...oye vey...

Your reasoning for DCC is, unfortunately, a bit...well, You've come up with a myth to perpetuate a belief system.  Or in otherwords, you've started with a result and then rationalized how that answer best fits the question.  Hardly scientific at all!!

The fact of the matter is, the motor inside the locomotive still runs off a DC voltage.  This does not change regardless of where you put the control source.  Ever. Well, ok, maybe we'll convert to AC power someday, though I'm very skeptical of this EVERY happening.

Now in the old days, which for me was 1989, we learned how to get that sort of performance you discuss with a basic powerpack and a finely tuned and calibrated wrist.  That's what we learned how to do with those hours spent running around the carpet oval: we calibrated our instincts to produce accurate visial train movement.  But of course, you want the train to do Everything Automatically and all you want to do is turn the knob, and you don't want to learn how your locomtoive naturally runs, you want it to do all that automatically for you too.  So this means we don't do that anymore.

So we have more devices in use to control the locomotive performance and you put a box in the locomotive.  However, your "box" does not have to be IN the locomotive in order to provide similar operation.  It could be in a box under the layout, or it could include a box with a rhetostat that then talks to the box under the layout.  Either way, the location of the box won't bother the DC motor one bot - it may make the perpherial features a little interesting, but this is where you turn on your brain box and remember what engineering capacity is available to us.

All the ideas you discuss in this article as being only available in DCC are equally viable in DC if you're willing to spend the time to electrically engineer the solution.  BEMF, for example, could just as easily be done using a couple capacitors in the motor circuit, so that any changes in direction require an electronic dump followed by an electronic gain to get moving again.  If you needed to make modifications to operational characteristics, a couple linear potentiometers with screw adjust in the circuit would give you an intermediary point at which you could augment how the locomotive responds to voltage, how much voltage charges the capacitors, etc.

The problems of constant lighting were also solved years ago.  Directional lighting, as complex as it looks, turns into a diode circuit that directs current based upon which direction the axle is turning.  Sound might seem like an issue, until you realize the volume control is accomplished with a slide switch, driver timing is accomplished with a mechanical or optical cam, and individual sounds have also been figured out by the manufacturers as well.

So the argument you have given is indeed a sieve without any wire between the holes.  Yes, water can fall out of a bucket without a lid, but has DCC all but made you forget about gravity which holds it there in the first place?

For those who are still operating DC, there are still layouts where more than one locomotive will never be not only unnecessary, but quite simply not feasible due to the limited arrangements of the trackwork.  Despite all the magical qualities of DCC, Trains still don't pass through each other, jump over each other, or step asside so another train can go past them.  And as long as this is true, DC is still a very inexpensive option for a very large number of people, particularly given the number of DC locomotives available in the universe, the short supply of space so many have, and the insatiable zeal so many have for collecting.  A calibrated wrist alone is a very CHEAP, particularly when one figures the saving per unit provides enough cash to purchase another 1 to 5 similar DC locomotives - depending of course on the price of the decoder and the price of the locomotive.

The greatest selling point about DCC at this point in time is that it is the easiest and cheapest way to put all your bells and whistles into one unit, set it on the track, and forget it.  It requires no thinking whatsoever to do it, either - you just put the decoder in, nowadays, and you;re done.  Most people, I reckon, never get any further inside their decoders beyond setting the road number.  In short, it comes down to a matter of convienience. 

At this point DCC also provides forward compatibility with the future, a furture you rightly state is pretty inevitable - in otherwords, you can take the unit to the much larger club layout, friend's layout, or your future layout, and run it there too.

But this arguement that a motor will behave differently on DC power from one intermediary device versus DC from another intermediary device, well, it's simply absurd!

Theory and practice

Benny:

Yes, at the heart of it, DCC is delivering DC to the loco motors - but you're playing semantic games.

"DCC" is Digital Command Control and "DC" is a straight power pack, to spell it out. Straight power pack control off-the-shelf doesn't have any of the loco tuning capabilty of DCC off-the-shelf.

Let's stick to what's commonly available off-the-shelf, shall we?

Sure, if you're an electronics engineer you can design your own "DC" circuits to do what DCC does and beyond - but how likely is that to happen for the 200,000+ average modelers out there?

Don't confuse pie-in-the-sky theory with reality.

Benny

Just reading what "could be done" in DC made my eyes glaze over, honestly.  As Joe says, how many people who want good performing locos and simplicity of operation are going to make things MORE complicated by trying to build all these "simple" circuits you talk about.  A new person coming into the hobby and even experienced people in the hobby that want to run trains realistically would ask the reasonable question - why would I spend so much time on a limited returns investment in DC when I could buy the $20 decoder and spend an extra $70 on an entry-level DCC system over a high end DC power pack?  No matter how you slice it, DCC is vastly simpler and still more powerful and capable for upgrades down the road.

But this idea of the internal

But this idea of the internal electronics within the locomotive is still no more pie in the sky than DCC itself.  It's just how this story has gone.  Indeed, there's the lastest round of locomotives which came with DCC/DC capability - they come with control boxes to control the additional features inside the ocomotive, such as bell and whistle.

And there are many people who still obtain very realistic control out of their locomotives using just their calibrated wrists.  Using low end powerpacks.  Essentailly, what this comes down to is the arguement between using your $90 solution [+$20 for each additional locomotive] versus a $5 or $10 pack - that's all that's needed to supply the variable operating voltage.

The premise of the arguement is the issue.  The fact is that DCC decoder offers a more convienient package - this is a nonissue.  But this idea that somehow the DCC decoder supplies the motor with something different than what the traditional powerpack supplies the motor, or what any stationary device can provide the motor, is simply bad mythbuilding. 

Mythbuilding

"But this idea that somehow the DCC decoder supplies the motor with something different than what the traditional powerpack supplies the motor, or what any stationary device can provide the motor, is simply bad mythbuilding." 

I'm not too sure about that.  With my DCC system I can program a whole lot of parameters into a decoder to manipulate throttle response (starting voltage, midrange and top end, back EMF characteristics, fine tuning so any mechanism can run with any other, etc.).  The very best wrist calibration with a top-end DC power supply isn't going to do that unless there's some kind of programming I'm not aware of.

I think Benny is referring to

I think Benny is referring to what the motor receives electrically. The motor only knows voltage and pulse width. How the juice came to be and what fashioned its wave prior to the wires at the motor is moot. The motor is responding to voltage that appears at its terminals (whether continuous or PWM) and the load on its output shaft. In that sense Benny is absolutely correct.

Still, DCC is a way cool way to supply power to a "dumb" motor in my book.

See, here's the thing; joe's

See, here's the thing; joe's arguement focuses just on the motor operational characteristics.  Thus, all the benefits of DCC in terms of sounds and lights are removed from the arguement.  We have further reduced the layout complexity and size down to a single engine operation - thus removing the terms necessary for calibrating two engines to work together.

This leaves us with these sorts of things you mention, such as starting voltage, midrange and top end, back EMF characteristics, etc and so forth.  If we speak only in terms of controlling DC motor function, it is then irrelevant if the box containing the voltage logic is in the locomotive or somehow stationary on the layout.  The functional output from that box is the same, regardless.  The only fundamental difference between DC and DCC at this point then is the length of the wire between the Control Box and the motor, whereas DC operation includes the length of the track to and from the locomotive.

At this point I've seen a number of variations on DC power supplies, including a couple pretty interesting home brew supplies containing all of $10 in parts and perhaps even less depending on where they salvaged the rotary switches and the transformers.   Of all the arguements to use For DCC, this is not one.

DCC is still using DC power to run the motor. 

If you really wanted to try me on this, take a DCC decoder and hardwire leads from the track input/output and motor input/output leads; take the track leads and plug them into the leads to your DCC powersupply, and take the motor leads and connect them to the rails.  In terms of motor performance, you will have every bit as much motor capability with this setup as you would if the decoder were inside the locomotive.  Only with this setup you could effectively switch out your engine on the fly, as some people switch out their decoders from engine to engine.  Food for thought...

Holy crap, and in my last

Holy crap, and in my last post I just discovered a way to make the coolest DC power supply you'd ever see...holy G-Wiz, batman!!!   And that's how you sell DCC to the last Analog holdouts!!!!

DC can not replicate prototype throttle response...

I recall during my frist time working for a particualr (model) railroad, being assinged on a USRA Light 2-8-2 #639.  I'm all excited, and hoping I don't make any mistkes.  So I turn the throttle knob, and nothing happens.  Uh ohh.  What did I do wrong?  Did I not select the correct Engine number.  Did I press another button to cause it to go into accessory decoder mode?  What is going on.  Next thing I know, the locomotive begins to move, then take off out of control.  So I turn the throttle back to zero but it doesn't stop! Fortunately, no equipment was in front of me I didn't crash into anything.  One of the other operators noticed the difficulty I was having, and he explained to me the locomotive speed curves were programmed to react like the real steam locomotives did as you applied the throttle of the locomotive.  You can't get that kind of response from a DC Pack.

Ken L.

That's because the DC pack

That's because the DC pack does not contain the digital logic circuitry contained within a standard DCC decoder.  The DC voltage output as determined by that logic circuit, however, is still DC power. 

All DCC does is augment the DC output to provide what appears to be realistic movement to you.  Put all the DCC logic circuitry inside a box [a powerpack, as they are traditionally known] and you have a powerpack that has all the capabilities of your DCC system without ever putting a single decoder into the engine.  Granted, this operation is limited to a single engine, or multiples with the same motor characteristics, but otherwise all normal DC wiring setups [blocks, etc] would function off this setup.

A cheap DCC system is what, MRC?  Bachmann's easy DCC?  So you hook the decoder up to the Easy DCC box, hook the other end of your decoder up to the tracks, and you're effectively doing the same thing you ever did with a DC pack...except now it's a digital powerpack instead of an analog powerpack.

DCC is not DC

FWIW  DCC does not put variable voltage DC across a motor. Instead it pulse-width modulates the full voltage to make the motor run fasters/slower.  Why? Because a true variable voltage throttle needs to do something with the voltage that's not being fed to the motor. For example: A DC power pack with a 14VDC primary transformer uses some kind of voltage reduction circuit to reduce that 14 volts down to 0V, 1V, 3 volts, 5.57volts or what ever.  If it's being reduced to 3 volts that means the voltage reduction device now has 11 volts across it. AND the same amount of current as goes through the motor.

Power = volts x amps

If the motor draws 1/10 amp then the voltage reduction circuit has to dissapate 11 x 0.1 or 1.1 watts.  Doesn't seem like much? But a 1W resistor is about 3/16" diameter and 3/4" long and you wouldn't want to touch it while it's running at full rated power.  What about  6V and .4 amps?  Now that circuit has to handle 2.4 watts -- definitely getting hot!

What would a DCC decoder do with so much heat to get rid of? Besides melt?

It runs in what's called 'class D operation'.  The DCC decoder is either fully on or fully off. When fully on there's lots of current flowing through it, but next to no voltage across it (all across the motor). No many watts there.  When fully off there no current but lots of volts. Anything times zero is zero. Again, there aren't any watts being disappated. But switching the outputs on and off rather quickly the motor is 'fooled' into thinking it's being driven by a variable voltage (rotational momentum) lets the motor run relatively smoothly. With a DCC decoder the power to the motor goes on/off thousands of times a second. With a 'silent decoder' this is increased to over 15,000 times per second -- which gets rid of the buzz you can sometimes hear in a DCC power loco with slop in the drivetrain and not much rotational mass.  The buzz is moved up in frequency to an inaudible range.

Side effects of pulse width modulation?  Yup. It tends to help a motor keep spinning at low rpms without 'sticking'.

Can a DC throttle also do this?  Absolutely, the TAT-IV throttles popularized by Linn Westcott (I hope I spelled that correctly!) started with a component of 'pulse power' then converted to DC as the throttle was advanced.  Rich Weyand's Cooler Crawler (TracTronics) throttles did something similar.

Actually there's no reason when you couldn't build a DC throttle that used pulse width modulation all the time.

But, if you're building a throttle with min throttle, max throttle, acceleration, and deceleration parametes you'll have a lot of work to duplicate DCC decoder functionality.

But you'll still be short of DCC functionality.

How were you planning to operate specific locomotive lighting functions?

How about whistle blowing?  Remember, the audio on DCC people have a lot of complexity in their loco controllers.

How about speed matching different locomotives so they'll run OK together from a single throttle.

If your DC throttle has min/mid/max settings, how do you deal with changing those settings for each locomotive that wanders into your block? It could be done, but now your 'simple' DC thorttle is starting to get a lot more complex. Especially if you want the DC throttle to remember all of the settings you picked for each of the DC locos you're controlling. Between sessions, after the power gets shut off.

DC also has the draw back of not allowing multiple locomotives to be controlled in a single electrical block. Yes, there were systems developed that allowed running multiple trains on a single layout at once. Kermit Paul (March MRH) developed a progressive cab control system that would do that. But despite tons of layout wiring it couldn't give independent control of two or more locos in a single electrical block.

Does DC have advantages?  Well, yes... When I visited Kermit Paul, he mentioned working on a layout where loco consists would be drawing 10 amps or more. How big a DCC booster would be needed to accomodate multiple consists powered from a single booster?  It could be done, but I sure wouldn't want my wiring to need to support 30 amps!  And if there's a short somewhere?  YIkes! That sounds like a good way to set the place on fire!

To sum it all up, yes DC has it's place(s). But for flexibility DCC has the upper hand with customization of loco performance charateristics, indidividual function controllability, and the ability to run multiple locos in a single electrical block (plus greatly reducing the sheer amount of wires needed for cab control -- let alone progressive cab control).j

'nuff for now.

Charlie

Charlie, this is a very good

Charlie, this is a very good discussion about DCC and pulse power - very nicely detailed.

You did miss one signal, though, and that was the fact that Joe limited us to a discussion of a small layout featuring a single locomotive operation.  He asked us to focus almost entirely on JUST the motor operation.  And my premise is, quite simply put, if you build a throttle out of a DCC decoder [aka put all the funtionality of DCC into the DC powerpack, and this would be the quickest way without reinventing the wheel] you gain all of the operational characteristics of DCC on a DC layout - DC seeing as how the locomotives set on the track are all essentially legacy Pre-DCC locomotives inside.

Now You mention this issue of changing the voltage settings for each locomotive, and this is a situation where DCC is behind: DCC has not yet gotten to the point where multiple operating profiles can be kept on the chip - someday, perhaps the memory will be on par to USB jumpdrives with enough space to hold LARGE sound files in MP3 format - like my entire music library, for instance.  However, thanks to the likes of things like JMRI Decoder Pro, it's a cinch to load an operating profile to a decoder.

So if I was Mr. DC cheapskate who did not want to decoder all my old DC locomotives, and I'm running a simple layout using only one locomotive at time, I could set up this one decoder in the throttle [likely a large scale decoder, one with the highest amerage rating, since most legacy locomotives have open frame motors which in turn have high current draw] and then do all my decoder setup via JMRI.  If I switch out locomotives and I'm really onry about each one operating to perfection, I'd then fine tune the decoder to the next locomotive, save that operating profile, and then switch decoder profiles every time I swap out the engine to the profile for the next engine.

End result, I only have to buy one decoder, and I can run the 150-200 DC locomotives many of these old DC hoggers swears they have, all without buying any further decoders.  In these regards, DCC is make cheap enough that these people no longer have an excuse NOT to use it.  It's not the cost of the inital startup that drives up the cost, persay, since it's on par with a good DC powerpack; it's the cost of the individual decoders in each additional unit.  Legacy conversions aren't all that simple, either.

No arguement though that in the long run, full out DCC is the best way to go.

One Locomotive?

Like the potato chips (who can just eat one); who can just have one locomotive?  While Joe just wrote about a small layout with one locomotive, DCC advantage goes up over DC when you move beyond just one locomotive, even for a small layout.

How many MRH readers have just one locomotive?

It's not how many locomotives

It's not how many locomotives are in the closet.  Nor is it how many cars and structures and other stuff that is in the literal hobbyshops known as our individual collections!!

Neigh, It's about how many locomotives can be run on the layout at once.

If the layout capacity is one locomotive, well, now we're fighting semantics and hype.

If I only have the ability to run one engine on the mainline at a time, then it doesn't matter how many are in the closet.  Especially if my fictional railroad is a sparse town on one end with minimal trackwork and a sparce town on the other end, again with sparse trackwork and the appeareance of an interchange with a larger railroad further off.  And connecting the two towns is a single track mainline with one passing siding half way through.

If I have DCC, then every single locomotive needs a decoder - even if I can only run one at a time [single track main, blocked spurs, a passing siding]or two at a time - one on each end due to a dual cab setup, on my miserly model railroad that would make Dave Barrows proud. 

If I have a DC powerpack, all my power expense is in that one powerpack unit and that expense is roughly equivalent to what it costs for a DCC kit, before decoders.  even after this expense, I have freed up of about $20 per locomotive...for more locomotives, of course!!!  All it takes to change my layout operations is to pick up locomotive A that has been on the layout for a week and switch it for locomotive B which has been in the closet for the last ten years.  If I need an "operationally feasible plan" to get the locomotive off layout, I route it off layout through the suggested interchange at Sparce Town B, and the new engine comes in in it's place.

You ask who in their right mind would have a layout this big.  Well, such a sparce layout could very well be a set of shelves along three sides of a room, in essence the entire layout being 10'x10'x10' but only 12"-18' wide and perhaps 3"-36" deep - because epic scenary can go down to the floor!!

Get creative...

Hee hee

What has Joe stated about the point of "Reverse Running" - to take a contrary approach to provoke discussion.  I say, Joe, you've done it again. 

Yep, Dave ...

... Works like a charm! (wink)

One Locomotive or Many

I have had DCC for well over ten years.  One of the common threads in a DC vs DCC argument is the cost to convert all of those locomotives to DCC. I probably have close to fifty locomotives but only about a dozen have been converted to DCC.  Its not cost and its not time.  It made me realize that I have a lot of "stuff" in the closet that I probably will never use.  As a result I have a written plan as to what I need for the layout operations I desire.  It helps me put off the urge to buy that cute locomotive.

It helps....but sometimes I just have to have it! 

"Provoke discussion" : 1st, Know your audience

Dear Dave,

If your particular brand of "Provoking Discussion" includes lobbing a grenade into a crowd and seeing how they react,
then I guess I can get that...

However, on any public forum, let alone a internationally-distributed publication,
making blanket statements without apparent regard for the audience,
(or stated in reverse, on the basis of some unfounded global assumptions about your audiences's needs, wants, and preferences,

and most critically, without due regard for the way humor and satire/sarcasm tends NOT to translate well in text-based communications), 

can't be a good move...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

nah, we've just gone towards

nah, we've just gone towards to "put a powerpack in each locomotive."   It's a good idea, of course.  But it's not entirely universally true.

It's called momentum...

Dear Ken,

Um, you _can_ get that kind of delayed response, from your loco on analog DC,
it's called the "Momentum" function, and is available "off the shelf" in the US$90 MRC Tech 4 260 powerpack

http://www.modelrec.com/search/product-view.asp?ID=1298

That said, what price that "OMG?!?!?" moment you had when you turned the throttle knob and it _didn't_ move?

How many "possible reasons for this failure" did you run thru before the loco actually moved?
(Congratulations BTW, for actually having the pressence of mind to be able to think of these options under such adrenaline situation!)

That sounds more like you were experiencing FEAR to me than FUN,
(and the fear that the loco may not pull up in time before taking a short 4+' dive to the floor it a very real fear IMHO!)

Happy Modelling,
Aim to Improve,
Prof Klyzlr

PS I read a review of a recent Toyota Corolla, in which it summed up the performance and handling as "not outstanding, but nothing out-of-the-ordinary, nice comfortable familar experience". It's a shot-in-the-dark, but I suspect that in their hobby time, most modellers want _predictable_, _expected_, "_comfy_" behaviour from their locos, just like a "if you know how to drive a car, you'll just get in a Corolla and immediately feel comfy" kinda way. Did you feel "Corolla comfy" when that loco didn't move?

You're a little late, Thomas Alva ...

Quote:

Holy crap, and in my last post I just discovered a way to make the coolest DC power supply you'd ever see...holy G-Wiz, batman!!!   And that's how you sell DCC to the last Analog holdouts!!!!

I think I first did this about 1997. Have done it again recently on a small layout to allow a very small non-DCC locomotive to be operated by an NCE controller. Works fine, but you have to be careful about watching for shorts. They now happen on the "wrong side" of the DCC receiver and aren't detected in the normal fashion.

Benny, you sure spend a lot of time solving problems that either don't exist or were solved a few decades previous.

For a number of reasons that should be obvious, this doesn't at all replace quality DC power packs for those who are staying fully DC. But it's an OK way run a non-DCC-equipped loco, particularly for an isolated section of layout and if you're careful about shorts.

The obfuscation-by-reductionism arguments don't hold water. Yes, DC is delivered to the motor -- duh. DCC allows one to individually manage the DC being delivered to the motor for as many locos as you want, wherever you want, on virtually any size layout, off the shelf with no special wiring or logic. 

I won't be back to this thread, as I'm sure the next few days will be filled with a flurry of tormented logic to defend the indefensible. Knock yourself out.

Byron

P.S. By the way, I'm not saying that everyone needs to be running DCC. If you like DC, stay with it.

I'm responding to a particular line of reasoning.

My DC DCC choice

When I started on this forum about 2½ years ago, I believe that I stated something to the effect that I would be kicking and screaming when dragged into DCC use.  Since then, I've examined the discussions here, and on the DCC and JMRI groups, about DCC, plusses and minuses, and also the troubles people were having.

I have Tech throttles; I have DC locos with clean gearboxes and wheels.  I'm a solo operator (that's the eventual plan, though I've just this week powered up the first sections of track, so of course I'm solo).  So what's the gain from DCC.

I have a variety of locos that I might run together.  So, change gearbox ratios?  Re-motor with different RPM/volt characteristics?  Been there, done that:  lots of work.  DCC allows speed curves to be set for each loco.

I like lighting on locos.  What if I want them off or on while operating?  I've used reed switches, and hidden toggle switches.  It's a pain.  DCC allows independent control of lights.  Even the fleet model decoders (4 packs, 10 packs) have 4 functions.

Wiring:  I'm wiring track blocks with detection for signalling, so there's lots of wire anyway, whether I'm in DC or DCC.  In fact, there is particular care to be taken with power buses that have an 8 mHz AC signal to rail that acts as an antenna.  But, I don't have to build any control panels.  I'll have a set of eight switches in a 6" x 1" fascia "panel" to turn off yard tracks.  That's it.

Can I figure it out without a how-to class.  Yup:  did that.  Had to memorize what a cab address and a loco address was and how to change it.  3 minutes!  Throttle, brake, momentum:  nothing new:  buttons and a wheel.  Consisting:  give me another five minutes of study.

So, here I am in May of 2011, having just received my order from Litchfield, not kicking and screaming, but deciding which loco gets the first decoder, so I can retire my Tech throttle to the workbench, and to power building lighting.

Troubles with DCC:  to paraphrase one popular forum recent entry:  read the manual; your question has been answered. 

I chose DCC, because it gives me solutions to many more of my problems than it might create.  YRMV.