The inspiration for this automaton comes from the "Little Miss Muffet" nursery rhythm many of us learned as children. The idea is that a little girl named Little Miss Muffet is sitting on a tuffet eating her curds and whey, when all of the sudden a spider drops down next to her and frightens her away. To achieve the basic affect of the nursery rhythm, Little Miss Muffet is sitting under a tree eating cereal. At a random interval a spider drops out of the tree scaring Little Miss Muffet, which causes her let out and scream and kick her legs. A split crankshaft controls the eating mechanism, while a combination of crickets, a pinwheel/ratchet system, and a shaft control the spider mechanism and Little Miss Muffet's response.
The design for the Little Miss Muffet automaton can be broken down into the mechanisms that control the movement, the materials used to create the automation, and the design process. Each one of these aspects is described below.
The Little Miss Muffet automaton consists of three mechanisms: the spider mechanism, the kicking mechanism, and the eating mechanism. Working together, the kicking mechanism and the spider mechanism form a fairly complex design and contain the computational part of the automaton, while the eating mechanism is fairly simple in design and contains no computation.
The spider mechanism is made from a combination of wood, Lego, two motors, a touch sensor, and a cricket (Cricket A). The main part of this mechanism is a wooden pinwheel with a groove in the edge for the spider's thread and seven evenly spaced pins on the front. The pinwheel is then mounted to the front of a ratchet that contains fifteen teeth. The entire mechanism is driven by two motors that are controlled by the cricket. The first motor (Motor 1) is responsible for turning a long pin that catches the teeth of the pinwheel allowing the spider to be pulled back up into its hiding place in the tree. The long pin that drives the pinwheel is wrapped in a small piece of aluminum foil. Each time this long pin makes a revolution the aluminum foil and the two wires coming out of the touch sensor complete a circuit. This part of the mechanism is used for computation and is explained further in the next section.
The other motor (Motor 2) determines whether the poll for ratchet is down, insuring the pinwheel does not slip and the spider doesn't drop, or the whether the poll is up, allowing the pinwheel/ratchet mechanism to spin freely under the weight of the spider causing him to drop.
The kicking mechanism is controlled by a third motor and another cricket (Cricket B). The motor (Motor 3) is connected to a shaft hidden inside the bench. The shaft has two sets of pins on it, one set for each leg. The pins poke through the two slits in the front of the bench when the motor is turned on, causing Little Miss Muffet's legs to kick. The pins are not glued to the shaft, so that each time a leg kicks the set of pins for that leg changes position slightly. This allows the kicking motion to look more natural and not quit so mechanical. Little Miss Muffet's legs are attached to her body with wire to allow them to swing freely.
The eating mechanism is independent from the other two mechanisms. It is driven by a wooden crank that containing a crank pin. The crank pin has a wire loop wrapped around it, with a shaft the goes through a slit in the grass and attaches to Little Miss Muffet's right arm. When the handle of the crank is turned, the shaft rotates causing Little Miss Muffet to eat from the bowl that is in her left hand. This part of the mechanism is purely mechanical.
Cricket A is responsible for controlling when to turn on and off Motor 1 and Motor 2. It is also responsible for sending an IR signal to Cricket B. Cricket B is the responsible for receiving the IR signal from Cricket A, turning on and off Motor 3, and playing a series of beeps that represent Little Miss Muffet's scream. Both of the crickets are controlled by a logo program that is stored onboard. This program is included in Appendix D.
At the beginning of the program Cricket A turns on Motor 2 to lift the poll of the ratchet, allowing the spider to drop and set up the entire system. After this occurs, it turns on Motor 2 in the opposite direction causing the poll to come to rest against the ratchet. Cricket A then turns on Motor 1 causing the long pin that drives the pinwheel to turn. A counter is incremented each time the long pin makes a complete rotation and the circuit for the touch sensor is completed. Once the counter has reached eleven, Motor 1 is turned off. The program then waits a random number of seconds and then turns on Motor 2, lifting the ratchet's poll. This causes the spider to drop, and Cricket A sends an IR signal to the Cricket B. Once Cricket B receives the signals it activates the kicking mechanism. Cricket B turns on Motor 3 which starts Little Miss Muffet kicking and screaming for four seconds. The system is then in its original state, and Motor 2 can be turned on to cause the poll to rest again the ratchet, and then Motor 1 can be turned on to cause the spider to "climb" back up into its hiding place in the trees. The whole system repeats itself four times, causing Little Miss Muffet to be scared a total of five times.
The construction of Little Miss Muffet was split into two parts. Leo worked on logo program to run the crickets and the spider mechanism. Jennifer was responsible for building the physical device, the eating and the kicking mechanisms, and the casing for the spider mechanism.
The housing and gears for the spider mechanism are made of Lego parts. The rest of the spider mechanism was made from a wooden pinwheel attached to the front of a wooden ratchet. A small piece of aluminum foil and wire was used to create the pinwheel touch sensor. The spider was made from half of a wooden egg with a lead fishing weight in its belly and four black pipe cleaner that extended across the bottom of the spider and trough eight eyes to creates the legs. Little Miss Muffet was made of parts from three different dolls. Her legs are from one doll, her right arm from another, and her body, head and left arm from the third doll. The box, the bench, the tree trunk, and the platform for the spider mechanism are made from quarter inch basswood. The leaves for the tree are made from fake ivy that has wire through the branches to allow it to be molded.
We did not use any particular construction techniques in this project. It was more trial and error. However, we did start with a sketch of an initial design. During the actual design phase, using of Lego parts for the spider mechanism allowed us to try different combinations of gears and pin sizes. It also allowed for the gradual replacement of the Lego parts by more precise wooden parts. The design for the box, the bench, and the tree were just does by visual guessing. Using a wire for the shaft of the eating mechanism allowed for bending and changing or angles.
The design process was fairly simple. There was little wavering from our original idea which made implementation easier.
We were looking for a design that contained as many aspects of the five attributes listed below. We believed that using these attributes as guidelines we could make a success automation. The five attributes were as follows:
1. The automata should be complex enough so people would be interested in the mechanism and the automation itself.
2. The automata should be incremental and/or scalable. i.e. It should be something we would be able to implement in the short time we had, and if possible, expand with any time we had left.
3. The automata should include a variety of materials such as wood, Lego parts, bright colors, and any other objects that would add to the interest and aesthetic appeal of the device.
4. The automata should include computation in a meaningful way. i.e. We wanted something more than producing sounds or having lights blinking. A device that interacted with the user and included some sort of randomness was ideal.
5. The automata should be fun to implement and to demonstrate to other people.
Based on these criteria, Jennifer said she would like to implement Little Miss Muffet, a traditional nursery rhyme recited by children.
The design of the Little Miss Muffet was not linear. We did not have any detailed description of what we wanted to do prior to implementation. We had a nursery rhyme to drive the design a rough sketch describing the main parts of the project (the spider mechanism, the kicking mechanism, the eating mechanism). However, we were learning and deciding how to solve problems along the way.
Fortunately, the use of wood and Lego parts helped a lot in this process. If we were to use more expensive materials, things could not have been modified and replaced as easily. This would have caused the situation to be completely different.
We had three major obstacles to over come. The first was that Lego did not have any type of ratchet. To solve this problem we had Glen help us create one using the laser cutter. The second was getting Little Miss Muffet to eat with a fairly stiff arm. This was solved by trial and error along with mutilation of two doll arms. We tied to use a molded arm that was bent at the elbow, but this caused Little Miss Muffet to never reach her mouth or the bowl. Then we tried a heavy thread as the upper arm and the elbow joint, but this didn't provided any padding to create an upper arm in the clothing and made the arm too floppy. Finally we were able to find a doll arm that was cloth for the arm with a molded had. This allowed us to place a bend at the elbow by using thread, giving the appearance of an actual arm that was not floppy and provided decent movement to the bowl and the mouth. The last obstacle was getting Little Miss Muffet's feet to hang and kick freely. This was solved by trial and error. It was finally decided to attach her legs to her body using wire that had been bent in the shape of a W. By placing each leg at one of the low points in the W, a pivot was created. The length of the W was shorted and lengthened until free movement was achieved.
There are a few things that can be learned from this automata:
1. Provides a good idea of how cranks, shafts, ratchets, and pinwheels can work together to create a system.
2. Provides the bases of how wood, Lego and other materials and be used together.
3. Provides a visual representation of traditional folklore. The automaton is based on a nursery rhyme recited by children.
However, most of the learning that occurs from building automata comes from building the automaton. The builder picks up skill such as the relationship between gear and their sizes, procedures on to use of different tools, properties of the different materials, and knowledge of design.
Ideally, for Little Miss Muffet to be more educational, at least in the constructivist perspective, we would have to allow kids to replace parts of it and add their own features. However, teachers could explore the automaton in different ways. For instance, they can ask kids to write about Little Miss Muffet and other children rhymes that they like.
Most of the mechanism is open for seeing and most of the computational aspects are not hard to deduce. The eating and kicking mechanism are not visible initially. However, one can examine the mechanisms more closely by sliding up the tree trunk. The mechanism for the spider is easy to see from its platform behind the tree. By running the automation one can easily figure out how the spider mechanism works, and what is going to happen next.
The crank shaft used for the eating mechanism can be compared with the Bone Ranger automata created earlier in the semester. The circular motion created by the crank shaft has been changed from the ostrich running into Little Miss Muffet eating, though this was not the inspiration for the mechanism. The spider mechanism was an original design and cannot be compared to any previously seen automations. The automation as a whole can be compared against many artist representations in various children's nursery rhythm books of Little Miss Muffet.
There is an intended response for the automation for two reasons:
The automation simply makes people smile when they see it.
Little Miss Muffet was an automation that was fun to build and fun to demonstrate. The fact that we started on construction early allowed us time to tweak the mechanisms, paint the automation, and add many finishing touches like housing for the crickets and a slide away tree trunk. Given more time we would have been able to replace much of the Lego in the spider mechanism with wood, and we may have been able to get the eating mechanism to reach both the bowl and Little Miss Muffet's mouth. However, overall we are fairly satisfied with the final product.