Page Originated 8/1997
Page Updated 06/13/2022
Last update:

MAKING YOUR LOCOS LOOK AND
RUN THE WAY YOU WANT

ROD MILLER'S DRIVE SYSTEMS

Locomotives That Work As Well As They Look

Turn That Roundhouse Queen Into The King Of The Road

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This is a description of my model railroad drive business. I encourage you to have a dialog with me so that we can fully discuss your interests and what I can do for you.

Custom Drive Systems

I refer to the process on installing a drive system as customizing a locomotive. As you will see below, there is much more to making a locomotive run reliably and smoothly than installing a ball bearing gearbox and a can motor.

A customized loco does the job: it runs every time the throttle is opened, it pulls a realistic length train, it stays on the track, and it looks right.

Any locomotive, domestic or imported, small or large, steam or diesel, painted or unpainted, can be customized. My drive customizing continues Jerry White's experience in providing hundreds of famous durable, reliable, hard working model locomotives, which today command a premium price because of their premium performance.

Note: please see the Exclusions section under this button for jobs I will not take on.

There are some folks who provide good drives; their designs and approaches differ from mine. However, there are also some inexperienced "drive experts" who are poorly equipped gear box and motor swappers who may do more harm than good.

"The bitterness of poor quality remains long after the sweetness of low price is forgotten..." - Unknown.

My approach to making a locomotive run well focuses on these areas:

Every time the electrical circuit between the rails and the motor is interrupted, the loco will hesitate or stop running. It won't run at all, or run smoothly if it does run, if the motor doesn't have constant juice!
I provide for reliable track to motor electrical connectivity.
If it sounds like a worn out coffee grinder when it goes by, the illusion is sorta shattered. If it won't pull a respectable train or run at a realistic speed, again the illusion doesn't work.
I fabricate and install a smooth, quiet, durable, and powerful drive system.
If it runs well but won't stay on the track, what good is it?
I ensure reliable tracking, e.g., your loco won't derail on track and turnouts that are built to NMRA standards.
I ensure that the basics that, well, make a steam locomotive right are there: couplers all around, correct lights, deck plate (if applicable), air and steam connections on the tender (if applicable), etc.

Here are the details on how I approach the above items:

The model is blueprinted (see Standards under the DETAIL tab).
Ball bearings are used on shafts that are high speed and/or are subject to thrust forces that will affect the mechanism, in all gearboxes, and in the high torque Pittman motor that is my standard unless it won't fit. Think all Pittman motors are the same? Wrong! You`ve got your inexpensive motor, and you've got your expensive, twice as powerful, smoother running motor - identical externally except for the part number. I use the latter.
Each gearbox is custom built with running fit tolerances and custom made gears, and is custom fitted to the locomotive. The gearbox is fabricated from brass sheet and tube, and is soldered together. The gearbox design does not rely on tiny gear box bottom retainer screw threads to clamp the gearbox (and the worm) to the axle gear.
Construction of a Gearbox
Standard ratios in steam locos are 15:1 and 30:1, and 7.5:1 in diesel and electric locos. Note that 15:1 combined with a 9000 series Pittman motor gives a no load top speed at 12 volts that is 1.1 times the driver diameter in inches which is the rule if thumb for maximum speed for a steam locomotive.
Steam locomotives are fitted with one gearbox per engine, e.g., two gearboxes on articulated engines. Normally on articulated locos I use one motor to power both gearboxes; this is much simpler, more reliable, and much less expensive than having a motor per gearbox (if desired I will power each gearbox separately); if you don't need lots of pulling power I can remove the drive from the front engine so that it coasts giving the effect of independent engines or you could do that yourself - just remove the gearbox and drive shaft and leave the axle gear in place - be to save the parts for the next owner of the model!
In simple steam locos the worm shaft is connected to the motor with a short piece of precision hose (the hose has demonstrated its effectiveness over the years), which is the ultimate in reliability - no moving parts in the motor-to-gearbox connection.
Diesel and electric locomotives have one motor per unit. A custom made tower transfers the drive down to one axle on one truck, and delrin chains are used to drive the remaining axles on that truck. A drive shaft is run from that truck's gearbox to the other truck, where a duplicate arrangement of gearbox and delrin chains is fitted. This drive is simple, quiet, and durable.
A custom made weight is installed in the loco;
1. A lead cylinder is selected from several that I cast in batches.
2. The cylinder is machined to fit the boiler and around the drive. The cylinder size varies depending upon the customer's preference; this is a large one, weighing 4 pounds 9 ounces.
3. After the weight has been fitted including sturdy mounting it is painted.
4. Finally the front of the weight is stamped with identification information.
5. The process for trucked locos is similar except that lead blocks are used for the fabrication of weights.
The springing is modified if needed so that the engine floats on the springs and all drive wheels contact the rail. If the locomotive was built without springing, the chassis is modified if to possible provide a spring suspension for the drivers.
On small steam engines if a large motor is desired it is located in the tender. The drive shaft to the gearbox in the engine is hidden under the deck plate. The boiler is free for a larger weight, further increasing the loco's performance. If a smaller motor is acceptable it is installed in the normal location in the boiler. The engine weight and suspension are fabricated so they are appropriate for the motor size.
Steam locomotives are balanced to have their center of gravity at the center of the drivers.
In electric and diesel locos the weights are installed such that the engine balances at the chassis center between the powered trucks.
On steam locos the tender electrical system is modified to provide reliable pickup and to eliminate shorts between the loco and tender superstructures. Diesel and electric locomotives are provided with all wheel pickup if they weren't built with it.
To support my point: which loco has the better electrical pickup - an 0-4-0 with a two truck tender, or a stock All Nation F unit? Answer: the 0-4-0 has better pickup because it picks up from the left rail with four wheels; the F unit picks up with only two wheels from the left rail. Both locos are equal for pickup on the right rail, where each picks up with two wheels. The diesel may have the advantage of weight, which will help improve contact.
Unsprung tender trucks are equalized to improve tracking.
All wheelsets are checked with the NMRA standards gauge and re-gauged as needed; major wobble in drive wheel sets are corrected to eliminate derailments (a wobbly wheelset will be in and out of gauge on the rails as it turns.)
Constant directional headlight and backup light are installed; shiny reflectors and clear lenses are custom made.
Coupler heights are checked and corrected if needed (rear coupler only on certain steam locos.)
Obvious missing details are installed; for example, the cab to tender deck plate, and air brake, signal, and steam lines on the rear of steam loco tenders.

Servicing Custom Drives

Servicing the drives is straight forward. Servicing is defined as lubricating the motor, the gearbox, on steam locos the drive wheels and associated moving parts, and on all locos the axle journals on trucks. The same process applies to drives that were built by Jerry White and by me with one change - see below.

When to service the drive is driven by how many hours the locomotive has been run since its last servicing. Locos that are run in exibilition use (run continuouisly for many hours on a daily basis) should be serviced once a year. Locos that are run in normal model railroad use (a few hours a week) should be serviced every five years. If you have bought a model with one of these drives and don't when know when it was last serviced it would be a good idea to service it before running continuously.

Tools

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Motors

Most but not all brives built by me and Jerry White will have a Pittman motor. These motors will have ball bearings on their shafts. There is no need to service these motors. Other motors may have either ball bearings on their shafts or oil impregnated bronze bearings (orange-ish color) on their shafts. The bronze bearings are lubricated with one small drop of generic motor oil on each end of the motor where the shaft emerges.

Gearboxes

First please look at the below images to familiarize yourself with the drive gear box design.

Both images shows the tube containing the worm. Each end on that tube where the drive shaft emerges should be lubricated with one drop of motor oil.

Note that on your loco there will be two screws at the bottom of the gearbox, one at the front and one at the rear. Remove only the screw at the front which on Jerry's gearboxes anb my early gearboxes an 0-80 hex screw (do it the right way and use a socket wrench not pliers to remove the screw), and on my later gearboxes an 0-80 cap screw; if you need a driver for this screw let me know an I will send one to you. The screw hole is .052". Insert a hypodermicl Use a hypodermice needleO.

Drive Wheels

Most but not all brives built by me and Jerry White will have

Electrical

Electrical work is very rugged and reliable the way I do it. Connectors are installed so you can separate major pieces such as the boiler from the frame without resorting to cutting wires or a soldering iron, and heat shrink tubing is used everywhere for electrical insulation. Circuit modules are securely mounted with a screw or double sided foam tape.

On DC powered models standard constant directional lighting is one constant light in the loco front that is on in the forward direction and one constant light in the loco rear that is on in reverse. Additional lights and/or lighting effects are extra cost. Incandescent bulbs are used since they look like incandescent lights, and in normal uses they will last as long as the model does. For DCC the lighting is determined by the customer.

The constant lights are implemented with voltage regulators. They do not take voltage away from the motor like diodes do, so you get the advantage of full top speed. Their disadvantage is the light doesn't come on until there is 5 volts on the rails, and the loco will usually be moving by that time. With DC diode controlled lighting costs extra; it has the advantage of turning on the lights before the loco moves, and has the disadvantages of being more complex (higher cost) and of reducing the loco's top speed.

Testing

It is extremely important that proper operation of the locomotive be verified before it is shipped to the customer. I want the locomotive out of the box to be ready to run for many hours. The last thing I want is for the customer to have to return the locomotive to me because something wasn't right that I could have caught and fixed before shipment to the customer.

A description of my testing can be read at Testing under the DETAIL tab.

Identification

Each of my customized locos is identified as such by "RM" and a serial number stamped on the gearbox bottom.

Gearboxes built for some customers but not installed by me in the locomotive are identified as such by "RM GB" and a serial number stamped on the gearbox bottom. Locomotives with "RM GB" on the gearbox bottom can not be viewed as having been customized by me, nor viewed as having my "drive" in them. Note: I no longer offer stand alone gearboxes.

Q and A

Q: OK, so what does that all get me?

A: You get a smooth running powerful locomotive. I use as large a diameter worm gear (axle gear) as possible. The larger diameter provides a greater torque arm for the worm, which provides smoother starts and reduces the load on the motor, which lowers current draw and decreases motor wear.

The shakedown run reveals surprising faults such as crankpins working loose, drivers working loose, screws working loose, and shorts that show up after wheels rub through paint that up to that time had prevented the short. I correct all those problems so that out of the box your loco will run smoothly, be powerful, and be maintenance free for many hours of actual operation.

The loco being tested pulls a train that includes specially built cars that combine heavy weight with drag so that thet loco can tested with the heaviest train it can start.

Q: Sounds like a custom made gearbox is a boondoggle since ball bearing gearboxes are available from NWSL and some imported locos come with ball bearing gear boxes.

A: First, consider that to install an NWSL gearbox kit someone has to disassemble the model and have the expertise to install the axle gear. Then the motor has to be connected to the gearbox worm shaft. I do all that when installing my drive. I have installed NWSL gear boxes and determined that the cost of doing so was about the same as the installed cost of my gear box, and since my gear box gives better performance I no longer install NWSL gear boxes. My gear boxes eliminate unnecessary gear box movement, such as yaw motion ofthe box around the axle, that effects running. Making my own gears assures absolute concentricity which gives smoother running. No other supplier of drive systems, including all the importers, uses an axle gear approaching mine in diameter, e.g., lever arm, and no other supplier of drives has a design that positions the worm relative to the worm gear independent of clamping action by the threads of the screws that retain the gear box bottom, i.e., the worm and worm gear positions are determined during the fabrication of the gearbox, and cannot be altered during maintenance - this ensures that the gearbox will always provide the performance for which it was designed.

Q: I've heard that Delrin chains stretch.

A: Not true. I have diesels in which the chains still sing when "plucked", and they've been in the locos for 25 years.

Ask My Competition

If you are thinking about having a "drive expert" do some work on your loco's drive, ask about their experience, tools, standards, and testing.

Warranty

Please see the warranty description under the WARRANTY button.

Thank you for your interest. Please contact me if you have any questions.

Page Originated 8/1997 Page Updated 06/13/2022 Last update:

MAKING YOUR LOCOS LOOK AND RUN THE WAY YOU WANT