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by Larry Shimp 


Aster says the Berkshire is designed for radio control so I thought I might as well put it in. It was more of a challenge than most locomotives v because of the extra features on the Berkshire: cylinder drains, blower, and whistle. Five servos were needed to individually control all these functions.

The radio is a seven channel digital (PCM) model by Futaba. This is a digital radio which makes it nearly immune from “glitching”, and the computerized control system allows extremely flexible programming. The radio may be expensive, but it can store programs for up to 10 separate models, so its cost goes down as more models are added. Included in each program are trim settings and servo travel parameters, so very precise settings can be set up and saved. Conventional analogue radios have trim tabs that can easily be bumped and the resulting changes can strip servo gears or rapidly drain batteries. The throttle is not spring loaded, and there is a convenient knob to control the valve gear position, as well as auxiliary on/off switches that can be used for the blower and cylinder drains. These features make operation very simple, and allow “hands off” running. The only draw back is the large size of the radio receiver, but it can be made to fit, as will be described.  

For more background on radios, see the excellent article by Ross Schlabach, posted on the SouthernSteamTrains.com website, on Radio Installation in an Aster USRA Mikado.. Ross also describes how to take advantage of the radio programming functions to include mixing features that will automatically open the blower when the throttle is closed. 

Servos are HiTec, two #HS-81 (with metal gears) and three# HS-55. With these components, the servos and receiver fit in the cab, with the batteries in the tender. Thus, there is only one plug to connect. I used as large servos as I could fit in to be sure there was enough torque to reliably operate the controls. Smaller servos are available and would simplify installation, but I do not trust them. 

The antenna can be kept as a coiled loop placed on top of the alcohol tank. For a better appearance, it can be built into a coal load as Ross Schlabach describer for the Mikado. If this is done, them a connector should be placed between the antenna lead from the receiver and the tender. Be sure to keep the original antenna lead length. 


Receivers and most servos run on between 4.8 and 6 volts (only micro servos cannot take 6 volts, and these are too small for locomotive use). Six volts ensure maximum servo torque and the longest running time. Battery choices are alkaline batteries or rechargeable: NiCad or Li Metal Hydride (LiMH). A 4 AA cell battery holder can be attached to the front of the water tank in the tender with double sided tape. With 4 alkaline cells it delivers 6 volts. These can be replaced with rechargeable AA batteries, but these (whether NiCad or LiMH) only put out 1.2 volts each, versus 1.5 volts for alkaline cells. The end result is that 4 rechargeable cells only deliver 4.8 volts. Thus, for rechargeable batteries, it is best to use a premade 5 cell, 6 volt pack. Look for the biggest one you can find (one made up of 5 aa size cells). LiMH is the best choice because their capacity is about 2 to 3 times higher than NiCads. In addition, these can be charged anytime without waiting for a full discharge first. The disadvantage is that LiMH batteries require a special charger to prevent them from over heating and being ruined. An alternative is a trickle charger, but this takes about 15 hours to deliver a full charge.

I put a power switch through the floor just inside the left front corner of the frame. The switch is invisible yet very easy to operate. The wire to the locomotive runs out on top of the tender frame through a small notch filed into the tender body behind the draw pin area. This is essentially invisible. The locomotive and tender wires connect under the footplate and above the draw bar.

Once the engine and tender are coupled, using the switch is much easier than unplugging the wires. One use of the switch is that when steam is being raised, it is possible to open the blower valve by radio control, then turn off the power to lock the servo in place and also conserve power.  

Servo installation:

The cylinder drain servo is under the cab floor. The key was getting a flat mounting surface for the servo. This was accomplished by replacing the drawbar attaching screw with a flat head screw countersunk in place, and cutting off the inside edge of the right hand cab mounting bracket (part # E2). I drilled and tapped a new 2 mm screw hole in the bracket to replace the hole in the cut off piece. The threads are in the bracket, not the locomotive frame, and the screw goes in from the bottom. The servo is held in place by a sheet brass clip attached with 2 mm screws (holes drilled and tapped in the locomotive frame) and the servo mounting ears were cut off. The original shoulder screw is put in the servo arm to hold the actuating rod. I filed the back of the arm thinner so that a nut could be put on the screw to secure it. The arm ends up in almost exactly the same pace as the original manual operating arm. Unfortunately, this servo (HS-55) is not very powerful so to make sure it can open the drains, lubricate the actuating cams with thick oil or grease, and use a 6 volt power supply. One nice benefit of this installation is that the servo helps to fill in the area under the cab where the stoker engine was situated on the prototype, and as such, helps to improve the locomotive appearance.

The reverse servo (#HS-81) fits on a simple bracket fastened to the cab floor. There are two pieces of brass sheet under the servo to bring the back of the servo above the flange on the bottom of the cab side. The servo is attached to the original reverser by a brass wire that goes through a hole drilled in the reverser just behind the handle. The two rear cab floor mounting screws were changed to flat head screws and the holes were counter sunk. This helps the reverser servo bracket and the receiver to fit better Because it was no longer needed, I disabled the ratchet wheel on the reverser shaft by removing its set screws.

The remaining servos are hung from the boiler bracket that holds the operating valves. I drilled and tapped two 2 mm holes in the bracket and two 2 mm holes in the steam manifold, in the area of the end plug. The plug was removed, and the screw holes were drilled through into the plug hole to provide clearance for the tap. Upon assembly, silicon sealer was used on the screws as well as the plug.

The throttle servo (HS-81) is at the top of the servo stack. The large servo was used to make sure there is enough power to fully close the throttle. It is attached by a wire to a new lever that was screwed to the original throttle lever shaft collar. The crossed lever operating geometry is compact and ensures full throttle travel.

Below the throttle servo are two HS-55 servos for the blower and whistle. The whistle is operated by a bent wire that pulls down on the original whistle lever. The blower rod is attached to a sheet brass bracket that fits over the original blower lever.

To get everything to fit, I had to bend the steam line to the throttle in two ways: 1) the S-bend was moved closer to the boiler to clear the left front servo bracket leg, and 2) the 90 degree bend below the banjo bolt was bent to a sharper radius in order raise the pipe up slightly. Before bending the pipe, I heated it to red heat with a propane torch. I also had to bend the steam gauge line to a sharper radius.


There is just enough clearance below the servo stack to fit in the radio receiver. As was explained earlier, the Futaba 8 channel PCM receiver is larger than most other receivers, but it will fit if all of the above steps are carried out. And there is still room so that the wires from the drain cock servo and the battery in the tender can come up through the existing slot where the drain cock operating lever used to be.  

Firebox door:

The firebox is no longer accessible with the servos in place. I recommend that the door be permanently closed (with silicone caulk or maybe a screw) to keep it from accidentally opening and possibly letting the flame burn some wiring or a servo. 


There are two empty slots in the receiver, one of which is used for lights. There is constant DC battery voltage available that can be tapped into using the black and red leads from a standard servo plug. This provides a very neat way to connect the lights. 

One benefit of lights is that they indicate the battery is getting low when they begin to flicker as the servos move. 

I put in working headlights and a "working" Mars light. Real Mars lights moved in a figure 8 pattern, the best I could do was to put in two bulbs that alternately flash from side to side. To make the headlight easier to work on, I replaced the tabs holding the light to the bracket with 1.2 mm screws (threaded holes in the headlight where the tabs were) using a 1.2 mm tap from NorthWest Shortline. The light lenses are made by MV products (model L173, 0.173 inches in dia). These are parabolic lenses with silvered backs. By drilling a small hole through the back they can be lit. The cast in sockets in the headlight were drilled out to provide a base for the lenses, and then a small hole was drilled in the center of each hole for the light bulbs. These holes were angled so they exited in the lamp body. For the Mars light, I first epoxied a lamp socket in made from a short length of 1/4 inch brass tubing. After the epoxy dried, I filled the tube with more epoxy, and drilled it to provide a recess for the lens (# L228) after it dried . I then drilled two small holes on either side of the base through to exit together in the back of the light housing. After epoxying the lens in place, holes were drilled from the back into the lens to provide lighting.  

All lights are incandescent bulbs about 1.5 mm in diameter that fit in holes drilled in the light housing bodies. To simplify the wiring, one lead of each bulb is grounded to the housing body by means of a 2 mm screw and washer fitted into a 2 mm threaded hole drilled in the rear of the housing. The wiring is nearly invisible. I attached pictures of the lights, but because of the camera flash, it is impossible to see that they are lit.


The Mars light electronic control is made by Circuitron, model ML-1, catalog # 800-1500. It runs on 3 volts so I added a Radio Shack adjustable electronic voltage regulator to bring down the 6 volt supply to 3 volts (using a 270 ohm fixed resistor and a 330 ohm resistor in place of the adjustable resistor according to the circuit on the regulator package). I covered the circuit board and voltage regulator in shrink tubing and installed the circuit by soldering the common lead to the whistle pipe. This keeps the circuit out of the way of the servos and the water sight glass is still clear.


The wires to the lights are Teflon insulated and run between the boiler casing and boiler, then enter the smoke box under the ceramic insulation and run out through small holes drilled through the smoke box door and light brackets just below the bracket securing screws. The wires were soldered to the light leads under the brackets and encased in black silicon.

If not for the Mars light, only one wire would be needed to power the lights. A possibility to do this is to replace the left handrail with a solid core, black insulated wire, and connect one end to the lights and the other end to a battery. On the prototype locomotive, the lighting wires ran through this left handrail, and doing so on the model adds the proper wiring connections from the lights to the handrail. But I thought a "working" Mars light was more important and went for three, internal, concealed wires.  

Southern Steam Trains expresses appreciation to Larry Shimp for his  generosity, expertise and willingness to write this article and provide the accompanying photographs for positing on our web site.  We are confident that this will be helpful if you are adding this feature to your Aster NKP Berkshire.  For our customers, who would like to be in touch with Larry Shimp, his email is DrkwoodsD@aol.com



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