I was building a 1905 era HO layout and need more dependable performance from my light steamers. I have used them on a Pocher/AHM/Rivarossi/IHC old time 4-4-0 steamer, Bachmann Old time HO 4-4-0 and a Roundhouse Oldtime 2-8-0 with great results.
We are using a Kadee #5 centering spring. I have tried in the past to use formed sheet metal pickups but they never worked well and were difficult to make.
The wiper pickups make even small locomotives run phenomenally. Even locomotives like the IHC Oldtime 4-4-0 will crawl at an unbelievable pace. The locomotives will traverse Atlas #4 Customline dead frogs with no problems.
Blackening the backside of the wheels presented a problem, the slippery nickle plating wouldn't blacken. Chemical blackening was tried and failed.
Neolube a dry film graphite conductive product was tried but it too would puddle and would not adhere.
Various grades of sandpaper were tried to rough the slick plating. 320 grit worked the best and the Neolube adhered quite nicely. Wrap the sandpaper around a wood coffee stirrer.
Rough the backside of the wheel while holding it in the truck frame. The sandpaper should be used to produce a uniform field of light scratches.
Paint the Neolube on with a stiff brush. Let it flow onto the wheel back. Test the adherence by rubbing the surface with a soft stick.
The Neolube gives a flat black electrically conductive surface to the back of the wheel.
Kadee #5 coupler centering springs are bent to shape to be used as wheel wipers.
Cut the detail off the truck bolster and file the surface flat.
Crimp the "hole" end of the coupler spring around the bolster.
Drill a clearance hole for a 00-90 screw in the wiper and tap the bolster. Putting the spring on a piece of wood makes it easier.
Mount the wipers one side at a time. Test for electrical flow and free wheel movement. Use 1/4" long screws to facilitate the wiper being removed from the wheel while remaining screwed to the bolster. The wiper should make paths in the Neolube.
Wipers can be added to the locomotive by making a bottom plate of PCB. The KD springs are cut in half and soldered to the board.