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JunkBot (2018)

The JunkBot is a non-functional sculpture robot I built to avoid throwing away some first-generation components removed from ROBART III in the course of progressive system upgrades over the years. The early version of ROBART’s Gatling-gun barrel, for example, is shown at image left, while an even earlier triangulation ranging system is seen at image right in the photo below. The body is an old space heater, the head an inverted volt-ohmmeter (VOM) I had in junior high school, topped by a pair of stereo cameras I bought at a local surplus store some years ago and never used.  The following images hopefully provide some tutorial insight into typical fiberglass construction techniques of interest to makers and builders.

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As seen below, the tractor-base sponsons were constructed from ⅛-inch plywood covered with fiberglass cloth, both inside and out. Prior to assembly, the plywood sides were predrilled for the track rollers, then redrilled after the applied fiberglass cured. The piece of ½-inch plywood at far right was fiberglassed to form a structural bridge across the two track assemblies, which also served as a mounting plate for the base of the space-heater body.

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The 14 track rollers were cut from wooden closet rod, drilled for ¼-inch axels (top image below), and capped on each end with ¼-inch fender washers epoxied in place (center). The tracks themselves were inverted rubber timing belts (bottom).

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While gluing up the tractor sponsons, I went ahead and fabricated the wooden camera-body cores (upper image lower right), which were later covered in fiberglass. The head-mounting adaptor (upper image lower left) and the filler for the old heater control openings (bottom center) were solid fiberglass. The finished camera bodies, head mounting bracket, and head pan-axis spacer are shown in the lower image below.

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Below are left and right views of the head mounting configuration, also showing the surplus lenses installed in the camera bodies.  Note the microphone ears mounted on either side of the head.

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The air accumulator for the pneumatically powered Gatling gun was fabricated from two pieces of 1-inch PVC pipe, capped at both ends and coupled in the middle, skinned with a double layer of fiberglass as seen in the upper photo below, then sanded smooth on the lathe as shown in the lower photo.  

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Removed from the lathe, each end of the accumulator was filled (one at a time) with a catalyzed mixture of short-strand fiberglass filler, which was allowed to cure as shown below.  The ends were then trimmed to length and sanded smooth, after which the entire component was primed and painted black.

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Like the camera bodies, the core of the gun body was cut to size from clear pine, skinned in fiberglass on all six sides as shown below, then sanded smooth, primed, and painted.  Mounting holes were drilled for the tilt axis shaft, pneumatic fitting, and gun-barrel spin axis.

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To cast the mounting bracket for the cylindrical laser sight that attaches to the gun body, a sacrificial wooden form was packed with a catalyzed mixture of fiberglass filler, covered by a release film of clear packing tape.  A wooden dowel the same diameter as the laser was pressed into this mixture, which was then allowed to harden. The ends of the form were cut off as shown in the upper figure below, after which the sides were cut free (lower image left).  The dowel and release tape were popped free of the casting, whereupon the fiberglass cradle was trimmed to length for mounting the laser (lower image right).

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The first step in the fabrication of the tilt-axis bracket for the gun involved laying up several layers of fiberglass to form a U-shape over a short length of 2-by-4 as shown at left below.  Once cured, this material was sanded smooth, then trimmed to shape in place (center photo) using a radial arm saw. To facilitate extraction of the sacrificial wooden form, a V-section was cut out on the band saw as shown at right.  The resulting fiberglass bracket was sanded to final shape and drilled for the horizontal and vertical pivot axes.

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The assembly at left in the photo below is the finished tilt-axis yoke for mounting the gun assembly to the right shoulder pod pan axis.  The laser-sight cradle and air accumulator are attached to the gun body as shown at right. One of the two end-bell components at image center was used to represent the tilt motor for the gun.

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Fabrication of the shoulder pods involved several steps as shown below.  The two wooden forms for the cowlings were covered with clear packing tape to ensure release (top), after which several layers of fiberglass cloth and resin were applied.  Once cured, the excess fiberglass was trimmed away, the tops and sides sanded smooth, after which several partial cuts were made into the bottom face of the forms to facilitate release (middle).  The forms were then pried loose as shown in the bottom photo.

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The wooden shoulder-turret forms were next turned on the lathe as seen at left below, then wrapped with fiberglass tape and resin and allowed to cure as shown at left in the center image.  (A dispensing roll of 1-inch fiberglass tape is seen at bottom right of this same image.) The turret-top recess seen in the center image has been filled with fiberglass filler in the right photo, then shaped and sanded smooth on the lathe.

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The shoulder cowlings were trimmed to fit the shoulder turrets and epoxied in place as shown in the left image below.  These assemblies were then held vertically with a temporary wooden dam to facilitate pouring filler into the lower cavity to reinforce the outboard joint (below center).  The assembly was then flipped and epoxied to the mounting bracket, which was then temporarily dammed (see clamps in center photo) for additional filling to reinforce the inboard joint (right photo).

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The prototype Gatling-gun-barrel assembly from ROBART III was attached to the gun body, and the tilt yoke temporarily suspended from the right shoulder pod for a fit check.  The triangulation-ranging sensor and fiberglass components for the left shoulder pod are shown at lower right in the left image below. The right image shows the completed right shoulder pod after painting, with the main air accumulator on the back now connected to the gun body.

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The left photo below shows a rear view of the completed left shoulder pod after assembly and painting, while the right photo shows the front view with the triangulation rangefinder attached.

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