My son and I built this motion sensitive animatronics prop of an alligator head in October of 2003. I am publishing ths story on Instructables for the first time.

The Idea
First of all, before I talk about the project itself, let me first explain why I decided to write about it and put it up on the website. Yes, appearing on Larry King Live is my ultimate goal. Obviously, this puny project is not going to make it happen. I wanted to write about it to tell the folks that regardless of what you see on "This Old House" and "Monster Garage", if you don't do something on a regular basis, or as a part of your profession, simple tasks can become a project. It can be very frustrating. However, the end results are very rewarding.

My son and I have been an avid fan of Discovery and TLC on the cable. We have enjoyed shows like "Monster Garage", "Junk Yard War", "American Choppers", and "The Movie Magic" (I think that's the right name of the show). All these programs have inspired both of us in terms of creativity, and having fun while creating something. I have been thinking about building an animatronics piece for some months. My original idea was to create a motion sensitive dinosaur head, which would open its mouth and breathe fire. I mentioned this to my colleague, JR sometime in September of 2003. I also told him, I wanted to finish the project by the Halloween (in the same year). JR, an electrical engineer by education, is a walking encyclopedia of engineering knowledge. How can a man with a baldhead hold so much of information, just baffles me. JR with his wisdom, right away advised me to cut down the scope of the project. He suggested making a motion sensitive alligator head instead, a comical alligator head. His point was to focus on the mechanics of the project and use stuffed toy from Toys R Us for the head. I conceded and the Project Alligator was conceived.

The Team
Let me set the record straight. Though I am an electrical engineer by education, I am no craftsman. My son volunteered to be the creative talent behind the mould and the paintwork. Considering that I scored only 17 marks out of 50 in my arts class in 8th grade, I gladly gave him the job of the creative director. Apart from JR, there are two other people who should be mentioned here. My buddy, Nasir, who is a master craftsman in woodworking projects, provided some pointers with the movement mechanism. My friend Venu provided company for beer at various brain storming sessions at the local bar. By the way, Bud, Coors, and Miller brands are NOT thought provoking beers. Last but not the least, there are many of you, the web surfers, who provided valuable suggestions in the mechanical design and the choice of material for the mould. I got help from the following newsgroups:

rec.models.scale and rec.models.railroad

Scope
I decided to include the following functions:

Alligator should open its jaws based upon motion and close it. This cycle should continue until the motion stops.
Its eyes should light up while the jaws are in motion.
It should create effect of exhaling fire by blowing air on confetti wrapped light.

After Thoughts
The project was definitely way over budget because I bought material in large quantities because I did not know how much I needed. I justified buying tools, which I perhaps will not use again. However, every bit of this experience was a MasterCard moment, priceless.

After After Thoughts
After making this beautiful piece of work, like a fool, I sold it on eBay for $100. Three years later, in December of 2006, when I got really bugged by thought that I should never have sold it, I contacted the buyer. To my surprise, not only I was able to contact him, I managed to buy the gator back from him. So, Anthony, thanks so much for being a great human being.

Step 1: Components

These basic components were purchased from surpluscenter.com and Home Depot.

In the picture below I have:
1. A 12 Volts power supply
2. Motion sensitive lights
3. Limit switches (2 of them)
4. Four pole double throw relays (2 of them)
5. Blower
6. 17 RPM gear motor

Step 2: Jaws

I decided to use the wooden tiles cut as the shape of the jaws. The tiles were leftover from the flooring upgrade; I got done a few years ago. The lower jaw was to remain fixed and the upper jaw was to move on a pivot. The wooded tile was the perfect material for this job because of its strength.

Step 3: Mechanical Assembly (Jaw Movement)

I decided against the crank mechanism because it would have been more complex to stop the crank mechanism at the right spot. The jaws were to be moved by a wire mechanism. The wire was to be wound on a shaft connected to a motor. The motor gets started by the motion detection mechanism. When the jaws would have completely opened it trips a limit switch, which reverses the direction of the motor. The jaws would close because of the gravity. However, release of the wire would make it close in a controlled fashion. When the jaws would close completely, it would trip another limit switch to stop the motion or reverse the motor if the motion was being detected again. I found this great website specializing in the old surplus material. I bought about $50 worth of the material from http://www.surpluscenter.com .

A 17 RPM motor was perfect for the winding mechanism to open the jaw. I decided to use a 10lbs fishing line instead of wire. Connecting a shaft to the motor was a challenge. The motor had a small shaft with 5/16" in diameter. With some advice from the railroad newsgroup, I decided to drill a small hole on the motor shaft. For the long shaft, I used a hollow brass tube from the local hobby store, whose internal diameter was 5/16". I drilled a through hole on the hollow shaft. The hollow shaft was inserted on the motor shaft aligning the three holes. A split pin was inserted through these holes making t a permanent extension. I inserted a long 5/16" bolt (With its head cut) into the hollow tube to make it strong. Believe me; this simple 'thingamajig' took me more time than it should have. Designing the electrical circuit was fun and one of my strengths.

Step 4: Electrical Components

The electrical components consist of the following:
1. Start the motor upon sensing motion
2. Stop the motor when the motion stops
3. Reverse the direction of the motor when the jaw is completely open or closed.

For an electronic enthusiast designing a motion sensor probably will be a breeze. However, I had to find a cheap solution without making it a big project like the motor shaft. I picked up a cheap motion detection light kit from the neighborhood Home Depot for $15. You may have seen the use of these lights outside the garages. There was one small challenge involved. The unit, as shipped from the factor is supposed to turn on or off a 110 Volts AC source. If you look at my circuit diagram, I needed the motion sensor to supply me a normally open (NO) push button type output. This needed some hacking. So I opened up the sensor unit. The sensor unit is rather simple. The electronics turns on or off a relay. The relay is a normally open single contact relay. On the circuit board, the hot wire (Black) was connected to one end of the relay switch. The other end came out as a red wire. Obviously when the motion is detected the relay coil turns on the switch and provides juice through the red wire. I carefully cut the laminated copper strip on the printed circuit board, which was connecting the hot wire to one end of the normally open relay switch. Using a multi-meter, I checked and re-checked the contact to make sure they were not connected. I soldered a green wire to the cut side of the relay switch, and brought it outside the sensor unit. So, now the unit has four wires coming out of it. The black and white wires provide the 110V AC to the unit to make it work. The red and the green wire provide the open and closed switch contacts, which I needed to trigger the starting of the motor.

WARNING: I must warn the readers, what I did was very risky. One mistake, and you will land up getting the hot side of 110V AC coming out of the green wire causing electrical shock and possible death.

C:\kumara\Alligator\website\Visio-AlligatorProject.pdf
Download

Step 5: Air Blower Assembly (Fire Breath)

This was rather easy. I picked up a blower fan from the surplus center. I mounted a 12V bulb with a holder on a sheet metal strip. Using super glue, I glued some transparent red and orange gift basket paper confetti on the metal strip. I could not find a rather soft hose to bring the air from the blower fan to the jaws. I used a left over hose from my sump pump. I connected two pieces together using bathroom caulk.

Step 6: Alligator Head

We decided to become creative and take our chances with the alligator head. Against JR's advice, I decided to build the head rather than using a stuffed toy. I built a wire frame of the head using a 14 gauge electrical wire. My son wrapped the wire frame with plaster wrap from the craft store. The plaster wraps are like these 2-3" wide band-aid type cheesecloth, which has a pre-applied layer of plaster of Paris. When wet the wrap becomes very soft. When the wire skeleton was covered with these wraps and dried, it became hard and gave a definitive shape to the alligator head. To make further shapes, we used a product called, Celluclay (instant papier mache). This stuff comes dried like paper dust. You add water and mix it like dough. It is great to make three-dimensional shapes. Thanks to all the folks at the rec.models.scale newsgroup, who contributed with many creative ideas to achieve the same result. I would highly recommend the book, 'Make Something Ugly for a change' by Dan Reeder for some great ideas. We used different shades of green to paint the head after it was thoroughly dried. Once the colors were dried we sprayed the head with gloss glaze, also from the crafts store.