I don;t have signals on my layout, because the real thing didn;t on the branch I am modeling, and much as I would like to add all that, I just can't bring myuself to do it. But we DO have signals and detection on the club layout, so I need to add resistor wheelsets to my cars. I purchased a reel of surface mount resistors from Mouser, and got some silver paint on eBay, so last night it was finally time to get cracking on this (I have to the end of June to get the cars detecable, and I also want to finish off at least one more GP7 so that I have 2 to pull my train with. I need to add a decoder and LEDs and pint the handrails of the second one,a nd they both need cab roof drip rails added). I've tossed all the packaging the wheels came in, but I did get one of those clear plastic wheel painting jigs so I used that to hole the wheelsets for gluing on the resistors and then painting the conductive lines.
Gluing on the resistors went better than expected, given they are so tiny. Naturally I did manage to drop one, I didn;t even bother to look for it, since it's not likely I'll ever find it. But I bought 1000 of them, so no worries. Dot of slow drying CA on each axle, then set the resistor on with tweezers. Keepign my hand steady to dropt he reistor in place was the hardest part. If they landed slightly crooked I just nudge them into place. I then just let the glue dry, it takes about 10 minutes. I suppose I could spray on some accelerator but given the cost of the silver paint I want no residue that could in any way make it not work properly.
Painting was the next step. The silver paint needs to be well mixed as silver particles are even heavier than most pigment particles in paint and it settles out nearly instantly. A common trick is to toss a couple of bb's in the jar - after they have been thoroughly cleaned off with laquer thinner so they carry no residue to contaminate the paint, but I didn't have any so Iresorted to vigorous shaking. The included brush in my brand was actually small enough, so I used it. The silver paint is veyr thin and tends to run away from the slippery plastic axles of the Proto 2000 wheels I use, but I was able to get a solid bead between the end contacts of the resistor and the metal part of the wheel. The paint? Basically I was capping it and shaking it between every wheelset. Otherwise all you get is carrier and not much conductive silver.
Here's where I started to get worried. After about 10 minutes the silver paint looked dry. So I tested the resistence with my meter. Open circuit. I looked carefully to see if there were any gaps in the paint - nope. Still open circuit. Bummer. Then suddenly I started to get a reading. right around the 10K value of the resistors I was using. Seems it takes a bit longer than 10 minutes for the paint to dry and the silver particles to become bonded and conduct. Eventually all 4 sets were showing a proper 10K so I took the first two and swapped them out on my one caboose, setit on the rails - and I get an expected 5-6K across the rails. Perfect!
Only about 50 more to go.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
It is nice to see a project WORK the first time out the the box. Well in this case, the bottle!
Bet you will get better buy number 49! LOL
Great timing. We just finished installing and clearing up the first BDL on our club layout. We were thinking about the resistors on the plastic axles. Silver paint is a great idea.
We're also going to install resistors on the siding portion of our turnouts so that the block shows detected when the turnout is thrown.
Where did you acquire the resistors and paint?
Springfield PA
Here's the web site with a tutorial on it, using P2K wheels. Most places show how to do it for all metal wheelsets, like Intermountain, where you glue the resistor at an angle across the insulated wheel. But I use all P2K wheelsets.
http://www.mpmrr.net/wheels1.html
This is the Mouser part number for what I got, tape strip of 1000 10k SMT resistors: 263-10K-RC. $15 for 1000.
Mopac Mike uses the Busch conductive paint but I couldn;t find it in stock anywhere - too many online places just list the Walthers inventory but if you check Walthers they also show out of stock and no expected delivery. SO I found this on eBay: http://cgi.ebay.com/CONDUCTIVE-18-SILVER-PAINT-15-grams-brush-cap-/270305463400?pt=LH_DefaultDomain_0&hash=item3eef760c68
One more step I haven't tried yet is to see if covering the silver and resistor with flat black will eat away the silver paint - on the inside axles of a house car you can;t really see it but on open hopppers I think it will be readinly visible as the car rolls along. Plus since I hold the wheels in the painting jig I suppsoe I should take advantage and paint the wheel faces at the same time, the P2K wheels aren't very shiny but in the caboose I used I had them all painted grimy black, and the two resistor ones are not painted and it stands out.
Randy.
How many resistors does it take before the detection circuit sees an occupied block? Would a lighted caboose set the signals to occupied? How much resistance does it take before a short is detected by the boosters or breakers?
One of the guys in our module group has signals on his modules controlled by photo LEDs between the rails. There are several in each block and has a timer attached that delays changing aspects from occupied to clear (approach). From clear to occupied it switches fast. If it was a complete system the previous occupied block would show approach. It works fairly well but a misplaced car can reek havoc if not over the LED.
Which system do feel is best. The photo LEDs or the resistive detection?
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Thanks Randy
Pete. It only takes 1 resistor to detect. There is a setting in the BDL168 that allows you to set for 20k or 10k ohm.
I've used photo led's in the past and they work. but are not as reliable as current detection. One problem I would have is with tank cars. Since they typically rely on light overhead the light sometimes gets around the round tank car and hits the led causing a false clear. IR detection helps with that as well as when you want to run with reduced lighting.
Each system has its uses. A phot detection system is great for specific location detection - say a staging yard so you know you are coming to the end of the track. Resistence detection automatically starts up in the current situation - if there's a car int he block it will indicate occupancy immediately on power up, it takes a bit of work with an optical system to remember the previous state.
Most system detect 10-15K with no problem, some one wheelset should be enough, but since contact varies when rolling, I'm doing two in each car for approximately 5K per car. Most of the club guys are only doing one axle, with a 4.7K resistor on it. I figure with two, if the car is half straddling a block boundary it should hold both of the occupied. I just think two per car is more reliable. When they first announced needing resistors and said they were using 4.7K, I raised an eyebrow enough to be noticed - then they told me they were only doign one axle per car. A pair of 4.7K is like 2.35K, starting to get into excessive waste of power territory when you have hundreds of cars on the track. A hundred cars with a total 2.35K resistence at a track voltage of 15V is nearly .7 amps. We've probably got 300 cars on the layout at any time, maybe more. That's nearly 2 amps wasted. With 4.7K it's less than an amp. So I'm doing a pair of 10K, for a total of 5K per car, still plenty to activate the detection circuitry plus 2 axles detectable for reliability.
I am also doing 10K resistors on two axles. I have been using the Intermountain 33" wheels. I did add one extra step in making these resistor wheel sets that really improved the connections. I used an exacto knife to scrap the back surface of the wheel and on the axle. This seemed to help make a better connection. I have about 150 cars done so far and only about 50 more to go ( I have to order another package of wheel sets).
Randy,
Out of curiosity, what physical size of the SMD resistor are you using? (I know they are 10K but are they 1206, 805 or 603s? ) I personally have been using the 603's and with the Intermountain wheels they are almost invisible. I also find the 603's cause the least amount of interference with parts on the cars.
I haven't bothered to paint them yet so I can't tell you whether the paint will mess with the conductive traces or not. I don't think it will affected unless you overly use solvent based paints.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
Mine are 1206. I wanted something I could actually see to glue down. I put them in the center of the axle, , which should clear most anything. The width is less than the axle diameter, and the height is only 1 tenth of a mm more than the 603 size, so unless I put an abnormal size blob of CA on the axle I don;t think there will be an issue.
After the first one didn;t seem to work I wondered if maybe that was the problem, so I scraped the blackening on the backs of the next one, and it didn;t make any difference. Then when I tested again after additional drying time, the first one worked withotu scraping, as did the second one. The next two I did without scraping, and they work. So whatever they use on the P2K wheels, it conducts fine and also seems to adhere the silver paint just fine.