Picture of Bug-Catching Spider in Web, Part 1
Bug and Spider on Web.jpg
This project is a collaboration between bhasudha and idesigner4 (me), students in the Fall 2012 course Things That Think (CSCI 7000) at The University of Colorado - Boulder.

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.
oh I see how you did this now, very well done. You should light that acrylic from the side to really make the web pop!
idesigner4 (author)  amandaghassaei2 years ago
Thanks! We did want to light the web as you suggest, so we built a small test rig to try it out (shown in step 10). One thing we wondered about is whether the LEDs would cause any trouble for the IR detectors, but we only got as far as testing for aesthetics before our deadline.
do you have the specs of the detecotrs you used? I've used white leds (which have a big peak towards the blue end of the spectrum, far from IR) with 780nm centered ir sensors and been fine. Many IR sensors even have a covering that has a very sharp cutoff at around 700nm that helps a lot with cutting out visible light, that's why a lot of ir sensors are colored black of navy.
idesigner4 (author)  amandaghassaei2 years ago
The best place to find the detector array details is in the Part 2 Materials List, which includes links to sources. I've included the detector link here.