This is a model of the Harman locomotive built in Melbourne for the Forests Commission of Victoria (FCV) for use on the 2' 6" gauge Tyers Valley Tramway in Gippsland. The sorry saga of the design, building and subsequent failure of the Harman to perform is documented in an article published in 'Light Railways' Issue 42, pp 12 -19, some years ago. For anyone interested, there is a free pdf available online.
http://media.lrrsa.org.au/biko041/Light ... 41_044.pdf
This beast was articulated on a similar principle to Schwarzkopf locomotives and was also geared. It was the Victorian timber industry's equivalent of Bullied's Leader, as it was overweight, stopped at every water tank, steamed well only when the planets were in the right conjunction and was modified several times for better performance without much success. It survived longer though, as it was shoved into the back of the shed at Tyers Junction and sat rusting and unloved from the late '20s until it was cut up when the line was closed and the site cleared in the early '50s.
The Tyers Valley Tramway was about 70 miles west of the area where the TVT is supposedly located, so a model of a Harman loco isn't particularly relevant to the timber trams in the area, but it looked like an interesting thing to build and was extremely unlikely to appear in commercial rtr form.....
With Australia heading into the usual Christmas shutdown, I was looking for a project that would use parts and materials I had in stock and came across the Harman while reading back issues of 'Narrow Gauge Downunder'. The 'Light Railways' article has a drawing of the original proposal, which did not match the photos as built. The NGDU article had a better drawing and some additional photos of the loco as built and some photos also turned up online that had been taken post WW2 of it mouldering away in it's shed, so the die was cast.
I thought about attempting to make a live steam model, but the boiler is very small and there's not much space in the model to hide an osmotor and drive shafts. The chances were a live steamer would perform like the prototype, somewhere between badly and not at all. So battery electric was the choice. The model is built to Fn3 scale (1:20.3) and 45mm gauge. Unusually for a timber tram, the Tyers Valley line was built to 2'6" gauge, but I'm not about to lay 37.5mm gauge track.
Being basically a diesel type mech, the first part made was a basic bogie to work out the design and do some test running. The first two photos show the drive arrangements and the third shows it under test on the track.
That was interesting, as there wasn't a lot of space in the bogie for a layshaft to couple the axles and the gearmotor, even though it was a small 6V N20 type. I had planned to fit slightly larger motors, but my preferred brand of Pololu have stopped selling their 16mm size gearmotor and the data sheets suggest that the N20 size has the same power and torque output, so theoretically would do the job.
The first motor bogie tested was fitted was a 6V N20 with 1:50 gearbox. When powered with 6 NiMH cells for the test runs, it almost achieved lift-off speed on the track, being clocked at a scale 55mph. Just a little high for a prototype that was hard pressed to achieve 2mph with a load in traffic.
The motor was replaced with a 1:100 reduction gearbox and this cut the speed to 25smph with 6 cells. The plan for the model is to fit a speed control, so with the replacement gearmotors fitted it should be controllable down to the prototype design speed of 10mph.
With the speed sorted out, the second bogie was built and both were fitted with the final detail parts, before work started on the chassis. The prototype frame was fabricated from massive RSJ sections and even more massive headstocks cut from steel slab. No wonder the loco was overweight. The photo shows the bogies fitted to the frame and on a test run to check clearances, that it could negotiate turnouts and get through the sharp curve in the triangle.
That leaves the boiler, cab and bunker to fabricate and fit. All conventional construction, mostly soft soldered brass sheet. As always the last 10% of detailing takes 90% of the modelling time, but the mechanical construction is finally complete and the model is now ready for the paint shop. Wiring and final detailing will have to wait until it wends it's way through the painting queue.......
The photo show the final result in the brass, waiting for a coat of paint. There is no documentation of the colour it was painted. It seems to be generally assumed that it was plain black, but the photos of it being delivered from the factory to the VR goods yard for forwarding to Moe suggest that it may have been painted in a two colour scheme.
The prototype Harman locomotive was replaced by a Climax locomotive after it's failure, which is what the FCV had wanted in the first place.
Both bogies are powered. Those little motors are powerful for their size, but I don't think only one would haul 2.8kg of loco plus a train as well. There is a plan B if two N20 motors aren't up to the job, but it's messy.
You and me both.....
With my penchant for oddball loco's I was tempted to have a go at this once I read the article, but at over a foot long it's too big for my line. I've always fancied a Shay and this has that look without the outward complications, but...
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After finishing two live steam loco paint jobs, I've moved on to wiring up the Harman so the mechanism can be tested.
I was a bit uncertain how well this model would run with just two little N20 gearmotors. Wiring has progressed to the point of track testing and it would seem the drive system is more than capable of doing the work.
To recapitulate, each bogie is driven by a Pololu 6V micro gearmotor with a 100:1 gearbox. The wheels are 33mm dia., which is quite large for this sort of loco, so the 100:1 ratio gear box was chosen to tame the speed, which was far too fast with the 50:1 ratio I usually use in small battery powered models.
Doubling the gear reduction also doubles the torque at the wheels. The power bogies can now slip the wheels at full voltage, which means the drawbar pull is limited by loco weight, not motor torque and a heavy train won't stall the motors.
The fully assembled chassis has a max. drawbar pull of 450g, which means it can easily pull a scale load of 10 loaded timber pairs at a scale speed of 10 mph. So it meets the design spec., which the prototype never did........
The photo shows the battery and control module fitted to the chassis during track testing in a gap between storm fronts last week.
By now it should have been completely wired, track testing completed and be passing through the paint shop. Ha.........
That's when Murphy and his disciple O'Toole stepped in and the R/C ESC intended for the model is as dead as a doornail. I'm now contemplating if it will be quicker to just build one of my manual speed controls, or wait for a new ESC to wend it's way here from the UK with the postal systems in Christmas overload mode.
The bright spot is that I now know that two N20 motors are up to the job of moving a 2.8kg loco and a train of ten loaded timber pairs.
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I started to build a Harman years ago but it's still pieces on a shelf somewhere.
I enjoy your 'testing' and calculations part of the build too.
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
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