It all started with a caboose

The inspiration for this project came from a friend and fellow modeler, Jon Harrison, who models the Cajon pass and its rail movements, topographically and prototypically accurately. It is impressive.  On the prototype, during the 1940’s one to three steam helpers would be assisting Eastbound freights. As was customary on the Sante Fe, the helpers would be cut in, in front of the caboose on the rear. When the train reached Summit, the rear helpers would cut off and back the caboose into a graded siding, where the brakes would be set on the caboose. The helpers would move out and position themselves for their return. With the siding switch thrown, the caboose brake would be released and the caboose would coast down the grade and couple onto the back of the train with no further train movements (most of the time). If the caboose didn’t make it all the way, the helper could complete the shove onto the rear of the train. Jon had tried many variations, but could not get his caboose to consistently connect to the end of his train. It needed a little extra boost to assure coupling. We discussed using a band drive around one of the axles (much like the old Athearn HiFi drive) powering the caboose simulating coasting, but the drag, when not energized, would likely be a problem. One  would also need to find precisely the right strength band to enable movement but limit the drag.

 
DC Motors and Athearn Truck

Mechanical Department

After thinking about this for some months, I thought a free-wheeling, un-geared traction motor (a small DC motor) might do the job. The motor shaft would support the two wheels, and turn freely when not powered. But it would have to be a dual shaft motor and very small. I actually started looking for two coreless vibrator motors that I could mount back to back. There are 4 by 6 mm motors, but when placed back to back, they require longer clearances for electrical lead attachments, and motors of that size have very little torque. I finally found a dual shaft N10 DC motor on Ebay: https://www.ebay.com/itm/262973201686

That was just about the right size. It also had a normal, wound armature.  The shaft was 1.0mm metal. It had to be insulated from the wheel rims, which I also wanted to be metal, not plastic.

The initial design would use Kadee wheelsets, which have metal wheels and plastic axles. The axle was cut close to the back of the wheels as possible, and then sanded down using a Dremel disk sanding tool.

 
Sanded Wheel insides

I started to lay out the axle centers for hand drilling when I realized that the 1mm holes needed for the motor shafts had to be as centered and as perpendicular as possible to eliminate wheel wobble. So I mounted each wheel in a three piece self-centering lathe chuck and drilled the 1mm holes in the plastic axle centers. I made a small depth gauge for each axle hole, so that it was about 0.5mm deeper than the motor shaft. This was so I could add a tiny amount of glue to hold the axle in place and have a bit of room to accommodate the excess glue. I used Loctite 620 shaft cement to do the job.

Before attaching the wheels, I attached the smallest ultraflexible wire I had on-hand. This was about 34 gauge stranded wire with a rubber not plastic insulation. Look for ultra-flexible “tone-arm” wire used in record players. I have had some good luck with the individual wire used in some computer mouse cables too. Miniatronics also offers some Ultra Flexible 30 Gauge Wire. Before soldering each wire to the motors, I looped the wire through the tiny eyelets, and bent over the eyelet towards the outside of the motor case. This gives the flattest attachment with maximum wheel clearance. Next I drilled two 1/16^th inch holes on opposite sides of the truck bolster to accommodate the wires entering the car floor. The motors with their glued wheels were then inserted into the truck. Two 1/8 inch pieces of .005 phosphor bronze metal were cut and AC glued to the motor housing top and bottom to stop the motor housings from spinning. After routing the wires through the car floor, the trucks were attached with 2-56 screws. I used Athearn plastic Bettendorf truck frames.

The other truck was prepped with Intermountain wheels, whose wheels were polished clean with a brass wire brush. Doubled 0.008 phosphor bronze wire was soldered to a small brass pad, drilled for to clear a 0-80 self

 
Wiper Assembly

tapping screw. Two such assemblies were screwed to the top of the plastic truck frame and bent to wipe each side of each wheelset, enabling four wheel pickup. Small wires soldered to the wiper assemblies were inserted in 1/16^th holes through the car floor to provide track pickup for the traction motors.

 
Bottom showing traction motors with torque arms attached and pickup truck

Driving for Traction

First I want to emphasize that the original intent was to give the Cajon caboose a kick as it was coasting downhill. That is a far cry from driving a 2-10-2 with a 50 car train up a grade. Nonetheless, I thought that the controlled Pulse Width Modulation (PWM) drive from a DCC decoder might be able to be “tuned” to control the motor pair in a single truck. The motors are rated 3-6 Volts and I figured that the BEMF control feature might come in handy. Putting the 2 motors in series should add the generated BEMF, even though it may be somewhat noisy or even erratic when the decoder reads it. I was concerned whether these tiny motors would have enough torque to move the caboose at all. I was also concerned whether these were strong enough to overcome the starting friction on a flat track. Slow speed control was a vague hope too. I really didn’t know how this would perform.

I used a Digitax DZ123 decoder, with torque and BEMF turned on. After a little fiddling around, I settled on these CV settings (using JMRI decoder terms):

Anxious to see if any of this would work, I tried it out here:

You’ll note that there is fair to good, but not superb control at low speed. I needed to add weight to the caboose to get enough reliable pickup from the rails. Motor torque for a single car was more than enough. Starting friction was and is an issue particularly with my wheel pickups. These could be limited to a single 0.008 wire instead of the two. I also made no attempt to adjust the drag on the pickup truck. Besides car weight, the Pulse Wdth Modulation (PWM) decoder control frequency was adjusted lower and was noticeably more effective. The kick start value may need more experimentation too. Nonetheless, I was amazed that this would operate with relatively slow starts and slow running speed. I could not get it to “crawl” along, but it clearly shows that it could be used to kick the caboose down the Cajon grade.

Work is continuing wit the Cajon Caboose. What follows is a video of the prototype, motor-equipped caboose simulating operations on Jon Harrison's Cajon Pass layout. Jon continues to tinker with this, but he has captured the essence of the operation we were intending to re-create:

Lindsay Ghost Car

In the mid 1950’s a model railroad vendor named Lindsay sold a “ghost car” – a boxcar with a motor drive connected to one axle of a freight truck. Reports are that it was used to increase the pulling power of the locos back then, but some modelers put the car on a spur and moved it about surreptitiously during an op session to the surprise and amusement of those present. I believe a European vendor offers a similar ghost car today.

Lindsay Ghost Car

Besides operating as a Cajon Caboose Kicker there might be some other possibilities for these single axle traction motors. This could include a tender or trailing truck steam booster motor. Small operating vehicles such as inspection cars and rail buses might benefit too.

An intriguing opportunity opens up for diesel modelers too, but not as traction motors per se. Consider the fact that these would actually operate as close to diesel-electric motors as one might see in HO scale (I do not attest to the quality of control however, without gearing).  As such when not powered and still rolling, if the motor terminals were connected to a low value resistor, they would act exactly like the dynamic brakes in a prototype diesel. The turning motors would act as generators. They could be used to re-charge on-board batteries or sink their power into a resistor and dissipate the power as heat, just like the prototype, and slow the train. How much? I have not tried that variation yet!

Now where is the switch for real dynamic braking on your proto-throttle?

‘Hope you enjoyed this. As always, appropriate comments and suggestions are always welcome.
Have fun! 
Best regards,
Geoff Bunza

NSWL PDT, Stanton

For the problem you’re trying to solve that seems like an interesting idea.  And I’m impressed that your gizmo ran as well as it did!  It did go a bit like a rocket, and the speed range doesn’t really seem to get down to what I’d call slow, but still pretty impressive.  My experience messing around with back-emf decoders and multiple motors is that neither series nor parallel is really great, but if I remember right I got slightly better results with parallel for the motors.  Also digitrax back-emf is not as good as zimo or loksound for slow speed.  If you want the best possible control at slow (or since there’s no gearing perhaps moderate) speed, try two really good back-emf decoders, one for each motor, programmed for the same address.  Probably not relevant for the problem you’re trying to solve though.

NWSL sold a PDT which was a motor parallel to the axle and geared to it, pretty much just like real traction drives.  That got discontinued a while back, but they now have the Stanton drive which is a truck with the motor perpendicular to the two axles, and geared to both.  In both cases there was a reasonable gear ratio.

I’m curious what that prototype drive in the photo your video was that did seem to be a motor on the axle - never seen a photo like that before.  The prototype traction drives I’ve seen pictures of and specs for are motor hanging off to the side of the axle and geared somewhere in the vicinity of 4:1 (usually expressed as something like 62:15), depending on speed vs power requirements.

@Ken re:Comments

Hi Ken,

I was amazed I had any control at all!

The key thing with this was it had to be free rolling when unpowered. The only other alternative would be to speed match a geared set and consist it -- which I would not come close to considering. The Digitrax decoder was available, that's why I used it. Trying other decoders may be attempted if I pursue this.

The PDT and SPUDs were all geared and never free rolling so all of them were out, and I don't know if any were made to fit a freight truck.

I pulled the photos from my own files. I don't know where the rusty one was taken. The modern diesel was taken at the Harmon shops in NY.
Have fun! 
Best regards,
Geoff Bunza

Got me hooked

Geoff,

Ya got my interest up. I'm going to give it a try. I'll need to order some motors first. I have another idea for mounting the wheels. I'll explain when I get to doing the project with pictures. Until then, great post.

Bernd

@Bernd Setting the Hook

Hi Bernd,

I thought you might see some opportunities with these.

Here are some more details from experimenting with the motors as presented:
-- I originally wondered whether these would have enough torque -- for one car -- no problem, how many cars this could actually pull is still an open question. It is possible to have both trucks powered with four motors (cheap at less than $1.00 per motor originally). The power pick up from the rails needs more attention to reduce the drag, especially in in Cajon caboose kicker application, as I want it to be free rolling otherwise. The motors are not coreless -- they have 3 pole armatures. Adding weight to the caboose did increase traction, ultimately with a trade-off with start up friction (not really a surprise when you think about it).

-- I used Kadee wheels which have metal wheels and a plastic axle. I plan (when I can find time) to use two insulated wheels from two Intermountain wheel sets as they have a metal axle set in an insulator on one side of the wheelset. I am hoping the metal axle (attached to the motor shaft in the same fashion as the Kadee wheels) will have improved free rolling abilities.

-- The limited control experiments with the DZ123 decoder indicated that BEMF can have a very positive effect with the two motors in series. I did not try much experimentation with the motors in parallel. A decoder with better low speed control capabilities should improve operation too.

-- While it is not of much interest to the Cajon caboose application, these same motors could be used with the pulley arrangement you demonstrated in other loco drives, and similar to the ones presented here:  http://www.clag.org.uk/axle-hung.html   

Ultra-tiny drive systems might enable interesting new models -- like working scale speeders. I look forward to see where your skill and insight takes this.
Have fun! 
Best regards,
Geoff

A couple of thought's

I'm thinking of using some other wheels sets also. My thought is to make a larger axle over the 1mm shaft diameter and an pointed end. I think I'll need to actually do one and take pictures than trying to explain.

Also was thinking of using four motors in series and controlling them with a Deltang 6 volt receiver/motor drive like I did on my Atheran wreck crane. 

I've tried the pulley arrangement with the square drive belts from Nigel Lawton. Here's an example. I used his square belts on pulley's I made.

I'll post more when I have the motors. 

Bernd

Fantastic

Lots of potential here. 

Interest and questions

Dear Dr Geoff,

Another inspirational project, dang Dr Geoff, you're unstoppable...

I have a future layout project which could definitely use this to replicate a specific prototype US SG modern-era operation (Research done and on-file),

however, it will require some additional custom control TUI work to make sense in real-time...
(possibly using a purpose-kitbashed "simple JMRi throttle" or 3? ).

Something which I'm obviously missing,
are the powered-axles held in the delrin truck by the motor-shafts extending thru the wheels,
(IE the tips of the motor shafts are acting as "pointed axle ends"),

or somehow otherwise?

I'd also love to see a qualified "minimum required tool list" to achieve this,
somehow I doubt a manual hand-held pin-vice, 1mm drill bit, 
and unlimited bundle of "unfounded self confidence",
would be enough to consistently/reliably achieve a suitably concentric/perpendicular/smooth-running axleset which doesn't bounce/wobble/shimmy down the track...???

Hmmm, now where did I put those Exactrail Railbox cars?

Happy Modelling,
Aimin to Improve,
Prof Klyzlr

PS Now that NWSL is back, could this be made into a more "plug-n-play" project by using NWSL shafts and shaft-bushings to adapt the motor shaft to common axle-dia + length?

PPS the "freerolling" characteristic is definitely a good thing, esp when such cars are in a regular loco-hauled train, but I can't help wonder what the co-lateral effects would be if the cars were being "driven" while-in-train:
- same direction but slower that the loco
- same direction, same speed,
- same direction, faster speed
- opposite direction, slower speed

esp as far as:
- threat to the DCC decoders
- BEMF "fighting" between decoders

???

@Prof re:Questions and Comments

Hi Prof,

I'm glad this could tickle your fancy! 

are the powered-axles held in the delrin truck by the motor-shafts extending thru the wheels,
(IE the tips of the motor shafts are acting as "pointed axle ends"),
Close -- the wheels are Kadee wheelsets with plastic axles and metal (sintered I think) wheels. The 1mm motor shafts were fitted into the cut off axles on the inside of each wheel after sanding down to meet NMRA wheel specs (in an NMRA gauge). I used Loctite 620 shaft cement to secure the motor shaft to the axle. One wheel needed a spot of AC glue to hold the axle to the wheel. The original Kadee pointed axle ends were retained. I will often build a prototype with plastic parts and later upgrade them to metal in some cases. Plastic is easier to work with, and cheaper material when I need to discard an attempt and re-do construction. This almost always happens in my projects. These days I assume I will build three prototypes before I get things right. I plan to upgrade the wheelsets and use two insulated wheels from two Intermountain wheel sets as they have a metal axle set in an insulator on one side of the wheelset. I am hoping the metal axle (attached to the motor shaft in the same fashion as the Kadee wheels) will have improved free rolling abilities.

I'd also love to see a qualified "minimum required tool list" to achieve this,
I started with a pin vice and 1mm bit! LOL but quickly realized the even a small deviation was going to cause problems. The wheels were cut at the back axle with a pair of flush-cutting, side pliers, then sanded down with a Dremel disk sander eyeballed to be 90 degrees to the rear of the wheel. This was a good call in the end as a perfect 90 degree angle was not necessary, and turning the wheel backside flat in a lathe tended to loosen the plastic axle in the wheel. I did resort to chucking the flattened wheel in a three jaw self centering check in my small unimat lathe, and used the tailstock to carefully drill a 1mm hole into the flattened axle on the wheel backside at slow speed. All other operations were done with hand tools: files, shears, etc. I suppose that a steadier hand than mine could make the pin vise and 1mm bit work, but it would have taken multiple trials for me to even come close. I strongly suspect that moving to use the Intermountain metal axles would make this operation more problematic.

PS Now that NWSL is back, could this be made into a more "plug-n-play" project by using NWSL shafts and shaft-bushings to adapt the motor shaft to common axle-dia + length?
Maybe. Remember that my original criteria was to place these in a freight truck. If you didn't need the axle points, and you had the appropriate sized shaft bushing(s) to fit the 1mm motor shaft and the receptacle for the axle on the truck, it might work. I don't know of any offhand that would work.

PPS the "freerolling" characteristic is definitely a good thing, esp when such cars are in a regular loco-hauled train, but I can't help wonder what the co-lateral effects would be if the cars were being "driven" while-in-train:
- same direction but slower that the loco
- same direction, same speed,
- same direction, faster speed
- opposite direction, slower speed
You are describing the same situation for a helper locomotive independently controlled with a separate DCC throttle. This could act as a drag on the train, bunch cars a bit (slacken the coupler connections) or ease the drag on the loco to enable a smaller loco to pull a heavier train.

esp as far as:
- threat to the DCC decoders
- BEMF "fighting" between decoders
I don't think there is a "threat" (meaning possible damage) to the other decoder (presumably in the loco). The BEMF reading in the loco decoder may bounce around a bit more, the traction motors are driven to "help" the loco at the head end. If the train is long enough, the circumstances facing the loco could be very different than a driven car in the rear of the train: one could be moving downhill and the other uphill, one on a curve and the other on straight track, etc. The BEMF's seen by two decoders (loco and rear car) would be measured independently, and applied separately.

With all of that said. remember that unpowered traction motors could be made to behave like dynamic brakes to slow a train, or used as regenerative brakes and charge batteries simply as a function of their movement (rolling). How about that possibility for charging independent, power-on-board models?
Have fun! 
Best regards,
Geoff

Just use the brakes

Here is a high level sketch of an idea:

How about just using the dynamic brake characteristics to simulate air brakes in each car in a train.  Put a single motor on a single axle of one truck per freight car.  Put a cheap decoder in each car.  That decoder's only function would be to activate the brakes.  It would not drive the motor, it would not use BEMF, etc.  Simplest version would be to have the decoder just switch a resistive load in and out across the motor terminals.  On/off braking.  More realistic one might have a resistor ladder, with the decoder selecting taps to determine the degree of dynamic braking force.  I haven't done the calculations to see whether a simple FET switch with its gate controlled by a decoder function output would be adequate for switching the resistor into the circuit, but I suspect that would be fine- a pretty simple circuit.  Also would need to calculate the heat generated in the resistor to see if that would be an issue in a sealed plastic box car.  (maybe put it in a old reefer with ice bunks containing real ice, and simulate the dripping water from the melting ice? ha ha)  Could program all the decoders in a train to the same address.  Or, with different addresses per car and a script, could sequentially apply brakes down the length of the train to imitate the propagation of air pressure changes.  Would not work for brake release on starting a stopped train though, because there is no dynamic braking force when starting up from a stop.

Anyhow, this is all very intriguing.  At this time, there is a lot of effort devoted to developing very small high torque motors for use in miniature robots.  There are tiny brushless pancake motors that have been printed on copper clad printed circuit material.  Here is a good description of one such effort that was described in the IEEE Spectrum magazine: https://spectrum.ieee.org/geek-life/hands-on/how-to-print-an-electric-motor  Not aware of anything in that direction that is commercially available at a price that would make sense for this application.  There are tiny electric motors that are sold for R/C airplanes.  But, they have been oriented towards high rpm/low torque applications.

Hoping that someone with some electric motor design chops will chime in.

Dennis

Success at Cajon Pass

Hi All,

Work is continuing wit the Cajon Caboose. What follows is a video of the prototype, motor-equipped caboose simulating operations on Jon Harrison's Cajon Pass layout. Jon continues to tinker with this, but he has captured the essence of the operation we were intending to re-create:

Neat

Pretty cool that it lets you replicate the prototype moves - nice!

So now...

@Prof K re:Kick Moves

Hi Prof,

Ok, so now, how do we control/provoke the impression of a "kick" move on flat track?
First, let me make sure what you mean by "kick move." I will assume that you refer to a loco in quick acceleration with an accompanying freight car, that rapidly decelerates with the coupler knuckles to the car open, so that upon quick deceleration, the car continues on in the same direction by itself leaving the loco behind.

This should actually be relatively easy, and could be accomplished in different ways:
1. Use a second throttle for DCC decoder control on the car equipped with traction motors. Start the car motors up before the loco deceleration, and the car should continue on its own.

2. Use a reprogrammed SMA20 decoder such that when you turn on a function in the car's decoder, it sequences the "kick" for motor on and then decelerating to a stop over whatever distance. Note well here that the car "deceleration" could be triggered by a magnetic sensor in the car (Hall effect device or reed switch) with a magnet on the track, to bring the car to a stop at a specific location.

3. Use a small 3 Volt battery on board with magnetic sensor, and two magnets on track, to turn on and off motor kick via tiny latching relay. Remember these are low current DC motors. DC control is also possible. This could also be modified in many programmatic ways by turning on and off a small Arduino on board to graduate the start and stop as needed.

Additional comment: At the point of magnetic switching, there could also be a electric uncoupler, anticipating the loco deceleration for the release.

If "kick move" refers to some other variation, please explain.
Have fun! 
Best regards,
Geoff

NOOO!!!

Dr Geoff,

you are an inspiration  but there is NO WAY I'm going to redesign the top end of the incline on Corrimal to replicate the prototype's gravity shunting of 20 loose-coupled unbraked loaded coal skips from the arrival track via a downhill run to an uphill stretch of track and the dead end, and then the reversing move that takes them downhill to the top of the incline and the start of the cable haulage on the incline down to the screens. NOOO!!!

BTW - some years ago Prof and I were considering how to replicate gravity shunting of wagons on another part of the layout. This might just happen now - but only after we've got everything else done and detailed. Your approach has been filed for future use. Thank you. 

And no, none of this is Prof's planned application,  

Kick'n hard (from the front to the back)

Dear Dr Geoff,

You take the term "Kick" corrrectly

The "2-throttle" ("Loco-Throttle" + "Car-Brake" units)
idea appeals for "2-person op crews" (1x Engineer and 1x Conductor/Brakeman),
bu the idea of "throttling-up" (more like "releasing the brakes on") the caboose, possibly out-of-sync with the loco,
brings concern about excessive wheelslip/wear on the caboose and general "Operator TUI Input/action =/= logical physical motion" cognitive dissonance...
(This is part of why I asked previously about Loco VS Caboose "speed/direction differential" testing).

As for the perceptually more-common "single operator" situation,
having the Caboose automatically "keep rolling" due to excess-Decel setting without any user intervention holds significant appeal to me... (also would make for an entirely-prototypical "don't shove it too hard" balance for the "engineer", lest the caboose meet standing-cars or spur end-stop with too-much momentum?)

I guess what I'm thinking of is more like an automatic "electronic flywheel" rather than a "needs manual intervention to drive" gag...

...and adding a SMA20 decoder, teamed with a ST "SoundCar" decoder for audio support,
is well do-able...

Hmm, better be cautious of feature-creep!

Happy Modelling,
Aim to Improve,
Prof Klyzlr

PS OzTrainz, I'm not thinking logging or mining with this...

PPS That said, this could well be the solution to modelling a "Hoodwinked" style "Japeth Mining" tramway...
 

Hmmm.

Anyone for an HO scale version of the Gringott's vaults, complete with a goblin run car?

Would these give any tractive force?

I'm thinking i might get another car or two up my 4% switchback with a powered caboose. I plan on carting one up to the mine anyway, to use as an idler car.

@John

Hi John,

Well... John, I'm glad you finally got control of yourself! 

Sometimes it's not the best idea to be enjoying large quantities of that Aussie beer while posting ! (Sorry, I just had to say that! LOL)

'Glad you enjoyed this. Have fun! 
Best regards,
Geoff

@Prof K re:Kick Moves

Hi Prof,

"Throttling up" really isn't much of an issue because it's likely to be less than the top speed achieved by the loco. Keep the car light and wheel slip is not a big deal either. The distinct advantage here is the lack of gearing -- free rolling ability. Depending on how far you want the car to go you might literally just want the car to roll to a stop by itself.

No matter how the car itself is powered DC/DCC/Battery consider that the Kick sequence could simply be started by some event (switch closure for example) and the rest be a simple timed sequence.

By the way SMA20 decoders can do near CD quality sound themselves.

Have fun! 
Best regards,
Geoff

@Michael T re:Tactive Force

Hi Michael,

Would these give any tractive force?
I have not run any tests of consequence concerning how much these could push or pull.
The caboose with some weight in it could climb a 2% grade. It could push a lightly weighted boxcar.
I would suggest, since I know the car's performance was very sensitive to the weight of the caboose, that another round of changing the decoder CV's might be in order. Also if I were going for max traction, I might consider powering all four freight truck axles and not just two.

That's not much to go on, but it's all I've got right now. I always looked at this only in terms of the Cajon caboose kicker, the rest needs follow on experiments, which I may or may not do.

'Hope this helps. Have fun! 
Best regards,
Geoff

Tender

I'm hoping someone picks up this idea and decides to try it with a steam locomotive tender and figures out how to use a motor on every axle to boost the pulling power of a locomotive. But maybe the boost of a given one of these little motors isn't that strong (yet). 

Possibilities with streetcars

Another great idea Geoff!

I ordered 20 of the little motors to do some testing. Looks like the motors are described in the auction as being rated at 3V each, so perhaps four of them in series under a car it may give a slow enough operation with enough combined torque to adequately propel a model around the layout.

If it all works out, I would love to try putting two groups of four axles under a big articulated Illinois Terminal class C freight motor like the one pictured here. I have been dreaming of building one but couldn't come up with ​an easily-produced drive for it that didn't stick up through the decks.

Keep up the great work!

AJ Chier

@AJ Chier re: Streetcars

Hi AJ,

I would be most interested in what you achieve. I have not gone very far at all into putting these to the real traction test. Good luck with your modeling. Please let us know how it goes.

Have fun! 
Best regards,
Geoff Bunza