I have no problem with BEMF - I just set it to shut off at speed step 10 just like you say. It works great - the loco runs smooth as can be at slow speeds - but the BEMF cuts out once the loco is running at a solid moderate speed.

Joe,

Do you have a screenshot that shows your favorite BEMF settings in Decoder Pro?

I've always found those pages to be just a bit mystifying.

I have seen several people come in at another forum all with the assertion that BEFM will cause problems with locomotives MU'd together.  Sounds like it is a red herring then if you can program the BEFM to cut out above a certain speed step.  Hopefully this programming won't be difficult!

Yes, it's true, BEMF is bad news in consists.

TCS decoders allow you to manually turn off BEMF using F6, if you enable that feature. It's a good idea in consists to use F6 to turn BEMF off.

If you have two locos in a consist with BEMF and if they are at all out of sync in their speed matching, you will get violent bucking. Once you understand what BEMF is doing you can understand why:

Loco 1 is consisted with loco 2, and both have BEMF enabled through speed step 10. Loco 1 starts moving at say step 2, while loco 2 is slightly slower at speed step 2. BEMF will detect loco 1 is lugging (being slowed down by loco 2 in the consist), so BEMF will increase the voltage to loco 1 in an attempt to speed it up. Loco 2 BEMF will detect it's moving faster than it should (being pulled by loco 1 speeding up) and BEMF will decrease the voltage to loco 2 in an attempt to slow it down.

The result is the two locos fight each other with violent bucking as BEMF attempts to alternatively speed up and slow down each loco. When you have this situation, BEMF is doing its job, but the result is not helpful. Also, the two locos may work fine when their speed is identical, but if you encounter some trackwork (a curve, a turnout, or a grade) that naturally slows one of the locos slightly because it's encountering the change first, violent bucking can suddenly manifest with no warning.

Better is to simply turn BEMF off in a consist, since the two (or more) locos tend to smooth out each others' performance naturally without the help of BEMF. BEMF is most helpful with a single non-consisted loco that needs to run at slow speeds through complex trackwork - like with switchers.

To address Jeff's request, here's my TCS decoder settings in one of my Athearn SD40T-2s:

If you're using TCS decoders with BEMF (and most TCS decoders sold these days include BEMF automatically), then I recommend you download their BEMF tuning guide.

Ah, the tangled web of DCC thickens!  I suppose some day it will become sophisticated enough to not require a good deal of customizing and programming, where perhaps decoders have some presets from the factory, perhaps like our Ipods have preset EQ settings for different types of music.  Then you could chose a running single preset or a running in consist preset and certain CV settings will be put in place to optimize performance depending on the situation.  I an envision that based on the information I'm reading about. 

When I first read your TCS T1 fleet decoder comments and viewed your video demo of an SP tunnel motor, I though oh cool, BEMF will help my lovely Athearn tunnel motors run more smoothly at low speeds, but I didn't realize that the same feature that does this is something we probably won't be using most of the time since tunnel motors do not run singly 95% of the time, but rather in consists of 3 or more typically.

Since I am presently in transition (euphamism for looking for full time work and no basement) I'm mostly educating myself and collecting equipment.  What I have on hand for now is a Digitrax Radio Chief system and a PR1 kit for setting up a programming track.  Unless I buy a different programming interface, thats what I will have to work with for the time being.  Of course computers have changed so I'll have to see if there is newer software that isn't aimed at Windows 98 but will work with Windows XP or eventually 7 when I come into the modern age.

CV10 controls the cutout of BEMF. The allowable settings are 0 to 128. These cut outs are arranged for 128 speed steps. I usually cut my BEMF at 20. The clubs system is 28 speed steps but my home layout is 28/128. You must disable BEMF and adjust Dither first. That way there is no loss of performance when BEMF is automatically cut off.

        Hope this helps

      Pete

 My feeling is there are really two factors that contribute to bucking in consists. Ones is the BEMF being too 'strong'. The other is a sloppy drive. The sloppy drive issue can cause severe bucking on downgrades in a single unit when BEMF is enabled. It's mostly the fore and aft play in the armature and worm - the addition of a few thrust washers can fix this up and smooth out things a lot. I wouldn't expect a high end loco to have this problem, but Athearn and Athearn clone mechanisms like P2K often do have the problem. The loading and unloading of the driveline just increases the BEMF contribution to bucking on level track with locos in a consist. Without BEMF, the one that gets 'stuck' gets a little nudge and just starts moving at the same speed as the other unit (assuming they are reasonably well speed matched). With BEMF - the decoder may have already jumped up the voltage in an attempt to keep the motor turnign so when it finally gets nudged byt he other unit it breaks loose and runs too hard before the BEMF can compensate.

 Personally, I like the auto fade out BEMF on the TCS decoders. I'm not a big fan of those options that work like 'cruise control' and keep the loco at a specified scale MPH no matter what happens. That may be nice for display/automation where you need the train to be at a certain spot at a certain time always, but real trains don't have cruise control. More load, steeper grade, etc. should require adding some throttle to maintain speed. Starting from a stop is the place where IMO BEMF is almost required. The smooth starts and steady creeping just generally aren't possible with BEMF off, unless you have an absolutely superb mechanism and motor.

                                               --Randy