Resistance wheelsets

[John]

To solve the unsightly resister glued to the wheel ..

Using some super glue ( I use tire glue) and wirepaint, you can place the SMD resistor on the middle of the axle, then paint the conductor on to each wheel .. I've done it this way
https://www.amazon.com/gp/product/B000Z9H7ZW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B002N4WCR0/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

[nkalanaga]

Making plastic wheels would be practical, as Micro-Trains and Precision Masters proved.  Since many people claim that plastic wheels get dirty faster than metal, that might be an issue, but I have never had a signal system, so haven't worried about dirty wheels.

And, yes, a good conductive paint would be very useful for those who already have quality metal wheels in their cars. 

One advantage of changing just the insulators is that no new tooling or processes would be needed.  They could be made in the same tooling now used, and the metal axles and wheels are already available.  Literally just a matter of changing the plastic fed into the machine.

[peteski]

And, yes, a good conductive paint would be very useful for those who already have quality metal wheels in their cars. 

There are conductive (and resistive) paints out there, but the problem is consistency.  The length, width, and thickness of the conductive paint affects the resistance, so it would be hard to be consistent when hand-painitng the "resistors" onto the wheels.

For those people using conductive paint to attach the resistors, is there a problem with the paint cracking (possibly due to thermal expansion), resulting in an open circuit?

[bbussey]

)
Also, imagine if we could convince manufacturers to stick to a single (0.540") axle length.  Then the only inventory that would be needed is wheel size, and maybe tread width.  Maybe we could convince ESM to pursue this ( @bbussey ).  Ahh to dream. 

.553” axle lengths and (semi) bulk packs first, hopefully this time next year. Then 28” wheels next the year after that, to support a well car release. Then we’ll see what the playing board looks like after 2023 regarding resistor wheels.

[Ed Kapuscinski]

.553” axle lengths and (semi) bulk packs first, hopefully this time next year. Then 28” wheels next the year after that, to support a well car release. Then we’ll see what the playing board looks like after 2023 regarding resistor wheels.

Every time I start thinking about the process of making my own, all I can think is "this should be automated". I can't imagine it'd be that hard with the right infrastructure in place.

[John]

Every time I start thinking about the process of making my own, all I can think is "this should be automated". I can't imagine it'd be that hard with the right infrastructure in place.

It's not that hard Ed .. just like making trees .. a few at a time ...

Seriously, I do about 20 at a time ..  glue the resistor down - then spread the wirepaint, let it dry for 24 hours, measure continuity /resistance - finally, coat the axle with clear nail polish to seal it all ..

[trainzluvr]

Reliable and professional grade conductive pen:

https://www.chemtronics.com/circuitworks-conductive-pen

CW2200MTP - Silver Conductive Pen - Mirco Tip, 8.5 g (0.3 oz.)

[jagged ben]

There are conductive (and resistive) paints out there, but the problem is consistency.  The length, width, and thickness of the conductive paint affects the resistance, so it would be hard to be consistent when hand-painitng the "resistors" onto the wheels.
..

Good points, but I think we could accept a large variation in resistance for any given wheelset.  If I'm going to paint two axles per car I'd happily accept anywhere from about 16-22k ohm per wheelset, for anywhere from 8k to 11k per car  (but not consistently as low as 8k per car).  So, like almost a 50% variation.  I can probably muster the skill to paint that consistently?

In tue amount of searching I've done I've found nothing close to what we'd need in resitive paint. 

[peteski]

Maybe some of these paints would be suitable for "painting" your own resistors?
https://www.emrss.com/collections/emf-shielding-paint
The descriptions do not mention resistance per square, but you might be able to get that info by contacting the manufacturer.

[John]

Maybe some of these paints would be suitable for "painting" your own resistors?
https://www.emrss.com/collections/emf-shielding-paint
The descriptions do not mention resistance per square, but you might be able to get that info by contacting the manufacturer.

That's probably left over from the F117 project

[trainzluvr]

MG Chemicals

841WB - EMF Shielding Paint (nickel flake)
Resistivity 2.7 x 10-2    Ω·cm
Surface Resistance @ 50 µm     1.3    Ω/sq

843WB - Electromagnetic Shielding Paint (silvercoated copper flake)
Resistivity 5.3 x 10-4    Ω·cm
Surface Resistance @ 50 µm     0.020    Ω/sq

[peteski]

Those MG paints (um, coatings) are too conductive to be useful for making resistors.

[trainzluvr]

Those MG paints (um, coatings) are too conductive to be useful for making resistors.

Oh I meant these for painting the traces on the wheels - just catching up to the conversation.

[jagged ben]

Those MG paints (um, coatings) are too conductive to be useful for making resistors.

You know this is funny.  I was initially sure you were correct and then I started doing the math and doubting myself, aI was getting that the 841WB - EMF Shielding Paint (nickel flake) (at Resistivity 2.7 x 10-2    Ω·cm, for a 2mmx1mmx0.5mm dab of paint) would result in a nearly perfect ~10,800 ohms.  So I was even looking at the amazon page considering what price was worth paying for a 15mL bottle and I saw the resistivity listed as 0.027 Ω·cm and I realized <headslap> I was misreading 10-2 as a positive exponent instead of a negative exponent.  I mean, it should have been written 10^-2 without superscript but also I shouldn't be so dumb.   

Anyway, to share the useful part of the math...
I estimate that on an an N scale wheelset our dab of paint  is going to be about 2 millimeters long and I'm going to say a mm wide by a half mm thick.  We'll change that to centimeters to match the paint resistivity spec, so L/A is .2 / (.1x.5), which is 40.    So the resistance of our dab of paint would be roughly is the resistivity spec (in Ω·cm) times 40.   Which means we need a paint with a spec of about 550 Ω·cm to achieve 22k.

[Maletrain]

Isn't the appropriate length the distance across the insulator between the metal wheel and the metal axle?  The current is only going to be flowing through the part of the paint that spans the electrical gap, no matter how far beyond that gap the paint dab extends.

A quick look at the back of an ESM wheel looks like the distance across the insulator is only about 0.5 mm or 0.05 cm.

So, wouldn't that cut your resistance calc to .05/(.1x.05) = 10/cm ? 

Which would mean that you would need a paint with a resistance spec of about 2,200 Ω·cm to achieve 22kΩ.

BTW, I think you need to correct your post where you wrote "L/A is .2 / (.1x.5), which is 40" to read "L/A is .2 / (.1x.05), which is 40."