FVM wheels, Occupancy detection

[Hiroe]

With wiring for proper signaling comes the need for effective occupancy detection. I personally prefer the induction-transformer method, as it allows me to keep my signal and track power circuits completely isolated, thereby preventing any DCC-signal leakage onto the signal logic. (I build my own logic boards for occupancy detection and signal drive, which lets me install appropriate signaling for complex interlockings.)
Problem is, the induction method only sees the locomotive load; and the tail of the train gets missed by the system, so the signals clear up before the train does. (I *could* use phototransistor-driven secondary detection; although that requires not only installing (large quantities of) said phototransistors in the track, but also regular adjustment for proper detection in varied light settings, especially with modular setups. Blah.)

All that said; having just read through the previous Railwire topic about FVM wheels (January 09, here), i got to wondering: Has anyone attempted (or succeeded) with installing SMT resistors on these, for use as occupancy detection shunts? Similarly, are such resistor-equipped wheels available for purchase somewhere? (I must admit, the FVM wheels look REALLY GOOD. So i'd prefer to use the FVM wheels for the shunts, to match all the non-shunt wheels i'm looking at installing.)

Alternatively, any other options i've failed to consider?



Also - those of you who have FVM wheels: any complaints thus far? Do the treads eventually take a shine from regular use, or do they need to be mildly polished?

--Drew

[eric220]

I'm actually looking at doing the same thing.  It's frustrating when I nice long freight train's caboose keeps flying past "clear" signals.  Here are some links that might help:

http://www.rr-cirkits.com/wheelsets.html

http://www.customsignals.com/documents/BD-20Instructions.pdf

http://www.trainternet.fr/Hint2_us.htm

The most popular method would appear to be 10Kohm SMT resistors and conductive paint.

[tehachapifan]

Another option.......

http://www.logicrailtech.com/dws.htm

Russ

[Robbman]

Has anyone attempted (or succeeded) with installing SMT resistors on these, for use as occupancy detection shunts?

Easy to do with CA and conductive paint.

[Hiroe]

Another option.......

http://www.logicrailtech.com/dws.htm

Russ

Nice! Any idea what the axle length is on these?

I might get a few to play with; but at more than $2 each, it would be much cheaper to make my own.

[ChrisNH]

Easy to do with CA and conductive paint.

There was an article outlining that in MRR:

http://index.mrmag.com/tm.exe?opt=I&MAG=MR&MO=2&YR=1993&output=3&sort=A

It seems like fussy work but worth a try.. at least on the cabeese.

Chris

[asciibaron]

i would want resistors on all cars (two per car).  a fleet of 25 cars is doable, but 125 gets to be a pain.

[Hiroe]

i would want resistors on all cars (two per car).  a fleet of 25 cars is doable, but 125 gets to be a pain.

Yeah, that's basically where i'm at. Too many cars, not enough time.

[Day One]

several N scale layouts in my area (and featured on the layout tour at the National N scale convention here in Portland) use FVM wheels with smt resistors soldered on. It works quite well.

[Hiroe]

several N scale layouts in my area (and featured on the layout tour at the National N scale convention here in Portland) use FVM wheels with smt resistors soldered on. It works quite well.

Soldered? How do they solder them on without killing the insulator? Resistance rig, or..?

[Day One]

I'll have to ask one of them how it's done and what value resistor they're using.

We talked to Matt (?) of FVM at the Portland show and asked him if it was possible to assemble the wheel sets with a resistive piece instead of the insulator and his response was that it had been tried and they couldn't get consistent enough results for it to work. That said, it would sure be nice if you could get them pre-built that way.

[haasmarc]

I prefer using conductive epoxy that I found at Fry's electronics.  Glues and creates the path in one step.  I use black paint to insulate the one end of the smt and the axle.  Works very well with TracTronics SECSI system.  I got tired of the conductive pens drying out.

Marc Haas

[Day One]

Almost forgot about getting back to you on this...it is CA and conductive paint they are using.
Didn't remember to ask what value resistors but I seem to recall it being 10 Meg Ohm. Again, I will try to verify this next time I see one of the guys that are doing this.

I'm usually not so slow and forgetful about this stuff but I'm expecting a new baby girl any day now and I'm definitely preoccupied lately!

[Nelson]

They are pretty easy to do. I prefer epoxy over CA. Epoxy is thick enough to hold the resistor in place until it cures and it also insulates the resistor from the axle. Then use conductive paint to connect one end to the axle and the other to the wheel rim

10k (10,000) ohm resistors are about optimum. This gives you a low enough resistance to detect a single car, but is high enough so that 50 cars don't load down the system. If you go much lower in resistance you will also need to use a higher wattage (larger) resistor which can lead to bolster pin clearance trouble



This is an Atlas wheelset with a 10k  1/10th watt resistor.
You can use a smaller wattage resistor, but they become very difficult to handle in smaller sizes.