Nickel plating - how to do it, how effective is it?

[mmagliaro]

I think you are right back here.   https://www.therailwire.net/forum/index.php?topic=37254.msg446883#msg446883

Without a wiper, or a LOT of weight, or a LOT of voltage, I really don't think you are going to get what you want.  It's the simple facts of the matter.  But with a functioning tender picking up you have it covered and don't need it.  I can see where wipers could be hard to fully hide with the spoked wheels and I agree, they would be unsightly.  But it also seems like you don't NEED their help.  If it's working with the all of the tender wipers tagging along and conducting here and there, be happy and call it done!

You might get a kick out of one of the test rigs I'll be using in this next phase of my testing.  I'll be wiring a set of leds to each axle/ wheel combo.  One that wipes the wheel only, insulated elsewhere, and then another wired through the chassis.  I will also be able to insulate an axle so I can test just one axle at a time, isolating the chassis so I can tell if the compensation pickup is working well.  This allows to test wheel pickup only, then wheel to chassis pickup, then compensated axle to chassis pickup.  Each has its own tell by which leds light or don't.  I'm not suggesting that you should do such a thing and in part because I don't think you need to.  In my position I feel I really do need to be pretty expert at these things, therefore the testing and education.  I think you've got good performance covered between weight AND playing the odds with so many chances to get your power.  And there's ample existing evidence that that works including your own experiences with this unit.

I agree, narrowminded.  I am making test rods to get the quartering working and a tender chassis.

Your LED fixture made me laugh.  I have thought about making exactly such a thing many many times.  "What if I had an LED wired in series with each individual wheel, so I could tell from the flicker which ones are working and which ones are not?"
No joke.  I have though about this on almost every project loco I've ever built.  But I never set such a thing up.
I think you will learn a lot from it.

Yeah.  I have 46 grams on 6 wheels.  But the center ones float somewhat and have the springs in them.
I have settled on leaving springs out of all the others, so it rides "hard" on the 4 corners and the center drivers can float on springs a little.

That is the combination that works the best.   46/6 = about 8 grams per wheel.  But it's less on the center drivers.
I should stack some heavy weights on top to see how significant that would be.  Something tells me that if this thing weighed
more like 66 or 86 g, the pickup problems would vanish.  But of course, that's impossible.  I've got it packed to the gills with tungsten now.

Anyway... thank you and everyone for your considered thoughts and ideas throughout all this experimentation.
I have a tender and rods to make.

[narrowminded]

I'd take bets that the wheels are picking up fine.  At least the ones carrying the weight.  I'd also bet that the loss is occurring at the axle to bearing and/ or the bearing to frame.  If you were to temporarily clamp an .008"/ .010" phosphor bronze wire to the frame and rubbing the wheels (a temporary wiper) it would tell a lot and might be confirmed knowledge for another day.   

[Chris333]

How about some silver bearing grease around the bushings.

[narrowminded]

How about some silver bearing grease around the bushings.

I have never tried any of those products and based on other silver laden products.  They have to find a direct path through the mess and able to carry the current.  In the few I have heard of the results were sketchy at best.  Have you had any luck with any of those products?  I'd be willing to try something but I fear that if it had enough silver to be reliable it would also clog the bearing and if not then the success would be as I've heard, sketchy at best.

[Chris333]

I've used it on needle point axel pickups and to help drawbar connections. Comes in a little syringe.

[mmagliaro]

Once again... great minds think alike.
I bought a syringe of that Chemtronics silver conductive grease.  I ordered it about 4 days ago.  Should be here Monday.
I wanted to try it and see if it made any improvement.  There is a video about it at the
http://www.sbs4dcc.com/ website (streamlined backshop) where they show a before/after of a Kato diesel
with the ratty white-metal frame-to-truck-contact pickups. 

I suspect it would be good for sliding and pressing contacts (like the bearings in the frame pockets).
That's where I want to try it first.  I am not sure I want to put it into the bearings.  I think, like narrowminded,
that it would either attract dirt, have too much grit in it (if it really has enough silver to be useful), and cause more
problems than it solves.  But in the frame pockets, where there is minimal motion, I can see how it might help.

I'll let ya know.  If I put a dab in each pocket and the engine can miraculously run at 2 mph without stalling, I'll be cautiously
optimistic.  If I can run it for an hour, and am able to repeat that test for several days, and then a month from now it still
shows that kind of improvement, I'll be a believer.  (but not until).   (And 2 mph is quite slow, but not as slow as this engine
can run with a Kato tender hooked to it, so I'm giving the grease a "break"... ha ha)

[narrowminded]

I could see needle points working.  Also they can work without help as they have all of the right conditions working for them as many current designs demonstrate, repeatedly.  A point contact has a very high PSI loading even at a very low force that will break through the oil, going metal to metal.  And being a point contact it has virtually no leverage over the driving force and therefore makes the contact needed without big friction losses.  It's a good arrangement for carrying current IF you don't need the option of open wheels like a steam engine or an open wheeled chassis like a PCC trolley.  On those the pickup all has to occur behind the wheels. 

What I think gets missed if you've never run the numbers on these types of joints is just how high the PSI loading is in a point contact and then again, how much it's reduced in what would appear to be a small bearing.  I know that I had to run some numbers myself to see it because there was nothing in my regular design work that gave me the seat of the pants feel or intuitive sense of how dramatic this is.  If you use some quick theoretical numbers you can see it.  Assume a .010" point where actual contact is made which I think is fairly generous if assumed brand new pointed axle parts, fresh out of the machines.  Then .005 x .005 =.000025" x 3.14159 =.0000785 square inches.  That isn't many square inches.  Then place just one ounce of force, 1/16 of a pound, on that pointed end.  That's .0625 pounds divided by .0000785 square inches and you get 800 POUNDS per square inch!  (Actually 796)  

Then do a bearing area the same way.  A typical arrangement might have a 1.5mm axle (.059") diameter through a .030" wall or bearing. Many want to use a bigger bearing in the interest of ruggedness or add a flange that is usually added to a .02 or .03 length but for this example let's assume it's .030" o'all length x .059" diameter.  .059 x 3.14159 =.1853" circumference x .03" = .00556"   We know it's resting only on the top half at best of that bearing so let's say it's 1/4 of that dimension (.00556" divided by 4) .00139 square inches.  That's not much either.  Or is it?  It's almost 25 times the area of the pointed example which I would say is a LOT different.  Then figure about 7 grams force (1 gram =.03527 ounces)  for a decent axle load (the weight per axle of an Atlas Classic loco I measured) and you get about 1/4 of the force, applied to near 25 times the area.  So the math is, 7 grams =.01543 pounds divided by .00139 square inches = 11 PSI (11.0356).  800 PSI vs: 11 PSI.   One's a great bearing and the other has a chance as a contact. Pick which one you want because Simon says... you can't have both.   Bottom line, what might appear similar at a glance is HUGELY different once scrutinized and what starts to become evident when pickup is troublesome is... a wiper is probably needed.

Now, this is not intended to be a thorough scrutiny of this and I'm sure you could find a million other variables that would change the exact numbers but I think the trend line and principle is well demonstrated this way.  And further making the point, the examples used are generous in their assumptions favoring the best case in the bearing example and the worst case in the pointed axle example.  I think the bearing is often larger and the pointed axle contact starts even smaller, favoring the bearing example and penalizing the pointed axle example.

[narrowminded]

That's interesting, Chris.  I too could see that maybe helping in a relatively fixed point or a plug-in connection that has some force squeezing on it.  I wonder how much of it is the silver that's really helping on something like a drawbar or the silicone carrier helping to displace dirt and sealing already cleaned parts from the atmosphere.  Kind of like Conducta-Lube which has proven itself at some level in practice even though it does not conduct electricity on its own.  I've often thought it helped to flush out a joint as much as it did anything else, then help to keep it clean or oxide free.

What gets used on low current industrial slip joints, similar in practice to what we're doing with wheel pickups, is to use a "special" lubricant to help keep contacts working.  The way that works as described to me is that it coats the surface, is able to be displaced by the wiper allowing the necessary straight metal contact, then as it passes it immediately flows right back to a uniform film after the wiper has passed.  Not unlike a ship going through water is how it was described.  Those products were basically silicone as I understand but at what viscosity and what if any other bits of witches brew were added I don't know.  There's a whole art to lubricants and it's just these kinds of details that make something great in one application and useless in another, even when they appear to be about the same thing.  I will check that out, though.  It may still add some longevity to an otherwise decent performing assembly which is what it did for those industrial slip rings.  I would hope not to rely on something like that at the fundamental level though as I find the type of device that REQUIRES things like that to be temperamental.  I'm sure I've used other words to describe it, too.

While you say you have used it you didn't say how helpful it was or the severity of the situation that it fixed was.  Any detail you might share?  I hope that doesn't sound obtuse but the curiosity is genuine.

[mmagliaro]

..,.
...

  I would hope not to rely on something like that at the fundamental level though as I find the type of device that REQUIRES things like that to be temperamental.  I'm sure I've used other words to describe it, too.

...

Bingo.  This is why I generally don't like oil or lubricants of any kind.  On metal-to-metal gears, they are usually necessary.  But nowhere else.   Oils and greases just attract dirt and goo.  They cover up for fundamental mechanism problems which always come back sooner or later.
Some of my less-favorite commercial engine makers overload  their engines with gobs of grease and oil to make up for sloppy-fitting
components. 

I will try this silver-bearing grease to see if it's snake oil or not.  But I just can't believe in my heart that it is a long-term solution to
anything.