How is it that in digital MRRing we can experience a stall out over a switch frog or other potential stall out areas in one direction and then not stall, at same place, in the other direction (or vise versa) ? In analog control it's understandable as polarity changes all over the system, under the pickup-wheel-arrangements and thus inviting problems at certain gaps ..But, if track polarity stays fixed at the wheel treads/tires/flanges in DCC you'd think loco would either always stall or never stall regardless of its direction; because the difference (I would think) is motor is reversing direction due to decoder commands, while wheels at stall potential points always 'see' the same polarity in both directions, rails not flipping/swaping poles under the wheels ...The direction of the train shouldn't make a difference pickup-potential-wise in digital control (You'd think). Yes, no, why ?
[FONT=times new roman, new york, times, serif]This is not odd at all. It has nothing to do with polarity. With DCC, a slight interruption by dirt or not enough pickups will cause a decoder to hiccup. All it takes is a slight interuption of the DCC signal. You will understand this more as you gain more knowledge on how DCC operates. [/FONT] [FONT=times new roman, new york, times, serif]That is why there is a lot of discussion on stay alive options for decoders. TCS has come out with a stay alive option which is being discussed in some DCC forums.[/FONT] [FONT=times new roman, new york, times, serif]A couple companies are marketing a digital control which is RF wireless that does not need track power but can also run on a DC or DCC layout. Onboard rechargeable battery is used and it is HO scale. Will these companies continue to sell this stuff? Time will tell.[/FONT] [FONT=times new roman, new york, times, serif]Digital control of model trains is continually evolving. Electronics are continually shrinking and battery technology is improving. Rich[/FONT]
First of all, track polarity does not stay fixed in DCC, it is actually reversing thousands of times per second, but the track polarity does not have anything to do with the stalls. If a loco stalls going in one direction but not in the other, the difference is not caused by the polarity of the voltage but rather the actual physics of traveling through the switch. For example, if the turnout's points pickup power from the contact with the rails, going through the switch in one direction might cause the points to momentarily lose contact while going through in the other direction doesn't.
I'm still in the infant stages of learning all of this but would add that I have seen some videos of "Normal" DCC Locomotives running on tracks and you see lights flickering and the engines stalling and videos of "Keep Alive" decoder installed Locomotives and its like night and day difference. In one video a guy runs a Keep Alive encoded locomotive over 20" of taped over track and it keeps on running. When I finally buy my first Locomotive, I am definitely going to put a Keep Alive in it.
When I see a stall happen in one direction but not the other one thing that often is the cause is that going one way the locomotive either forces the points of a switch or the free ends of a section of track to make contact with the adjacent rails or track joiners but not in the other. This is not so much a DCC thing but a track-work/electrical issue. A DC locomotive running on DC power probably skated through that area for a moment, but a DCC loco losing its digital signal will get confused and stop.
Thanks..All very astute answers..Robert above points out that the AC is reversing thousands of times a second..I savvy that. Yet, as this is so still in a way supports my concept. IE, unlike analog DC RRs were poles are flipped to reverse motor, being this is occurring thousands of times in digital in a way neutralize or equalizes both rails ( - & + occupy the metal mass near simultaneously )...But for sure I am NOt an electronics expert.
Actually, I experience the opposite. Or rather, little difference at all which way I am going, if a know a switch to be a problem switch. In the few instancs I do notice it, the end result ends up being how long is the otherend of the switch, is there enough run to keepone end of the engine powered (orat least coasting) while the other end is off in typically, but not alwYs, if I hit the plastic frog first, i can glide over the bothersome switch. If it hit thepoi ts first, i die.
I'm with you in that infant stage of DCC, and with all the reading and viewing I've been doing it still seems as if I'm far behind the learning curve. But those Stay alive Decoders do seem well worth the price of admission. But so far they only come in HO scale that I'm aware of, I have a couple of them installed in my HO locos but haven't completed anything besides my HO test track to try them on. Can't wait till they come out in N scale
Morgan (above), this is the general fear for most who have stall outs on switches..Of course I/we are aware of the loco length hopfully being enough to always have one wheel drawing current (- polarity) and one wheel passing current out (+ polarity). if this was always the case there'd be nearly no stalls except for dirt on track/wheel..It seems that there becomes a position of the engine where either one pole is completely isolated. And/or with steam, drivers perhaps being lifted the the thickness of a human hair, say, by a too high frog or say, bent switch (arced/tweaked via spikes/nails or such) and the other drivers lifting being in the same rigid frame .. BTW, If you are in HO and using Atlas code 83 switches, they are not plastic frogs..They have a thing coat of black paint on metal..These frogs Can be powered to end stall-outs..But this is another subject... While on this subject though, another ever more mindboggling occurance is the stallouts at 'power routing' switches when the points are in fact making contact with the running rails ! I don't mean the short-out due to wrongly thrown points..I mean points are lined correctly and ARE touching outter rail..Yet train stops until you either squeeze the point tighter against the rail or nudge the throw rod in same direction..I.E. It's miniscule a contact but IS a contact ..Yet, more mass is needed between the two converging rails (point and running rail) to complete the circuit !! I'm trying to correct this very problem as we speak with an older curved Shinhara...It CAN be cured but ground throw has to be installed p e r f e c t l y...
Before I switched to DCC my locos would not stall on switches but I did notice the headlights blink. I usually run multiple locos so the following loco would push the lead loco over the frog and or dirty track. With my entrance into DCC I noticed that the same locos would stop in the same spots and the second loco would not push the lead loco as it died as well along with getting the 5 beeps from the command station (Digitrax). All of the stalling I have now can be attributed to the command station detecting a short circuit and shutting down the track power. Most of the time it happens in one direction only. I alleviated most of the problem by applying nail polish to the rails coming off the frog. It just has to be reapplyed occasionally. It happens on my home layout (N), my clubs HO and N layouts as well as my clubs traveling show layout. All wheel drive and all wheel power pickup was supposed to cutdown on stalling but DCC command stations are more sensitive to short circuits with their electronic circuit breakers.
