Brass Technical Tips
January Brass List 1998
"Optimizing Electrical Pickup and Current Flow For Best Performance of your Locomotive"
Here we are at the fourth issue of these metallic ramblings. By now, the dust should have settled from the model/household entrance event and you have got it to go (Tips #1 October, 1997), you have eliminated any shorts (Tips #2 November, 1997) and you have a working knowledge of cleaning and lubrication materials and techniques (Tips #3 December, 1997).
With all that well in hand, we will next address guidelines which should help you in your pursuit of attaining the full performance potential of your locomotive. This month, we will tackle the prevention of what are probably the most common causes of poor locomotive performance; electrical pickup and current flow maladies. To accomplish this, we will describe an electrical 'tune-up' process.
To begin , we will address the most common configuration; that where the tender picks up from one rail and the locomotive picks up from the other. As the tender contains the largest number of parts that must pass current reliably, it is usually the most trouble prone. Hence, we will start there and work forward into the locomotive in our 'tune-up' process, on a point by point approach.
1) Tender wheel rims:
These must be clean. Clean both sides, not just the un-insulated rims that do the electrical pickup. Clean wheels roll better and contribute to good overall performance.
2) Tender truck sideframe axle journals and axle ends:
Both must be clean and bright, and lightly lubricated. Pay close attention to the inside of the journals, where the axles rotate. These tend to collect dirt and grime, which impede current flow. These areas also often wind up collecting spray paint residue, because of inadequate masking. Don't assume that these areas are pristine, just because the model is custom or factory painted, they occasionally will get paint over-spray in these places, as well. A good way to clean journals is with a round or square toothpick. Jam it in to set its shape and rotate; put in a rotary tool for faster results. Do not use abrasives or files here, you do not want to alter the shape of the journal interior, especially those for needlepoint axles.
3) Tender truck bolsters and companion frame bolsters:
More moving contact surfaces here! These are almost always raw brass and tend to tarnish and collect dirt. Polish these surfaces bright! Be careful again, on painted models. Even if these areas look clean, they may have an 'inadvertent' application of clear-coat on them. Check the threads and surfaces of the attaching screws and springs also, cleanliness here contributes to the reliable passing of electricity from the trucks into the tender chassis, as these parts encounter various track conditions.
4) Tender drawbar pin:
This part must be clean and bright. You may encounter either a plated pin or a brass pin, depending on the vintage of the model. Plated pins are more trouble free, but brass pins are equally reliable if kept clean and bright. Pay particular attention to the attachment of the pin to the tender chassis. Both sets of threads must be clean and the pin snugly screwed in.
Again, watch out for paint or clear-coat over-spray on these areas, and the pin itself.
Before we leave the tender, a few words on overall tender electrical pick-up are in order here. In the smaller scales, such as HOn3 or small HO tenders, it is sometimes the practice to add rail wiper pick-ups to augment the pick-up that the wheels do. Personally, I have found it more beneficial to add interior weight to the tender itself, in these cases. In light tenders, wipers must be perfectly adjusted to perform a reliable pick-up function, without causing tracking and derailment problems, which are more likely to occur in light tenders anyway. I have found that it is much more beneficial to add weight to a 'small' or light tender, as this improves both electrical pick-up AND tracking. This approach is also specifically beneficial to the tenders of Oriental Ltd. Locomotives in their HO scale 'Powerhouse' series. How much weight, you ask? Well, every case is unique and one answer is 'enough'. However, this is understandably lacking in quantitativeness, so a general stab at starting guidelines is: For small HO tenders, including the aforementioned 'Powerhouse' ones, try one-half to one ounces of weight, for HOn3 and similar sizes, try starting at one-half to three-quarters of an ounce. Incidently, the older tender-drive HOn3 locomotives, that many buyers shun, have terrific electrical pickup because both the locomotive AND tender have adequate weight.
To forestall the latent critics, who are always waiting to jump on an opinion, let me point out once again, that there are few absolutes in many areas of brass tinkering. The suggested approaches in these columns, are formulated both to be successful and to be achievable by the average modeler. So, then, it is recognized that there are cases where rail wipers (or sliders, as they are sometimes called) do have a place in certain applications to improve electrical pick-up.
Thus, if you have been addicted to these with successful results, far be it from me to try to dissuade you, there is no arguing with success.
5) Drawbar assembly:
The hole(s) for the tender pin must be clean and bright (See Tips #3 December, 1997). The contact tension wire must be present and soldered to provide good tension at the point of contact with the tender pin. The wire will provide the best overall contact if it is adjusted to be close to the center of the tender pin hole. Yes, I know that this makes the attachment of the tender to the locomotive a bit more troublesome, but it avoids trouble when running. This contact wire is vital to the reliable passage of current to the locomotive motor, even more so than the drawbar hole for the tender pin. Again, refer to Tips #3 for cleaning tips.
The locomotive end of the drawbar usually consists of an attaching shoulder screw, a spring, an insulated shoulder bushing into the locomotive frame, an insulating washer on top of the frame hole, a wire terminal going to the motor and a final nut to hold everything together (sometimes you will encounter a threaded wire terminal which eliminates the need for a nut - Ah-ha, you are invited to provide your own pun here). Ideally, the shoulder screw should go through the drawbar first and then the spring, so the drawbar has the most electrical contact surface in this critical area. That is, both the shank of the screw as well as the inner surface of the screw head. Sometimes, a reversed installation is encountered, with the spring between the drawbar and screw head: This is not nearly as good!!!! To belabor the point, intentionally, watch out for painted or clear-coated parts here. It is OK to paint the drawbar to hide it, just keep paint out of the areas that pass electricity, specifically, the holes at both ends and adjoining surfaces, as well as the contact wire where it mates with the tender pin.
6) Wire from Drawbar Terminal to Motor:
We have now managed to sneak into the locomotive interior itself, completely unbeknownst to the crew up above in the cab (except they may be experiencing some discomfort, as the your locomotive is probably upside down by this time; if it isn't, it should be). The next thing to check is the physical integrity of the wire from the drawbar terminal to the motor. Look close and wiggle things gently. Is there a good solder joint at both motor and terminal connections? Is the wire intact, no broken strands at the connections? Minimum amount of bare wire to avoid shorts? Wire insulation in good shape?
7) Other Wiring Involving the Motor:
Wiring to the motor may involve a number of other wires installed for headlights and such. A simple headlight installation (non-constant, non-directional) is usually wired across the motor terminals, i.e. in parallel with the motor. The light itself, here, will not impede the flow of electricity to the motor. But any connections involving this should be checked to make sure all is solid, especially where you may have more than one wire connected (soldered) to a motor tab. Constant and/or directional lighting installations usually involve diode setups, and as such, are wired in series with one of the motor wires. This makes operation of the motor more dependent on a solid installation of such components. Again, make sure that all joints/connections are solid and wiring is in good shape.
As a final caution here, look closely at the wiring for open frame motor installations.
Usually, the drawbar lead will be wired directly to the motor brush arm (OK as long as the wire has sufficient flexibility to avoid interfering with the brush tension or position). You may encounter a case, though, where the wire is soldered to a tension wire, at the top of the brush arm. This is just a tension contact here, and both the wire and the inset at the top of the brush arm can tarnish or oxidize. Disassemble this connection and scrape/polish the contact areas clean and bright, and reassemble.
8) Motor Connection to Locomotive Frame/Chassis:
Open Frame Motors: Most, but not all, of these are constructed so the motor brush for the right rail pick-up is connected directly to the motor frame, and the motor frame is mounted, via a screw, to the locomotive frame itself. This is a reliable connection. But, like all others we have discussed, the contact surfaces have to be clean and paint-free. It is not uncommon to encounter a painted model where the hole for the motor mount screw has been painted, and reduced the area of electrical contact between the motor frame and locomotive frame. Make sure that the frame area for the screw is clean and paint-free. It is mostly the screw head contacting the frame that passes the current from the locomotive frame to the motor frame. For motors with a separate wire from the right rail motor brush (the brush is insulated from the motor frame), check the integrity of the wire and connections, as you did for the other motor lead. One end of the wire should have a solid connection to the locomotive frame itself.
Can Type Motors: Can motors usually have an insulated housing, and, as such, require a lead from the appropriate motor terminal to the locomotive frame. Some installations simply have a lead from the motor tab to the motor mount bracket only. This approach may or may not be adequate, depending on how the bracket is attached to the locomotive frame itself. Some later motor installations mount the motor on a torque arm, which is then mounted to the gearbox. In such cases, the motor wire attached to the motor mount bracket is not an optimum connection. It will do an OK job, but the motor will receive the right rail current much more reliably if this wire is augmented with an additional flexible wire directly from the motor tab to the locomotive frame itself. This will assure that the motor is getting right rail pick-up from all drivers, not just mostly from the driver mounted to the gearbox.
9) Drivers, their Axles and Frame Contacts:
The areas where the drivers axles contact the frame are intrinsic to good right rail current passage to the motor. The axles here should be reasonably clean (no accumulated mess of old dirty lubricants). The areas where the axle journals contact the frame must also be clean. It is not uncommon to find paint in these areas, again due to inadequate masking. The slots in the frame, where the axle journals are installed, must be clean and reasonably bright. In some older models that have unsprung drivers, the driver axles will rotate directly in the frame axle slots, but the same rules apply. And last, but not least, we have come to the drivers themselves. By this time, it should be ingrained in your psyche that cleanliness is next to..... well, very very holy. The driver rims should be spotless, especially the right hand side set. See Tips #3 December, 1997 for cleaning guidelines.
We have run the circuit here (pun intended). We have started at the tender and left rail pick-up, followed its path to the motor, and then followed the path from the other motor tab to the right rail. In essence, the key here is that all moving connections and contact areas are clean and bright, and all threaded or soldered connections are solid and tight. OK folks, that rhyme was unplanned and just 'happened', honest. However, as long as it's here, we might as well use it as a slogan for electrical connections; 'Clean and Bright, Solid and Tight'. Maybe it will aspire to the classic 'Lefty - Loosey, Righty - Tighty' for bolt installation and removal.
Gadzooks, it's become obvious, even to me, that I've been at this terminal long enough, so that's it for this month.
See you next time.