2,4 and 6 Functions

[mreagant]

I'm not clear what additional functions come with a 4 or 6 function decoder.  If I understand correctly, 2 function provides light reversal and direction.  What else do you get with 4 or 6?

I thought this had come up before, but I couldn't track it down.

[wjstix]

"Loco Lighting and Other Features of DCC Mobile Decoders

In addition to address and motion characteristics, most DCC decoders control constant directional lighting and in some cases offer additional function outputs.

DCC decoders usually have at least 2 functions available (sometimes these are set up as directional lights so that your headlights go on and off automatically when you reverse the engine). Large-scale decoders have as many as 8 functions available.

Some decoders have special effects lighting built in so that you can activate additional locomotive lighting like Mars lights, ditch lights, cab lights, etc. Additional functions can be used for smoke units for steam locomotives, sound units, and much more. These extra locomotive functions are accessible from full-featured command stations. Some DCC decoders include a mobile decoder and sound decoder in one unit.

Adapted from "Digital Command Control: The Wave of the Future", by Zana and A.J. Ireland. "

From:  http://www.tonystrains.com/tonystips/dccprimer/components/dec-mob-specfx.htm

[mreagant]

Thanks for reminding me of that David. BEMF is one of those things I never think about, and frankly am not sure if I'd notice if a decoder didn't have it.  The additional lighting issues would be obvious, but few, if any, of my locomotives have need of those. 

If I understand BEMF correctly, it provides for smoother operation by filling out the possible/potential fluctuations in voltage.  If that is even close to correct, then I'm not sure why a recently installed Tusnami--at $125 plus installation of another $125-- on my Kato NW-2 continues to hop-skip along the track, replaying the start-up sequence about 2 times per 18 inches.  Annoying is the kindest word I can think of.  If the Tsunami doesn't have BEMF, then I'm mystified why not given the price.

It's not a clean track or wheel issue as I've cleaned the NW-2 wheels 'till you can see your face in the treads, and almost every other DCC loco, sound or otherwise, that I have skips merrily along over the same track sections.

Although this was not the initial question, I'd really like a suggestion about how to sort this matter out.

[Texas Zepher]

mreagant

I'm not clear what additional functions come with a 4 or 6 function decoder.  If I understand correctly, 2 function provides light reversal and direction.  What else do you get with 4 or 6?

You get whatever you hook up to them.  Nothing says one has to hook function 1 and 2 to lights.  One could put the decoder into a big hook and use 1 to rotate the boom, 2 to raise/lower it, 3 to raise lower the hook. 

On a locomotive one could hook a smoke unit to function 3, or the radiator fans, 4 for front coupler, 5 for rear coupler, etc... etc... 

[WSOR 3801]

 Sounds like the NW2 may have other pickup problems.  It is built like a N scale diesel, just bigger, with tabs for power pickup.  Your installer probably earned the $125 for the install.  Room for the decoder and speaker has to be milled out on this engine. Maybe things weren't put back together just right.  These units are very difficult to put back together. 

The Tsunami has Back-EMF.  Some of the new Athearns with factory Tsunamis are having similar problems, traced back to a less than premium pickup arrangement.  A bit of paint removal usually clears this up.  

 

[CSX Robert]

mreagant

...If I understand BEMF correctly, it provides for smoother operation by filling out the possible/potential fluctuations in voltage.  If that is even close to correct, then I'm not sure why a recently installed Tusnami--at $125 plus installation of another $125-- on my Kato NW-2 continues to hop-skip along the track, replaying the start-up sequence about 2 times per 18 inches...

Well, actually you don't understand Bemf compensation correctly. What you are having is a problem with electrical pickup, which will not be helped by Bemf compensation. The Tsunamis do come with a capacitor which is supposed to help with intermittent pickup.

Bemf compensation reads the Bemf voltage off of the spinning motor and compensates for variations in the locomotive's speed due to variation's in the locomotive's resistance to movement caused by the drive line or track work. Some people like it because if configured correctly a locomotive will maintain the same speed whether on level track or going uphill or downhill. To me, the biggest advantage of Bemf compensation is that it helps with smooth starts and stops. As an example, if you give an engine enough throttle to just barely start moving, any increase in resistance, such as a slight bind in the drive line or sometimes even crossing the frog of a switch(it would be nice if all of or drive lines and track work were perfectly smooth, but sometimes that is just not the case), will cause the engine to stop. Increasing the throttle to overcome the increased resistance will cause the engine to suddenly increase speed once it passes the increased resistance. Even with momentum setup on the engine this can happen, because it is just like slowly increasing the throttle. With Bemf compensation, when you hit increased resistance to motion, the decoder will automatically increase it's output to overcome it. Likewise, when it sees a decrease in resistance, it will automatically decrease it's output to maintain a constant speed.

Some sound decoders(the Tsunamis included) have another use of Bemf, which is not the same thing as Bemf compensation, although it can be used in conjunction with it. That is, the decoder can adjust it's sound depending on how much load is placed on it(Soundtraxx refers to this as "Dynamic Digital Exhaust").

[mreagant]

Thanks, guys.  Very helpful stuff.  I now get BEMF, I think.  If I can't resolve the NW-2 problem I'll be back for more ideas.  I'll check the wipers first.