Introduction: Bug-Catching Spider in Web, Part 1
The story of our bug-catching spider automaton goes like this: A giant evil spider resides in a big web. One day an unfortunate lady bug gets trapped in the web and the scary spider pounces on it.
We came up with the idea for this six-week project together and discussed implementation possibilities at length, particularly with respect to moving the spider and detecting the bug. For example, although we ended up using IR sensing for bug detection, we considered several other possibilities including touch sensors and image processing. At that point, the highly modular and reusable nature of the project components allowed us to build separately, and we are posting our Instructable as a two-part series.
Part 1, described in this Instructable, shows how to build the following elements:
* The frame to which everything is attached
* The spider web and associated lighting
* The spider mover, which is an XY table beneath the web
Part 2 shows how to build the remaining elements:
* The bug
* The bug detector
* The spider
Please note that due to a course deadline, the Part 1 Instructable was published before the documentation was complete, so watch for ongoing updates to the later steps.
Readers who would like to build this project should be aware of the following limitations
The XY table moves nicely under human power, but not with the servos, and we think this outcome is a result of the materials not being sufficiently rigid. It's possible that adding another servo to move the lower slider from both sides would be helpful, too. Here are some alternative Instructables XY tables to try:
Low Cost Hobby Servo XY Table
Internet Arduino-Controlled T-Slot XY Table
DIY CNC Router
Our intent was to be able to display the web in any position, such as leaning against a wall. For this reason, we used strong magnets on both the spider and the mover. Although this idea worked well with models during pretesting, the final spider clings too tightly to the web and doesn't move well. For this reason, we would recommend a different spider / mover magnetic connection, as well as stronger servos to help overcome drag.
The spider's orientation is fixed. We had discussed using a rotating arm on the spider mover, with the pivot point toward the front of the spider, but did not build it due to time limitations. This arm would have allowed the spider to turn as it moved forward along an arc traced out by the spider mover.
Step 1: Materials and Equipment
Image note
A single representative materials photo is provided here. In the photos that appear throughout this Instructable, selected materials are shown from multiple viewpoints — we hope that this approach will make them easier to understand.
Materials - Frame and Web
(1) quarter sheet plywood (2' x 4'), 15/32" nominal thickness, actually 7/16" ($12.45)
(-) 1/4" x 12" basswood, 1-1/2" total width ($1.50 - estimated; was supplied by our lab)
(1) 22-1/2" x 23" x 1/8" acrylic sheet ($12.00 - estimated; was supplied by our lab)
(4) 2", double-wide mending plates ($3.22 for pack of 4)
(16) #6 x 1/2" flat head wood screws ($1.18 for pack of 18)
(8) #6 x 5/8" flat head wood screws ($0.56 total)
(8) #8 x 3/4" pan head wood screws ($0.72 total)
(4) 1/4 x 20 T-nuts ($1.00 total)
Materials - Spider Mover
(2) 3/4" strips of plywood previously described
(-) 1/4" basswood previously described
(-) 1/8" x 24" basswood, 8" total width ($6.00 - estimated; was supplied by our lab)
(2) 3/8" x 48" wooden dowels ($1.98 total)
(4) 0-80 x 5/16" round head machine screws ($0.52 total)
(4) 0-80 hex nuts ($0.64 total)
(14) 6-32 x 1/2" pan head machine screws ($0.98 total)
(14) 6-32 hex nuts ($0.70 total)
(4) 8-32 x 1-1/4" pan head machine screws ($0.40 total)
(4) 8-32 hex nuts ($0.24 total)
(4) 1/4-20 x 7" full thread carriage bolts ($2.36 total)
(8) 1/4-20 flange nuts ($1.20 total)
(1) #8 x 3/8" eye hook ($0.15 - estimated; was supplied by our lab)
(8) 3/16-1/4 hairpin cotter pins ($2.34 total)
(4) 1/2 x .385 x 1 nylon spacers, note interior dimension fits around 3/8" dowels ($2.24)
(6) zip ties ($0.09 - estimated; were supplied by our lab)
(1) Arduino Uno and USB cable ($32.00 - estimated, were supplied by our lab)
(2) hobby servos ($30.00 - estimated; were supplied by our lab)
(-) electrical wire, assorted colors ($2.00 - estimated, was supplied by our lab)
(2) 1/16" x 1/2" strong disc magnets ($1.80 - estimated; were supplied by our lab)
(4) 1/16" x 1/8" strong disc magnets ($1.00 - estimated; were supplied by our lab)
(1) 18" x 24" white poster board ($0.50 - estimated; was supplied by our lab)
Materials - Lighting
(1) 50-micro-LED holiday light strand ($5.84)
(2) 1" angle brackets ($0.30 - estimated; were supplied by our lab)
(2) #6 x 1/2" flat head wood screws ($0.12)
(2) 6-32 x 1/2" flat head machine screws ($0.12 total)
(2) 6-32 hex nuts ($0.10 total)
Equipment
Computer
Laser cutter
3d printer
Table saw
Radial arm saw (or other saw capable of miter cuts)
Milling machine
Drill press
Dremel with cylindrical grinding bit
Scissors
Clamps
Measuring tape
Assorted screwdrivers
Pliers
Supplies
Weld-It Contact Adhesive
Wood glue
Scrap basswood (1/8")
Scrap lumber
Scrap acrylic
Scrap fabric
Sandpaper assortment (320 - 1000 grit)
Double-sided tape
Toothpicks for applying glue
Pencil for marking materials (for drilling, cutting, etc.)
Personal Protective Gear
Safety glasses
Dust mask
Earplugs
Hair tie
Additional Materials, Equipment and Supplies for Part 2 (Bug, Bug Detector, and Spider)
See the Materials Needed page in the separately published Part 2 of this series
That's a long list of parts! How did you know what to get?
To help us understand the design and the relationships among the parts, we created a computer model before starting. Of course, there were some changes along the way....
Step 2: Web Frame Pieces
Purpose
The purpose of the frame is to have a place to attach all of the other modules (web surface and lighting, spider mover assembly, bug detector). Its dimensions will depend on the final size of the acrylic sheet used for the web (see tip below).
Design
Since our acrylic was approximately 22-1/2" x 23", our frame has a 22" x 22" opening and an overall size of 28" x 28" (3" width on each side). An overhang of 1/8 - 1/4" is desirable to maximize the web's visible area while allowing attachment hardware to remain hidden. Miter joints are used at the corners. Step 13 explains how the four pieces of the frame are joined together using mending plates.
Materials
(1) quarter sheet plywood (2' x 4'), 15/32" nominal thickness, actually 7/16"
The selected thickness of plywood offered sufficient stiffness plus depth for attachment hardware while being reasonably light. At the end of the project, about 9" x 4' plywood plus scrap remained.
Construction
Using a table saw, we cut four 3-inch wide strips down the length of the plywood. After that, we used a radial arm saw to miter the ends of each strip at 45°. The first miter cuts were made as close to the ends of the strips as possible. The second cuts were made so that the final length of each frame piece was 28", with the cut angle perpendicular to that of the first cut.
Although the frame could have been assembled at this point, we waited until all modules to be attached were complete. This approach allows holes to be marked and drilled into the frame pieces prior to assembly.
Tips
Your acrylic sheet, on which the size of the frame is based, should fit in the bed of your laser cutter.
Although we knew at this point that that light transmission through the web would be enhanced by polishing the edges, we didn't know that a good way to accomplish this task is by using the laser cutter to trim the edges. If we had planned for trimming, we would have slightly reduced the interior dimensions of the frame (1/4" smaller than the associated dimensions of the web post-trimming).
Step 3: Support for Spider Mover
Image note
Some of the images are cut off (most apparent in the hardware collection image, which readers should click to view in full).
Purpose
The purpose of the spider mover support, henceforth called the X, is to provide a base onto which the remaining parts of the spider mover module can be assembled. The X also allows for easy transport of the work in progress, facilitating movement between locations for storage, testing, and photography.
Design
The diagonal dimension of the X is approximately 1" shorter than the diagonal between the outside corners of the frame (difference of 1/2" at the end of each arm).The two pieces used to make the X come together at the center in a cross-lap joint, which prevents them from moving relative to each other.
An eye hook underneath the center helps to manage wires running to a servo that moves above it. Carriage bolts, which will be used to connect the X to the frame, are added now to serve as feet.
The holes in the X include a blind pilot hole for the eye hook, a hole 1/2" from the end of each arm for its carriage bolt, and another hole approximately 3-1/2" from the end of each arm at its lower slider support attachment point.
Materials
(2) 3/4" strips of plywood previously described
(1) #8 x 3/8" eye hook
(4) 1/4-20 x 7" full thread carriage bolts
(8) 1/4-20 flange nuts
(1) 18" x 24" white poster board
The plywood makes a surprisingly stiff and strong X.
Our original carriage bolts, shown in the photos, were 5-1/2" long. After the spider mover was completely assembled, however, we decided that they weren't long enough, opting at that point for 7" bolts. We were surprised to learn that carriage bolt threads run all the way to the head only on 6" or shorter bolts, so we had to have the last inch of threads cut into the longer bolts at our local hardware store.
The poster board is not part of the final product, but it plays an important role during the construction process.
Construction
Using a table saw, we cut two 3/4-inch wide strips from the plywood sheet used in the previous step, and then chopped the strips to the desired length (38-1/2") with the radial arm saw.
After that, at the center of each piece, we marked the width of the crossing piece. Our milling machine allowed us to remove the material in this area to half the depth of the piece. It was during this operation that it became apparent that our plywood was subject to severe splintering, an ongoing problem during this project. After seeing the result from the first pass of the mill, we subsequently used scrap wood to support and surround the pieces, avoiding further splintering as the milling bit exited the side. The tear-out is visible in the two close-up views of the center of the X.
At this point we used wood glue to join the two parts, clamping until the glue dried. However, we recommend that our readers just do a press fit here.
Next, we put the four frame pieces onto a flat surface in their expected positions, and placed the X on top to confirm that its size and the desired positions of the carriage bolt holes were correct.
The next step was to find the positions of the holes for the lower slider supports. To accomplish this task, we needed to be certain that the supports were the correct size. By making a paper prototype out of laser-cut poster board, we learned that it was not possible to cut precisely at the edge of the material. We also noticed that other minor corrections in the design were required, both related and unrelated to the size observation. As as result, we reduced the length of the lower slider supports by 1/8".
Once we were satisfied that the patterns for the paper prototype were accurate, we cut the two lower slider supports from basswood (shown and described in the next step). We were able to mark the positions of their attachment holes by placing them in their final positions on top of the X.
Then we drilled the through holes in the arms and the blind hole in the center of the X. Again, after seeing tear-out beneath the first arm hole, visible in the close-up picture, we placed scrap wood underneath while drilling. As noted above, if we were doing this again, we would drill the arm holes before gluing the pieces together.
To wrap up this step, we installed the hardware. The eye hook was put in first, while it was still convenient to place the X directly on a flat surface. One flange nut was put onto each carriage bolt and positioned about an inch from the head. After pushing the bolts through the holes in the frames, we installed and lightly tightened the second set of flange nuts against the arms.
Tips
Old issues of Popular Mechanics were helpful in researching the construction of cross-lap joints. As an alternative to the milling machine, consider using a router table or a table saw (requires several side-by-side cuts or a dado blade).
To ensure that the nicer-looking side of the plywood ends up facing the viewer, cut the cross-lap opening into the nice side of the bottom piece and into the less nice side of the top piece.
Make sure that the lower slider supports are exactly parallel before marking the positions of their attachment holes.
The eye hook could also be placed on the top side of the X.
When assembling the carriage bolts to the X, push them through from the bottom (less nice) side. Also, be sure that the flat sides of the flange nuts face each other.
Step 4: Lower Slider Supports
Purpose
The lower slider supports hold all of the components necessary to support and move the lower slider. These components include the rails, servo, and slider arm.
Design
The two supports have similar dimensions, though only one support has a slot for a servo. We suggest that readers who attempt this project create two identical supports to allow for the installation of another servo and arm. Such a design would permit the lower slider to be moved from both sides simultaneously.
Because the servo horn's center of rotation is not directly in the center of the servo body, the position of the servo slot is offset slightly from the center. Once installed, the servo horn's center of rotation ends up at the exact center of the support.
The tabs and slots at the ends of the slider supports provide connections for the end caps that hold the rails in place. To allow room for the parts of the end caps that extend beneath the support, spacers are included between the X and the supports.
We were interested in creating a spider mover that could easily be disassembled and reassembled in the future. Therefore, our design calls for machine screws / nuts and other removable parts that don't cause damage; wood screws are not used.
Materials
(-) 1/8" x 24" basswood, 8" total width
(-) 1/4" x 12" basswood, 1-1/2" total width
(1) hobby servo, horn removed
(4) 6-32 x 1/2" pan head machine screws
(4) 6-32 hex nuts
(4) 8-32 x 1-1/4" pan head machine screws
(4) 8-32 hex nuts
The file with templates for all laser-cut parts in this Instructable is included here (.ai format, generated by Illustrator).
Construction
This step provided an opportunity to determine the dimensions needed for certain laser-cut holes that appear throughout the project. Although the paper prototypes mentioned in the previous step were helpful up to a point, wood prototypes were needed in case the laser's interaction with the material resulted in slight dimensional differences. By making prototypes from scrap 1/8" basswood, we learned what hole diameters to specify for 6-32 and 8-32 machine screws.
Our experiments also provided information about the correct size for the rectangular servo slot, as the design of the servo wire attachment point required the servo to pass through its slot at a slight angle during installation. Due to the thickness of the wood, the long dimension of the slot had to be a tiny bit longer than the long dimension of the servo.
After finalizing the hole dimensions, we laser-cut the two supports from 1/8" basswood. We also cut four 3/4" square spacers from the 1/4" basswood. Next, we attached the servo to its slider support with the 6-32 machine screws and hex nuts. Finally, using the 8-32 machine screws and hex nuts, we attached the slider supports to the X with the spacers in between. In both assemblies, the screws were put in from above to achieve a better appearance.
Tips
Remove the servo horn before installing the servo and set it aside. It will be reinstalled in a later step. Also confirm that the servo is installed in the correct orientation, that is, with the horn's center of rotation at the exact center of the support.
If you didn't keep track of which holes in the X correspond to a given support, try setting the supports down in both possible ways to find the arrangement with better parallelism. Use the screws (but not the nuts) to keep them in place while you measure.
To make it easier to mate a machine screw and nut, hold the nut to the hole with light finger pressure to assure its correct orientation. Then put the tip of the machine screw into the nut and turn it until it catches. This is much easier than trying to get the nut started on the tip of the machine screw in mid-air (which is where it will be if you push the screw through the hole first).
Attachments
Step 5: Sliders
Image notes
Images that are cut off by the display algorithm are annotated as a reminder to click them for viewing in full.
Purpose
The lower slider (long) carries the support for the upper slider, and the upper slider (short) carries the spider attractor. The two sliders move perpendicularly, allowing the spider attractor to go anywhere on the surface of the web.
Design
Each slider consists of a cross-piece with two holes, sleeves that line the holes, and one or two carrier pins.
The upper slider has a single symmetric carrier pin held in position by its two sleeves. The lower slider has an asymmetric pin at each end, held in position between a sleeve and the central portion of the slider (which fits directly under the upper slider support to keep it from sagging). This offset design permits the slider to pass next to the body of the servo that hangs from the upper slider support, rather than through it! The bottom of the slider end cap fits into small notch next to the hole.
We started out using shorter sleeves, as shown in the last two photos, but we thought that the longer sleeves would be more likely to prevent twisting relative to the direction of motion (that is, loss of perpendicularity).
Underneath, a carrier pin connects to the end of the arm that moves the slider; on top, it connects to the component that the slider carries. The pin is long enough to pass through the arm and a washer below it; a hole is included near the bottom for a hairpin cotter pin to hold it all in place. In testing, we found that the washer and pin were unnecessary; the pin stays in the arm without them.
Materials
(-) 1/8" basswood previously described
(4) 1/2 x .385 x 1 nylon spacers, note interior dimension fits around 3/8" dowels
(1) symmetric carrier pin (3d printed from custom design)
(2) asymmetric carrier pins (3d printed from custom design)
The files used to create the 3d printed parts are included here (.stl format, generated by Maya).
Construction
Once the slider crosspieces were laser cut from 1/8" basswood and the carrier pins were 3d printed, the assembly was straightforward. We slid the correct carrier pin(s) over the end(s) of each crosspiece (the slot in the carrier pin is visible in picture 6, as is the hole for the cotter pin). Then we pushed each sleeve halfway through its corresponding hole.
Tips
Although the sleeves fit snugly in their holes, we used adhesive in a later step to ensure a permanent installation with the sleeves centered and straight. Hold off on applying the adhesive now, as it should be used only after each slider is in place on its rails.
It may be possible to lighten the lower slider and other long basswood parts by incorporating cutout areas; however, testing would be needed to assure that performance (e.g., stiffness) is not affected.
Step 6: Lower Slider Rail Assembly
Image notes
Images that are cut off by the display algorithm are annotated as a reminder to click them for viewing in full.
Purpose
The lower slider rails serve as a guideway for the lower slider. The end caps hold the rails in position.
Design
The rails themselves are wooden dowels, sanded smooth to reduce friction inside the slider sleeves. We had originally planned to use metal tubes, but switched to dowels because they were significantly less expensive.
The ends of the rails fit into the end caps, which incorporate a three-step interlock system that is intended to hold them securely in place at the ends of the lower slider supports:
1) A tab in the support fits horizontally through a slot in the end cap.
2) A pin attached to the end cap fits vertically through a hole in the tab.
3) A hairpin cotter pin secures the end cap pin in place.
The end cap pin has two important features. First, it clips over the end cap; note that the end cap is notched so that the end cap pin can be shorter. Second, it covers the backs of the rail holes in the end cap.
We were disappointed to learn that this end cap design didn't work very well. The hole in the tab was a bit too large for the pin, which allowed the end caps to wobble back and forth along the axes of the rails. As a result, the ends of the rails sometimes failed to stay in their holes. To address this problem, first we added springs made from bent zip ties to push each end cap inward. Although the springs were quite strong, it was still possible to inadvertently push the end caps out of position, allowing the rails to fall out. We could have made new, longer rails, but because we had already completed the sanding we were reluctant to do so. Instead, we tried inserting thin squares of wood inside the holes that the rails fit into, effectively shortening the distance they had to cover, This approach was somewhat effective, but not ideal because it reduced the depth of the holes. In the end, we laser-cut small circles from scrap basswood and glued them to the ends of the rails to extend them.
Knowing what we know now, we would redesign the end caps to be much simpler and more secure. First, we would make the dowels longer, so that they would extend past the holes in the end caps and be secured from the outside (perhaps with a hairpin cotter pin). Second, rather than using the end cap pin, we would include a third wooden piece placed perpendicular to both the lower slider support and end cap.
Materials
(1) lower slider (long) constructed previously
(-) 1/8" basswood previously described
(2) 3/8" x 48" wooden dowels
(4) end cap pins (3d printed from custom design)
(4) 3/16-1/4 hairpin cotter pins
(4) zip ties
The file used to create the 3d printed part is included here (.stl format, generated by Maya).
Construction
To make the rails, we sawed two long pieces from each dowel. The length of each rail was the distance between the far sides of its two end caps (the four rails were equal in length). Then, using progressively finer sandpaper, from 320 up to 1000 grit, we smoothed their surfaces until the slider sleeves slid quite easily along them.
After laser-cutting the four end caps and 3d printing the four end cap pins, we put together each of the two rail assemblies in the following sequence:
1) Installed one end cap to the lower slider support as described in the three-step interlock sequence above.
2) Slipped one end of the lower slider over a rail.
3) Installed the second end cap with the rail in place.
We made the zip tie springs from the tip ends of the ties, using about 2-1/2" of material from each tie. To make each tip fit better into the extra space in the hole around the end cap pin, we narrowed and thinned it using a Dremel with a cylindrical grinding bit. By holding each spring in a bent position with pliers, we were able to insert the tips deeply into the spaces.
As noted above, we also adjusted the rail lengths by gluing on 3/8" diameter circles laser-cut from 1/8" basswood.
Finally, ensuring that the slider was perpendicular to the rails and that the sleeves were correctly positioned within it, we permanently installed the sleeves by using Weld-It Contact Adhesive to glue them to the slider.
Tips
To bend the zip tie springs more easily, warm them a bit in your hand first. Slow bending works best.
When installing the springs, be sure to wear safety glasses! Also pay attention to which way the spring is facing during installation — the end opposite the tip should face the end cap.
Step 7: Upper Slider Support
This page is a work in progress
Purpose
Design
Materials
(-) 1/8" basswood previously described
(1) hobby servo, horn removed
(4) 6-32 x 1/2" pan head machine screws
(4) 6-32 hex nuts
(4) 6-32 x 1/2" pan head machine screws
(4) 6-32 hex nuts
Construction
Tips
Step 8: Upper Slider Rail Assembly
This page is a work in progress
Purpose
Design
Materials
(1) upper slider (short) constructed previously
(-) 1/8" basswood previously described
(2) 3/8" x 48" wooden dowels FIXME
(2) end cap pins (3d printed from custom design)
(2) 3/16-1/4 hairpin cotter pins
(2) zip ties
Construction
[see lower slider rails description]
Note: Use of adhesive once slider is in place
Tips
Step 9: Slider Arms
This page is a work in progress
Purpose
Design
Note: The smallest holes in the arms are for the servo horn
Note: Initialize servo positions from Arduino before attaching arms
Materials
(-) 1/8" basswood previously described
(2) servo horns previously reserved
(4) 0-80 hex nuts
(4) 0-80 x 5/16" round head machine screws
(2) arm pins (3d printed from custom design)
(2) large arm washers (3d printed from custom design)
(2) small arm washers (3d printed from custom design)
(2) 3/16-1/4 hairpin cotter pins
The files used to create the 3d printed parts are included here (.stl format, generated by Maya).
Construction
Note: Double-sided tape, scrap wood
Note: Put over carrier pin first
Tips
Step 10: Lighting
This page is a work in progress
Purpose
Design
Note: Mention concern about interaction of LEDs and IR detectors
Materials
(-) 1/8" basswood previously described
(1) 50-micro-LED holiday light strand
(2) 1" angle brackets
(2) #6 x 1/2" flat head wood screws
(2) 6-32 x 1/2" flat head machine screws
(2) 6-32 hex nuts
Construction
Tips
Step 11: Spider Attractor
This page is a work in progress
Purpose
Design
Note: the spider attractor was designed and provided by my collaborator, bhasudha; more details may appear in Part 2.
Materials
(-) 1/8" basswood previously described
(2) 1/16" x 1/2" strong disc magnets
(4) 1/16" x 1/8" strong disc magnets
(-) Smooth fabric
(-) Packaging tape
(2) 6-32 x 1/2" pan head machine screws
(2) 6-32 hex nuts
Construction
Tips
Step 12: Spider Web
This page is a work in progress
Image note
The main image shows how the web looks in the frame; assembly is described in the next step. Also, the web was inadvertently rotated 90° before we took the picture, so gravity is to the left!
Purpose
Design
Materials
(1) 22-1/2" x 23" x 1/8" acrylic sheet
The file with the template for the laser-etched web is included here (.cdr format, generated by Corel Draw).
Construction
Note: Test cuts on scrap acrylic
Tips
Attachments
Step 13: Web Frame Assembly
This page is a work in progress
Purpose
Design
Materials
(4) frame pieces prepared previously
(1) web prepared previously
(-) 1/4" basswood previously described
(4) 2", double-wide mending plates
(16) #6 x 1/2" flat head wood screws
(4) 1/4 x 20 T-nuts ($1.00 total)
(8) #8 x 3/4" pan head wood screws
(8) web holder clips (3d printed from custom design)
(8) #6 x 5/8" flat head wood screws
We actually used pan head screws to attach the mending plates, but we show flat head screws in the parts list because they would have been a better choice.
Construction
Tips
During assembly, ensure that the nicer-looking side of the plywood will end up facing the viewer.
L-brackets can be used instead of mending plates. Our original design called for butt joints rather than miter joints, for which the L-brackets would have been less appropriate.
Step 14: Spider Mover to Frame Assembly
This page is a work in progress
Purpose
Design
Materials
(1) spider mover constructed previously
(2) slider arms constructed previously
(2) servo horn attachment screws previously reserved
Construction
Tips
Step 15: Spider Control
This page is a work in progress
Purpose
Design
Materials
(1) Arduino Uno and USB cable
(-) electrical wire, assorted colors
Construction
Tips
