# Massoth XLS BEMF Slow Speed Issue



## East Broad Top (Dec 29, 2007)

I've got an LGB Forney (China manufacturer, if that makes a difference with regard to the motor) fitted with a Massoth XLS decoder (Forney sound file). At issue, with the BEMF motor control turned on, the locomotive lurches to a slow-to-moderate crawl as soon as I bump the throttle to speed step 1. Adjusting the start voltage does nothing to change this behavior. Adjusting CV3 to a moderate level of momentum mitigates this to some extent, but I'm hoping to figure out how to program it to a slow-to-very-slow crawl at step 1. I've played with some of the PI values (CV 60something) but those seem to have no affect.

Turning off BEMF load control allows me to have slow speed control, but then the BEMF chuff goes all wonky.

Thoughts?

Later,

K


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## Cougar Rock Rail (Jan 2, 2008)

Hi Kevin,

So the fact that the chuff goes wonky when you turn off the BEMF makes me think that whoever installed the XLS didn't use an axle sensor, but instead is relying on the decoder to generate the chuffs. Personally, that never works for me...it drives me nuts to see/hear the chuff out of time. So...you could add the axle sensor/hall effect unit that Massoth makes, which is easy to install and which will solve that problem, but then there is the slow speed issue if you wanted the BEMF on. It really is a matter of experimenting with those few CV's...and you will never get it as good as a Zimo decoder (at least in my experience) but you should be able to get it very good. On my LGB Heidi I also found it smoothest with the BEMF shut off. I find that the LGB motor blocks that have the extra reduction gearing will always make for a better slow speed performance than the ones with direct worm to axle drive because of the motor loading, so ultimately there is only so much you can do with CV adjustment. 
One other trick that works very well is to adjust the speed curve so that you have a more parabolic shape so that more of the speed steps are concentrated in the lower speeds where you need it. 
Is it possible for you to email or post a copy of your CV settings? 
Also...can you read out what firmware version your decoder has?

Keith


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## Greg Elmassian (Jan 3, 2008)

Sounds like the motor is likely damaged (internal partial short in a winding) to the point that the BEMF signal makes the decoder nuts.

I've had "BEMF" insanity in several cases.

You should be able to tune the BEMF parameters way down so that it's basically off in terms of motor control response, but still on to allow the BEMF signal to trigger the chuffs.

Greg


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## Cougar Rock Rail (Jan 2, 2008)

Greg is right in that you have to basically keep backing off the BEMF strength, but I haven't heard of motors causing the chuff to go nuts--interesting.
LGB did have some cheap Chinese made Buhler motors that failed prematurely back (I think) in the early 2000's, from exactly what you mentioned Greg. When I took one apart, it was like new otherwise, but I suspect poor coatings on the wire led to the internal shorting, overheating and subsequent failure.
Kevin, how old is this loco?

Keith


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## East Broad Top (Dec 29, 2007)

It's not that the BEMF isn't doing its job of properly regulating the speed regardless of load; it's doing that very nicely, and speed control is very smooth consistent throughout the entire throttle range. It's just that when I turn up from speed step 0 to speed step 1, the loco goes from dead stop to around 3 - 5 scale mph, then proceeds to run very smoothly at that speed. I'd like to tune that down to about 1 - 2 smph if possible. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

Reading your first post I keyed in on "lurches". Your last post sounds more like a CV2 issue, but let's investigate a bit more.

With BEMF off, what is the value of CV2 that lets you start at the desired speed?

Greg


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## East Broad Top (Dec 29, 2007)

With BEMF off, CV2 = 20 gives me a nice slow crawl at speed step 1 (Note: I'm using 28 steps). When I turn BEMF on, I've got to dial CV2 back to 0 in order to not have the loco take off like a scalded rabbit as soon as I bump the throttle. 

Even with the throttle set to 128 speed steps, the slowest speed (not changing any settings other than speed steps) is still about the same, albeit at speed step 2 instead of 1. 

In the grand scheme of things, it's not objectionable; it's just not quite as slow as I've gotten other DCC decoders to go with BEMF motor control. It could just be a limitation of the board's software, too. It's not anything I'm going to loose sleep over, but I figured I'd ask here since I haven't played with this decoder before. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

Sure sounds like a crappy motor, the BEMF is compensating for a bad winding in my estimation.

A CV2 of 20 is pretty darn high in my experience. I'm often down under 10, although that's my 23-24v track voltage.

Greg


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## East Broad Top (Dec 29, 2007)

I'm at roughly half that (14 volts), and values in the 10 - 30 range are common for my locos which don't use BEMF. When you compare that as a percentage of the whole, it's also right in line with my Revolution-equipped locos, whose start voltages are usually between 10 - 20% (also at 14 volts). 

Dunno. I had it running on the railroad this morning, and in practice it's not as objectionable as it seems on the workbench. I tried more tweaking of the PI parameters last night to no avail. It's probably as good as it's going to get, but I remain open to suggestions...

Later,

K


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## Greg Elmassian (Jan 3, 2008)

The big tipoff is that for a good running DC loco, there should not be a huge difference in CV2 settings (to make it just start moving as SS1) between BEMF on and off.

The only thing that explains your situation is that the motor has a lot of physical friction at zero rpm, or that there is an abnormal and probably erratic current draw

The BEMF gets confused and gives you this weird behavior. Or the decoder firmware is not good. Try another loco with the same decoder, you will soon see if it is the decoder or the loco.


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## East Broad Top (Dec 29, 2007)

There's always that possibility, Greg, though there's nothing about the operation of this loco which would indicate to me that any of that would be the case. Current draw is well under 0.5 amps throughout the speed range, and it's a darned smooth running loco. It's every bit "typical LGB." 

At this point, I'm not going to worry about it. In actual operation in the garden, it's not like one cruises at SS1, and the momentum dialed into the decoder carries it from stop to the target speed smoothly enough. The only CV adjustments I can think from the instructions which might affect that are CV 60 - 62, but tweaking these seemed to have no impact. 

Thanks for the insight.

Later,

K


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## Cougar Rock Rail (Jan 2, 2008)

I couldn't figure out why you needed a value of 20 for CV2 either--mine are all less than 5 for LGB locos, but I think it's the fact you're using such low track voltage. Are you using an HO system or why such low voltage? 
Still, you should be able to get it to work better than it is so something else must be going on. What software are you using to program it? Can you print us out the CV list so we can have a look? My guess is that by using such low track voltage, you're asking the decoder to make larger/more dramatic changes to compensate. My experience has been that if it's working good without the BEMF on, it's possible to get it almost as good with it on. I don't think it's a friction issue or it wouldn't work so well with the BEMF off. Does it act the same way when running light vs pulling a heavy load? If the motor is wonky it should show up under load. 

Keith


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## East Broad Top (Dec 29, 2007)

I'm battery power, hence the lower voltages. Again, the start voltage of this loco is not out of character with others I've done, so it's not anything which would raise red flags for me. I'm not using a PC to program this board, so I can't print out the CV values for everything. The motor control values under BEMF, CV2=0, CV5=180, CV6=90, CV3=100, C4=50. For the PI control variables, I reset things to the default, CV60=2, CV61=60, CV62=255 after adjustments to them seemed not to have any affect on start speed performance. 

The load compensation works very well. When I have the loco on rollers and lift it off, the drivers increase speed only momentarily before the compensation slows it back down to the original speed. Likewise when I introduce more drag on the wheels, it boosts the voltage to the motor to keep the speed constant. So there's nothing there that seems out of sorts. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

So you have a DCC decoder and are battery powered, what is your DCC interface?

Greg


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## East Broad Top (Dec 29, 2007)

For this installation, I'm using an Airwire Convertr, which then feeds a Tam Valley Depot booster. For programming the decoder, I use an MRC Prodigy Advance2 command station. (Performance is the same on both platforms.) 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

Let us know if the same decoder works better on a different motor. I suspect the BEMF is not real happy with the lower voltage, that's a pretty low voltage for G scale.

There has to be some voltage drop through the Convrtr, and the voltage output of the Tam valley booster is something I have not measured.

You might be down near 12 volts or under to the decoder itself. Have you measured it? A simple full wave bridge with a small electrolytic capacitor can measure the true RMS value of the voltage to the decoder.

Greg


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## East Broad Top (Dec 29, 2007)

Alas, the decoder installation is complete in this loco, and everything's buttoned up. It's not worth it to pull the decoder, install another one, and test it just to satisfy my curiosity. This isn't my locomotive, so the decoder it came with is the one it's leaving with, anyway.

Having said that, I do have another Massoth decoder (the XXL), and two other LGB locomotives (future projects, so they're still track-powered at this point). I hooked up that decoder, and used it to power the two LGB locos. Performance was virtually identical to the XLS in the Forney. I bumped the throttle to SS1, and the locos started up to a moderate crawl. In no case (either these two locos or the Forney) was the speed above 3 scale mph with the throttle set to 28 speed steps. (I figured "3 - 5" in my earlier post for the Forney; measuring it with a timer and ruler pegs it at around 2.8.) 

When I switched to 128 speed steps, the speeds were all right around 2 smph. Both decoders are similarly adept at maintaining constant speed regardless of load. (And both use the default PI settings.) 

That leads me to believe that there's nothing "wrong" with either the decoder or the motor in the Forney; it's just the nature of the decoder. In reality, if you told me a decoder would allow my loco to creep at 2 mph and maintain that speed regardless of load, I'd say "works for me!" And--again--with momentum dialed into the decoder, it doesn't lurch forward, but ramps up to that speed. You don't really ever "notice" that's its slowest constant speed, because how often do we actually run our locos a their slowest constant speed?

The only reason it jumps out as being different is that my QSI decoders (which are infinitely more complex with regard to customizing motor control) allow constant speeds well under 1 scale mph. I was thinking maybe there was some programming with the Massoth which would allow a similar level of customization. 

At this point, I'm satisfied that it's just the nature of the decoder, so I'm not going to worry about looking for any kind of a "fix." It's not a big deal in normal operation, and the ability of the BEMF control to maintain a constant speed regardless of load at all speeds is top drawer, so I know it's doing its job. 

Thanks, gents, for your thoughts on this. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

I noticed a comment earlier, and again reinforced in your last post.

Why do you want a loco to maintain a set speed regardless of load? That's not prototypical. 

No offense, but I thought you were striving for prototypical operation, and if I remember right, you have a pretty flat layout.

Just curious, because you have to do a lot to the PID parameters to "force" this.

Greg


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## East Broad Top (Dec 29, 2007)

It's the default setting of the Massoth decoder, Greg. Massoth's literature goes into detail as to how it works, and how the three variables interact with it. Airwire's throttles do the same thing when you turn on "cruise control." 

The loco I'm working on belongs to someone else, so this feature wouldn't be at the top of my list of priorities for the reasons you mention; my railroad is relatively flat, and I don't mind my trains speeding up and slowing down a bit in response to grades and curves. While all of my Airwire throttles have this feature, I rarely turn it on. However, my grades are mild, and my trains _only _speed up or slow down "a bit." 

When you start pushing grades steeper than 3%, "a bit" turns into "a lot." When you run on my dad's railroad, you've got to know where the grades start or your train will get away from you very quickly. (Or stall if you're going uphill.) I do find the "cruise control" feature on the Airwire throttles to be very helpful on his line, especially on locos which are otherwise hard to control on steep grades. (Bachmann's K-27 comes to mind as an example, though it wouldn't fit through dad's tunnels.) Likewise for modelers whose normal operational scheme involves a lawn chair and cold beverage, this kind of speed regulation is a great feature to have.

Later,

K


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## Greg Elmassian (Jan 3, 2008)

Got it, yes, I forgot you said the loco was not yours, sorry.

Interesting that "cruise control" is default on the Massoth, need to read that, very weird.

Remember that I have a 3.4% grade up, and a 5.5% grade down on my layout, assuming running counterclockwise. 

I can guarantee you that since I run up to 50 car trains, I probably have experienced the "a lot" more than most people. I can barely hold onto the coupler with the train on a grade. That's 200 pounds of train trying to roll back down the grade.

I'll read up on the Massoth, but I'm guessing that the "cruise control" settings of the BEMF and a somewhat touchy motor are the culprits.

Clearly the problem went away when BEMF was off, so with "normal" BEMF settings, it would probably be fine (still mystified by the defaults on that Massoth).

Regards, Greg


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## East Broad Top (Dec 29, 2007)

> _but I'm guessing that the "cruise control" settings of the BEMF_


In thinking about it, the Airwire "cruise control" will cut out below a certain threshold. So if the Massoth unit is always in "cruise" mode, it probably needs a bare minimum voltage going to the motor to do its job. My guess is that it sends this absolute bare minimum voltage at SS1 and goes from there. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

But if the Massoth "cut out" the cruise control at low speeds, then, it would act like BEMF off at low speeds.

You are seeing the opposite, runs really nice at low speeds with BEMF off, and with BEMF on cannot start nicely.

Greg


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## East Broad Top (Dec 29, 2007)

Greg Elmassian said:


> But if the Massoth "cut out" the cruise control at low speeds, then, it would act like BEMF off at low speeds.


Airwire cuts out the cruise below a certain throttle setting, but the Massoth does not. I think that's why there's a baseline voltage on the Massoth that needs to go to the motor at SS1 under BEMF, so it has enough to work with. I think when it does that, it ignores CV2. This is conjecture on my part, but comparing it to how Airwire does their "cruise control," it sounds reasonable.

Later,

K


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## Greg Elmassian (Jan 3, 2008)

nope, no dcc decoder ever ignores cv2, and you have already proved that by reporting that changing from bemf on to off requires different cv2 setings, or did I miss something there?

no quality decoder (meaning acceptance by the majority of DCC users, i.e. in HO too) ignores BEMF parameters unless they state at what speed step they are operational, and those are usually very adjustable.

since this is not your loco, and you are not keeping it, some of this thread is now kind of rhetorical... I would be interested to see how the unit performed with "normal" BEMF parameters, i.e. those that help prototypical operation and smooth running, not parameters that induce an artificial "cruise control"...

Greg


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## East Broad Top (Dec 29, 2007)

*Here's a link* to the manual for this decoder. Look on page 18 for an illustration showing the three components of what they call "PI Load Control" (what we're calling "cruise control.")

CV62 is the only parameter of those three that has an impact on the starting speed at SS1. It's got a range of 1 - 255, and you've got to dial it way back to <25 for it to have any noticeable impact on the start speed. When you roll it back that far, you lose a lot of the stability of the cruise control (which is to be expected), but you also lose the BEMF chuff calibration. Here seem to be your choices:

1) High value for CV62 = steady speed control, good chuff calibration, moderate (3smph) start speed

2) Mid value for CV62 = moderately steady speed control, okay chuff calibration, moderate (3smph) start speed

3) Low value for CV62 = limited steady speed control, no chuff calibration, slow start speed.

If you don't need the auto chuff, and don't want the "cruise control" aspect, you can use a low value for CV62, but at that point, you may as well turn the feature off. (According to the manual, you can program the decoder to turn this feature on and off via a function key.) If you need the auto chuff, as is the case with this specific installation, you live with the 3smph start speed and go from there. I can't see any way to adjust it without messing up the chuff calibration. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

OK setting the 3 BEMF parameters is dicey and few people understand it well.

Only playing with one of the parameters not going to work well.

On top of that, I see that this decoder is very elementary, if you had a more capable decoder, you would see the 3 BEMF settings (which are not described in industry standard terms) might also have 3 or 4 setting ranges, so your BEMF parameters can be different at different speeds. For reference, the QSI does this, and I believe the Zimo also.

If you want to make this run better, you need to adjust all 3 parameters, just modifying the "strength" and ignoring the "retardation" (wow is that poorly documented) and the maximum (CV's 61 and 60) won't help much at all.

I really think you ought to look at CV63, the "slow approach" setting, where you basically switch from "slow approach" settings to "regular load control" settings, which means to most people a special setting going very slow to transition to the "normal" BEMF.

You stated your issue was starting out, not the rest of the running, so CV63 seems the place to start, as well as a better set of BEMF settings. 

Properly set up, I think you could make this loco run much better.

I also suggest you get a manual from a manufacturer that explains BEMF clearly and with industry standard names, not this gibberish in this manual... I know they were trying to put it in layman's terms, but they really presented little on how it operates, and thus did not do the user any service in understanding how to set things up.

Finally, I am very much unimpressed and disappointed in Massoth in setting these parameters so the train runs like an automaton, or a toy. A real train does not maintain constant speed under varying conditions.

Greg


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## East Broad Top (Dec 29, 2007)

Greg, I tried various combinations of adjustments to those three parameters to no avail. I agree, CV63 might be the first place to look to improve slow-speed response, however, the decoder I have is of an older firmware release, so it doesn't appear to support it. 

The decoder is what it is. I can think of many folks for whom trains running at a constant speed regardless of the grade of the track would be 100% in line with what they're looking to accomplish for their railroads, so I woudn't write the decoder off as a "disappointment" by any stretch. 

If you can point me to a good, easy-to-understand reference on BEMF and PID parameters, I'd love to read it. I've asked on the QSI forum for easy-to-understand explanation about what the heck it is I'm adjusting when playing with those, but no one seems to be able to put it in plain English (even the manufacturer's usually-helpful tech guys.) I usually end up going to your site and trying the values you have listed. That typically works well enough, but "why" they work as opposed to others remains a mystery. There was a recent discussion on the Soundtraxx forum about the same thing, likewise without any clear explanation as to what does what and why. Someday, someone will figure out how to explain it clearly. I mean, the Cubs are one step closer to the World Series, so anything's possible, right?

Later,

K


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## toddalin (Jan 4, 2008)

East Broad Top said:


> Someday, someone will figure out how to explain it clearly. I mean, the Cubs are one step closer to the World Series, so anything's possible, right?
> 
> Later,
> 
> K


Was predicted long ago to happen is 2015!


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## East Broad Top (Dec 29, 2007)

It's pure coincidence without my flying car!!! 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

Kevin, it's sad to say that I have never seen what I would consider a good explanation. I have degrees in engineering and understand the process, but the explanations given are either purely technical (which means you need to understand the integration of the factors over time already, i.e. already understand), or so much BS that the "friendly" explanation still does not help the practical use of these parameters.

They are tricky at best to manually adjust. There are some products that allow an automatic calibration of the PID parameters (Parametric, Integral, Differential) and perhaps that is best. I worked with one company for a number of years to determine PID parameters for various locos, in fact my findings were actually used for the factory defaults.

I realize this does not help, but it does answer your question 

Regards, Greg


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## Cougar Rock Rail (Jan 2, 2008)

Greg, I don't think it's fair to be critical of a device you obviously don't understand, but given you always look for an excuse to slag Massoth, I'm certainly not surprised. 
Similarly, I find it odd you complain about the Massoth's ability to keep the speed steady under varying loads--that is exactly what the BEMF is supposed to do according to the definition under DCC wiki! I guess you are used to decoders that aren't able to provide this at all speeds. At any rate, it absolutely should be possible to adjust those settings, along with others, to achieve good running characteristics. My suspicion is that feeding it with such low voltage is not helping the cause either. 
Kevin, have you confirmed that you are actually changing the CV values by reading them back? Many DCC systems from the HO world aren't consistently able to program some of the European decoders (NCE springs to mind). Is the Airwire system somehow interfering with the operation of the decoder by applying it's own version of "cruise control" as you call it, or is it just an interface with no active components?
Do you have the manual that came with that specific decoder and it's subsequent firmware? If not, you can read the decoder version, then look at the appropriate manual on the Massoth website. This will make sure you're adjusting the proper CV's.
There are other tricks to make better low speed performance as well. For example, you can cut the top speed down and adjust the speed curve, to compress more of the speed steps in the lower part of the curve. Also, by default Massoth decoders usually have a switching speed function, which is meant for more slow speed resolution. Does your decoder have this function or has it been disabled? 
If you really want to optimize this decoder, you have to at least take the time to understand it fully so you can start eliminating the variables and get to the root of the problem.

Keith


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## East Broad Top (Dec 29, 2007)

Greg, when the experts can't clearly explain what's going on, the chances of programming PID parameters becoming anything other than hit-or-miss (aka "dumb luck") are pretty remote. It's something we live with, and something we become glad we don't have to do quite as often as newer generations of decoders appear to handle it increasingly well. 

Keith, I'm definitely able to program the CVs, as I'm noticing at least some degree of change with each setting. (That, and readback reflects the changes.) I'm using either the MRC Prodigy Advance2 or the Airwire/Convertr to program the boards. I can't do readback with the Airwire, so that's where the MRC unit comes in. 

Both of the Massoth decoders I'm playing with are older versions of the software. The XLS (the one in the Forney) is version 1.2 (current is 2.5), while the XXL is version 2.0 (current is 2.3). Neither of these support CV63, so that option is not available with these decoders. I don't have the PC interface, so re-programming them with new software is not an option, either. I'm limited to the functionality they have. Both decoders do support "switching speed," however there's little difference in performance at SS1 whether that's engaged or not. (It's probably 75% instead of 50%.) 

At this point, I think both of these decoders are about as optimized as they're going to get. It appears to me that the subsequent revisions in the software were done to mitigate the issues I seem to be having, so likely someone at Massoth noticed the behavior, too. 

Later,

K


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## Cougar Rock Rail (Jan 2, 2008)

Hi Kevin,

Wow those are really old decoders...current firmware is 3.6 and I believe you can only go so far with those ones before a hardware change was made at around 3.5.
It is definitely the case that they have been making incremental improvements to slow speed performance with additional BEMF features.
As you say, it's probably not worth trying to squeeze much more out of those particular ones, at least not unless you had the programmer which makes adjusting all those speed curve settings much simpler.

In general I think all the manufacturers could do a lot better job of sending out decoders optimized for each particular loco, or at least making settings available if the owner wanted to do it. The best ones I've found are the Zimo Dappen sound projects, but of course you pay a premium for it. This of course takes a lot of time, as Greg mentioned that he helped out one of the manufacturers in this regard and he no doubt spent a lot of time doing it. I suppose it is a personal thing...some like momentum, some don't...etc.

Keith


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## Greg Elmassian (Jan 3, 2008)

Keith, I don't know where you come up with the expression that I'm critical of something I obviously do not understand. 

Please tell me what is the obvious thing that I do not understand. I could give you a class on BEMF, it might take a few days to give you the basics but I assure you I understand it.

When a company comes out and thumps it's chest about how great it is, and is the best, etc. etc. then they have to be ready for some criticism and to meet higher expectations. Massoth is often promoted as the best and Massoth fans often report they bought it because they were told it was the best.

I don't complain about customer service in a KMart. I do complain about customer service if it is not top drawer at Neiman Marcus.

BEMF is not "supposed" to do anything, it is a technique that _can _do various things. Most people use it to further smooth out motor performance when there are little things that can cause intermittent friction, like all the moving parts in a steamer. This improves slow speed starting and running.

Taken to an extreme, you _can _tune a system so it goes a constant speed no matter what the grade.

If I was running a toy layout or needed unattended running at a constant speed with significant grades, I might use BEMF this way.

By the way, why do you think the DCC wiki is the ultimate authority? It's like these forums, mostly populated with the more vocal people, not necessarily the most knowledgeable. The editors of the Wiki are not gods.

Finally, there can be a point where the difficulty of properly tuning a decoder becomes way too big a pain in the a** for most people.

This is why certain manufacturers have a built in calibration procedure to set these parameters for you. 

Greg


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