Refusing to accept that poor performance was normal for Z scale model
trains, an engineer sets out to devise a better electrical contact to
eliminate stalling at slow speeds.
This story does not relate a saving of multi-millions of company
profits or an earth-shaking engineering fix. Rather this is about a
simple electro-mechanical design improvement to a relatively
unimportant hobby item that still made many hobbyists happy This falls
into the category of ‘spare time at home’ engineering problem solving.
Many electrical, mechanical, civil etc. engineers are, will be, or have been into the art of diorama and model railroad construction (or
railroad modeling if you prefer). So are many non-engineers both male
and female. The hobby appeals to all with an artistic and creative
bent, and offers technical challenges and satisfaction to those who are inclined to tackle artistic and technical challenges. In their spare time they create accurately detailed and realistic three dimensional sculpture and animated operational miniaturized scenes past and present.
I've been an avid railroad modeler for thirty years, starting with
hand-spiked HO scale (1:87), then progressing to N scale (1:160) with
good results. Then eight years ago I decided to try Z scale (1:220)
with very disappointing results at first.
The problem? Accustomed to reliable performance from HO and N scale
locomotives, I discovered that the performance of the Z scale
locomotives left much to be desired. Smooth slow speed running without
stalling was impossible to obtain no matter how clean I polished the
rails and wheels. When I called to inquire, the locomotive manufacturer claimed that no one had ever complained about this before. The online Z scale community accepted this as one of the drawbacks to this scale – the locomotives just did not make very good electrical contact to the rails. Vendors claimed "That's just how these things work. Poor performance is normal."
I almost gave up at that point, then I got mad and swore that
mechanical beasties the size of my pinky were not going to get the
better of me. I took them apart and saw immediately what the problem
Larger scale (N, HO, S, G) model locomotives have springy (beryllium
copper or phosphor bronze) wheel wiping contacts for electrical contact to the wheels which do the electrical pickup from the rails. This particular brand of Z scale locomotive did not have any electrical contact wheelwipers. The electrical path was the haphazard contact between the wheel axles and internal axle journals. The slightest bit of dirt in these inherently poor contact areas caused these locomotives to consistently stall at slow (realistic) operational speeds of under 30 scale mph.
Obviously the electrical contact to the wheels had to be improved. But
I tried several things. First was to verify that my failure mode
assumption was correct. I uncoiled little railroad coupler springs to
obtain springy metallic wire, then fitted this wire into the
locomotives to press on the wheels from above and electrically bypass
the axle journal contact. Saw an immediate 1000% improvement in
performance. But this approach had a problem—if the locomotive was accidentally driven across an isolated block where the opposing block polarity was reversed (operator error), the thin wires burned up before the PTC devices in the power packs would shut down from the overcurrent short circuit.
OK, I needed a more robust wheel wiping contact that can handle a few
amps during operational goofs. So I used flat phosphor bronze contacts
from another part of the same locomotive (supplied by the locomotive
manufacturer whom by then was beginning to take an interest in my
efforts) and found that they solved the problem in both wheel contact
and overcurrent tolerance. But they were a pig to install.
So finally I did some careful measurements and did a phosphor bronze
design that could be easily fitted into the existing mechanical
structure and would bear down on the tops of the wheels to press each
wheel independently onto the rail and at the same time provide
electrical continuity. Had a few thousand of them etched from a single
sheet of phosphor bronze by a local metal shop. Cost me a bit of money
while unemployed but decided the gamble was worthwhile—I was still in the mode of custom-built model railroads and was hoping to sell a reliable locomotive as part of the kit and kaboodle. This design worked amazingly well, could not believe the first tests that they actually fit into the wheel mechanism and kept running at low speed without any more stalling.
After verifying that the slow speed stalling problem was no longer an
issue, I wanted to find out how robust the wheel wiper design was. I
built a small tabletop railroad that I could run an upgraded locomotive 24/7.
Many times after running overnight, I would get up in the morning to
find the test locomotive off the rails, in many cases on the table, in
a couple cases on the floor. For many days this was a mystery. Then I
got lucky and finally witnessed during daylight hours the cat attacking the moving locomotive and batting it off the rails. To a cat, a Z scale locomotive is about the size of a mouse. All subsequent tests got moved to the garage so feline interference was no longer an issue. After 400 hours with almost undetectable wear I decided the pressure on wheeltop approach to wiping contacts was viable.
Wheelwipers: Simple concept, superb conductivity.
Even then I did not know what I had. At a following train show I had some of my modified locomotives running, there was another gent
displaying an incredible Z scale empire. We admired each others’
displays, then he asked me “How do you get your locomotives to run so slow without stalling?” I showed him my wheelwipers and he said "Can I buy some of those?"
Since then, I have been selling the wheelwipers online and installing
them for those who would rather not do the work themselves. A nice
work-at-home job. Another upside to this is that manufacturers of Z scale locomotives are now providing product with reliable electrical wheel contact. A big improvement in the hobby quality.