Aristo Center Cab Switcher Tips

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center cab switcherThe Aristo Center Cab Switcher is a small diesel locomotive modeled after a generic design of many small industrial engines. There was no real prototype for this loco, but it is credible in size and proportion. Many small switchers were made with a center cab and a small (150 to 300 hp) engine/generator set under each hood.

Aristo has apparently taken two short hoods, the cab and battery boxes from their RS-3 and put them on a new frame with a new die cast power brick. Unlike the L'il Critter, this locomotive has engine exhaust ports. There are NO smoke units.


Performance and Detail

center cabThe Center Cab is a very smooth and quiet engine. There is some audible gear noise, but the sound of the wheels on the rails is louder than the mechanism. The engine is moderately weighted and has good pulling power. It won't pull as well as the larger heavier diesels, but since the motors are full sized, a little weight in the body may improve that. I did run my standard Tractive Effort Tests on the center cab and it did fairly well, pulling about as well as other Aristo diesels that haven't had additional weight installed. Most of the engine weight is in the truck castings, there are no internal body weights. There are also no traction tires.

The slow speed performance is good, the slowest steady speed is about 1 tie per second either loaded or running light. The top speed is lower than other diesels, this locomotive more closely matches the top speed of a C-16 than the other Aristo Diesels. Typical industrial diesels could not exceed 40 mph due to their non-swinging truck design. The truck sideframe models a welded up truck similar to ones found on many small engines.

There are two switches underneath the loco for the motor and the non existent smoke. These can be reached while the loco is still on the track.

The paint job is a little more complete than the older RS-3's. On this unit, painted in an ATSF style, the ladders and their metal eyelets are all painted.

The wheel treads are wider than most wheels. This doesn't seem to harm anything, but the engine looks a little odd from the bottom. After extended running on my very dirty track, the wheels picked up a slight haze, but there was no sign of pitting. Power pickup was good considering the track it was running on which probably hasn't been cleaned since last year. The engine did respond to the bad track by speeding and slowing as it gained and lost power, but it did so smoothly without the jerkiness of some locos. It never did actually stall.

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Scale and Clearance

This is a very short locomotive so that it will handle tight turns quite well. It has minimal overhang under any conditions so that there are likely few railroads it won't fit on. The locomotive is 12" long over the end steps and 15" long over the coupler faces. The engine is 4" wide and 5-5/8" tall. The wheelbase of the truck is 2.343". The trucks are 5.3" on center.

Since there isn't a real prototype for this engine, its "scale" is open to interpretation. However, the engine size is consistent with the 1/29 scale of the rest of the Aristo product line.

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Center Cab Power Bricks

center cab brickThe Center Cab brick is a die cast metal assembly. It is self contained and is very easy to remove from the loco. There are two screws in sides of the A-frame that mounts the truck. Removal of these screws releases the truck. The wiring is connected to the loco with two plugs. These are differently sized and keyed so that it is not possible to switch them or plug them in backwards.

There are four screws on each side that hold the brick halves together. To disassemble the brick, remove two wheels on one side by removing the screws in the center of the wheels. The wheels are centered on the axles with tapers and may bind a little, but a little prying will pop them off. Then remove the four screws on that side and pull the halves apart. The screws that hold the case halves together are anchored in plastic insulating spacers.

center cab exploded brickThe truck has a conventional can motor and worm gear drive. The motor has a bypass capacitor and a device that appears to be a surge suppressor soldered across its terminals. The motor is also wrapped in electrical tape to insulate the can from the dicast case halves. The power pickup wires are connected through lugs screwed to each case half. Note that the wires are just crimped into the lugs and can come out. This may not be visible due to the sleeving. If you have a truck apart, it might be reasonable to cut off the sleeving, remove the wire from the lug, put some more sleeving on the wire, solder it back to the lug and then heat shrink the sleeving over the soldered joint.

Each axle runs in two ball bearings that are pressed on the axle. Power is picked up on every wheel and transferred to the case halves through the bearings. These bearings should provide a long bearing life, even if the loco is more heavily weighted.

thrust bearingOlder Aristo bricks used screws as thrust bearings and sometimes they would squeak loudly. Also, if the screws were misadjusted, either the motor bearings would have to take up the thrust or the lash screws would add drag as the adjustment was quite critical. This brick uses a spring loaded thrust bearing instead so that adjustment is not required. The thrust bearing does not add appreciably to motor drag.

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The Center Cab comes with standard Aristo knuckle couplers body mounted and a set of hook and loop couplers in the box. The existing couplers extend way out from the engine but they do work with other Aristo rolling stock on 2' radius curves. On S curves, the couplers get pretty contorted but they still work.

There are probably many ways to install Kadee couplers, but I choose to use a method similar to one that I used on the RS-3. I have a box if Kadee #831's so that I was inclined to use this standard truck mount coupler. The coupler mount is similar to the RS-3, but it isn't exactly the same. The post on an RS-3 has a ridge at the right height to position a modified Kadee #831. The Center Cab post does not have this ridge so that it must be modified somewhat to mount a Kadee.

center cab coupler postThe post is just under 0.25" in diameter and is nearly the right height to hold a #831 if the mounting hole on the #831 is drilled out to 0.25". The coupler box then rests on the pilot and the whole assembly comes out just a tad higher than the optimum height. The coupler cannot droop because it is supported by the pilot. However, the coupler can slide up on the post unless something stops it. The RS-3 had ridges at the right spot, but these ridges are missing on the Center Cab. I cut a short piece of 0.25" ID brass tubing and slid it over the post. With the coupler box in place, I pushed the tube down to the right position with a toothpick and then applied a drop of Zap-CA to hold it in place. The existing coupler centering spring must be trimmed shorter so that it will fit in a #70 hole drilled in the back of the coupler body

center cab kadee mountedWhen the Kadee #831 is mounted this way, much of the coupler box is back inside the pilot and is not visually obtrusive. The coupler is also mounted much closer to the locomotive than the stock Aristo coupler.

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Lighting and Electrical

center cab internal viewWhen splayed open, the Center Cab reveals that there is little inside the unit. A distribution board is mounted to the frame and the hood wiring plugs in. There is no overt provision for a DCC decoder or a command receiver, but since all the necessary wiring is accessible on the top of the distribution board, it would be an easy job with a knife to cut the appropriate traces to make the necessary connections. There is quite a bit of room inside both hoods for batteries, sound systems, and control receivers or decoders.

center cab schematicThe schematic of the Center Cab is dead simple. The main distribution board on the frame interconnects the motors and power pickups. Lighting wires are taken off the board to go to each hood. The lighting is the same as on recent RS-3's but it cannot be turned off. There are incandescent lights for the cab and the number boards. The headlights are yellow LED's. These can be seen in the daylight, but do not cast any form of beam at night. There is a "smoke" switch but no smoke unit to switch. The switch just terminates on a pad on the circuit board.

yellow vs white LEDThe two LEDs on each end are wired in series with a 470 ohm current limiting resistor. This sets the diode current at about 20 mA, just right for a White LED. I have installed one bright white LED in place of one of the stock LED's in this picture. The white LED is so bright, that getting this picture was difficult but it can be seen how much more intense the white LED is in comparison to the wimpy stock yellow LED. As viewed by eye, the difference is even greater than the photo indicates.

center cab at nightWith the headlights modified, the Center Cab will cast a non trivial beam in darkness. The intensity of the light cannot compete with sunlight but if you run at night, it makes a considerable improvement.

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center cab smoke unitThe Center Cab Switcher DOES NOT have smoke units, but it doesn't appear that it would be difficult to install LGB smoke units. The stack is nearly big enough to take one dropped in from the top. A little work with a 3/8" drill bit and a rattail file can open the stack sufficiently to allow an LGB or Seuthe smoke unit to fit. I am not sure that I want to install $40+ worth of smoke units in this inexpensive locomotive, but it could be done.

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Disassembly of the Center Cab

While the Center Cab is not difficult to take apart, there sure are a lot of screws that need to be removed to do it. Due to interference between the sideframes and the hood and cab mounting screws, it is easier overall to just bite the bullet and strip the whole thing down short of removing the bricks. Remove all four sideframes (2 screws each). Then remove 14 more screws underneath to release the battery boxes, hoods and the cab. Both hoods and the cab come off as a unit.

If you think that you might want to get into this loco more than once, then when you reassemble it, leave out the hood screws that are obscured by the truck sideframes. These aren't really necessary to hold the hoods on because there are tabs in the battery boxes that also secure the hoods.

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Radio Control Installation in the Center Cab

rc schematicI installed a new Crest CRE-55491 On Board Train Engineer in the Center Cab. The installation was pretty easy. Although the rewiring was fairly extensive from a schematic point of view, it only took 8 circuit board cuts. Six of the cuts are on the main board and one on each headlight board. The cuts separate the main circuit board into 4 isolated sections, the power bus, the motor bus and one section each for the front and rear headlights.

In order to use just the four wires that already go between the frame and the shell, the functions of the four wires were reassigned. One brings power up to the shell. The other three activate one each of the three lighting circuits, the front headlights, the rear headlights and the cab/number board lights. The power going to the shell is derived from the internal bus of the 55491. This bus is available by tapping power from the positive terminal of the 220 uF capacitor on the 55491.

modified center cab circuit boardThe cuts can be seen as light marks on the board, two near each end and one in the upper center that cuts through BOTH thin traces.

The code set switch is mounted to project through the frame right right next to the switches. The 55491 itself is hot glued sideways to the frame. The previous motor switch has been reassigned to control the cab and number board wiring.

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Battery Power Installation in the Center Cab

cc with batteriesAfter the track powered RC installation was in and working, I converted the loco to track or battery powered operation. For this conversion, I selected NiMH batteries. 15 AA cells were made into two packs, one of 7 cells and the other 8 cells. The packs were installed in both hoods with foam mounting tape so that they cleared the truck pivots. The 55491 was mounted with hot glue on top of one of the packs. A charging jack was mounted on the floor underneath the circuit board.

cc battery schematicFor this installation, I elected to use the "tri-modal" configuration. This allows the loco to run from straight track power, track powered R/C or battery powered R/C. Since two DPDT switches were already there, this installation was pretty easy.

I basically hacked most of the traces on the circuit board to disconnect everything but the front and rear power pickups and the motor connectors. All of the traces to the switches were cut and replaced with wire. Note that the printed wiring board has both sides of each switch paralleled on the circuit board. It is necessary to wick all of the solder from the switch terminals and then carve out the traces between the poles of the switches.

The schematic shows the general wiring of the tri-modal configuration. One switch controls the source of power, and the other switch controls where the motors get their power from. The lighting wiring was left the same as it was in the track powered R/C configuration. The circuit is designed to charge from 24 VDC.

The headlights are wired the same as the track powered RC installation but I abandoned the marker and cab lights. These are incandescent bulbs and draw too much current to run from batteries. Also, I reused the switch for another purpose so I just left the incandescent bulbs disconnected.

The antenna of the 75 MHz 55491 is about 18" long. It is routed around the frame following the shell outline. In this configuration, the R/C range is 10 to maybe 20 feet.

whip antennaThe range that I got with the less than ideal antenna arrangement needed improvement. I had tried other arrangements in the past with the antenna wire wound around the top of the loco, but these were usually mechanically unsatisfactory because they complicated disassembly of the loco. This time I tried a whip antenna made from about 1 foot (30 cm) of 0.020" (0.5 mm) music wire. The wire is so thin that it is nearly invisible past a few feet especially if it does not contrast with the background. The wire can be seen coming up from the front deck just at the nearest corner of the hood. It can also be seen contrasted against the house in the background.

whip antenna mountingThe wire antenna was secured to the front pilot assembly with a self tapping screw. The antenna wire comes through a 0.026" hole in the deck just outside the cowl and is bent to fit around the screw head. The antenna wire from the receiver comes though a small hole drilled in the frame just inside the cowl and is also wrapped around the screw.

This arrangement yielded about triple the former range. There is reliable control to 30' and some control to 50'. The wire is long enough so that it will scrape low obstructions some, but it is flexible enough so that it just slides underneath and pops back to vertical after clearing the obstruction. Smaller music wire would work as well, I happened to have the 0.020" diameter wire handy.

It is somewhat ironic that in the years since I installed battery/RC into the Center Cab, it get LESS runtime that it did before. Since it is a 75 MHz RX, it doesn't integrate well with my 27 MHz trackside TE cab control system (except when switched to run as an analog loco on the track) OR my DCC command control system. To run it with the DCC stuff, I have to carry around the 75 MHz TX in addition to the DCC throttle. Before I installed DCC compatible controls for my interlocking route control system I had to carry around a 27 MHz TE to control the routes, a DCC throttle to control the loco and a 75 MHz TE to run the Center Cab. This was too much.

Once I installed a DCC interface to the route control system, I only had to carry the DCC throttle and I tended not to run the Center Cab because it was not DCC capable. Then it occurred to me that I could have it both ways....

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DCC Installation in the Center Cab

I recently ran the Center Cab at a train show for many hours. The battery didn't go flat in about 2 hours of running, but I had difficulty with radio range and also in setting a precision speed so that the Center Cab stayed in speed sync with another track powered train running on the same loop. The Train Engineer just doesn't provide the precision speed control that DCC can provide. I didn't run it often on the GIRR for the same reason. The loco itself is very capable and, as demonstrated at the train show, extremely tolerant of really bad track. All we could run successfully were the smallest of locos. An FA, which is pretty tolerant loco in itself, would derail in many places. We didn't want to stop the show to diddle with the track so anything that had troubles was simply set aside. The Center Cab ran for hours without derailing at all.

I've worked out a method to leave virtually all the functionality that I had with the loco before intact, but I can still add DCC.

center_cab_dcc_rc_schematic.jpgThis is the scheme that I have settled on. It is a slightly modified version of the tri-modal configuration. The difference is the addition of DCC and the removal of absolutely straight track power. To run on DC, the loco depends on the DCC decoder to analog convert. The former "power" switch now only switches power to the radio receiver so that it isn't possible to run the motors straight from the battery as before. The motor switch now selects between the output of the radio receiver or the DCC decoder. The power selector switch also serves to disconnect the battery to turn the loco "off" when in storage or during charging.

I had abandoned using the incandescent lighting with battery power operation due to their current draw, but I will reconnect those lamps to be controlled via a DCC function and powered only by the DCC decoder. The CRE-55491 happily accepts DCC track power although it totally ignores the DCC data on the track. Therefore the power for the headlights still comes from the RX. It provides the "Blue" wire function as it is either connected to the battery or the track and it will see whatever power that is available so that it can make the + Common voltage that is present on the "Blue" wire. When the DCC decoder is inactive (because the loco is running on battery power) the incandescent lights are off. The DCC decoder can be programmed to enable whatever function is selected for the cab/marker lights when analog converted so that these lights will be either controllable with DCC or on if analog converted.

The headlight controls are wired in parallel via optical isolators to both the DCC decoder and RX. When the loco comes to a stop, the CRE-55491 turns the headlights off. As long as the CRE-55491 is remembering that it's last speed command was to stop, it won't mess with the lights when it isn't being used. Then the DCC decoder can control the headlights. When switched to battery power, the DCC decoder is inactive and it leaves the headlights alone allowing the CRE-55491 to control them. To make this work, I need to use the "ground" pin on the RX so that the power supplied by the RX blue wire will return to the RX. There is a grounding ambiguity without the optical isolators. If the RX is switched to battery power and the loco is sitting on powered track, there is no ground return for the headlights to the DCC decoder. Use of the optical isolators will eliminate that issue.

I tried to fit an available MRC322 in there but it just wouldn't fit. The MRC322 has a sort of a sound system but it just doesn't analog convert very well at all. A QSI decoder would fit where the TE RX is now and it has sound but to buy a new one and make it work with the battery I'd need a GWire receiver and an Airwire transmitter as well. This would total about $400 out of pocket, too much. A DG583S would fit well but it doesn't have sound. A DSX sound decoder doesn't have the volume for outdoor use. A Phoenix P5 would work, but it's pretty expensive too.

A Dallee system will barely fit in addition to a DG583S. The Dallee will integrate well in this configuration and will operate properly when either the DCC decoder or RX is running the show. So, since I have a DG583S already and a Dallee board would cost about $94, this looks like the route I will take. The conversion to DCC costs nothing additional out of pocket and adding sound costs $94 which I can optionally do later.

081220_girr_cc_dcc_install_6070.jpgThis is the Center Cab with the DG583S installed. I followed the schematic shown above. Since I am using the "blue" wires from BOTH the RX and decoder, I had to add one wire going between the frame and shell. I actually added three wires because that is what my swap meet special plug/socket harnesses have and if I ever do add sound, I'll need the other two wires for the speaker. I did find a place for a small speaker which can mount in the "rear" hood facing into the cab. I'd have to drill some holes in the "back" of the cab and take out some cab windows to let the sound out, but it would work.

The two optical isolators are mounted "dead bug" fashion with foam tape in the middle of the circuit board. They just fit underneath the cab insert.

There was one ambiguity that I had to work out. This loco doesn't have an FRA required marking to designate the "front." Normally, there would be an "F" painted on the side of the frame at the front of a loco. Diesels run happily either direction so that the "front" is usually determined by the position of the control stand. In the Center Cab, the only thing that isn't symmetrical is the control stand in the cab. It's orientation determines the front. In this installation, the RX is at the rear, the decoder at the front. I have set the headlights to conform to these conventions for both the decoder and the RX.

The analog conversion capability of this decoder is quite good when running on straight DC track power. One would hardly know that a DCC decoder is in the loop. However, the decoder doesn't like PWC on the track at all. It will run, but it's throttle response is poor and the loco is jerky at some speeds. This decoder can also activate one set of functions to be on when analog converted. This is done by programming CV13 as per the decoder programming instruction book. I've set it to run the headlights directionally and to turn on the cab lights.

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Sound Installation in the Center Cab

center_cab_dcc_rc_sound_schematic.jpgIf I elect to install a Dallee sound board, I would wire it like this. The Dallee board needs an independent source of track power, it gets that from the input to the RX which is powered one way or another. The motor inputs to the Dallee are optically isolated on the Dallee board. The trigger inputs won't have a ground return when the RX is running on battery power, but the RX cannot command them anyway and the decoder will be inactive so that it cannot command them either. However the motor sound will run when the RX is running on battery power.

It took me awhile, but I eventually did install a Dallee #731 (44 ton) sound system in the Center Cab. I choose this particular system because:

However, the installation didn't go as easily as I had hoped. With all the other crap that was already there (battery, TE RX and a DCC decoder) there wasn't room for the sound board under the hoods or cab.

090811_girr_cc_switcher_dallee_install_speaker_mounted_7722.jpgWhile testing the board on the bench, I also realized that it really could use a good speaker and the speaker that I had planned to use wasn't going to cut it. There was no place to install a better speaker and no room for the board. Something had to give.

I elected to rip the cab interior out of the loco and use the cab volume for the sound installation. The speaker is mounted against the roof with epoxy putty sealing it in place. The "enclosure" is now in front of the speaker and the sound is emitted from the back of the speaker.

090811_girr_cc_switcher_dallee_install_installed_7723.jpgI removed the side windows (which I would have to have done anyway) to let the sound out of the loco. Now the board can be easily seen through the window openings, I'll probably jam some black paper in there to hide the board a little. However, I can get to the volume and speed controls on the board by working through the cab side windows.

090811_girr_cc_switcher_dallee_install_board_mounted_7724.jpgThere are a total of 12 wires that go to the Dallee board. There are two track power wires, two motor wires (optically isolated on the board), two wires going to a storage capacitor, two speaker wires and four function wires. All these wires plug into the Dallee board so that I didn't install a separate multipin connector. I can still remove the shell entirely if I want.

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© 2000-2009 George Schreyer
Created July 12, 2000
Last Updated August 13, 2009