GP7/9 & body mount centerset Kadees with 3D printed components


USA Trains GP7/9 & Body Mounting Centerset Kadees with 3-D Printed Components (and other issues)
Ted Doskaris
Initial Release
October 29,2018

Shown below is the USA Trains "Geep" with installed 3-D printed coupler box having Kadee centerset coupler & pilot plug.

In this vignette (article), reference will be made to the front and rear of the loco. The short hood end is considered to be the front (signified by "F" mark near steps in above picture) and long hood end the rear as shown below.

That said, it's understood that many prototype GP7s and some (mostly Eastern railroads, e.g. N&W, Southern) had their "Geeps" with control stands oriented toward the long hood - being identified as the front of their locos.



Couplers & 3-D Components
CamPac Component Installation
Non Coupler Issues:
Dismantling Loco
Intermittent Switches
Cab Removal
Adding Extra Weight
Cooling Fan Experiment
"B" Unit Adaptation

Obtaining CamPac Products




Items to be described include installation of 3-D printed components (coupler box, pilot plug, etc.), Dismantling the loco, Intermittent switch board switches, Adding extra weight, Cooling fan experiment, and adapting the GP7/9 to a "B" Unit with 3-D printed parts.

Described examples will be the USA Trains GP7/9 locos, using Southern Pacific & Union Pacific road names. Other than road name, the locos are like all other USA Trains GP7/9 units. The example locos happen to include the factory dynamic brake blister on the top, but it's of no relevance with respect to couplers, etc. whether equipped with air tanks or without anything there.


Couplers & 3-D Components

Kadee Centersets & 3-D Components:

Since the advent of 3-D printers, I decided to use this technology to mount Kadee centerset couplers on the GP7/9 from the start - bypassing the use of discretely made parts. Accordingly, much of the information herein will be concerned with what's entailed when installing "CamPac" 3-D printed components on the loco to accommodate Kadee centerset couplers from the 907 kit. Hence, the Kadee 907 Kit must be obtained in addition to the CamPac components.

The CamPac components include the coupler box with integrated fairing, mounting pedestal, and pilot plug. They are designed by me, Ted Doskaris, in concert with Colin Camarillo who has a resin type 3-D printer and offers the components for anyone else desiring to use them. The components, also, afford more prototypical realistic appearance to the loco.

The overall loco with all installed factory and CamPac components is illustrated below.

Note: The installed CamPac components are made from black or gray resin and can be painted as done in the loco above to better match its livery.


CamPac Component Installation

Note: In addition to what is to be subsequently described, it's helpful to refer to document, "Installation Guide USA Trains GP Series Cam Pac Components", particularly if the loco being worked on was acquired used or fitted with factory knuckle couplers or aftermarket couplers.


3-D Coupler Box Installation:

Coupler Installation:

The Kadee 907 kit's coupler, springs and lid are to be installed into the CamPac BoxTM as illustrated below.


Pilots' Preparation:

The loco should be carefully placed on its top supported from tipping over in such a way that roof parts (horns) are not at risk of damage.

For adapting the loco to accept centerset couplers, illustrated below is a minor modification to be done on both front and rear pilots, including example techniques.  Factory detailed parts need not be installed on the pilot - in fact it makes it easier to work on the loco if they are not installed.

Pedestal & Installation:

Shown below is the pedestal to be mounted in the loco's chassis.

The mounted pedestal with CamPac coupler box installation is illustrated below - to be done on both ends of the loco.

As in example shown above, If needed, shim the box for coupler alignment to the Kadee 980 gauge.
Coupler alignment on the other end of the loco may be slightly different due to tolerance variations.


Pilot Plug Installation:

The pilot plug is installed as illustrated below - to be done on both ends of the loco.



Non Coupler Issues

Note: The loco does not need to be taken apart when installing CamPac components.

In the event problems arise that are internal to the loco, like intermittent electrical switches, the body shell will need to be removed to gain access. I had such an experience with open circuit and erratic switch performance in respective SP and UP locos. I also added miniature cooling fans and extra weight to the locos that necessitated loco dismantling.

Dismantling Loco

In order to access all possible chassis to body shell fastening screws, a truck's motor block may need to be removed, though just set aside with wires still attached. This is particularly required for the front truck if all screws had been installed. For the rear truck motor block removal is not needed, albeit with some difficulty getting at a couple of screws.
In order to remove a motor block only one side frame need be removed, and then by manipulating the block it can be withdrawn from the still attached side frame - illustrated below.


Comment about Chassis Screws:
In the event some chassis screws are lost, or it's desired to utilize all fastening locations (not all may be factory utilized), aftermarket screws can be obtain as I had done via Amazon, albeit sent from China with a few weeks to get them.


Illustrated below is the front truck area of the loco depicting the "hidden" locations where folks may wish to install screws if they were not there to begin with.

Now for all the fastener locations:

Illustrated below are the locations of the body shell to chassis screw fastener points, some of which may not be factory utilized and are hidden out of sight.

As seen in the above illustration, the fastening screws are recessed down within chassis tubes (posts). Once all the screws are backed out / removed, the body shell can be lifted from the chassis.

When placing the loco upright, typically only a few screws may fall out. There may be 8 to 12 main long screws and 4 platform shorter screws. (The factory or other folks may or may not have used all possible fastening locations.) If the shell does not appear to be coming off, double check that all possible screws have been completely backed out. The shell may need to be "rocked" front to rear to help dislodge it since the interior sides typically rub against the chassis posts.

After the shell is removed from the chassis, its electrical connectors can be separated from the chassis receptacles. Labeling them is highly advisable for future reassembly.


GP7/9 Internal Components:

Should the need present itself, the internals of the loco are shown closer up below:
(Only shown is the early version GP7/9)

Both sides of the switch circuit board are shown below.


Intermittent Switch Board Switch/es:

First, a little background info:
To date, I have two USA Trains GP7/9 early version units - one Southern Pacific & one Union Pacific. Both units were pre-owned; however, they were in excellent physical condition. I did get several parts from USA Trains to replace some missing and a few damaged ones, and I replaced the traction tired axle sets with all metal wheels sets. That said, both units had switch problems. The UP unit ran intermittently - mostly due to oxidized switch, and the SP unit Sound switch did not work - being open circuit, also, attributed to oxidation.

The 4 switches on the circuit board are double pole double throw (DPDT) open frame slide type, possibly made by Taiwan Electric. Being open frame and not sealed, it seems they are vulnerable to contamination and oxidation, but on the other hand, they are accessible for cleaning.

I had removed the Sound switch (shown above) with the initial intent to reinstall it in the opposite direction since that side of the switch worked. But with the switch out, and spraying its internals with CAIG Laboratories DeoxIT D5, the open circuit side worked.


Cab Removal

Occasionally a window may become dislodged and fall within the cab that can't be readily manipulated back into its location (as on both my units) or something else needs to be serviced. Before attempting to remove the cab, the body shell must be removed from the chassis as previously described.
Accordingly, it should be understood how things fit together and what needs to be done first as illustrated below.

See below illustration for how to remove the cab from the body shell. Replacing the cab would be done in the reverse order.

 With the cab removed, a dislodged window can be placed back where it belongs without having to remove the floor with engineer - albeit was some awkwardness. Using a small amount of tacky type adhesive on the window's flange surround before inserting it will keep it in place.

For information about taking the cab completely apart, see "Cab Disassembly" described later in this vignette.

Adding Extra Weight

Because I dispensed with wheels having traction tires I added a small amount of extra weight. I placed the additional weight in the fuel tank area for best low center of gravity - albeit forfeiting this location intended for a sound speaker.  For weights, I used a stack of Simpson Foundation / Bearing Plates available from Home Depot and others. The chosen plate measures about 2 & 1/2 inch square by 1/4 inch thick.

Note: Several additional weight plates could be added to what is shown above.

Cooling Fan Experiment

I came across a few miniature fans rated at 12 vdc & 110 ma being closed out for 99 cents each and got 4 of them, so I thought I try to install a couple in each of my GP7/9 units.

Note the molded in directional arrows on the side of the fan representing rotational and air flow direction when mounting it. This correlates with voltage polarity applied to the electrical leads (red wire +, black wire -, blue not used).

When operating the loco in a different direction with resultant voltage polarity reversal, a bridge rectifier is needed to maintain fan power. Since the fan current rating is 110 ma, a component capability of 2 amps having 4 leads with center mounting hole was chosen made by Micro Commercial Co (MCC P/N UD2KB100-BPMS-ND) obtained via Digi-Key along with 4 pin connector (P/N A31310-ND) - illustrated below with fan.


Fan Mounting:
The fan located above the loco's switch board is mounted on a bracket, and the bracket is mounted via threaded spacer on the end of the toggle bolt used to retain added weights as previously described.

The bracket was cut out from a strip of a steel, illustrated below.

The bracket, taking advantage of two existing holes, is dimension as illustrated below.

The rear fan was mounted on the "forked" aluminum heat sink used for the Darlington transistor with the inboard facing fins re-bent horizontally. Illustrated below is the heat sink before its fins were re-bent and before the fan was installed.

Illustrated below is how the fan is installed on the heat sink after the fins were bent.

Note: The two metal finned resistors on the left were added to mitigate motor inrush current the same way as was done for USA Trains GP38. This is described in the Vignette for the USA Trains GP38 .


Fan Electrical Connection, etc:
For track power use with 24 vdc capability that I have, the fans were electrically "daisy chained" connected in series. If the fans had been rated for 24 vdc, they would be electrically connected across each other in parallel.

As previously shown in the specification, the fans do have an operating range of 4.5 vdc to 13.8 vdc. So when placed in series as done in this experiment, the two collectively should operate at 9.0 vdc, and they did.

I, also, wanted to see if the running fans would force enough air to cause the loco's body shell roof fans to turn, so they were located with that in mind.

Illustrated below is the SP loco with the fans and electrical components installed. Power to the bridge rectifier (leads identified with symbols ~ ~) was done by 2 pin plug connected to the switch board's "sound" receptacle.

Linear DC or Pulse Width Modulation (PWM) input power can be applied to the unit, and fans will operate; however, PWM provides better results.

Illustrated below is the UP loco with the fans and electrical components installed. In this example additional components were added compared to the SP unit. In this case, filter capacitors were installed advantages to PWM input power application compared to flat line DC input. PWM allows the loco's lights and installed fans to better function before the loco wheels start to turn.  The filter capacitors were obtained from my Local Electronics Store.

The experiment setup illustrated below was done for PWM operation with the UP unit having filter capacitor.

The results are described and seen in the below illustration. Note that the filter capacitor 4700 µf value is much more than needed to maintain a virtual flat line DC charge to the amplitude of the input pulse between pulses.
So the fan's current draw between pulses is well maintained at a DC voltage level by the capacitor with fans running but wheels not turning as depicted in the red colored surround.


Observation about air flow and loco's roof fans:

The miniature fans installed in the GP7/9 are rated about 10 to 13 cfm air flow that can be felt; however, it was not able to cause the loco's roof fans to turn with the body shell installed.

Even without the input air restriction imposed when the body shell is installed on the chassis, the GP7/9 roof fans are erratic as to their willingness to turn and also seem affected by their physical positioning. In comparison, I noticed the roof fans in the USAT GP38 unit free wheeled much more readily. Though I did not install a miniature fan in the GP38, when having placed a running miniature fan connected to a 9 volt battery at a moderate distance to its roof fans, they turned too rapidly. (The GP38 has two larger roof fans compared to the GP7/9 that has two groups of 2 smaller fans.)

"B" Unit Adaptation

With the use of 3-D printed components, the USA Trains GP7/9 can be made into a booster "B" unit.
The following information serves as a preview of what has been done to date by me, Ted Doskaris, in concert with Colin Camarillo with a pre-production example.

Prototype History:

Three prototype railroads had "Geep" booster ("B" unit) versions.


Loco Preparation for "B" unit:

An example USA Trains Union Pacific loco will be used to show how to adapt it to a "B" unit using pre-production CamPac 3-D printed components.

The body shell is to be removed from the chassis as previously described for the Southern Pacific unit.

Cab Disassembly:
The following Illustrations are virtually the same as what was done to remove the cab on the Southern Pacific unit; however, go further to show how to take apart the cab in order to separate the "winged" platform.



Ceiling Lamp Removal:
The ceiling lamp assembly can be removed so it can be serviced or reused in a "B" unit cab.


"B" Unit Conversion with 3-D printed parts:
The "B" unit subassembly is slid down on the body shell's "rails" that were used with the original factory cab.


Platform Plugs:
3-D printed plugs are used to fill in the slots intended for the original factory cab's clip attachment.

The user is to paint the components to match the livery of the their loco.


Obtaining CamPac Products

If interested in obtaining CamPac products and / or desiring to bring the "B" unit to fruition, contact Colin Camarillo via his Web site.



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