Atlantic's works: Portable layout update

[Atlantic 3279]

Purists may care to look away now, especially if of a sensitive disposition.

The truth revealed: Each side frame cut from a double layer of 40 thou plasticard, with brass top-hat bushes inserted. Cheapo nylon gears as sold at some time by Squires, 42:1, and the 42 tooth final gear is only just small enough to be compatible with 22mm coupled wheels. TWO of the small cheap Mitsumi motors that everybody was buying a year or two back as if there were no tomorrow. Coupling rods (which I dealt with first) shortened to 26mm centres from a set of 29mm rods I had lying around spare.
At least they are proper Markits wheels, axles and crankpins in this case, and the distinctive bogie will be from one of Mike Edge's handy etches. For my first time, I've used phosphor bronze wire for the pick-ups, prompted by Baz Oliver's enthusiastic and repeated recommendation. I'll see whether I notice any advantages. Brake gear and trailing truck to follow...

As schemed out:

As realised:

I could have stolen, or copied, the chassis from a complete but unbuilt Craftsman kit that I also have, but I didn't want to compromise that kit in case I want to build it or sell it at some stage. I didn't want a frame design that was meant for an XO4 type motor in the cab anyway. I could have cut the frames from brass, but plastic is quicker and easier to use, is of less concern to me if the experiment ultimately lacks success, and is already black so needs no primer and paint. I could have ordered a directly suitable set of rods, but I didn't.
The tricky bit was to get two worms to mesh nicely, with both driving the same axle (even if via separate intermediate gears, which in this case cannot be conveniently removed and neither can the motors unless absolutely necessary). I couldn't adjust the first one so as to run perfectly and then remove it to leave the wheels free to be driven by just the other motor while I tweaked the second worm-to-wheel mesh. Looking and listening for signs of even, free running required rather more care than usual.
I was however rather pleased with the accuracy I managed to achieve in matching the chassis wheelbase to the modified rods. I'd kept the holes in the rods small, and used tight-fitting pins in a piece of wood as a jig to set the new rod centres. After using the new rods to transfer dimensions to directly the frames, then drilling the frames and fitting the bearings plus the wheels, I was delighted to find that the smallest drill bit I had that would enlarge the holes in the rods enough to just take a crankpin immediately produced just enough clearance for the whole wheel and rod assembly to rotate freely and evenly with no hints of tightness. I don't know how much it helped, but as I had no plans for springing or compensation in this case, and the wheelbase isn't very long, I made the rods un-prototypically in one solid piece. Perhaps by doing away with any scope for "double slop" due the joint on or near the centre crankpin I had done myself a favour???

[jwealleans]

Can you do a Francis Webb and have them going in opposite directions?

[drmditch]

Can you do a Francis Webb and have them going in opposite directions?

Unfair! There are coupling rods!
Now if the motors were side-by-side and if different sizes...…...

[Atlantic 3279]

Intriguing ideas - for another time perhaps?

The motors at present are wired in parallel, just like having two locos on the same track, each motor subject to the full voltage that the controller can create, but receiving only half (I presume) of the current that the controller can supply. I wondered about the alternative possibility of wiring them in series, imagining that each one would then be on half voltage (and thus speed-limited) but getting the full current. I didn't know whether I'd get better, or poorer low-speed torque that way and less risk of trying to draw too much current from the controller. I had a bit of a look for relevant info on the mighty web and came away none-the-wiser.

[Horsetan]

Can you do a Francis Webb and have them going in opposite directions?

Now this I would pay good money to watch. It would be a bit like Marty Feldman's eyes.

Back in the 1970s I think a fella named Jack Newton scratchbuilt a BR 9F with twin motors. It seemed like a good idea at the time.

[manna]

G'day Gents

Bit different having two motors, but if it works !

I'm glad I bought those cheap motors when they were easily available, still around but a bit harder to find, locally, I get mine from China, although they have doubled in price 2 quid each !! plus postage, so I buy half a dozen at a time.

manna

[NZRedBaron]

So, why are you installing two motors anyway? I didn't see if you gave a reason why.

[jwealleans]

"For more information, please reread."

[Pebbles]

Does anyone knew where to get 6ft 6inch x 6ft 6inch coupling rods from? I know that Gibson doesn't do them.

[Atlantic 3279]

Maybe my penny-pinching alteration of rods I already had wasn't such a bad idea then?

The reason for two small motors instead of one of a decent size is covered fully in both the eighth post on the previous page (the first one with a picture of the A5) and in the top post on this page.

[Horsetan]

Does anyone knew where to get 6ft 6inch x 6ft 6inch coupling rods from? I know that Gibson doesn't do them.

No, but AGW does produce universal rods, which you can trim down to the 6'6" measurements. Lanarkshire Model Supplies also produce their own universal rod fret.

The V4 has a weird 6'6" x 6'4" wheelbase which is the exact mirror image of the one used for the Hawksworth 15xx shunter on the Western Region.

[Atlantic 3279]

Yesterday morning I was thinking that I had "dropped a clanger" when building the Mike Edge bogie for my A5, having rather carelessly failed to notice in the process that I was using the wide EM/P4 bolster/stretcher rather than the narrower OO item. I had visions of ruining the neatly laminated sides as I tried to unsolder them from the bolste, and was exploring other ideas in my mind, such as sawing the thing in half and then re-joining the reduced-width halves using some bridging pieces.
My "blunder" actually turned out to be a master-stroke in disguise, as when I tried the only suitable wheelsets that I had available, the inward projection of each central boss still cleared the axleboxes of the bogie, leaving enough clearance for free rotation and for an idea I wanted to use in order to get electrical pick-up from one side of the wheelsets. I have a feeling that the OO spacer would have allowed the wheelsets un-necessary amounts of sideplay, giving a less realistic appearance to the relationship between the wheels and the bogie frame.
In order to get electrical pick-up I wanted to make the axles live to one rail, keeping the bogie insulated from the loco body by means of driving its mounting screw into a block of plasticard epoxied in position between the main frames at the front of the loco. A thin flexible wire from the bogie frame to one side of the motor supply circuit would complete the job. I planned to arrange the trailing truck to pick up in similar fashion from the other rail. The minor snag was that I had wheels with plastic spokes, so my usual trick of drilling the insulating bush between the axle and the wheel and forcing a stub of wire into the hole to bridge the gap wasn't applicable.
I instead bridged the plastic spokes using some pieces of 0.45mm brass wire as shown in the image below. The head of the "question mark" shape was formed around a drill shank a bit slimmer than the axle, so that the slight springiness of the brass would make it grip when slid over the axle gently from one end. I turned the foot of the "question mark to one side so as to have a little more to solder to the back of the tyre - above rail head level.

The wheel shown twice in the composite image is one of the trailing set, a Sharman item I believe. I know it ought to be an eleven spoke 3' 9" wheel, but my options from stock were this one with ten spokes at 15 mm dia, or an old type generic Romford/Jackson/Markits twelve spoke 14mm. As I was more or less obliged by limitation of choice to use some (correct) ten spoke 14mm Sharman type wheels for the leading bogie, I didn't think the coarser scale trailing wheel would look very good.
More soon...

[Atlantic 3279]

Here's the underside of the functionally complete chassis as it currently is, after testing, minor modifications, and re-testing. There's a small soft coil spring around the bogie screw, above the bogie, to assist with control and pick-up pressure. Although the bogie behaves satisfactorily on the track I may in due course fit a different spring, perhaps when I get more weight into the body, because the bogie is currently rather floppy when the loco is being handled. Initial testing had revealed another useful feature of my accidentally chosen EM width bogie, as I was able to extend the lateral slot with a file to give it more sideways travel.

The rear truck I initially had as just the brass tube on an arrangement of springy nickel-silver wires which created down-force and allowed a long-radius turning-in action on curves, with gentle side control, all in one go. The side control proved to be a liability with the shallow Sharman flange profile in combination with my imperfect OO code 75 (ish) track standards. When running bunker first around a curve of any sort, a crossing gap or slightly irregular joint in the outside rail usually encouraged the wheel to climb over the rail. What it would do on Peco code 100 I would rather not imagine. The rear wheelset obviously need to have a much more neutral "floating" attitude to the track. I therefore reverted to a more conventional solid radius arm on a free pivot with just a springy wire bearing down on top, providing a little more tracking force and completing the electrical circuit. I may add a flexible, insulated, soldered electrical wire in due course. I'll build up the width of the rear frames in areas clear of the wheels now that I know that the rear truck has enough lateral movement. The very narrow original frame here was a deliberate arrangement to ensure a strong structure, easily and rapidly built, with no unrealistic daylight through or around the rear wheels.
You may notice that I've also filed some segments out of the edges of the cut-out in the running plate. Initial testing had shown that the tops of the oil pots on the coupling rod bosses were just capable of touching the structure, creating scope for a short circuit or a mechanical tight spot.

Scale top speed, light engine, is just short of 70mph - JLTRT?
I can now return to matters much more purely cosmetic .

[Horsetan]

Your name is Jack Newton, and I claim my five pounds

[Atlantic 3279]

You have me at a disadvantage there. You'll have to explain further...