What Causes That Loss of Power in Loco After Direction Change?

[peteski]

As you and I mentioned it earlier, I believe it is a mechanical (contact) problem.  Still, what is the end goal?

I'm fairly sure that a good cleaning will resolve the problem.  If you don't want to try cleaning to see if that resolves the problem, then what is the next step?

We can theorize for a long time, but will that be helpful? I guess that since only 3 people responded so far, it make sense to wait for others to chime in.

[tehachapifan]

Not disputing the need for cleaning. The goal was to try to identify any additional factors that may be contributing in this scenario.

[jagged ben]

Are we talking DC or DCC here?

What I'm going to suggest may or may not hold water.  But the idea is this, going back to MKs post way up top: You get some gear backlash that stalls the motor at low voltage.  The stall current causes a voltage drop which makes the loco LED drop out.  Electricty is actually still flowing, but at too low a voltage to do anything.

This theory would make more sense with DC than DCC.

[tehachapifan]

This is with DCC. Can't recall if I ever noticed in back in the DC days or not.

[peteski]

This is with DCC. Can't recall if I ever noticed in back in the DC days or not.

And to cover other possible questions, you are certain that the DCC power is cut off from the locomotive?  For example the headlights which were turned on before the stall are now dark, and sound emanating from the (sound) decoder before the stall is also silent?  We already covered the motor's behavior (dead).  Is that correct?

I also do not understand the quest to hypothesize about "other factors". We are all making guesses here.  To me it would make sense to clean all the electrical contact areas and check whether that resolves the problem (this is also a guess on my part, based on the info you provided).  I'm not sure what other factors you are expecting.  What seems to be occurring is a total disconnect of the track power from the decoder (it has to be caused by multiple connections failing, since the loco has more than one path for the power to be supplied to the decoder).

I would also still like to find out exactly how you clean the wheels.

[tehachapifan]

Wheels cleaned via paper napkin wet with 91% IPA laid over track method.

Yes, this is a total loss of all power....sound (if equipped), lights, movement....everything.

Going back to those earlier Kato drives without the contact strips (the switcher drives in my case), when I would first get them (admittedly, almost always pre-owned) and no matter how much I cleaned everything, some would do this power loss upon direction change thing a lot. But, with those drives, there's a ton of shifting that goes on. The trucks shift forward or back quite a bit in the frame depending on direction, the loco would sometimes even rock slightly (when I believe the worm may have been climbing over to the other side of the truck tower gear) and, IIRC, the slight crab angle of the loco would reverse. My theory is that all this movement with these drives may sometimes cause the actual contact between the trucks and frame to physically separate, if even so slightly, where no amount of cleaning would completely resolve it. Those old switcher drives have no flywheels, so that loss of physical contact, if that was indeed what was happening, meant an immediate stop. This is what I was was after in this thread....is there some other factor that is in play with current diesel loco design (with contact strips) that no amount of cleaning will always completely address? Perhaps the answer is no....but I still wonder why the first sign things need to be cleaned seems to be immediately following a direction change.

...incidentally, those old Kato (sometimes Concor) switcher drives seem to only improve (a lot) over time. They quiet WAY down and the stall-after-a-direction-change thing improves a lot as well. Perhaps as the gears break-in more, the worm climb I mentioned (if that is even really a thing) is not as pronounced and doesn't cause that frame/truck separation as much. Hard to say for sure. BTW, on those drives, I swap the wheel with the traction tire out with a wheel without one and , if it is a Concor drive with brass(?) wheels, I replace them with the Kato wheels.

[Steveruger45]

Hmmm.  Sounds like it is movement in the drive/trucks due change in thrust directions breaking contact with the frame mounted pick up strips.  You could prove this one way or the other by temporarily soldering on some esu decoder wire from each truck axle cup pick up to each frame pick up strip.
Finding a fix is very dependent on what is the cause🤔

[tehachapifan]

Hmmm.  Sounds like it is movement in the drive/trucks due change in thrust directions breaking contact with the frame mounted pick up strips.  You could prove this one way or the other by temporarily soldering on some esu decoder wire from each truck axle cup pick up to each frame pick up strip.
Finding a fix is very dependent on what is the cause🤔

Interesting idea. Perhaps this is why Atlas(?) has opted to go to soldered wires vs. contact strip on recent models? I recall stating in another thread that I didn't understand the decision to change from the contact strip design as I believe that is a really solid and proven design. I seriously doubt there's any physical separation occurring there upon a direction change. The only thing I can see, which I believe peteski alluded to, is perhaps there could be a tiny spot of oxidation(?) in the transition point between where the truck contact hits the contact strip when running forward and when running in reverse (due to the slight shift of the truck in the frame when changing directions)?

[tehachapifan]

...I'm more inclined to think that, if any physical separation is occurring, it lies within the relationship between the axle points and the axle cups. peteski's photo of the axle cup contact strips with the worn holes at the top of the axle cups indicates to me that the axle points are not always firmly inserted into the center of the axle cup (which I think many of us knew anyway). Instead, it appears the points must float around in the cups to a (large?) degree. Also, there always seems to be some lateral play of a wheelset, also indicating axle point s are not always pressed against the center of the axle cup. Perhaps when the loco direction change occurs and torque(?) thrusts the wheelset from one side of the truck to the other, somewhere there is a brief loss of contact between the axle point and axle cup. Add in any possible gear climbing/remeshing(?) that may occur in the process, perhaps not allowing the axle point to cleanly slide along the inside of the axle cup to its new position when running the other direction. With all the other wheels, perhaps it's rare that all axle points on perhaps one side lose contact with their axle cups at the exact same time, but once in a while maybe they do. Add in a little grime/oxidation/whatever in maybe only one cup and perhaps this then becomes more likely. Thoughts? Sorry about the overuse of "perhaps".

[Steveruger45]

Gauging the wheels not only for track  but also for axle gear to truck frame slot clearance and good but not overly tight wheel point to cup pickup Is worth investigating too.  I’ve done this on all my locos together with polishing the truck/cups/pickups at all contact places and same on the frame strips too and don’t have any problems like this at all.  The lifelike gp38s and gp60’s I have do have a lot of fwd to aft truck movement relative to the frame and direction of loco, far more than my other brand locos, and they run really sweet.
BTW I don’t overly lube the trucks at all. Just a pin point of conductor lube on the axle cups when i reassemble after overhaul.
As far as Atlas changing The trucks to “wired-to-frame” I think this was more to do with putting the speaker in the fuel tank and that speaker location making it difficult to also have the more normal pickup strips. Plus it removes four moving contact points and therefore probably thought to improve the chances of avoiding customer complaints with sound drop outs. Just. IMHO.

[peteski]

Evne the tightest Kato mechanisms have quite a bit of play in all the moving parts.  If there was no play, the model would run really poorly (if at all).  So yes, shifting occurs during change of direction, and even when the model is moving in the same direction.  The trucks shift in relation to the chassis, the wheelset axles shift in the bearing cups, worms shift and so does the motor shaft (and any other moving part shifts too).    The problem is when all the electric pickup contact areas end up not making contact at the same  time.  I'll repeat that regular cleaning should take care of the problem.

I think your reluctance to give your models cleaning (due to the complex lighting installs) really exacerbates the problem that other modelers seldom experience. Otherwise we would see similar problems mentioned in the online forums more often.

Also, I think the wheels might be part of the problem.  To me a paper towel and alcohol aren't quite enough.  I feel that some more physical cleaning is required to get the tread cleaned and burnished.  My wheel cleaning method consists of first using the trusty Minitrix brass brush wheel cleaner.


Then the 2nd and final step is to use 99% IPA and a paper towel.


Wheels cleaned this way are problem free for me.

As for the other problem areas, I clean out the bearing cups using those Tamiya pointy swabs moistened in Naphtha. I also clean the pointy axle ends.  Then I  drop a tiny amount of light oil in the cups.  Then I take care of the nubs on top of the trucks. if you look at the surface of those nubs, it is fairly rough (from the stamping process). I polish these nubs (while the truck is apart) using a multi-grit fingernail polisher. 



Then I take it one step further.  I use my Dremel with a  small polishing wheel and a polishing compound to polish those nubs and also the contact areas on the pickup strips to a mirror-like finish.



I leave the contact areas on the pickup strips dry (no lube).  This results in problem free operation.

If you have one of those Minitrix brass brushes, give it a try before using the paper towel. If not, I recommend getting one of them.

As for the recently wired trucks on Atlas locos I believe someone mentioned this was  done because their fuel tank area was modified for speaker install, and there was no way to add the pickup strips.  I prefer wire-free installs (for ease of maintenance) and don't have the problems you are describing.

[tehachapifan]

...I think your reluctance to give your models cleaning (due to the complex lighting installs) really exacerbates the problem that other modelers seldom experience....

I don't disagree with what you said but might take exception to the above statement. I'm inclined to think that the vast (and I mean VAST) majority of modelers never, ever clean out the axle cups on their locos. I would guess it's probably only maybe 1-5% that actually do, but that's a total guess.

[peteski]

I don't disagree with what you said but might take exception to the above statement. I'm inclined to think that the vast (and I mean VAST) majority of modelers never, ever clean out the axle cups on their locos. I would guess it's probably only maybe 1-5% that actually do, but that's a total guess.

I can't argue that either way. I apologize if I offended you.
There is quite a bit of pressure per square inch between the axle point and the cup. IIRC, we estimated it to be in pounds (due to very small contact area). Your electrical contact problems are probably elsewhere. Wheels, or the contact strips.  Fixing the problem by slightly nudging the model seems to confirm it is a contact problem affecting all the contact points.

[CRL]

Back in the day when we had mechanical tuners & volume pots, there was a spray-on product called “tuner cleaner” by a number of manufacturers that would take all the audible “scratch” sounds out of your stereo gear.

Has anyone tried using something like that to clean the electrical contacts. I wouldn’t get it on any painted surface... just in case.

[John]

I would guess it's probably only maybe 1-5% that actually do, but that's a total guess.

I do it when I do an annual shop availability    most of the time it's the alcohol paper and trix thing