Best Of Arnold SW1 - what's inside (technical review)

[peteski]

I waited for an N-scale SW1 for a long time.  I even saved an article published many years ago in the N-Scale Magazine on how to kitbash one of these but I never got a round-tuit.   IIRC, it was by our own Randgust.
The article was by John Palecki and it was published in July/August 1993 isue of the N-Scale magazine.

I own many examples of Arnold models (both original and new company's). Most are of European prototypes. I have also seen the reviews of the U25C, so I sort of knew what to expect in this model.  While the U25C had an impressive shell and lots of added-on details, I wasn't very impressed with its mechanical design, but since I really wanted the SW1, I decided to get a couple B&M examples.

Upon arrival, the first thing that impressed me was the design of the packaging.  While to most modelers this is not a big deal, to me this seems to indicate that someone at Arnold has actually put some thought into the package design - as opposed to the standard type of packaging others (and even Arnold) have used in the past.



Arnold is a European-based manufacturer. Most European model RR manufacturers use a fairly similar packaging method, which usually results is the jewel case's lid not fully closing over the bottom part of the case. That is because the European manufacturers include a large bundle of paperwork inside the box.  There is the standard parts diagram and list of part numbers, sometimes there is a writeup of the prototype's history, a warranty card (usually in a dozen of languages), and often some sort of inspection certificate.  Some of those documents are letter-size pieces of paper, folded multiple times to fit in the box.  All the paperwork creates a fairly thick bundle which is usually placed under the vacu-formed plastic nest for the model. However the jewel case and the nest aren't designed to hold that extra thickness of the paperwork. Because of that the nest sticks up over the top edge of the jewel case's bottom and the lid does not fully settle down over the bottom of the case. That often leads to the lid being rather loose. Several times I have almost dropped a loco out of the box by grabbing the case by the lid's sides, forgetting that the lid is not on tight.

But in this example, someone actually seems to have considered that wad of paperwork and instead of doing what was always done, they redesigned the vacu-formed nest the hold the folded paperwork on the side of the box.  That is a big improvement since not only it allows the lid to fully close, it also makes accessing the paperwork very easy.  The 2-piece top-and-bottom-half nest design is also a good way to protect the model during shipping and in storage (better than the standard single-piece nest). Excellent job Arnold!

Sorry to be gushing so much over a jewel case's design, but the small change they incorporated into the decades-old packaging design has really impressed me.


Moving onto mechanical and electrical design, here is the parts diagram.



Shown above is the electrical schematic I created of the internal circuit board and the 6-pin DCC dummy plug which is for running on DC.

As expected from an European manufacturer there are the standard RFI (Radio Frequency Interference) suppression components (L1, L2, C3).  The circuit breaker and over-voltage protector ZD1 (I suspect it is two 14 Volt Zener diodes) which I guess was included to protect the rather delicate motor.  The C1 and C2 are included to prevent the LEDs from flickering from the motor's BEMF voltage when running in DC mode.  The diodes D1 and D2 supply positive voltage to headlight LEDs in both DC and DCC modes.  I'm not sure why there is another capacitor across the track voltage pickup circuit on the dummy decoder plug. It might be part of the RFI suppression circuit for DC model. The circuit board is 0.032" thick and it mounts slightly above the top of the frame.
The shell is held onto the chassis by 4 dome-shaped bumps on the side of the chassis.  This design is similar to many other locomotives from companies such as Kato or Atlas.  Before I tried to separate the shell from the chassis I removed the air tank moldings by gently pulling them down towards the track. They are retained (press-fit only, no glue) by 2 tabs each, pushed into openings in the frame under the walkways.  Next, grip the metal fuel tank part of the frame and pull the shell in the opposite direction.

If trying to separate the shell and the chassis by pulling them in opposite direction is not working, wedge a small flat blade screwdriver between the underside of the walkway and the frame and use it as a pry bar to try to lift the shell off the frame. Also be mindful of the handrail mounting tabs which protrude through the steps moldings - those small tabs can interfere with removal of the frame. Those tabs can be trimmed flush with the steps walls to better facilitate shell removal. Also, the circuit board is slightly too wide in the cab area which will require some finagling while pulling the shell off.


After the body is removed, examine the bumps which hold the shell on. Some might have some metal flash which should be removed to ease the shell removal in the future. The following photo shows an example of the metal flash which shoudl be removed. I used a hobby knife to remove the flash.


This photo shows the chassis with the circuit board.  The wires connecting the truck electric pickups and the motor seem rather long.


I'm impressed with the clever way Arnold handled illuminating the rear headlight.  They uses a vertical circuit board to position the LED behind the rear headlight lens. The LED also has a black plastic cover with a small hole in it which prevents light leakage into the cab. That circuit board is narrow enough to fit between the rear cab windows and it has an opening in it as to not be visible through the windows in the cab rear door.  Well done!  The circuit board is black which further hides it in the cab. To make it even less visible I painted the visible edges with black Sharpie marker (not shown on this photo).  The LEDs used are warm-white type and they provide a decent representation of the light provided by incandescent bulbs.


As I mentioned earlier, the circuit board is slightly too wide at the cab area (it is wider than the metal frame). For the ease of future disassembly its sides in the cab area can be filed slightly just enough to clear the cab opening in the walkway (the above photo shows how much wider the circuit board is). The fiberglass/epoxy laminate the board is made of can be filed easily.


Unsoldering the wires and removing 2 screws holding the circuit board exposes the motor and the worms.  The motor is held by 2 plastic motor mounts which can be unlatched from the frame from the underside.  The two black plastic covers which retain the worm bearings are simply press fit over the worms. There are 4 fine plastic pins in each cover which plug into holes in the chassis to keep the lids in alignment. A bit unusual is the fact that Arnold uses couple of pieces of black foam tape stuck on top of the covers to keep them down. When the circuit board is installed it compresses the foam tape keeping the worm covers down.  You can also see the black wires coming up from the trucks through oval-shaped holes in the chassis.


Removing the plastic cover over the worm reveals the heavily lubricated worm and universal coupling.  Going by what looks like small particles of brass in the grease I would guess that this model had a decent factory break-in period.


This is the bare chassis with all the components removed (except for the air tanks under the walkways).


Bottom of the truck.  Traction tire is installed on one of each truck's wheels (2 tires total).


The truck mounting area on the bottom of the chassis.
The next 3 photos show how much lubrication was applied to this model at the factory. Way more than what is customarily recommended.  But this is not something only Arnold does - most manufacturers seem to over-lubricate their models at the factory.






Next is the motor.



Arnold uses a small coreless motor similar to the motors used in recent Bachmann steam locomotive models, and to those used in small radio-controlled cars and helicopters.  While it is a coreless motor, it is not quite as efficient or durable as the top-of-the-line Maxxon or Faulhaber coreless motors, often used by modelers for re-powering their models. The motor body is 0.653" (16.6mm) long and 0.275" (7.0mm) in diameter.  It has 1mm shafts.



This is the motor with its back cover removed.



The rotor basket removed from the motor.  This motor uses a 3-windings rotor basket. This is equivalent to a standard 3-pole electric motor, but due to the absence of iron poles in the rotor, and the way the windings are constructed, it doesn't cog like a standard 3-pole motor. Higher-end coreless motors usually use 5- or 7-windings rotor baskets.



The other end of the rotor basket.



Photo 13 shows a closeup of the motor's brushes. Unlike the replaceable carbon-based brushes used in conventional N-scale motors, these are made from thin metal fingers.  While coreless motors use much less current than conventional motors, I wouldn't expect these brushes to last longer than a few hundred hours of operation.  That is probably sufficient for the the life of the model owned by an average modeler.  If you are planning on frequent and heavy use of your SW1, I would recommend purchasing a spare motor from Arnold.



The flywheels (and I use that term very loosely) are tiny: 0.217" (5.5mm) in diameter and 0.137" (3.5mm) long.

To me, a true flywheel in a model should have enough inertia to make the model coast some distance after the DC power is removed from the track. Many of the N-scale models from other manufacturers (like Kato or Atlas), use larger flywheels, which combined with very low-friction mechanisms, allow the models to coast some distance after power is removed from the track.  But in the SW1, with such tiny flywheels and fairly high-friction mechanisms, there is not enough inertia to enable this model to coast for any appreciable distance. Once the power is removed, it just stops dead on the track.  So instead of calling these flywheels, I would simply call them couplings for the universal joints which plug into the openings in the flywheels' ends.

My writeup was too long - continued in the next post.

EDIT: Photobucket disaster - moved all the photos to local gallery.

[peteski]

Next is the breakdown of the trucks.



The trucks are snapped into the frame. Once the truck wires are unsoldered from the circuit board and the board is removed the trucks can simply be pulled out from the bottom of the frame. Some gentle rocking while pulling it out will aid in removal.  This particular truck was not properly installed at the factory. The arrow shows where the wire, instead of going straight up was bent into a U-shape over the truck's frame. When the truck was installed in the frame the wire ended up pinched between the truck's frame and bottom of the loco's frame. This restricted its rocking motion and could have caused problems when the loco was running over rough track or starting up or down an incline.


Removing the sideframes/gear-cover exposes the gears in the truck. All metal axles are fixed in the frame (they do not rotate) and the gears are free to rotate and slide sideways. It looks like there was some problem with the large thin center idler gear sliding too far on the axle, so there is a piece of what looks like black heat-shrink plastic tubing installed on the axle.  But that tubing is rather very short.


Side of the truck's frame showing the electric pickup wipers and the axle ends.  What seems unusual is that there are 3 different diameters of axles used in this truck. The worm-wheel/compound gear uses a 0.8mm axle, the idler gears use 1mm axles and the wheelsets have 1.5mm axles.  I'm puzzled as to the reason why the worm-wheel/compound gear needs a 0.8mm axle instead of the 1mm ones used with the other gears.


The wheelsets use 1.5mm axle and one wheel is insulated using a plastic insert as shown in this photo.  The wheel's face profile is not realistic, but not strange looking like some other manufacturers use.  This is not a problem since the wheel face is mostly hidden by the truck's sideframes.  The wheel diameter is 0.249" (40") and it has a 0.020" flange.



The left wheel is the one which has a traction tire (but it is shown removed).  This model has 2 traction tires - one per truck.  In this photo, the traction tire would be on the left wheel, but I removed it for the photos. Thus, there is a shallow groove (for the traction tire) visble in the tread of the left wheel.



When I first noticed that Arnold used wheelsets with plastic gears pressed onto metal axles, I was a bit concerned.  I have seen several locomotives using this type of design, where the the plastic gear splits after a couple of years due to excessive stress from the axle.  But upon further examination I felt confident that the gear on this locomotive will not be prone to splitting.  Instead of making the hole in the gear undersized, and depending on that tight fit to lock the gear onto the axle, Arnold uses linear knurling of the axle to positively lock the gear in place. The gear can be fairly easily slid along the axle, off the knurled area, which means that there isn't much stress generated in the gear's center.  Also noteworthy is the groove on the axle end which holds the insulated wheel. That groove positively locks the plastic bushing in the wheel's center, preventing it from getting out of gauge.



As it is quite common in N scale model locomotives the wheel gauge is tight, as shown here placed against the NMRA gauge. All the wheelsets on both of my models were tight in gauge. They ran ok on Peco and on standard Atlas code 80 track, but they would not run over Atlas code 55 turnouts. They would derail at the frog.  I contacted Hornby/Arnold about this, and I was told that the tight-gauge I've observed on my models was not a widespread problem.

Due to the wheelset's construction it will be somewhat difficult to re-gauge the wheels. In order to do that properly (keeping the gear in its proper location on the axle) both wheels would have to be pushed outward on the axle. The insulated wheel might not be too difficult to move but the one directly press-fit on the axle will most likely be tough to move.



I used a Mascot brand gear puller to get the wheels properly gauged.  I moved both wheels out to keep the gear in proper alignment with the other gears.



Here are all the gear components of the trucks (degreased and ready for reassembly).


The gears reinstalled in the truck frame.  Visible is the longer piece of black tubing I installed on the center idler axle.


Components of the universal joint and the worm.  The worm shaft is a bit unusual. It has a 1.5mm diameter where the bearings are but then it steps down to 1mm to accept the universal coupling.  I don't understand why Arnold didn't just make the entire shaft 1mm in diameter. Smaller shaft creates less friction in the bearings and there would be fewer machining steps involved. Maybe the model's manufacturer already had either the bearings or the worms readily available with 1.5mm bore and only had universal couplings with 1mm bores?

The bearings are made of brass. It might be sintered brass but I'm not sure - it looks like solid brass to me. There are also clear plastic trust washers on both sides of the worm, and there isn't much forward/backward play when the bearings are installed in the loco's frame.  The plastic universals look similar to the ones I've seen used in brass models.
Next 3 photos show the assembled worm, bearings, universal coupling and the motor's flywheel (I use that term loosely).







The motor end of the universal coupling fits in the flywheel and the motor shaft fits loosely in the bore in the coupling, It is a somewhat floppy connection.


Here is the worm and universal coupling installed in the loco's frame and coupled to the motor.  This is a single-start worm.

The final gear ratio of this model is 35:1. That is quite good for a switcher with a high-revving coreless motor.  The model should be capable of reliable slow speeds and it should have plenty of low-end pulling power.

UPDATE: I ran this model on layout using Peco track.  It is well-built layout with excellent track work. As expected, this model has an excellent slow speed performance and the top speed is much lower than average diesel locos. It can really crawl! I'm sure this is due to well chosen gear ratio.

But the electric pickup is spotty (even on straight freshly cleaned track with freshly cleaned wheels).  The same track where another loco has no problems picking up electricity.  The spotty pickup is most apparent when the loco is running at a crawl.  The problem might be the blackening layer on the wheels and I'm sure the 2 traction tires aren't helping either.  Maybe things will improve once the blackening wears off the treads. Also, once spare parts are available I'll get rid of the traction tires.



The walkways have a "tread pattern" molded on them. But it is not quite like the real thing, and way out of scale. It looks like rows of rivets.

The tread pattern on walkways of N scale models is one of the things modelers disagree about.  To me a truly-scaled tread pattern in N scale model would be so fine and shallow that it would probably disappear under a coat of the not-to-scale-thickness paint we use on our models. The oversize tread patterns which manufacturers use to me all look out-of-scale and unrealistic. But many models want that oversize tread pattern and complain of the model's walkways are smooth.  As far as this model goes, I don't have any prototype photos to check whether what Arnold uses is a real tread pattern for this loco, but I doubt it was just a bunch of rivet-like bumps. So to me this in not good feature on this model.
I was also asked how the shell was put together.  The next 2 photos show the inside of the shell.




The walkway is separate and it is not glued on.  The hood and cab are also separate pieces which snap together but the snaps on the sides of the hood have some solvent glue flowed into them. However I think that they can still be separated without any damage.  The handrails are super-glued to the shell.  The windows are also glued in from the inside - those might be a bit tougher to remove.  The stack, bell and headlights are also glued in.


When reassembling the model I recommend tucking the truck pickup wires into the worm opening as shown in this photo. That will provide some extra wire length when the truck swings and possibly extra length of wire if it gets damaged during soldering.


Here is the loco chassis and circuit board reassembled with all the wires trimmed and soldered to the board. It now looks much neater than the original assembly.  I also lightly oiled all the shafts and applied a small amount of Teflon grease to all the gears.  A hint for resoldering the wires: The original lead-free solder used in this model has a fairly high melting point (which if the soldering is not done fast enough can easily melt the delicate insulation on the wires). I had to crank my soldering iron's temperature up to around 750 degrees F to melt that solder. After unsoldering the wires I used solder wick and some paste rosin flux to remove all of the lead-free solder from the solder pads for the wires. When reattaching the wires I first trimmed the wires and tinned them using standard 60/40 electronic solder which has a lower melting temperature (I select 650 degrees F on my iron). Then I solder those wires back, again using the 60/40 solder. The lower soldering temperature is less damaging to the wire insulation.


The couplers used in this model are a bit unusual. These couplers were initially used in the Arnold's initial U.S. prototype model:  the U25C.  But I don't own that model so I never had a chance to examine these couplers up close until now.

The coupler follows the typical split-shank design utilized in many MT (Micro-Trains) N scale couplers.  But the coupler head itself is quite a bit smaller than that of the the MT coupler.  Here is the Arnold coupler on the left, with N scale Micro-Trains coupler on the right.  Appearance-wise the Arnold coupler's shape and size is closer to the prototype knuckle coupler.  But the overall molding quality is not quite up to MT standard. The surface of the Arnold's parts is rougher, the mold draft angles seem to be a bit larger, and there is some flash on the parts (a piece of flash is visible in the photo above).  Also, the metal uncoupling pin is round in cross section so it can easily rotate out of proper alignment. MT uncoupling pins have flattened shape so they cannot rotate out of alignment.


There also seems to be a bit of a compatibility problem between the Arnold and MT couplers as shown in the above photo.  I'm surprised that this was not mentioned when the U25C (which was the 1st model to use this coupler) was introduced.  While I have not yet tested this model on a layout, I clearly see this problem on a piece of test track on my work bench. As the above photo shows the opening inside of the Arnold coupler knuckle is too shallow. The MT coupler hits the back of the opening and the knuckles do not clear each other to couple properly.  If some force is applied to shove them together (or if one of the couplers is swung slightly to the side then they will couple. But a gentle-coupling doesn't seem possible. I guess I will have to test this loco on a layout to see how well it will couple to other brand knuckle couplers.  This problem might also be fixable with some small trimming of the Arnold coupler. I will revisit this coupler in more details in the future.  It is a good looking coupler - too bad that it doesn't seem to work very well. I think that the opening behind the knuckle probably only needs to be about 0.005" deeper for it to work more reliably with MT couplers.

UPDATE:  I tested the loco on a layout and it was not easily coupling to MT coupler-equipped cars. I The couplers had to be slammed together hard to get the couplers to coupler.  But the Arnold couplers easily coupled to Accumate couplers.  Those were the only 2 kinds I had handy to try.

Overall, I'm quite happy with the model's appearance and performance.  Thanks to its gearing ratio of 35:1, and a coreless motor with good torque, this model has excellent slow-speed performance and realistic top speed.  It was able to pull 30 40' Micro-Trains boxcars on a flat and tangent track, but that number will go down as the train travels through curves or up an incline. Small switching locomotives don't normally pull 30 cars in any case.  But the jury is still out on the longevity of those low-end coreless motors, since they do not have replaceable brushes. Hopefully replacement motors will be available from Arnold for years to come. While this model is not 100% perfect, Arnold has a winner on their hands.

On the other hand, I'm a bit put off by the price when comparing this model to much better-made models from Kato. Just like Victor Miranda says, I think that for what I get here for the price, the model is overpriced.  However, it is the only game in town...


EDIT: Photobucket disaster - moved all the photos to local gallery.

[Ed Kapuscinski]

I must remember to move this to the Best Of forum when it has run its course here.

Amazing work here Pete! Thanks for sharing it with us.

[Doug G.]

Thanks Pete! Very thorough!

Doug

[GaryHinshaw]

TLDR.

(I kid - great review!)  But you forgot to include the scale icon. 

[Chris333]

You compared it to the Kato NW2. I don't remember ever getting slow speed out of the Kato. I ended up putting a gearhead motor in it. If this runs slower, it'd be worth the extra $.

Oh I updated the schematic:

   Plus no cab rub! 

[MVW]

Well, that's just, like, your opinion, man.

Just kidding. An exhaustive dissection, incredibly well documented. I'm not a tinkerer, but I can certainly appreciate the time and effort, and recognize the value for others. Nicely done.

Jim

[jagged ben]

Coupler surfaces being rough is a good thing; it makes them less likely to slide off each other and come uncoupled under strain.  That coupler looks so much better than anything else I've seen, as long as it works as well with it's own mates as other brand, it oughta be the new standard.

[peteski]

TLDR.

(I kid - great review!)  But you forgot to include the scale icon. 

Guilty as charged - but you already fixed it for me. 

Chris is a DC modeler - all the power to him.  Although I think that Irecall him running a loco with a sound decoder in it.   

I just wanted to explain the circuitry to the modelers who might wonder why there are so many electronic components in a simple DC loco.

Thanks guys - now you all know why it took me so long to post this info.

[eja]

WoW!

I don't want an SW1, but your review reminds me why I participate on this forum. 

That is some serious effort on your part and an excellent write-up regarding this new locomotive.  Thank you very much for your effort !

Ed Anderson ....aka  eja

 

[up1950s]

So that's why it's so quiet . The noise can't escape the lube O plenty . Thanks for all the time and effort of the write up Pete .

[Joetrain59]

Great job Peteski. And now I now why I had difficulty getting cab end of shell back in place. I had 1 air tank come off, and a hell of a time trying to get it back into it's mounting slots. It's slippery, and an odd shape. Just used some white glue on inside to adhere it to fuel tank.
 Now, I wonder if the rear LED board can be used for MTL SW1500? No experience in getting parts from Arnold/Hornby.
 Joe D

[peteski]

Great job Peteski. And now I now why I had difficulty getting cab end of shell back in place. I had 1 air tank come off, and a hell of a time trying to get it back into it's mounting slots. It's slippery, and an odd shape. Just used some white glue on inside to adhere it to fuel tank.
 Now, I wonder if the rear LED board can be used for MTL SW1500? No experience in getting parts from Arnold/Hornby.
 Joe D

Thanks Joe.

If you look at the parts breakdown (included in the first post), Arnold does not sell the rear LED board separately. You would have to buy the complete circuit board (which has the LED board soldered on it).  I don't think that would be very economical.

[ChristianJDavis1]

This is a very interesting an well-done review. For people like me who like to take things apart the second they get them, it is a nice change of pace from, "here is the model, I do not like it because..." Have you thought about doing more reviews like this? I doubt you would want to do one for every model (seeing as @spookshow does an excellent job already), but I think it would be interesting to see the fine details of the interiors of the models you own, as well as observe your unique thought process.

[mmagliaro]

Splendid review and photos, Peteski!

There are things about what you show here that I don't like in this engine, but mostly, I really like it.
It looks serviceable, kitbashable, and has decent bones.

I worry about:
- that inexpensive coreless motor
- the little rubber shrink tubing thing they put on the axle to keep the gear from sliding over (maybe a thin bit of something
sturdier in there that wouldn't induce so much friction if the gear happens to rub against it?)
- the plastic gears cracking on those splines

But I will hope that the gears don't crack and the coreless and tubing can be upgraded.

Overall, I still really like it, and thank you again for the nice review!