TVT - Mihirung, the Demon Duck
Posted: Sun Nov 01, 2020 1:02 pm
The name of the new loco comes from the Mihirung, which were a group of Australian giant flightless birds and the last of them disappeared along with the other local megafauna about 30,000 years ago. The name is of aboriginal origin, as the last ones were still around when the first humans arrived. https://en.wikipedia.org/wiki/Dromornithidae
The Mihirung were once thought to be related to waterfowl, which is why one is nicknamed the demon duck, but they are now thought to be related to landfowl. The largest one was 3m tall and 500kg in weight and is named Stirton's thunderbird. That's a very big chook.......
The model had been in the planning stage for a long time, as I wanted an emergency loco for towing in steam locos and their train from inconvenient parts of the track. There were three holdups, one was working out a suitable prototype, next was the transmission and the last was working up enough enthusiasm for a diesel with a long build time.
In the event, this project started as we came out of the first lockdown and continued, and continued, and continued while we were in the second lockdown.
It should perhaps be pointed out that I'm a card carrying Luddite and no CADs or 3Ds were harmed in the building of this model............
The first part of the project was to build a powered bogie, as there's not much point in continuing if this bit didn't work. The design did work and the basic mechanicals are shown in the next two photos. The motor is a Pololu with a fully enclosed gearbox and the final drive gears are standard 0.8 Mod acetal bevel and pinion gears. Much of the design delay was looking for a way to couple the two axles together. Suitable small chain was difficult to find and expensive when found.
The eventual design was based loosely on the Mk1 power bogie used by Tri-ang back in the mid '50s. The bogie design only worked because the gauge is 45mm and the prototype bogie had a long wheelbase. The clearances are tight, so it would require major changes to be usable on 32mm gauge. The motors had been in stock for several years for another project and when I dug them out it turned out that I had ordered too high a gear ratio, so the pinions driving the layshaft have a ratio of 1.5:1 to increase scale speed to a reasonable level.
Once one bogie was assembled and bench tested, it was a quick job to make up the second one. They were fitted to a temporary plywood chassis, with a battery pack and a couple of switches to confirm the speed calculations and ensure they would run on the layout without problems. The test lashup is shown in the next photo. during a test run. Using eight elderly NiMH cells gave a max running speed of 20 scale mph, which is what the bogies were designed to do.
So, now that the mechanical design is tested and working it is on to the chassis. The design is simple enough, steel plate for most of it, with brass angle for the side sills and assembled with rivets instead of soldering. I'd have preferred an all steel chassis, but couldn't find a source of 1/2" x 1/16" bright steel angle locally. The next photo shows the completed chassis testing clearances out on the track on a cold wintry day.
The next job was installing the electrickery. The loco was intended to be r/c control from the start and the battery, receiver, ESC, and the rest were built into a self contained module that is bolted to the chassis. The next photo shows the working bits out on their first test run on the track.
At this point in time, I was about a month into the build, it was the middle of winter and Victoria was shut down at level 4. My sheetmetal skills aren't really up to building the body of a diesel in brass and anyway r/c works better in a plastic body. I had a good supply of polystyrene sheet, so that was the path followed for building the body work on the model.
The first issue was that the chosen prototype had a very liberal supply of louvres scattered over most of the body access doors, so that was the starting point for body construction. The next photo is a composite and shows the first attempt at louvres on the left, which didn't work and the second method on the right that did.....
The first method is one I used in the distant past in HO. A sharp chisel is pushed into the polystyrene sheet to raise a louvre, then step and repeat. This was going to require a jig of some sort to line up the louvres and ensure even spacing. Even with all that, the edges can still be ragged and with something like 500+ individual louvres to make, this wasn't a very good idea.
The second method I've also used before in HO and involves insetting a louvred panel into each door panel. Luckily Evergreen make a suitable sized weatherboard sheet and I had some in stock, so this was the path forward. The photo is a test piece and you can just see the joints where the door has been assembled from various size strips, in much the same way as a traditional wooden louvre door is made.
The next photo shows the body section assembled, which is the short hood in front of the cab. Tedious, but the construction went well. The body is heavily constructed as a box laminated up from 2mm plastic and is 4mm thick in most places. This gives enough thickness for the corners to be easily rounded without reducing the strength of the assembly.
The bodywork of the prototype was made in sections, presumably for ease of maintenance and I followed the same practice, so the next photo shows the cab. The windows had to simulate the rubber mountings of the prototype, so were made to slightly overlap the window opening to form a recess, so the glazing could be fitted for the correct appearance. The piece of steel in the front right of the photo is the tool I made for rounding off the corners of the polystyrene bodywork. Two sizes of quarter circles were milled in the corners and the tool is used like a cabinet scraper to round off the corners of the bodywork.
The next part was the the hood over the transmission. The first photo shows this ready for the battery boxes to be fitted and the second shows one of the battery boxes. Not sure what the fittings on top of the hood are, some sort of vent as far as I can tell, as the exhausts were further back on the engine cover.
The next section was the motor cover and this is shown in the photo below. The raised section on the prototype engine cover was a sliding panel used for access to the top of the motor and this was made removable on the model for access to the charging socket and switches. The exhausts on the prototype were flush with the top of the hood when first built and can be seen in the photo. The other items are the scraper and one of the little sanding blocks used for shaping the bodywork. The sander is just two pieces of polystyrene scraps glued together and a piece of abrasive paper fixed down with double sided tape. When the abrasive wears out it can be easily replaced.
The last body section was the cooling group at the rear and this is shown in the photo below. I've been accumulating bits for this model for a while and the grills are an example of this. At one time K&S sold a range of etched mesh sheets and I bought some about the time they started to disappear from the shops. They are no longer available, but I had enough to do the job. The radiator cores are simulated with panels of corrugated polystyrene sheet and the cooling fan was fabricated from brass sheet and turnings.
The cab windows on the prototype were large and some sort of cab interior was called for. I couldn't find a decent photo and in the lockdown the preserved ones were out of reach, so something typical based on a later loco from the same builder was knocked up out of scraps to fill the space. It is fitted separately to the underframe so that the interior can be accessed if necessary and the photo below shows it installed in the cab.
Finally......... The body parts were bolted down and the handrails fabricated and fitted. The next photo shows the more or less complete model sitting on the track during another test run in a rare burst of late afternoon sun in the depths of a Melbourne winter.
At this point a problem arose when the loco was first tested under load. The model has a very long overhang at each end and this plus the coupler mounting was causing derailments on parts of the wye which has the sharpest curves on the track.
Back to the drawing board....... The bogie pivots were moved closer to the headstocks (the bogie stayed in the same place, just the pivot was moved off centre) and the couplers were recessed back into the headstock. The next photo shows the first successful test run with a full train some weeks later after the modifications. Things were looking up and the sun was out as well.
The model is fitted with working headlights and marker lights powered by the ESC. The next photo shows the wiring arrangement inside the front hood. The resistors for the LEDs are fitted to a small pc board so that only two wires need to be run into the front and rear hoods instead of eight. The plug on the input wires is so the body can be easily dismantled for service as needed, without resort to a soldering iron. There are other plugs in the wiring, including the bogies for the same reason.
This model fought hard all the way and there was a lot of light leakage from the LEDs, which showed through the bodywork when in the dark. This was finally cured by fitting the LED in a brass tube to stop light passing through into the bodywork and using a thick coat of silver paint to stop light leaking from the back of the LEDs lighting up places in the body not intended to be lit. I've found silver paint better than black paint at blocking light, but either way takes a lot of paint to be light tight.
The weather was still too bad for painting at the time so I got on with other things until I finally ran out of excuses and started the long fight to paint the model.
The last photos show the more or less finished model sitting for its family portrait, and yes I still hate modern paints.......
The livery is based on the first colour scheme used on the Clyde-GM G8 and G12 diesels that ran on the BHP owned Iron Knob Tramway from the Whyalla steelworks to the iron ore mines in the Middleback Range in South Australia. It's a variation of the common 'bow wave' colour scheme used on '50s EMD diesels.
Electronics and Performance
The r/c installation was simple, as the model has plenty of space under the long hood. The r/c parts all came from Tony Walsham at RCS here in Oz and come with the usual high standard of service and backup from Tony.
Basically I just plugged all the electronics in and it worked first time without any issues. The transmitter is a Deltang based RCS TX-1 now a few years old, the receiver is an RCS RX107-EM and the ESC is an RCS Omega-10, which is a 100 Watt low off ESC. As usual with RCS gear, it all works out of the box, if you follow the instructions. With the plastic body radio reception is at least as far as I can get from the loco and stay on my own property, so range is at least 30m when tested.
The model is fitted with two Pololu #3228 25mm gear motors with a 34:1 gear ratio, one in each bogie. As mentioned above, this was too high a reduction for a large slow revving motor and the layshaft had to be geared up 1.5:1 to give an overall drive ratio of about 23:1 and bringing the scale speed up to reasonable levels. The acetal gears are 0.8 Mod and fairly meaty, so should be strong enough for the trains the loco will be running. They also run quietly if properly meshed.
This motor and gear combination has plenty of torque and even though the loco weighs just over 4kg, there is enough torque to slip the wheels when driven up against the buffers. Drawbar pull is 1kg, so it will pull the Garratt and ten bogie wagons back from the far corner of the track without noticing the load.
I've had no problem with MFA-Como gear motors in other models, but I'm impressed with these Polulo gear motors. They use less current and with a fully enclosed metal gearbox are also much quieter when running. Since the photos were taken, the final drive gears have been shielded to reduce dirt ingress, although with my track being raised off the ground dirt isn't as much of a problem as it is on a ground level track.
TVT Story
There isn't one really. If the TVT had really existed it would have closed in the '50s without dieselisation, same as the VR narrow gauge lines.
The model is based on the 3'6" gauge EMU Bay Railway 10 class diesel hydraulics built in the early '60s by Walkers Engineering of Maryborough in Queensland.
http://www.railtasmania.com/loco/loco.php?id=10
There are theories that they were based on a North British built diesel hydraulic design built in the '50s for India. Perhaps so, as there is a passing resemblance to the Indian Railways metre gauge YDM-1 class. They were more reliable than any North British built diesel though, from what I've read.
All four 10 class are now withdrawn, but they survive in preservation, with one in Tasmania, two in NSW and one modified example on the Walhalla Goldfields Railway in Victoria, which is built on the trackbed of the old VR narrow gauge line to Walhalla.
Walkers went on to develop the 10 class design as a shunting loco and sold many locos to some of the state railway systems in Aust. Most are now withdrawn, but many were rebuilt and live on as 2' gauge diesels on cane tramways and a few are scattered around on preserved railways. Preserved examples include two of the QR DH class variant which now run in VR colours at Puffing Billy in Victoria.
If PuffRail can run a Walkers diesel I guess I can as well, but I did draw the line at VR blue and gold paint. The original EBR livery was two tone blue, which were the school colours of my high school, so that was a non-starter as well........
Regards,
Graeme
The Mihirung were once thought to be related to waterfowl, which is why one is nicknamed the demon duck, but they are now thought to be related to landfowl. The largest one was 3m tall and 500kg in weight and is named Stirton's thunderbird. That's a very big chook.......
The model had been in the planning stage for a long time, as I wanted an emergency loco for towing in steam locos and their train from inconvenient parts of the track. There were three holdups, one was working out a suitable prototype, next was the transmission and the last was working up enough enthusiasm for a diesel with a long build time.
In the event, this project started as we came out of the first lockdown and continued, and continued, and continued while we were in the second lockdown.
It should perhaps be pointed out that I'm a card carrying Luddite and no CADs or 3Ds were harmed in the building of this model............
The first part of the project was to build a powered bogie, as there's not much point in continuing if this bit didn't work. The design did work and the basic mechanicals are shown in the next two photos. The motor is a Pololu with a fully enclosed gearbox and the final drive gears are standard 0.8 Mod acetal bevel and pinion gears. Much of the design delay was looking for a way to couple the two axles together. Suitable small chain was difficult to find and expensive when found.
The eventual design was based loosely on the Mk1 power bogie used by Tri-ang back in the mid '50s. The bogie design only worked because the gauge is 45mm and the prototype bogie had a long wheelbase. The clearances are tight, so it would require major changes to be usable on 32mm gauge. The motors had been in stock for several years for another project and when I dug them out it turned out that I had ordered too high a gear ratio, so the pinions driving the layshaft have a ratio of 1.5:1 to increase scale speed to a reasonable level.
Once one bogie was assembled and bench tested, it was a quick job to make up the second one. They were fitted to a temporary plywood chassis, with a battery pack and a couple of switches to confirm the speed calculations and ensure they would run on the layout without problems. The test lashup is shown in the next photo. during a test run. Using eight elderly NiMH cells gave a max running speed of 20 scale mph, which is what the bogies were designed to do.
So, now that the mechanical design is tested and working it is on to the chassis. The design is simple enough, steel plate for most of it, with brass angle for the side sills and assembled with rivets instead of soldering. I'd have preferred an all steel chassis, but couldn't find a source of 1/2" x 1/16" bright steel angle locally. The next photo shows the completed chassis testing clearances out on the track on a cold wintry day.
The next job was installing the electrickery. The loco was intended to be r/c control from the start and the battery, receiver, ESC, and the rest were built into a self contained module that is bolted to the chassis. The next photo shows the working bits out on their first test run on the track.
At this point in time, I was about a month into the build, it was the middle of winter and Victoria was shut down at level 4. My sheetmetal skills aren't really up to building the body of a diesel in brass and anyway r/c works better in a plastic body. I had a good supply of polystyrene sheet, so that was the path followed for building the body work on the model.
The first issue was that the chosen prototype had a very liberal supply of louvres scattered over most of the body access doors, so that was the starting point for body construction. The next photo is a composite and shows the first attempt at louvres on the left, which didn't work and the second method on the right that did.....
The first method is one I used in the distant past in HO. A sharp chisel is pushed into the polystyrene sheet to raise a louvre, then step and repeat. This was going to require a jig of some sort to line up the louvres and ensure even spacing. Even with all that, the edges can still be ragged and with something like 500+ individual louvres to make, this wasn't a very good idea.
The second method I've also used before in HO and involves insetting a louvred panel into each door panel. Luckily Evergreen make a suitable sized weatherboard sheet and I had some in stock, so this was the path forward. The photo is a test piece and you can just see the joints where the door has been assembled from various size strips, in much the same way as a traditional wooden louvre door is made.
The next photo shows the body section assembled, which is the short hood in front of the cab. Tedious, but the construction went well. The body is heavily constructed as a box laminated up from 2mm plastic and is 4mm thick in most places. This gives enough thickness for the corners to be easily rounded without reducing the strength of the assembly.
The bodywork of the prototype was made in sections, presumably for ease of maintenance and I followed the same practice, so the next photo shows the cab. The windows had to simulate the rubber mountings of the prototype, so were made to slightly overlap the window opening to form a recess, so the glazing could be fitted for the correct appearance. The piece of steel in the front right of the photo is the tool I made for rounding off the corners of the polystyrene bodywork. Two sizes of quarter circles were milled in the corners and the tool is used like a cabinet scraper to round off the corners of the bodywork.
The next part was the the hood over the transmission. The first photo shows this ready for the battery boxes to be fitted and the second shows one of the battery boxes. Not sure what the fittings on top of the hood are, some sort of vent as far as I can tell, as the exhausts were further back on the engine cover.
The next section was the motor cover and this is shown in the photo below. The raised section on the prototype engine cover was a sliding panel used for access to the top of the motor and this was made removable on the model for access to the charging socket and switches. The exhausts on the prototype were flush with the top of the hood when first built and can be seen in the photo. The other items are the scraper and one of the little sanding blocks used for shaping the bodywork. The sander is just two pieces of polystyrene scraps glued together and a piece of abrasive paper fixed down with double sided tape. When the abrasive wears out it can be easily replaced.
The last body section was the cooling group at the rear and this is shown in the photo below. I've been accumulating bits for this model for a while and the grills are an example of this. At one time K&S sold a range of etched mesh sheets and I bought some about the time they started to disappear from the shops. They are no longer available, but I had enough to do the job. The radiator cores are simulated with panels of corrugated polystyrene sheet and the cooling fan was fabricated from brass sheet and turnings.
The cab windows on the prototype were large and some sort of cab interior was called for. I couldn't find a decent photo and in the lockdown the preserved ones were out of reach, so something typical based on a later loco from the same builder was knocked up out of scraps to fill the space. It is fitted separately to the underframe so that the interior can be accessed if necessary and the photo below shows it installed in the cab.
Finally......... The body parts were bolted down and the handrails fabricated and fitted. The next photo shows the more or less complete model sitting on the track during another test run in a rare burst of late afternoon sun in the depths of a Melbourne winter.
At this point a problem arose when the loco was first tested under load. The model has a very long overhang at each end and this plus the coupler mounting was causing derailments on parts of the wye which has the sharpest curves on the track.
Back to the drawing board....... The bogie pivots were moved closer to the headstocks (the bogie stayed in the same place, just the pivot was moved off centre) and the couplers were recessed back into the headstock. The next photo shows the first successful test run with a full train some weeks later after the modifications. Things were looking up and the sun was out as well.
The model is fitted with working headlights and marker lights powered by the ESC. The next photo shows the wiring arrangement inside the front hood. The resistors for the LEDs are fitted to a small pc board so that only two wires need to be run into the front and rear hoods instead of eight. The plug on the input wires is so the body can be easily dismantled for service as needed, without resort to a soldering iron. There are other plugs in the wiring, including the bogies for the same reason.
This model fought hard all the way and there was a lot of light leakage from the LEDs, which showed through the bodywork when in the dark. This was finally cured by fitting the LED in a brass tube to stop light passing through into the bodywork and using a thick coat of silver paint to stop light leaking from the back of the LEDs lighting up places in the body not intended to be lit. I've found silver paint better than black paint at blocking light, but either way takes a lot of paint to be light tight.
The weather was still too bad for painting at the time so I got on with other things until I finally ran out of excuses and started the long fight to paint the model.
The last photos show the more or less finished model sitting for its family portrait, and yes I still hate modern paints.......
The livery is based on the first colour scheme used on the Clyde-GM G8 and G12 diesels that ran on the BHP owned Iron Knob Tramway from the Whyalla steelworks to the iron ore mines in the Middleback Range in South Australia. It's a variation of the common 'bow wave' colour scheme used on '50s EMD diesels.
Electronics and Performance
The r/c installation was simple, as the model has plenty of space under the long hood. The r/c parts all came from Tony Walsham at RCS here in Oz and come with the usual high standard of service and backup from Tony.
Basically I just plugged all the electronics in and it worked first time without any issues. The transmitter is a Deltang based RCS TX-1 now a few years old, the receiver is an RCS RX107-EM and the ESC is an RCS Omega-10, which is a 100 Watt low off ESC. As usual with RCS gear, it all works out of the box, if you follow the instructions. With the plastic body radio reception is at least as far as I can get from the loco and stay on my own property, so range is at least 30m when tested.
The model is fitted with two Pololu #3228 25mm gear motors with a 34:1 gear ratio, one in each bogie. As mentioned above, this was too high a reduction for a large slow revving motor and the layshaft had to be geared up 1.5:1 to give an overall drive ratio of about 23:1 and bringing the scale speed up to reasonable levels. The acetal gears are 0.8 Mod and fairly meaty, so should be strong enough for the trains the loco will be running. They also run quietly if properly meshed.
This motor and gear combination has plenty of torque and even though the loco weighs just over 4kg, there is enough torque to slip the wheels when driven up against the buffers. Drawbar pull is 1kg, so it will pull the Garratt and ten bogie wagons back from the far corner of the track without noticing the load.
I've had no problem with MFA-Como gear motors in other models, but I'm impressed with these Polulo gear motors. They use less current and with a fully enclosed metal gearbox are also much quieter when running. Since the photos were taken, the final drive gears have been shielded to reduce dirt ingress, although with my track being raised off the ground dirt isn't as much of a problem as it is on a ground level track.
TVT Story
There isn't one really. If the TVT had really existed it would have closed in the '50s without dieselisation, same as the VR narrow gauge lines.
The model is based on the 3'6" gauge EMU Bay Railway 10 class diesel hydraulics built in the early '60s by Walkers Engineering of Maryborough in Queensland.
http://www.railtasmania.com/loco/loco.php?id=10
There are theories that they were based on a North British built diesel hydraulic design built in the '50s for India. Perhaps so, as there is a passing resemblance to the Indian Railways metre gauge YDM-1 class. They were more reliable than any North British built diesel though, from what I've read.
All four 10 class are now withdrawn, but they survive in preservation, with one in Tasmania, two in NSW and one modified example on the Walhalla Goldfields Railway in Victoria, which is built on the trackbed of the old VR narrow gauge line to Walhalla.
Walkers went on to develop the 10 class design as a shunting loco and sold many locos to some of the state railway systems in Aust. Most are now withdrawn, but many were rebuilt and live on as 2' gauge diesels on cane tramways and a few are scattered around on preserved railways. Preserved examples include two of the QR DH class variant which now run in VR colours at Puffing Billy in Victoria.
If PuffRail can run a Walkers diesel I guess I can as well, but I did draw the line at VR blue and gold paint. The original EBR livery was two tone blue, which were the school colours of my high school, so that was a non-starter as well........
Regards,
Graeme