ‘sucked’ across without disturbing the ballast. It dries far quicker than the messy method of using diluted PVA and is much easier to remove if necessary.
For the areas between the tracks I used very fine, almost dust, granite chippings mixed with grey weathering powder applied to ordinary PVA brushed on. Finally the whole lot was airbrushed again with a rust coloured paint and some black over the areas in the platform where locos would stand.
Three signals and two points on Tinworthy are driven by servos. When first installed two signals and a point had digital servos and the third signal and one point had analogue servos. All the servos are driven by Heathcote servo driver boards via relays switched by the MERG CBUS system.
I found that the two analogue servos ‘twitched’ when a loco was driven past but not the digital ones. According to the Heathcote web site, they recommend digital servos as they do not twitch at startup.
I am not an electrical expert but I understand that the amount the servo moves is determined by the control pulse coming from the control board which has controls to determine the start and end points of travel of the servo. However there appears to be a degree of overthrow before the servo cuts out and the position is then maintained by the gearing in the motor. This is fine when working a signal but with a point the end point needs to be set so that the point blade is hard up against the stock rail (which is why in the prototype there is a facing point lock) and therefore the digital servo is continually trying to reach the cut off position and the result is ‘chattering’ of the servo. This doesn’t happen with analogue ones. If the throw of the servo is adjusted so the point blade only just reaches the stock rail then the chatter is eliminated but there is the risk of trains derailing because the blade is not ‘locked’ in place.
So do I twitch or do I chatter!
Recent postings on the forum of MERG suggested that by using omega loops or ‘Z’ loops the chattering of a digital servo can be eliminated and the loop keeps up the pressure of the point blade on the stock rail. I have tried this and it has solved the problem.
So now I don’t twitch or chatter!!
Yes, a change of name. Comments by my wife has led to a name change as she didn’t think Tavistowe was appropriate and suggested an alternative!!
Tin because Tavistock is a Stannary town and ‘Worthy’ because it is a typical Devon place name. So the layout will now be known as Tinworthy.
I have now finished laying all the track and wiring it all up. I can now have UP and Down trains.
I have temporarily laid in the platform bases and marked out where the goods shed will sit incorporating a point servo.
The first train is an auto train which consists of an auto coach of 1927 and a 64xx Pannier tank. Both recently constructed from etched brass kits.
Next jobs are to paint the track, add cosmetic chairs to the point work and add ballast……..
Track laying has continued and I have now completed two boards. I have also wired up those two boards complete with all the associated point motors.
I have programmed the main CBUS module in the control panel and the modules on the two boards which control the point operation and all the section switches and which controller of two controls that section. This wasn’t without its problems as two of the modules had the wrong version of firmware in their PIC controllers and stubbornly refused to be recognised by the computer used for programming! After many trials and tribulations where I was literally pulling my hair out [useful as I can’t get a haircut at present!!] I managed to upgrade them and now have a fully working system. All with only a 4 way cable connecting the control panel to the layout. You can see a 64xx pannier and a diesel railcar which have been run all over the existing tracks.
I intend to hide the point motors at the front of the layout with a removable scenic board and the ones at the back with suitable buildings. I have mocked these up in paper and they include warehouses, a stable block and a garage for the local bus.
Also shown here is mock up to show where the platforms and station building will be sited.
One more board and the fiddle yards to go.
In lockdown and in between all the jobs in the house and garden, work is progressing on laying the track work on Tavistowe. It’s amazing how much mess accumulates on the boards while working;
The main line at the Plymouth end is complete up to the single slip which allows access to the goods yard. This end has been wired up and all the point motors added. I have decided to mount the motors on top of the board to allow ease of adjustment if needed. This area will be covered by the local cattle market on a removable piece of scenery. The main track is the 3mm Society 14.2 plastic sleepered track with code 60 bullhead rail. The points are all handmade with a mixture of copper clad strip and 1/32” plywood strip. Cosmetic chairs will be added later using the ones produced by the 3mm Society. All the trackwork is glued to the cork base with a PVA based Tacky glue.
The motors are Hoffmann point motors which work on 15vAC and have built in switches for the frog polarity. The relay to the side of the motor is the interface between the point and the MERG CBUS modules. The relay switches the point motor and in turn is turned on or off by outputs from the CBUS. The actual CBUS module [a CANACC8 for those interested] is mounted under neath the board. One of the points seen here is servo operated as there wasn’t room for another Hoffmann.
I fear that the wiring underneath is a bit of a ‘spaghetti junction ‘. Luckily the baseboards include holes to carry wiring around the layout. I am basically trying to keep the CBUS data wiring to the front of the board and the track power and AC feeds to the rear in order to reduce any interference between the two. Here you can see the twin servo board on the left which drives the point and the intermediate starter signal when it is installed. The relays on the right switch the servos on and off in response to an output from the CBUS. In the middle is the connection of the CBUS and its associated 12vDC power
That’s enough for the moment. The grass needs cutting………
In between all the jobs around the house and garden that are being found for me I have been able to make a start on Tavistowe at this horrible time of forced isolation at home.
I have laid the cork underlay on the boards and glued point templates in position. I first printed them out on tracing paper and then stuck them in place using a copy of the whole layout printed from the Templot plan as a guide. I intend to construct the points off site ,so to speak ,on templates printed on thin card and then install them in the relevant position on the layout.
Even though I haven’t laid any track yet I have built the control panel!
I have repurposed the locking lever frame I had on Eggesford to suit Tavistowe much as most heritage railways have done. I also worked out all the sections, point motors and signals I would need. I then wired up the panel to the MERG CBUS module which will control the output from the panel. This interface is done through a diode matrix as can be seen in the picture below.
This all means that there is only a 4 way cable carrying the CBUS signals on two wires(blue and yellow) and a 12vDC power supply on the red and grey. This compares with 2 x 25way cables that would be needed if wired in the conventional way. Once the trackwork is done and all the point motors, signal servos, and section feeds have been installed then I will program the module to get it all working. Well that’s s the theory!!!
To be continued………
As I said in a previous post, I have decided to use the MERG[Model Electronic Railway Group] CBUS system to operate the new layout.
I purchased 2 kits to make a test board. One to accept the input from switches and the other to control relays which I intended to use to drive a point motor and a Heathcote servo board. The other intention was to program it by the ‘Slim’ method which doesn’t need a computer input. Constructing the kits was fairly straightforward and the initial testing told me they were working. I followed all the instructions to teach the relay driver to respond to the switch but alas this was where I came unstuck. The relay switched on when I closed the switch and only switched off when I closed it again…….
After lots of reading around the Merg website and the forum I discovered that there was a problem programming the relay driver using the onboard switches. I therefore decided I would have to go down the computer route to set up the modules. I purchased a USB4 kit to provide a connection to the USB port on my Laptop and also a GIZMO kit to monitor the whole system.
Now a load more reading about the program to be downloaded to set up the system- 3-4 large documents on the website-and then yet another learning curve to get to know how the program works. Eventually with a lot of trial and error the last ‘light bulb moment’ occurred and I had a working test board! I can now work a Hoffmann point motor, control a servo for operating signals and switch LED’s on and off. Whow!
Now that I have worked out how to do it, it will be relatively easy to scale it up to the rest of the new layout but there is still more learning to do…… it will have to wait until the terrible Covid 19 epidemic is over as the Merg kit shop is presently closed.
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