in an
(Scott Phillips @ N-Scale Supply)
in an
(Scott Phillips @ N-Scale Supply)

(North Raleigh Model Railroad Club)

in your

Photo Courtesy of N-Scale Supply

The Doodlebug is a nifty little model which, at first glance, has plenty of room for a decoder installation. However, upon closer inspection, that tempting passenger compartment may not the ideal venue for a decoder after all; those side windows and cabin lighting would put the decoder (no matter how minute) on full-time display for all to see. It would further compound the matter if you wanted add passengers and other details (livestock, carry-on parcels, etc.) to the interior. Oh, what a dilemma! But where else could one hide a decoder?

As the old saying goes, "Hide in plain sight." I must credit Scott Phillips (N-Scale Supply) with envisioning the decoder slung underneath the chassis, looking somewhat like a baggage compartment. Being a shameless 'idea poacher,' I decided to give it a go....and I'm glad I did.

The following series of pictures shows how I did the installation of a Digitrax DZ120 decoder.. There's nothing magic here, and I hope other Doodlebug owners with DCC urgings will give it a try.

At the end of this writeup is a collection of inputs on Doodlebug decoder installations from other modelers: helpful hints, other approaches, etc. It's entitled "Further Thoughts..."   There are also links to DECODER REVIEWS , which make for informative reading.   Take a look.

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Step 1: Remove the shell. There are three small latches on each side of the shell; they're part of the window glazing, so you'll need to slightly separate the shell sidewalls and glazing from the frame on both sides. Start at the back and work your way forward; the shell and frame should separate with relative ease.

Step 2: Unsolder the fireman's side track pickup wires from the lamp board. Unsolder the leads and remove the clear plastic diffuser and attached mini-lamp from the cabin. Now remove the two screws that attach the lamp board to the frame; set the lamp board aside (we'll be making some changes to the etch pattern on this board later).

Step 3: Remove the motor -- it's attached with two small Phillips-head screws from the underside of the frame. Also remove the first two drive shaft segments (you 'll need the space to work). Now flip the frame over onto its back. Here we go....

Step 4: Warm up the ol' drill -- we're gonna' make a few warranty-voiding modifications to the frame. Before starting, study the picture for a minute to ensure that the three hole locations are clear in your mind. Temporarily attach the decoder in the location shown; then, using a 3/32" bit for all holes, drill hole #1 about 1/4" in front of the decoder and centered on the frame. Drill hole #2 just to the rear of the front motor screw hole (refer to the photo often). Finally, drill hole #3 a bit farther forward that I did; get as near the front track as you can without interfering with the truck movement.

Step 5: Using a piece of 3/32" O.D. tubing (unshrunk 1/16" heat-shrink tubing works great; available at Radio Shack), "line" the three holes you just drilled to prevent the metal edges from abrading the delicate wiring; cut the tubing flush with the top and bottom surfaces of the frame. Now route the decoder wires thru their respective holes:

(a) Hole #1 (rearmost) -- yellow and black wires
(b) Hole #2 (center) -- grey and orange wires
(c) Hole #3 (frontmost) -- red, white and blue wires

Step 6: Now the most delicate part of the operation. The potential for damage to the motor is very real -- I can't overemphasize the need for patience and caution! Temporarily replace the motor in its mounting position; hold it in place with your finger. With a scribe (or a dot of paint), mark the location of Hole #2 (the middle one) on the underside of the motor frame. Remove the motor, and using a 1/16" bit, carefully drill a hole thru the motor's plastic frame in the location you just marked. LIMIT THE DRILL'S PENETRATION to 1/8" -- this is important! You must limit the depth that the drill bit penetrates to the thickness of the motor's plastic a hair. Failure to do so will likely result in possibly fatal damage to the motor's commutator. If you don't have a reliable way to limit drill penetration, I strongly suggest you use a pin vise in lieu of a drill motor.

Step 7: Route the grey and orange wires thru the hole you just carefully drilled in the motor frame -- grey on the fireman's side, orange on the engineer's. Snake the wires under the brush caps as shown. Route the red, white and blue wires against the wall of the drive shaft well (study the photo), and attach them to the surface with Goo or the stickiest tape you can find (you want to keep them out the driveshaft's way....especially when the front truck swivels). Reinstall the motor and the driveshaft segments.

Step 8: Using a new #11 blade in your Xacto handle, we're going to make a few "improvements" in the stock lamp board. Looking at the bottom of the board with the headlamp LED facing away from you, we're going to make two cuts to the copper PC trace on the left-hand side of the board (engineer's side. Make the first cut just below the board mounting hole, and the second cut about midway between the mounting hole and the top end of the trace.. Remove enough copper to ensure that there can be no shorting (1/8 - 1/4").
NOTE: Use a low-wattage soldering iron for all operations; 25 watt max (15 is better); be very careful not to overheat any components!
Shorten and solder the red wire to the center piece of the trace (the piece still bridging the mounting hole); solder near the top of this trace.

Step 9: Reinstall the lamp board (don't forget the small piece of insulating paper under the board). Route the blue and white wires in front of the engineer's side mounting screw (see photo). Solder the blue wire to the engineer's side (right) lead of the LED. Clip the lower lead (nearest the flywheel) of the resistor and bend slightly to the right; solder the white wire to the just-clipped end of the resistor. Now solder the orange wire to the lower right pad on the lamp board, and the grey wire to the lower left pad (refer to photo).

Step 10: Connect the black decoder lead to the black wires from the front and rear track pickups; solder and insulate. Stash these wires and junction underneath the passenger seats. HOORAY! You're now ready to test-run your improved D'bug.

Good luck (and make sure to keep the still- unattached yellow wire out of the way during testing). At some point, you're going to want to set CV61 to "01;" this will allow independent control of the cabin lighting (yellow wire) on F4, while maintaining direction headlamp control (still F0).

Step 11: No doubt your test run was successful and you're ready to complete the details. Start by removing the tape holding the decoder temporarily in place. Affix a piece of black plastic tape to the underbelly where the decoder will reside (provides insulation), then bond the decoder in place (I used Goo) and let it set up (I taped it in place while it set). Reinstall the plastic cabin light diffuser/mounting bar.

Option: I suggest replacing the stock lamp and resistor with a 12 volt/50 ma lamp (Miniatronics 18-012 or equiv.) in series with a 39-51 ohm (1/4 watt) resistor to limit cold inrush current. Attach the non-resistor lead of the lamp to the same point on the headlamp LED where the blue decoder wire is attached. Attach the new resistor to the yellow lead (the other end of the resistor being attached to the new lamp).

You're done! Now, try running it again, making sure to verify correct operation of both the headlamp and the passenger cabin lamp. Make sure you test run around your tightest curves to ensure that there's no interference between the drive shaft and the wires near it. Before reinstalling the body, dress all wires either across the top of the frame or below the body attachment clips; there's no room for wires along the sides of the "engine compartment." When reattaching the body, the frame goes in "nose first;" the headlamp LED must properly nest into its cranny in the front, then everything else snaps in place.

Step 12: Run and Enjoy! If you have a moment, Email me and let me know how you did and if you came up with any improvements or helpful hints I should include in this tome.


1. Dana Zimmerli reports installing a Digitrax DN146 decoder into the 'bug by mounting it backwards on top of the motor, replacing the light board. "No drilling required, no machining, the only thing that may be tricky is that it's backwards, so I replaced the front headlight with another LED which is wrapped back to the front," sayeth Dana, "just make sure you use insulating tape to hold things down and keep from making shorts." For a full writeup on this installation, visit Dana's Page on the NDCC web site.

This methods sounds good to me.
I just may have to get another 'bug and try it;
if anyone else does, let me know how it comes out.
Thanks, Dana, for a good suggestion.

2. [Still thinking...]

LENZ LE077xf
Smallest decoder. Low cost.
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Do You Know of Someone Who Has?
Send Me an EMAIL, and I'll Link to It...
or Display It On This Page (Your Choice).

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Updated 6-22-06