Steam Locomotive Cab Simulator (Continued)

Construction and Design Revision

Construction was performed in three major phases: control and gauge elements, cab structure, and visual projection system. Procurement of items was the first step. This ranged from major purchases of video system elements to aluminum and steel raw material. Considerable metal and woodworking was required throughout all three phases using basic hand tools, bench drill press, bench grinder, table saw, and belt sander.

The first element constructed was the speed gauge. As the �realities� of fabrication surfaced, revisions to the design drawing were continually made in parallel. The speed gauge �as-built� design was used as the basis for subsequent design revision and fabrication of remaining rotary gauges. The two brake pressure gauges were a modification of the design in that dual servo motors driving concentric shafts were required. The water level gauge, or sight glass, was the second element to be constructed. It was unique in that a servo driven linear movement was involved. Construction of some components was required to test the design before committing to full fabrication, such as visually simulating a water column inside a transparent tube.

As in the case of gauges, the controls fabrication process revealed necessary minor revisions to the design of each assembly. The brake valves were constructed first, and turned out to be the most complex and difficult to accomplish. However, this produced several �lessons learned� for application to remaining controls. A lot of hours were devoted to hack sawing, bending, grinding, and drilling the mild steel used for levers. Aluminum and wood work were always a pleasant relief from the challenges of steel.

The cab wood structure started with the sub-floor and progressed in order of backhead assembly, left side wall, right side wall, rear wall, front wall, and roof. The backhead assembly includes a firebox and working fire door. It was designed to also support controls and gauges on the visible interior cab side, and electronic elements, wiring terminal strips, and power distribution attached to the non-visible reverse side. It effectively became the central integrating element of the entire simulator.



To represent the interior lath on walls, pre-machined 4�x8� �beadboard� wall paneling was used. A roof vent was somewhat of an afterthought during fabrication and was added not just for realism but for its ventilation purpose as well.

Following fabrication and initial assembly of the cab structure, each control and gauge element was installed. This in effect provided a final integrated validation of the spatial relationship to the engineer�s station. During this process the plumbing (steam, water, and brake lines), sound system, bell/whistle controls, and an interior cab light were also installed. Wiring was installed from each active element through the structure (out of sight) to the rear of the backhead. The floor boards were fabricated and installed last after all other interior work had been completed.

Following cab disassembly, the interior walls were painted green, typical of many steam locomotives. All exterior surfaces were painted flat black. The visual projection system was constructed as a separate set of modules, to be attached to the cab during final assembly. The system is comprised of a rear projection screen, first-surface mirror, digital image projector, and enclosure. The system structure was fabricated, fully assembled, disassembled, and painted flat black (interior and exterior).

The firebox was a unique challenge to develop a credible way to visually represent intense fire. The method, through considerable trial and error, evolved to a combination of randomly blinking colored lamps (five independent channels of red, yellow, and blue) and blower-driven white silk �flames� (loosely suspended with black thread). The blower also provides circulation of air behind the backhead for cooling electronics.


Final Assembly

The initial phase of final assembly was essentially a repeat of the initial assembly done during construction, except in the final room location. First the cab physical structure was put together followed by the controls and gauges. Power distribution and electronic components were then installed on the accessible rear of the backhead, all control and gauge wiring connected, and the firebox installed.



The visual projection system was then installed. The screen support element of the system barely fit through the room door, which was nearly a fatal design oversight � testimony to the need for careful design and advance planning. One is reminded of the classic tale of building a boat in the garage (or basement) that was too big to subsequently remove!

Finally, some finishing touches were added. These included boiler cleanout plugs, test placard, and inspection form, oilers (long spout, small push-bottom, and tallow pot) for the warming shelf, and a seat for the engineer.

Calibration and Test

Each control and gauge was functionally tested using a Parallax Stamp processor controlled through a serial PC interface. It was at this point that a serious oversight was discovered. The potentiometers were advertised as being 300-degree rotation stop to stop. The control designs were based on this degree of travel, which had been verified mechanically. However the linear electrical range was only 270 degrees. With some null adjustment and a throttle gearing change-out, the oversight was remedied for all controls except the reverser. It was decided to mechanically restrict the travel of the reverser in the reverse quadrant, which is much less critical than the forward quadrant range to locomotive operation.

It was also discovered during calibration that the gauge servos procured and installed subsequent to the speed gauge were somewhat nonlinear. Since the pointers were installed with each servo at null (the midpoint on each dial face) they drove beyond the low end point and short of the high end point. The nonlinearity was compensated for in the Parallax Stamp processor (using a calibration curve) and the pointers mechanically recentered.

Alignment of the visual projection system utilized a static MSTS image from a PC. A plan view of the integrated cab and visual system, plus a representative view through the engineer�s windows are shown below.

Conclusion

Initial limited operation has been achieved by using a PIE X-Keys unit and software to emulate keyboard commands recognized by MSTS. However, full operation is pending a method for interfacing analog control inputs and gauge outputs with the MSTS software. Although a ReDAC input/output module with software drivers has been acquired from PIE, the lack of an API in MSTS prevents its use.

A workaround is being investigated using Optical Character Recognition (OCR) software to read the MSTS Heads Up Display (HUD) parameters and a custom software driver to output the values from the PC to the Parallax Stamp for processing. This method is similar to how the RailDriver console interfaces with MSTS.

During the interim, while an interface is being developed, two historical branch line routes have been modeled to explore MUTT�s use in research and museum applications. Both of these were circa early 1900s; one mining related in the California Mojave Desert, the other logging and quarry related in east Texas.

Part 2 of this article will focus on Operation, and will describe completion of a fully functional interface, computer and software considerations, experiences as an �engineer,� and lessons learned for those interested in pursuing similar projects.

Doug

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