Construction Photos & Description
40" Saucer

Construction of a strong motor mount spool was the first step.  The core consisted of 7 1/2" diameter flexible phenolic tubing covered with two layers of 8 1/2 oz kevlar/carbon fiber.  Next, 1/2" centering rings made from a synthetic material (stronger than plywood but slightly lighter) were made.  Holes were drilled in the spools to allow for 4 38mm motor mount tubes which are canted toward the center and also slanted to maintain spin (produced by the spin motors which fire before the main motors).  The spool, motor mount tubes, and centering rings were sanded and glued with epoxy.  A 3/16" bulkhead was epoxied inside the bottom of the spool and a 1" long section of coupler was epoxied in place to provide space for an electronics compartment.

A hot wire foam cutter was used to cut the foam sheets into discs and ribs.  This foam cutter was constructed using a 24 volt 3 amp transformer, nichrome wire, an electric light dimmer, wire, PVC pipe, and washers, nuts and eyebolts (to protect the PVC).  It is necessary to have the nichrome wire under some tension, to adjust the temperature of the wire using the dimmer, and to choose a reasonable feed rate.  (If you stop the movement of the wire through the foam, it will melt out a void around the wire.)  Very little practice and experimentation was necessary to produce good results.

A wooden template taped to some foam sheets to guide the wire while producing the ribs.  It was necessary to keep the wire tight and perpendicular to the foam and to use a reasonable feed rate to avoid cutting the foam at an angle.

  The discs were marked with the location of the spool and where ribs would be placed.  Next locations for 20 LEDs were marked and drilled by holding some very thin brass tubing perpendicular to the foam and rapidly twisting the tubing on the foam.  The sharp edge of the tubing cut the foam cleanly.  The holes were reinforced with fiberglass tubing made by wrapping a brass tube with wax paper, 3 layers of 4 oz cloth and one temporary layer of masking tape to compress the fiberglass while it was curing.  The resulting tubing was then stripped of masking tape, removed from the brass form, and cut to length.  The short fiberglass tubes were then epoxied into the foam.

(outside view of bottom of saucer)

Mounting of the LEDs was accomplished by using them to replace christmas tree lights and epoxying the holders into plywood discs.  These were in turn epoxied to the foam.  This provided a mount strong enough that LEDs could be replaced with another color if desired.

The resulting appearance of the LEDs is shown below.

The top of the saucer was treated in a similar fashion.  A hole was drilled to allow protrusion of the spool through the foam so that parachute deployment would be cleaner.  Building foam requires much less force to bend parallel to the grain of the bubbles in the foam than to bend perpendicular to them.  Care was taken to match the direction of the grain of the foam in the top and bottom skins of the saucer.  This is necessary to make certain that the saucer is symmetrical.  (That process was very successful in the smaller 28" saucer.)  The insides of the outer edge of both the top an bottom sections of the saucer were beveled so that they would mate better when later glued together.

Short sections of foam were cut with the grain running toward the outside edge of the saucer.  These were glued on the bottom of the top saucer skin to thicken the saucer edge.  (This later proved to be a problem because it caused an unbalanced stiffness in the top and bottom sections and also made bending of the top section very difficult.)

Twelve ribs were used to force the foam tops and bottoms to bend uniformly and to provide additional strength and support in the structure.  (After it was too late to make a change, it was discovered that in this larger dish, a total of four additional ribs were needed to prevent some sagging in the surface due to the larger diameter and the thickener shown above.)  The additional ribs shown in blue in the image below should have been placed midway between the existing ribs where they foam was stiffest.  The grain of the foam in the image below is running top to bottom.

Some ribs and one of the arming switches are shown below.

Extremely reliable switches were desired for arming the timer and the lift motors.  The switch (in the center of the photograph) consists of a t-nut, a brass screw, and a brass washer.  A wire was soldered to the t-nut, and another wire was soldered to the washer (on the other side of the centering ring).  A very short section of insulation from some CAT5 network cable was cut and placed around the screw near its head to prevent the screw from accidentally making contact against the brass washer when the screw was unscrewed a little to open the switch.  (Be careful not to allow any epoxy or foam debris from drilling to get between the screw and the washer when you fiberglass the saucer later.)  Note that the switch is inverted in the photo.  The washer was heated and pressed into the synthetic centering ring.  It was then removed and after the wire was added, the washer was superglued in place.  The hole in the t-nut was covered with a dot of tape then the t-nut was secured with fiberglass cloth.  After cure, the hole was re-opened to allow the screw to pass through as necessary.

The photo below shows a short aluminum tube (in addition to the top of the arming switch).  The short metal tube will later contain an LED which indicates the arming status.

After experimentation to find the proper weight to close the switch at 2 revolutions per second (at the test mounting location), a momentary switch lever was fitted two layers of accordion-folded copper wire.  The wire was then soldered in place as a weight and covered with heat shrink.  The disc was spun up again using the switch to control a piezo.   Counting revolutions of an LED and measuring time, the switch closure was calibrated by trimming the weight (after soldering).  The mounting of this switch is shown below.  To reduce stress on the switch during landings, it was mounted on the centering ring outside the electronics compartment This reduced the required lever length and lever weight.  Although upward thrust will occur only after switch closure, care was taken that acceleration under thrust would not deflect the lever sufficiently to bind the weight thereby preventing proper subsequent re-opening of the switch after rotation ceases during landing.

Hot glue was used to secure all the wiring to the dish.

Epoxy was used to glue the top and bottom sheets to the spool and to the ribs.   While the epoxy was curing, masking tape was used to hold the edges of the top and bottom together and in alignment.  To prevent the tape from tearing, it was necessary to double the thickness of the tape on the ends of the foam where the grain made it stiff.  First, opposite ends of the dish were taped where the foam was most stiff (positions 12:00 and 6:00).  Next, the right and left sides were taped making certain that the foam was evenly distributed (sections on the top and bottom were equal in length and equally bowed).   This placed tape at 3:00 and 9:00.  Then, the spaces between were taped in the same manner (always 180 degrees apart) until the entire circumference was covered with tape.

After epoxy cured, the tape was removed.   A steel rod was placed through the center of the dish so that the dish could be rotated.  The hot wire foam cutter was mounted in a fixed position and the dish was rotated to trim the edge of the dish to a perfectly uniform diameter.  This was a tricky process because the epoxy dramatically affected the cutting and tried to cause the wire to wander in or out.  Using a very hot wire helped.  But, thick epoxy was still problematic.  The dish was round enough that very little material was removed from the perimeter (1/4" at most).  Next, the edges of the dish perimeter were removed with sandpaper to produce an even more rounded edge.  Care was taken to avoid excessive erosion when sanding "with-the-grain" as opposed to against it.  Presence of epoxy between layers of foam presented the only significant sanding obstacle.

You can see the locations of the LEDs thru the cloth.  Leaving the fiberglass on provides some measure of protection for the LEDs and allows most of the light to pass unimpeded.  (Note: In later steps, I taped aluminum tape to the end of brass tubing and cut it in perfect circular masks with a razor blade. These matched the diameter of the LED wells and were used to cover the fiberglass during painting.)

Fiberglassing the curved surface was a challenge because the fiberglass does not compress evenly when taped on the other side.   After laying out the fiberglass with perpendicular threads running square to each other, opposite ends of the threads were taped evenly to produce a square "+".  Then tape was added in the middle of each un-taped section alternating opposite sides.   It was necessary to pull the tape at extreme angles in some areas to take up slack from areas which were not forgiving.  This was necessary because of the varying angle of the fibers at different locations.  I mention this because it is NOT apparent from the photo and because an attempt to keep the tape at a consistent angle would result in wrinkles.

The bottom cone section was constructed from three foam discs glued together with VERY little fiberglass.  The discs were rotated on a 3/16" steel rod while a hot foam knife was used with a 45 degree template to cut them into a cone section for the bottom of the saucer.  Fiberglass was placed on the smaller diameter of the surface and the edges were wrapped around the sides and taped to the back of the cone in a manner similar to the fiberglassing of the main saucer dish shown above.  This required some adjustment to prevent wrinkles.  After epoxying and partial cure, the flat surface of the top and bottom of the cone section were cut free about 5/16" inside the outer diameters and the extra fiberglass was removed.  The process was repeated for a second layer of fiberglass.

A thin sheet of plywood was added to the bottom of the saucer cone to protect it from flame and to provide additional landing strength for the lift motor and spin motor mounts.  Because the lift motors were canted for rotation and also toward the center, the hole shapes were carefully determined.  Holes in 4 letter-sized cardstock sheets were cut to the exact dimensions of the motor mount tubes.  These sheets were individually placed over the motor mounts and the saucer's center hole was marked and cut in each.  They were then taped together and marked so that after removal, they could be re-assembled in the precise orientation.  Motors tubes and templates were marked (A, B, C, D).  A section of angle aluminum was placed along the edges of opposing motor mount tubes to allow marking the template for precise hole enlargement alignment.  After un-taping and removal, the distance between the outside edges of opposing motor mount tubes was recorded. This was used to mark the template, then a short section of motor mount tube was used to mark the elongated hole for cutting.  The template was used to mark the plywood.  A dremel tool was used to cut the holes.  The result was a perfect fit with no unnecessary wood removed.

A sidewalk, and much refitting and sanding was used to reduce the outer diameter about 1/8" to precisely fit the dimensions and 45 deg angle of the bottom saucer cone section.  Fine tuning was made with a wood sanding block.  Fiberglass pulp and epoxy was used with a popsicle stick to fill the void produced by the rounded edge of the foam between the cone section and wooden cap.

The motor tube and launch rod tube joints were then filleted with fiberglass pulp and epoxy.  Adding the cone section after the top and bottom of the dish were joined was slightly difficult due to the curvature of the dish surface.   Next, the joint between the cone section and main dish were filleted.

Motor tube fiberglassing:

Spinning the saucer and dropping it 3 ft on a lawn without motors in place resulted in slight damage to one motor mount tube because of an overlooked 1/3" dia twig.   So, before the bottom cone section was epoxied in place, the tube was repaired and two layers of fiberglass were added to the motor mount tubes where they extend below the bottom of the spool.

Construction of the dome:

Various sizes of foam discs were cut with a 3/16" hole in the center, stacked, and glued (with VERY little epoxy) to produce a rough shape.  A steel rod was placed through the holes and into a plywood base which had been taped to a work table.  Two plywood half-moons were cut and sanded then taped to the table to serve as a template for cutting the dome that was placed between them.  Next, guided by the template, the hot wire foam cutter was used to slice off sections of the foam.  The foam was rotated a few degrees and the process was repeated until a very good dome shape resulted.

The steel rod was replaced with a piece of threaded rod with 2" discs of wood on the top and bottom of the foam to protect it from nuts which held the assembly together.  Superglue was used to secure the tightened nuts and the assembly was placed in a drill press.  The drill press table was adjusted to contact the threaded rod so that it could not mend.  The drill press was turned on and a piece of sandpaper on wood was used to true the surface of the dome.  It is necessary to hold the wood steady and to pay special attention to the joints between layers of foam because the foam immediately adjacent to the joint erodes much easier than the joint with glue on it.

The dome was covered with a layer of fiberglass which was folded over the bottom and taped.  Epoxy was added to the top and about 1/3' of the bottom at the perimeter.  After the epoxy was mostly cured, the fiberglass on the bottom was cut about 1/4" inside the perimeter on the bottom and removed.  A 7 1/2" centering ring was used to mark the bottom of the dome and the foam was cut on the mark. One layer of the foam inside this mark was removed.  The inside of the dome was cut and sanded out to produce a cavity for the dome parachute.  Another layer of fiberglass was carefully placed over the dome and overlapped and taped into the cutout section.  It took a great amount of effort to get the fiberglass smooth and unwrinkled on the dome and between the dome and centering ring.  To keep the distribution of the cloth even at the bottom, the top of the dome was epoxied down to but not including the bottom edge and allowed to cure.  Only then was the centering ring removed and epoxied back in place.

A 1/2" thin-walled brass tube was used like a drill bit to cut a hole in the center of the dome.  A thick short 1/2" aluminum tube (long enough to extend 1/2" past the inner surface of the dome) was epoxied into the hole.  Care and practice fittings of the dome on the disc (with launch rod) were used to insure that the hole and aluminum tube were properly aligned for the launch rod to provide perfectly horizontal unhindered rotation of the saucer.  The inside of the dome was subsequently covered with a layer of 4 oz fiberglass.  And, 4 layers of 4 oz fiberglass were used to secure a short loop of  kevlar chord to the side of the dome wall.  This was used for connection to the dome's parachute webbing.

The dome's aluminum nipple extension into the parachute compartment is used to hold a disposable paper tube between the dome and a corresponding nipple from the electronics compartment.  This tube prevents the parachute and lines from wrapping around the launch rod during spin-up and from being cut and launch.

Electronics compartment -  Need to add photos of dual eyebolts in compartment 

 Need to add photos of Arming LEDs and switch holes 

Testing of spin rate with spin motors: (A video will be posted.)

For test purposes, the final weight of the saucer was approximated by adding all webbing, batteries, and two 38/720 cases filled with D cell batteries.  Two D motors were taped at a slight angle on the bottom closures of the of the J350 motors.  The dish was suspended and the motors were ignited. A video camera was used to record the spin rate.

These motors each produce 16.84 Newton-seconds of thrust.  At video frame rate of 30 frames per sec, the first revolution after burnout was completed in 15 frames.  This corresponds to 2 revolutions per second.  So, the estimated spin rate for other motors (not compensating for the small effect of the mass of the spin motors) is shown in the table below. Note: the target rate is a minimum of 4 rps to a maximum of  7 rps.

At first I was concerned that the excessively high rotation rate (9.8 rps) might cause the image from the lights to overlap resulting in solid rings of light rather than patterns.  However, videotaping of the final spin test with two G104T motors revealed an actual spin rate of a little over 7 rps with 2 water-filled J350s in 2 lift motor slots and the other 2 lift motor tubes each filled with 1 D cell and 2 C cells.  The appearance was remarkable.  I suspect that this will be a spectacular launch with the spin motors and lift motors lit. 

The cant of the thrust motors will supply an additional 5 rps to the dish.  That should overcome rotational loss from friction as the saucer ascends.

Final motor mount size for 2 G104T motors was based on rotation rate observed during small motor spin test.  The two spin motor tubes were mounted partially inset on the bottom of the plywood disc canted about 15 deg out and about 12 deg down.

It's bigger than it looks in the photos.  Titanium dioxide pigment was mixed with epoxy to produce a shiny bright white surface that was downright intimidating.  The surface reminds me of the white starship trooper helments in Star Wars.

Glow-in-the-dark paint was made by adding 6 oz of Aqua colored and 1 ounce of Green colored Strontium Aluminate-based powder to 1 pint of automotive inner clear-coat (without UV inhibitor).   I was not able to produce a good surface with a compressor and spray gun and wound up painting on the mix with a paint brush.   Despite all attempts to smooth it out, the coverage of the powder was uneven and thinner than desired.  The saucer is now a dingy yellow with uneven coverage.   However, at night, it produces an eery blue-green glow which can be seen at a distance.  A UV lamp charges it well.  But, just leaving it exposed during daylight for 10 minutes produces a good glow well after sundown.   Glow time is about 8 hours.  However, the glow is much brighter at first.  The light drops below perceptible levels in about 9 hours.