A question and a comment for DCC users

Model Railroader Electronics and DCC
1

I have been reading lots of threads about consisting, speed matching, BEMF, etc. Not being a DCC user on my own layout, only a DCC operator on friends layouts, I have not commented on these threads as I did not have anything constructive to add.

But it got me thinking, so here is my question/comment.

As a DC user I find that identical units, like say 3 Proto 2000 GP7’s without decoders, run perfectly together on the pulse width control of my Aristo Train Engineer. And I find this to be almost universally true, all brands, all models, forward, reverse, etc. Is it possible that the trouble some people experiance with the speed matching muliple identical units in DCC is a decoder problem?

It would seem to me, if three units run well together on DC, and I install identical decoders, set all CV’s the same, they should still run the same. BUT, if the decoders are different brands/models or maybe even just different production runs with slightly different “generic” components, that could explain why the units respond differently or require extensive speed matching.

I may be completely wrong here, but surely I would think one would be well advised to use the same decoder in all units of a “set” of diesels expected to run together?

Just a thought, your thoughts please.

Sheldon

2

Sheldon, you mean if you start all 3 of your GP7’s 3 foot a part from each other and after 3 times around the bench all 3 engines will still be 3 foot a part? I don’t think so. One of the reasons DCC owners speed match is the decoder is the weak link, if one is pulling harder it may cause the decoder to over heat. Heat is not nearly the problem in DC as DCC.

According to my Digitrax manual if your DCC engines are close to each other in speed, you do not have to speed match. Speed matching only has to be done is there speeds are vastly different.

Plus, part of the fun is playing with the CV’s anyway.

Cuda Ken

3

I suppose that one could assume that two or three identical models within the same production run could run somewhat identically. However, one of the pluses of DCC is that it is not necessary to do this. If I want to consist an Atlas Goldline GP40, a Trainman GP38-2, and an Athearn blue box SD40-2, I am able to do so. The Gold line engine comes with sound, the other two need decoders added. Even if I use the same decoder in these other two, they will probably not run the same without some fiddling of the decoder. And once that starts, then the decoder I’d use would be whatever is my preference at that time. And what about the sound unit? Should I remove the decoder from that so I can re-install the same decoder that I just put in the other two engines?

I can’t comment on your Aristo Train Engineer system, as I know nothing about it. Maybe it’s a good thing, maybe it isn’t. But I do know that I’ve seen folks try to run different model engines on straight DC, and they do not run perfectly together.

4

Ken,

First, I did not post this to get into the DCC vs DC debate. I am simply curious about all the stuff I hear from DCC users, on here and elsewhere.

As to the idea that three locos would stay the same distance apart for a long distance if not coupled, that is a straw man argument, it does not matter what happens when they are uncoupled, only how smoothly they run coupled together.

Fact is, I and many DC users run non identical locos, steam and diesel, double/tripple headed with no problems, but again, not the point.

I would suggest this is only fun if the results are successfull, some DCC users seem quite frustrated with this.

Again, not looking to argue, just offering a thought.

Sheldon

5

Any 3 identical Proto units will run identically to each other? Nope…sorry,…doesn’t happen. A locomotive’s performance changes when you 1…warm them up and 2…wear them in. The idea is to have the units run very close to the same speed throughout their speed range.

That is where DCC shines over DC. I dont have to limit my GP9s to be brand specific, I can run my Protos with my Atlas/Katos and my Athearns and with my Brass units…no issues…ever.

David B

6

I am not going to defend how well my muliple unit lashups run on DC, except to say yes, my diesel lashups are mostly all the same brand. And I am more than happy with how well they run together. I fully understand the advandages of DCC in matching different brands/types/etc.

My post was based on serveral questions, posts, comments, on this board and off, from people having trouble speed matching and complaining about identical locos running different in forward than reverse, etc.

Since my MATCHED units run so well on DC, I did not understand why some would have problems getting MATCHED units to run well on DCC? And I offered a common sense theory to those with more experiance than myself.

That is all. That was my question. No one has addressed it. So far everyone has just attacked the idea that my MATCHED units run well together on DC. Why is that?

Yes, all my GP7’s are the same brand, heck 75% of my diesels are the same brand. It suits my modeling needs. This thread was not about that.

Sheldon

7

Sheldon, neither did I. I have ran both DC and DCC, both have there plus.

As far as it is how well they run together I will give you that to a point. My case against that is my Proto 2000’s E-6’s. I have 2 powered A’s and 1 power B unit. One of the A’s was faster than the other A and the B, so it was made the lead engine in the consist. Talk about pulling power! I was running a DC MRC 9500 transformer, I did not have a DCC system at the time. One day while I was cleaning them, I happened to remove the shell of the lead A unit. The truck power wires where melting, if you like a pictuer I can post one. Wires where not gone to the point where it hurt the engine, but was heading there.

Cuda Ken

8

Also, I did not say they ran “identicaly”, I said the MU units “run perfectly” - my experiance is they need not run identicaly to do the job. - but once again, that was not the point.

Sheldon

9

So, what is the point of this thread then?

I have no issues with any of my units running with any of my units with DCC. The issue arises when people decide to “jump in” to programming before reading on how to properly adjust decoders to allow for MUing. It is a matter of adjusting CVs in the proper order to make all you units react the same way to the throttle.

When they are properly programmed, the units will start to creep at speed step 1.

In terms of using the same decoder in similar locos having differences in the way the loco responds to it…I haven’t come across the issue and I deal with this all the time. The difference in CVs arises when you mix decoder brands, nothing more.

If you search for “Speed Matching” you will come up with many threads that show someone how to do this with DCC.

David B

10

David, Thank you. I was simply puzzled that units that ran well together without DCC would be a problem with DCC. Your suggestion that the individuals with this problem are not programing them properly makes sense. Especially the “in proper order” part. Thank you for the explaination.

Sheldon

11

Sheldon, there are many variables, and our typical DCC user doesn’t know what they are, nor how to account for/correct them so that widely disparate engines can work nicely synchronized through the speed step range.

Let’s start with speed steps: how many people ever tackle setting up a speed table? One in ten users would, I think, be a charitable guess, but that would be a biased guess based on my assumptions. It may be much worse, it may be something like one in three users. If you don’t go to the trouble of setting up speed tables in two or more MU’d locos from different manufacturers, you are likely to wear one or both engines severely in a short time.

As was mentioned, engines perform differently in either direction, and they perform differently once they are used for a while in one operating session…that is, when they have warmed internally. I have one or two models where the decoder sets the chuff rate. It may be good at 10 mph, but off a bit at 30, or it may be good at any speed near the start of a given operating session, but off by 1/5 of a revolution near the end when the drive is spinning better.

Then there is the problem between decoders. The master volume on a LokSound, if I recall is CV60 or something like that, while the QSI’s have an index that must be accessed using two separate CV’s. I found the instructions for my LokSound decoders to be baffling in some respects, not user friendly. The QSI decoders are much easier to manage if you ask me, and that is because of their instructions. Same for the Tsunami.

Some decoders have BEMF, some don’t, some permit torque compensation, some don’t, the programming and charateristics for other functions also differ.

I am not in a position to discuss your experiences and your methods knowledgeably, so I can’t offer any useful compariso

12

I find that DCC in Proto engines helps them run closer to others, in that the diodes for the constant lighting are removed, and the lighting is handled by the DCC board. I can run P2K, Genesis, Atlas and Athearn RTR with each other, as long as they have similar decoders. Mixing decoder makers doesn’t always work.

In 1:1 scale, some engines load faster than others, so I don’t worry too much if a model gets going a little quicker than another. With a load, things kind of even out.

13

Crandell,

Thank you for the detailed explaination, some of which I knew, some I did not.

Again, this was not at all about what I do, but trying to understand what some of my friends and others I read about are having trouble with. Your detailed explaination, and info from others confirmed most of my thoughts about this and clarified things I was not completely aware of.

There is nothing special about what I do when it comes to this topic. Except maybe the fact that the Aristo Train Engineer is a better than average DC throttle and provides a constant 12 volts on the rails as soon as you touch the throttle. The DC signal is a square wave pluse, the width and timing of that pluse is varied to control the loco speed.

So when you first touch the throttle the pulses are short and widely spaced. The inductive nature of the motor resists this signal but resistive loads like lights come right on before the loco moves. As the pulses become closer and wider, the motor begins to turn, but instead of only having the “push” of a few volts, that “push” is 12 volts. This provides smooth high torque starts.

Todays and yesterdays DC model locomotives run very well on this type of system, much better than many traditional linear voltage rheostat or transistor throttles.

I’m sure this has the effect of minimising differences between matched, or reasonably matched MU’d locos.

Again, most of my MU sets are the same brand/model. But some I commonly run are not. Examples:

Proto 2000 2-8-8-2 with Bachmann Spectrum 2-6-6-2

Bachmann Spectrum 4-8-2H with Athearn Genesis 2-8-2

It is simply a matter of testing, not unlike speed matching with CV’s. In this case some combos work, some don’t.

Since I model the time and place that I do (1954), and sinc

14

I’m a DCC user and I try to read everything I can on this forum because I’m new to the hobby. DCC is the one thing that got me started. I have an A+B P2K that I paid to have Litchfield put decoders in. because of space constraints they put in different decoders. Sound and motor in “B” unit, motor only in “A” unit. Until I speed matched them the locos pulled very differently, I could easily tell they were fighting each other.

My point is: If they are DC and reasonably close how can you tell if all three are pulling together or one dragging and two pulling etc. unless you separate them under power?
have fun [:)]

Lee

15

Back to math class…one in three is actually better than one in ten. Did you mean one in thirty?

16

Lee,

Did you run them on DC before he decoder install? I have two, three units sets of Proto2000 F units, DC, they run fine together. Based on what David, Crandell and others have said here, and as I suspected, it was the two different decoders that made them run different. And that is fine since DCC provides a way to adjust that.

Long before DCC, for decades, we have run DC locos together. As long as the drives, motors, gearing are the same it usually works fine. It is better to try to put the faster ones in front, but not always a big deal.

If you are pulling enough cars to need two or three locos, than the load will even out quickly as each one from rear to front comes under load. If your not pulling enough cars to need them, why are they there?

Obviously you cannot MU widely mismatched DC locos without risk of damage and generally poor operation. But, regardless of brand, if they are close, it will and does work.

Sheldon

17

Hah! Thanks for pointing it out…I actually meant to say that it was much better. The math was okay, not my choice of adjectives. [:D]