One of the things that has become clear to me is that any non-BEMF decoder is an operational disappointment. The majority of the Cedar Branch & Western's engines are custom motored, geared and wired. When equipped with a LokSound decoder they produce outstanding fine motor control and consisting.
A search for a cheaper means of upgrading my fleet resulting in the purchase of various brands of decoders with assorted claims which led me to believe they, too, could provide the fine motor control of my current fleet. This is not meant to single out any vendor, but the claims fall far short of their abilities:
Torque Compensation
LocoMotion
Torque Compensation for ultra smooth low speed performance
After installing seven various decoders and fine tuning their performance with Decoder Pro it has become apparent that without the control of BEMF the starting speed, consisting speed, and speed table of the decoder will be a disappointment. The forward and backward speed differs despite the trim settings. The locos run out of sync in a consist. The speed table in forward motion differs from reverse. The starting voltage changes as the engine warms up, and is different in forward than reverse. My final thoughts are that I could have had the same results in DC without the expense and trouble of converting these seven engines. As money becomes available the slow change to LokSound decoders will continue.
In short, only true BEMF allows the fine, precise control of an engine. These seven mid-cost decoders are nothing more than a way to operate a former analog locomotive on a DCC system. So why spend the money on anything less than the best? How many DCC newcomers have faced disappointment after their dreams of finer control failed to materialize? After all, that is one of DCC's biggest selling points.
Rant over. I'll duck now. Fire at will!
The Cedar Branch & Western--The Hillbilly Line!
Before BEMF all there was was silent drive Dither, T.C. and trim. I have spent many an hour adjusting CVs to speed match and set up the smooth running of my locos. Decoder Pro can not speed match and adjust starting and T.C. CVs without your input so why use it. With all the fiddling with CVs I have all my locos running great and you realy can not tell which have BEMF and not. There are times when BEMF is undesirable such as in consists and helper sets. The only time I have found BEMF usefull is yard duty and switching. On the main line I like to keep control of my train and dont realy need cruise control.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
I have a couple of sound loco's with BEMF. The biggest benefit I get from them is the diesel ramping up when going into a hill which adds realism and is pretty darn cool. I have no problems with the non BEMF loco's though and am quite happy with them.
Springfield PA
I'm sorry but I disagree, I don't find BEMF the answer to smooth operation. I have a number of locos that run very smoothly without BEMF. And if you try to consist 2 or 3 locos without turning off the BEMF you can get some pretty strange and noisy operation. I have a loco that ran pretty well with a TCS decoder with BEMF turned off, with it turned on the loco ran very rough.
I'll concede it sometimes it takes a little more time and effort to program a non BEMF loco, but the I don't think BEMF is only the way to get a smooth running loco.
dragenrider none BEMF decoder is an operational disappointment.
I am starting to wonder about it as well. I had a PK 2000 eat a Digitrax DH 163, and replaced it with a DH 123 and it does not seem like the same engine. On the other hand, I hve 3 PK 1000 F-3 used as a constis with DH 123's that Simon speed matched and they run great.
Dragenrider, what none sound decoder do you like? I am thinking about NCE or Total Train Contol next.
Cuda Ken
I hate Rust
cudaken Dragenrider, what none sound decoder do you like? I am thinking about NCE or Total Train Contol next. Cuda Ken
Cuda Ken,
Right now there is no decoder I like as much as LokSound. That would be true with or without sound. It's the motor control and the lighting options, too. Now given, I haven't tried any other sound decoder. Nonsound so far includes NCE, Digitrax, and Bachmann.
dragenriderRight now there is no decoder I like as much as LokSound.
Dragebrider, far as Loksound I have one in a PCM Y6 b and it kicks caboose!!!! It craws around the bench with a 65 coal train. My main is around 65 feet and it can take it 20 minutes to go around one time.
dragenridercudaken Dragenrider, what none sound decoder do you like? I am thinking about NCE or Total Train Contol next. Cuda Ken Cuda Ken, Right now there is no decoder I like as much as LokSound. That would be true with or without sound. It's the motor control and the lighting options, too. Now given, I haven't tried any other sound decoder. Nonsound so far includes NCE, Digitrax, and Bachmann.
There are a Loksound decoder without sound (sort of), it's called Lokpilot, also made by ESU.
/stefan
I used many an NCE D13SRJ decoders, which do not have BEMF, and had no problems with creepy-crawly operation. Also some TCS T-1's from before they added BEMF. All were in decent locos (the worst quality one was Proto 2000 - to give some idea), and they ran very well at tie counting speed. The big difference between those and BEMF decoders was if I added drag to the train - the BEMF decoders just kept goign at the same slow speeed, the non-BEMF decoders needed more throttle to maintain slow speed.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinkerThe big difference between those and BEMF decoders was if I added drag to the train - the BEMF decoders just kept goign at the same slow speeed, the non-BEMF decoders needed more throttle to maintain slow speed.
I have not played with enough BEMF decoders to have an opinion. With my limited experience, like many of the others, I do not seem to have the problems attributed to non-BEMF decoders presented by the original poster.
I prefer a mild BEMF effect, if it's goign to be there, because no matter how carefully you maintain a loco, there will always be some friction in the mechanism. A mild BEMF< especailly at low speeds, helps to maintain a minimal crawl, but it isn;t absolutely necessary - a lot depends on the loco. The 'dither' feature of older TCS decoders was enough to run a P2K loco with no problems, the superior quality motor and mechanism in the Stewart Baldwin switchers ran great at a crawl with nothing more than the basic torque compensation of the NCE D13 decoders. Toruq compensation just overcomes the power loss of the high frequency drive at slower speeds.
At the other extreme was I think the Zimo display I saw at a train show, they had a loop of large scale track on a board at a 45 degree angle, and the loco went the saem speed up and down, absolutely no change. That's some pretty strong BEMF, and to be honest not realistic at all. For reliable automated operation though it's almost a must.
The BEMF in the newer TCS decoders is a nice tradeoff. It seems strong enough to keep the loco moving at a constant low speed, but it will slow down if you greatly increase the load. It drops off as speed increases, so other than starting up, you're back to the 'when goign up a hill, you need to add throttle or the train slows' mode of operation. Plus it's easily configured to be switched completely off with a function key so you cna use it to creep out of the yard, then turn it off for realistic operation up and down grades.
A couple points I would like to make for the newbs who don't know the ins and outs of BEMF.
BEMF and consisting
BEMF and consisting can be a no-no if you aren't careful. BEMF feedback is very sensitive and can detect the slightest change in speed. When you have two BEMF engines running together, there is always going to be a SLIGHT difference in speed. As a result one engine is getting pulled "faster" and another is getting "pulled slower" The BEMF will actually pick up on this slight speed difference and try to compenstate IN A BAD WAY. It can make the slower engine go slower and the faster engine go faster as each tries to compensate. Pretty soon the two decoders are fighting one another yelling, "You're going too fast." "No you are going too slow!" and it becomes a tug of war. Only certain decoders (I believe QSI and Soundtraxx Tsunami) offer a compensation adjustment which allows for a bigger speed variation before the BEMF compensation begins. You need to read the manuals on this.
BEMF and slow speed operation
This is where BEMF really shines. How often do you see engines constantly changing speed from 3MPH->8 MPH ->5 MPH ->6 MPH ->0 MPH->4 MPH while in a yard at the same throttle setting? Trains don't change speeds in real life yards. So why should they on your model yard?
BEMF solves this problem. So you don't have to worry about herky-jerky motion when doing slow speed manuevers. BEMF can compensate for slight voltage drops, and slight slight gear binding issues. This is a real boon for steam modelers.
BEMF and high speed main line operation
It's true, when a train hits a grade change in real life, it speeds up or slows down. It's up to the engineer to compenstate for this.
BEMF is sort of like modern cruise control for your car. If it needs more speed, it will apply more juice. This makes the model more "automated" for the MRR at the throttle. Luckily several decoders (ie: QSI) offer a high speed throttle BEMF cutoff. What this means that as your train goes on the mainline, you can reduce the amount of BEMF at higher speeds. So your train will slow down going up hills, and speed up coming down, just like in real life. Yet your slow speed yard performance will remain the same.
BEMF and realistic sound
BEMF can detect when the engine is more or less under load. For example, when climbing a hill, the motor works harder, and requires more power. When going down a hill, it has to work less hard. When accelerating, it works harder. When stopping, it works less.
Steam QSI and Sountraxx Tsunami decoders will chuff louder when working harder. Diesel QSI and Tsunami will spin up a diesel motor to the next higher notch. When working less, QSI and Soundtraxx Tsunami BEMF will reduce the chuff, or spin down the motor to the next lower notch.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
DigitalGriffin -Thanks for the detailed explanation.
So I guess I need to look for the actual letters "BEMF" and not torque compensation or other corperate speak. Any general rule of thumb for which decoders have BEMF? My eyes start to roll back into their sockets when I start comparing decoder specs.
The decoder I use the most is the Digitrax DZ125. It's BEMF equipped and I can see the difference between them and a Bachmann decoder which does not have BEMF. The locos without BEMF tend to slow down going upgrade and speed up going downgrade. The locos with BEMF may slow down or speed up a tiny bit but I haven't really noticed it. There's also a marked difference when I'm using the MRC Synchro Sound sound box. With a BEMF equipped loco the sound is well balanced and doesn't shift a lot in speed steps. With a loco without BEMF all bets are off. At times the engine sounds runs wild and doesn't match the locos speed at all and at other times shifts rapidly up and down in engine speed sounding like a hot rod revving up at a traffic light. The Bachmann decoders I have in some locos are just a stop gap measure. These will slowly be replaced with DZ125's
Dr. Frankendiesel aka Scott Running BearSpace Mouse for president!15 year veteran fire fighterCollector of Apple //e'sRunning Bear EnterprisesHistory Channel Club life member.beatus homo qui invenit sapientiam
If a decoder has BEMF, it says BEMF. This is pretty darn consistent. Where features vary is what each manufacturer calls their motor drive - supersonic, silient running, high frequency all mean the same thing. Another difference is in how functions are counted. Some count the headlight as one, others count it as two. IMO, counting it as 2 is most accurate - so a '4 function' decoder has F0F, F0R, F1, and F2. ie, how may wires does it have to connect lights or whatever. Also, torque compensation is not BEMF - and the name for that varies from manufacturer to manufacturer. As an explanation when a DC motor is driven with pulse width modulation, it gets full voltage pulse of varying width. The wider the pulse, the more average voltage it sees and the faster it spins. At low speeds (thus low voltage) the pusles are quite narrow. This means the time that the armature windings have to attract to the next magnet pole is relatively short - resulting in low motor torque exactly when you need it most. Decoders that offer torque compensation under one name or another alter the drive slightly to give an extra 'kick' to the motor at low speeds to overcome some of the torque loss. A decent loco and a decoder with good torque compensation cn handle super slow creep sppeds about as well as a BEMF decoder.
loatharSo I guess I need to look for the actual letters "BEMF" and not torque compensation or other corperate speak. Any general rule of thumb for which decoders have BEMF?
I wish I could give you recommendations. Unfortunately I stay strictly to sound decoders for my fleet. The Lenz Gold and Silver series have an excellent reputation for slow speed BEMF.
I do have one Lenz Gold. It was very easy to set up, with a minimum of parameters to futz with. However I have never consisted it, so I can't tell you how it cooperates with other decoders. And the documentation on the BEMF features is "spotty" at best.
BTW: Randy gave an excellent detailed explination between torque compensation and BEMF. I personally think BEMF is still superior because torque compensation can't make up for track voltage variations, slight binding, and drive gear variations.
The big thing I've noticed with BEMF is that it really can help smooth out the operation of some engines. I had an old Athearn F7 that ran fine but was severly affected by up and down grades. When I added a decoder with BEMF it could run on it's own at a steady speed with it's train and didn't require constant fiddling, which I liked. I find that really good running engines like Atlas ones generally don't need BEMF, they are not as affected by grades the way some engines are.
One downside re BEMF I found is that Digitrax decoders with BEMF have a "jump" in them...as you speed up, it seems like at about 7-8 scale MPH they jump up a few MPH to like 10-12 MPH then steady out again and run fine. Not sure why, but now that TCS decoders have BEMF I probably won't install any more Digitrax ones...partly because TCS instructions are so much better than Digitrax.
wjstix -Thanks! That's what I'm interested in. Consistant speeds on grades. I don't really do any consisting.