My first attempt at resistoring wheelsets

Resistor your wheelsets

This is my first blog entry so please excuse me if I mess it up badly.

I've only been collecting/modelling for about 3 years now, with a layout that is only in the planning stage.
I have the EasyDCC system from CVP, (IMHO one of the best).
CTI system for computer control and layout realism, and the Rob Paisley block detection sensors. (the ones geared toward DCC)
Presently, I have 30 locos with about 180 pieces of rolling stock.
I will list all part numbers at the end of this article, for those interested.

My desire was to be able to detect locos & rolling stock wherever they may be on the layout.
Block occupancy for signals and collision avoidance, to me, is a "must".
This meant detection by whatever means, IR, magnetic, current, ambient light, or whatever.
Magnets attracts debris, IR is usually hard to hide away, plus lots of wire for hook-ups, ambient is asking for failure. (my opinion, my blog)
 
I chose current detection for all purposes. Being under the layout keeps it out of view. I can wire to my hearts content, and no little fingers will be tempted to see how it works. This eliminates IR led's, photosensors, etc. on my RR world.
Of course this means resistoring wheelsets, or power pickups to tell CTI what's occupied and what's not.

I order parts from alot of sources in my business, and found some things to experiment with.
Mouser.com was the best source for what I was after...And now, "the rest of the story"

After a little math session, I decided that 1 miliamp ( 1ma.) per axle would provide a decent level of current for detection without overloading the power booster. The lower the resistor value, the hotter it will become. After all, with all four axles resistored, total 4 ma./car (usually) it would still take 250 cars to consume 1 Ampere of current (20%) of my boosters capability. This value keeps heat way down per resistor, allows for very small resistors (needed for where they must be placed) and they vacuum up easily when dropped. (YES, you will drop them!!!)
You must remember that when installed, these resistors will be riding just inside the flanged tire of the wheel and dare not make physical contact with spikeheads, guide rails at turnouts, or ballast. (Hence, the small size)
So I found a resistor at MOUSER.com that I thought would fit the bill...10000 ohms (10Kohms 1/10th watt smd) surface mount device, or chip style, if you will. These little critters can be purchased on a plastic covered paper roll in various quantities. I chose a roll of 1000 as they will stay fresh for a very long time, without refridgeration, and many will be lost to gravity, stuck on your elbows, in your pant cuffs, etc. Besides at 1.6 cents each, $16 ain't too much for the peace of mind large quantities on hand brings.

Well, I tried using many soldering techniques...as I have been soldering for 35 years now, and I think I may soon get it right.
I do not care how cool, hot, large, or small your soldering equipment is...FORGET IT!...you will destroy more wheelsets than you can probably afford.
The metal wheelsets I'd chosen were the Atlas #22020 (I think that's right), in packs of 12 (enough for 3 cars/pack).
These little gems have both flanged tires impressed onto a plastic hub, which is pressed onto the shiny axle from each end. This insulates each "tire" from the axle, preventing your power booster from seeing 4 short circuits on every car. Put a short across the rails and you can watch a neat static display of railcars, while real smoke rises from your power system.
Pulling out a pack of these, I proceded to destroy 3 wheelsets before resigning myself that heat will certainly destroy one or the other end of these wheelsets. They will forever wobble, run out of round, out of gauge, or look awful.  Now what??

Behold! MOUSER.com sells a pen, yes, a pen, that will dispense conductive paint on demand. It conducts electricity very well, is solderable after 5 minutes of drying time (when used elsewhere except Atlas N gauge wheelsets) and doesn't stink up the house when used.
Intended primarily for the purpose of re-drawing foil traces on PC boards, I thought why not.   

I actually succeeded in getting a few together without losing my religion.

Detailed steps will follow:
After acquiring some of these metal wheelsets, resistors, CA glue,  conductive paint pen, benchtop gripper (3rd hand), angled headed tweezers, opti-visor, paper towel, isopropyl alcohol, a good ohmmeter, and lot's of time, try doing things in this order.

Lay off the coffee and other nerve shattering agents for a few days. (You can thank me later)
Gauge all sets to be resistored. This must be done before, as it will not be possible after resistors are applied!!!
Place 1 wheelset in gripper with the axle nearly vertical, but not quite. I found the angle best when the axle was pointed at my lap.
Remove a few, (3 or more) resistors from the packaging and put them where they are easily seen and found.

Take care not to get CA on either end of the resistor, if you do discard it, it's not easy to get CA off and also not worth the hassles involved.
Place the smallest drop of CA you can get on the white (ceramic underside) of the resistor.
Using tweezers, place this resistor on the inside of the lower wheel with one end in contact with the shiny axle. The resistor will not quite span the black plastic hub. Set this one aside and let it cure, preferably overnight. The CA must be given time to set. Let us not rush things, for surely, Murphy will pay you a visit. I would suggest doing a few more while we're at this stage. Besides the glue needing time to cure, unless you are crazed, this is not a good time to be thinking conductive paint.

After a good nights sleep, read all the instructions on the paint pen....I said all the instructions.
Shake the pen for at least a couple minutes before use. You should hear the stirring slug rattle inside.
The pen has a springy plug valve which will recess into the funnel end when pressed against a firm surface.
Paint flow is regulated by how hard you squeeze the barrell of the pen (sorta' like the toothpaste concept)

WARNING, this stuff dries VERY, VERY quickly. That is why the paper towel and alcohol are necessary.
Wet a spot on the paper towel with isopropyl alcohol. This will be how you clean dried paint from around the tip of the pen.
I found that a few times of tapping the paint pen into the dampened (alcohol towel) and a quick wipe on a dry place, seemed to clean the tip the best. You will discover frustration in getting the paint where it is needed, but I started with applying it to the end of the resistor closest to the wheel flange worked best for me. Clean that tip quite often....clean it again, this time do all sides!.
Set this wheelset off to the side and do another if you still want more punishment, or just admire your work.
The CA is imperative or the next phase will put you back about 4 steps. Once dried, these wheels are ready for the most critical and hard to do step. That is getting paint from the inside end of the resistor to the shiny axle. If you don't press the springy valve against the axle, it will slide off without releasing paint. This is just an aggrevation if it slid away from the resistor, if it slid toward the resistor, you probably broke the resistor, got paint on top, or worse underneath it, and produced a short. After Murphy, I successfully scraped paint off of a couple resistors and wheels when things had gone awry.

Some points to remember:
This paint is alot easier to scrape off when fully and completely dried.
Keeping the paint tip clean is a must, must, must!
Both wheels are insulated from the axle, so if you don't want double the headaches, place a trace of paint from the axle outward to the tire on the end without the resistor. This will produce a short from the axle to the wheel, so be cautious of metallized trucks!
Don't be afraid of a little excess paint on the axle at this point. Excess paint is easy to scrape off most surfaces.
If things aren't quite right, put this one off to the side. I tell you now that attempting a correction of excess paint, not enough paint, clumps, loose resistors are best corrected another day. This stuff has to have time to set up. Patience grasshopper.
About the time you think all is well, use that ohmmeter from wheel to wheel.
As in my situation, a reading of 10K ohms was the goal. Got something else? Examine your work, clean up excess paint/glue, and ohm it again.
Something amiss? ohm from axle to wheel...this isn't rocket science. 
If all checks ok, good resistance value from one wheel to the other. It's now time to cover that paint and resistor so they both have a chance for survival. I used more CA to cover both. Now lets be careful out there, CA on the tire surface can, no, will be a pain to correct.
Dried CA is pretty hard stuff. I imagine it could be painted over for appearances sake.
Install the wheelset carefully into the trucks.
OHM IT AGAIN!
Only you will know the value of resistored wheelsets on your road, and whether it was worth all the labor involved.

DCC voltages are usually around 12vacd (max)for N scale. DC will at times be considerably lower voltage. Use ohms law to find your desired resistance value. (It's in the public domain, I think)

CA glue type is strictly your choice, but a gelled type may be a little easier to work with than the runny kind.
The resistors I used were MOUSER.com for the 1000 piece roll, MOUSER# 71-CRCW0603-10K-E3    $16 USD
Paint pen made by CircuitWorks (fine point of the 2 sizes),           MOUSER# 5168-2200MT                     $23.71  USD

I will try to get some photos for my next entry.

For you older folks "30", for the younger, "Look it up"

--Joe--