TVT - Down in the Forest Something Stirred

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TVT - Down in the Forest Something Stirred

Post by GTB » Sat Mar 18, 2023 4:09 am

Well sort of......

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.

Harman-a.jpg
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Harman-b.jpg
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Harman-c.jpg
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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. :shock:

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.

Harman-f.jpg
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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....... :roll:

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.

Harman-i.jpg
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Harman-j.jpg
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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.

Hmmm........

Regards,
Graeme

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Re: TVT - Down in the Forest Something Stirred

Post by philipy » Sat Mar 18, 2023 6:23 am

Nice build Graeme. I'm not quite clear as to whether both bogies are powered?
I do like the look of that loco, shame it was so unsuccessful in real life, just hope your version gets on better. :D
Philip

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Re: TVT - Down in the Forest Something Stirred

Post by ge_rik » Sat Mar 18, 2023 7:27 am

Beautiful - as always with your builds.
It seems remarkable to me that such small gear motors can provide the power needed.

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Re: TVT - Down in the Forest Something Stirred

Post by GTB » Sat Mar 18, 2023 8:36 am

philipy wrote: Sat Mar 18, 2023 6:23 am I'm not quite clear as to whether both bogies are powered?
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.
philipy wrote: Sat Mar 18, 2023 6:23 am just hope your version gets on better.
You and me both.....

Graeme

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Re: TVT - Down in the Forest Something Stirred

Post by philipy » Sat Mar 18, 2023 9:40 am

I thought only one motor would be pushing it a bit!

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... :roll:
Philip

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Re: TVT - Down in the Forest Something Stirred

Post by Trevor Thompson » Sat Mar 18, 2023 9:45 am

That is a very nicely made loco. I am particularly impressed with the motor drive system. I am following your example with geared motors. I have bought some to try and I'm amazed how quietly they run.

Trevor

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Re: TVT - Down in the Forest Something Stirred

Post by BertieB » Sat Mar 18, 2023 10:08 am

That’s terrific. It looks great.
Last edited by BertieB on Sat Mar 18, 2023 5:55 pm, edited 1 time in total.

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Re: TVT - Down in the Forest Something Stirred

Post by Peter Butler » Sat Mar 18, 2023 10:41 am

Absolutely stunning work and so well thought out.
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Re: TVT - Down in the Forest Something Stirred

Post by GTB » Mon Nov 13, 2023 9:02 am

A bit more progress on this model.

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........ :study:


The photo shows the battery and control module fitted to the chassis during track testing in a gap between storm fronts last week.

Harman-k.jpg
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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.

Graeme

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Re: TVT - Down in the Forest Something Stirred

Post by gregh » Tue Nov 14, 2023 4:27 am

What a beautiful model.
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.
Greg from downunder.
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Re: TVT - Down in the Forest Something Stirred

Post by -steves- » Tue Nov 14, 2023 9:18 am

Never cease to totally amaze me :thumbleft:
The buck stops here .......

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Re: TVT - Down in the Forest Something Stirred

Post by Old Man Aaron » Tue Nov 14, 2023 11:08 pm

Good stuff. :salute:
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Re: TVT - Down in the Forest Something Stirred

Post by GTB » Fri Mar 15, 2024 12:35 pm

This model is still no nearer to a tin of paint since the last update, but it has completed it's load test with flying colours.

It's good when a plan comes together...........


The photo shows the loco running around the track today, trundling along in late afternoon sunshine at about 20 scale mph with a scale load of ten timber pairs in tow. Theoretically it would pull twenty, but I don't have that many timber pairs and anyway the Harman was only designed to pull ten.

Harman-l.jpg
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If you scroll to the top of this thread, you'll find photos of how the model is powered. Since there is presently some discussion on powering battery electric locos, that will show my current design standards.

The loco weighs 2.8kg and is powered by two 6 volt N20 gear motors with mitre gear final drives and manual speed control. Power is supplied by 6 Eneloop AA cells and the motors draw about 300mA each when running under load, so say around 3 hrs running time on fully charged cells.

Usually I use 50:1 gearbox motors, but in this case the driving wheels are relatively large at 34mm dia., compared to the 20mm dia. wheels on most of my rail motors. The large wheels meant the model was travelling at a speed of 55 smph at 6V when first tested running light engine.......... :shock:

The gear motors were changed to ones with 100:1 reduction and the speed at 6V running light reduced to a much more reasonable 27 smph. Note that doubling the gear reduction ratio doubles the output torque, which is also desirable. In this case with a 2.8kg loco, it means that at 6V the motor can't stall, as the wheels will slip first.

I've learnt enough over the years to read the data sheets of things like small motors and that is the starting point when I build a battery electric.

Relevant to recent discussion, with these N20 gear motors, there is no difference in the performance at the output shaft between the 6V version and the 12V version. What is relevant to model design is that the 6V motor will draw twice the current as the equivalent 12V one to give the same performance.

Like all engineering design, there are trade-offs. A 12V motor will use less current and so will run for longer on each battery charge, but then you have to find space for twice as many battery cells as needed by the 6V version. :roll:

Note, the N20 motor comes in high, medium and low power varieties. The HP is three times the power of the LP and the MP sits halfway between the others. I use the high power ones and buy a brand name motor with a label, in the reasonable expectation that the performance will match the data sheet. Good luck with online no name specials.......

Regards,
Graeme

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Re: TVT - Down in the Forest Something Stirred

Post by drewzero1 » Fri Mar 15, 2024 3:18 pm

Looks great, and sounds like it's running well to meet or exceed the prototype. I really appreciate the battery power and motor figures as my current approach of "what random junk can I cram into this to make it move" has been, shall we say, unreliable. Seems like it's worth it to do the math, as you have. Not bad at all for a year's progress! :thumbup:

(I got a bit confused when I saw the month and day of the first post... I knew you Aussies were in the future but two whole days didn't seem quite right! :sleepy1: )

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Re: TVT - Down in the Forest Something Stirred

Post by LNR » Sat Mar 16, 2024 7:21 am

It's not a bad looking loco despite its reputation. Great modelling again mate.
Grant.
PS. Are you digressing because your other step is a big one!

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