Dual-motor A3

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GWR_fan
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Dual-motor A3

Postby GWR_fan » Wed Jul 19, 2017 7:39 am

Today I modified a BR transitional loco "St. Simon" from the Yorkshire Pullman train pack to fit a later loco drive chassis from Hornby R2675. This is basically a premium drive with Railroad rods and cylinders. The mod went reasonably well but involved a lot of surgery.

Having a couple of spare five-pole tender drives I found one that matched the loco drive chassis for speed. The dual drive would run at a snail's pace with no complaint from the tender drive. Initially I did this just as a joke but now I am considering leaving the tender drive as part of the consist. I can easily swap back to an unmotorised tender. Just as a test I held the tender coupler and applied power and the loco proved to be very difficult to restrain. I would not be surprised if fourteen plus coaches would be easily within its capacity.

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alex3410
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Re: Dual-motor A3

Postby alex3410 » Wed Jul 19, 2017 8:21 am

So long as the motors are matched I can't see it being a problem, in fact, it will be interesting to see how much it can pull compared to a single motor.

The only thing to watch out for is differences in the speed at different power levels, they may match at 1/4 power for example but at 1/2 one may be taking on more of the strain than the other. If it's going to be long term and you run DCC you can fine tune each chip to make sure the speed matches all of the way through its speed range.

if you do play around with it it would be really interesting to follow, one of my many 'to do' projects is refurbish the Tri-ang blue double ended diesel this one and I was considering using two power bogies.

GWR_fan
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Re: Dual-motor A3

Postby GWR_fan » Wed Jul 19, 2017 8:33 am

Alex,
as a kid I had the green and orange version. One motor was hard enough to make for reliable running.

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Mountain
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Re: Dual-motor A3

Postby Mountain » Wed Jul 19, 2017 10:08 am

I remember being offered a pre production Trix (Which didnt make production) class A2. It was a lovely model and had loco and tender drive as the model was made for Trix to evaluate which drive they preferred. The shop wanted over £100 for it £140? and I didnt want to pay that for it. It was a lovely model though in LNER apple green.

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Re: Dual-motor A3

Postby Bigmet » Wed Jul 19, 2017 10:12 am

alex3410 wrote:...The only thing to watch out for is differences in the speed at different power levels... one of my many 'to do' projects is refurbish the Tri-ang blue double ended diesel this one and I was considering using two power bogies.

The advantage with the tender drive for double motoring is its spur gear driveline. Any mismatch in speed between the worm gear (non-reversible) driveline of the loco and the tender motor can thus be freely taken up by the tender motor.

Two independently motored worm gear drivelines in one chassis is a recipe for accelerated wear, unless you luck into two very well matched motors. A pair of spur geared motor bogies are very little trouble at all as the speed matching is not critical.

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Bufferstop
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Re: Dual-motor A3

Postby Bufferstop » Wed Jul 19, 2017 5:12 pm

Double tender-drive Scotsman anyone?
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GWR_fan
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Re: Dual-motor A3

Postby GWR_fan » Wed Jul 19, 2017 11:59 pm

The loco hauled 24 coaches on my R4 test layout with ease. I could not fit any more cars as the loco was nose to tail. It performed flawlessly through all speed ranges with no sign of complaint from the tender drive.

Given that fourteen coaches was considered a reasonable load on the prototype, such hauling capacity from the model is mere fantasy.

I found that the siderods on the loco were too close to the wheel rims with resultant sparking occurring when the pilot truck wheels touched the slidebars. The rods were persuaded to give more clearance and the sparking was gone.

Edit: surprisingly, a stock five-pole tender drive performed just the same. The only real difference was that the dual motor loco had a higher terminal speed. That said, the single tender drive top speed was more than enough.

Bigmet
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Re: Dual-motor A3

Postby Bigmet » Thu Jul 20, 2017 11:46 am

GWR_fan wrote:The loco hauled 24 coaches on my R4 test layout with ease...Given that fourteen coaches was considered a reasonable load on the prototype, such hauling capacity from the model is mere fantasy...

Actually they worked more than that at need, 20 was normal during the war.

As for the A4,
It could do more...

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RAFHAAA96
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Re: Dual-motor A3

Postby RAFHAAA96 » Sat Jul 22, 2017 10:01 am

I tried dual motoring a gutless ring-field Class 56 diesel and whilst the conversion was simple the task of matching the motors using a single DCC decoder was almost impossible, so I had to go to twin decoders.

The single decoder problem was one motor would comtrol well but the other would drag its wheels until a highish throttle setting was reached when it would kit in and the loco would race off.

With two decoders I could set the tardy motor to kick start and by way of fiddling with the speed curves of each end in Decoder-Pro I got it running fairly well across the speed range possible on my small layout.

Rob
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Bufferstop
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Re: Dual-motor A3

Postby Bufferstop » Sat Jul 22, 2017 10:57 am

I'd say part of the problem with running two ringfield motors in tandem, is the common problem of ringfields performing better in one direction than the other. I suspect it's down to the armature pushing the commutator against the brush springs in one direction and pulling away from them when reversed. There being no positive end stop in the motors design. The design of both the X03/04 motors and the type 7 have a similar problem but are held in check by the mesh of the worm drive's high level of friction. It's notable that the Meccano X04 copy cat for Hornby Dublo 2 rail models had an end stop bearing in a nose extension of its frame, suggesting that they had encountered this problem during development.
It's a case of reinventing the wheel, as old advertisements for Romford and other motors from the 30s through to the late 50s show designs with the same sort of bearing. Triang Rovex obviously understood the problem, their twin worm motor bogie, based on a Romford design, had end bearings consisting of a ball bearing in a cup surrounded by an oil pad. Probably their most successful motor design. Its rather low reduction ratio was compensated by a powerful armature/magnet design. The poor design of the same components wasting the advantage of the multi gear chain reduction of the ringfields.
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D605Eagle
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Re: Dual-motor A3

Postby D605Eagle » Sun Jul 23, 2017 2:53 am

I must say that my re engineered ringfields with thrust washers either side of the armature, tight shaft bearings and virtual lack of play are very smooth and predictable runners, but take about 20 - 30 hours of running to be fully run in. One thing I can't get round though is the quite large variation in magnetic strength of the ringfield magnet. I think this more than anything else is responsible for different running characteristics.

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Re: Dual-motor A3

Postby GWR_fan » Sun Jul 23, 2017 4:05 am

I have dual motored several Hornby ringfield locomotives and while I replace the traction tyres on one block plus provide additional power pickups, I find depending on direction, as the loco enters a curve one motor block is forced to pivot laterally marginally lifting the inside wheels. If these wheels are the power pickup wheels then the loco momentarily slows down until the wheels once again pickup power. If the outside wheels are power pickup wheels then movement is not affected.

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RAFHAAA96
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Re: Dual-motor A3

Postby RAFHAAA96 » Tue Jul 25, 2017 1:36 pm

I have tried neo magnets in couple of ringfield s with mixed success.

A one piece neo worked fine in an old 3 pole Class 90, but a two piece arch shaped neo made the 3 pole motor so notchy it would only run on high throttle settings. Low speed control was impossible, so I reverted to a new motor housing complete with a new magnet.

Rob
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