Structures and Mechanics with fischertechnik The Marvelous Mixer – Level 3

1. Structures and Mechanics with fischertechnik The Marvelous Mixer – Level 3

2. What You’ll Learn… • The history of the electric mixer • How to establish design specifications for a machine • The mechanics of planetary gears and how they function • How bevel gears work • How kitchen mixers use complex gearing to perform a difficult task Stuff You’ll Need… • Fischertechnik Profi Mechanic + Static Set • Mechanic + Static Activity Booklet • Mechanic + Static Assembly Instruction • Digital camera

3. ePortfolio Suggestions… • Before you begin the activities in this Learning Launcher, write down anything you may already know about electric mixers and how they work. • List three interesting things you learned from the What You Should Know… section. • Keep a glossary of new words you learn. Pay particular attention to the bold, italicized words you find. • Include your list of stand mixer design specifications in your project planner. • Take pictures of your fischertechnik models and label each of the parts. • Take a picture of a real stand mixer or find one on the internet and show how it is similar to, or different from, your model. • Answer each of the questions in the Activity Booklet. Record your observations in your Project Planner. • Create a narrated video demonstrating how your stand mixer works.

4. What You Should Know… Before beginning the activities in this Learning Launcher • You should already be very familiar with the fischertechnik construction system. • You should be familiar with the different types of simple machines and understand the basic principles of each. • You should understand how different kinds of gear systems work and be able to calculate gear ratios. If you are not familiar with any of these concepts, you should review the What You Should Know… section of the Level 1 Machines and Gears Learning Launcher.

5. What You Should Know… The Marvelous Mixer… We invent machines to make our lives easier. Machines help us perform many jobs that are difficult, dangerous, time consuming, or sometimes, just plain boring. Mixing cooking ingredients is a task that often fits in the last two categories. It is tedious work that requires considerable patience. And a strong arm! But how often do we stop to think about how these machines work?

6. What You Should Know… The History of the Electric Mixer… Like many machines, the history of the electric mixer runs deep. Even prehistoric man had specialized tools to help with food preparation. Over 3,000 years ago, Southwest America’s ancestral Puebloans used rocks called mano and metate to grind seeds and grain. They would then add water and mix the grain into tortillas to cook on a stone over a fire. The first electric mixer was invented by Herbert Johnson in 1908. Johnson was an engineer working for the Hobart Manufacturing Company, an Ohio company that made electric coffee grinders and meat choppers. His inspiration came from observing a baker use a metal spoon to mix bread dough. He knew that there must a better way. His machine became known as the KitchenAid, after a company executive’s wife supposedly commented, “I don’t care what you call it, all I know is it’s the best kitchen aid I’ve ever had”. KitchenAid remains a leading brand of mixer today!

7. What You Should Know… The History of the Electric Mixer… The original electric mixers were stand mixers. Hand-held electric mixers weren’t manufactured until 1952. Unlike today though, stand mixers weren’t commonly found in the home. When the U.S. entered World War I, the company’s early production was devoted to supporting the war effort. Industrial-size KitchenAid mixers became standard equipment on all U.S. naval vessels. But even after the company entered the residential market in 1919, few homes could afford them. The original countertop mixer sold for $189.50. That’s the equivalent of over $2,000 in today’s dollars! By comparison, you can buy countertop stand mixers today for under $100! How many machines have gotten cheaper over the last 90+ years?

8. What You Should Know… In this Learning Launcher, we will examine the stand mixer and the complex gear system that makes it work. But before we begin to explore it’s mechanics, take a moment and think about the form and function of an electric stand mixer. What does it need to do? What does it need to look like? These requirements are called design specifications and are a critical part of the engineering design process. Engineering design is really just a specialized form of problem solving. When engineers design a machine, they start out with a detailed description of the problem they are trying to solve. In addition to how they need the machine to perform, they need to think about things like size, weight, reliability, cost, etc. Write down as many design specifications for a stand mixer as you can think of in your project planner. List at least four before continuing to the next slide.

9. What You Should Know… The Marvelous Mixer… What were your design specifications? Here are some you may have considered: • A stand mixer must be able to mix ingredients thoroughly. It must be able to mix ingredients evenly in all areas of the mixing bowl. • A stand mixer must be powerful enough to mix thick substances like bread dough. It should also be fast enough to mix thin substances and perform its job quickly. • Mixing blades must be removable for cleaning. They must also be interchangeable so you can use different types for different mixing jobs. • It will need a locking device so the mixing bowl does not move during operation. • It must be reliable enough to perform repetitive mechanical motions over a long period of time without failing. • It must be big enough to mix ingredients for most common household cooking tasks, but it shouldn’t take up too much counter space. • It must be relatively inexpensive so most homes can afford them. • It must be easy to operate. Whew! That’s a lot to ask of a machine!!

10. What You Should Know… The Marvelous Mixer… Let’s explore that first design specification in more depth: A stand mixer must be able to mix ingredients thoroughly. It must be able to mix ingredients evenly in all areas of the mixing bowl. It would be fairly easy to use a standard toothed gear pair to transfer motion from the electric motor to the mixing blade. But that would only produce a simple rotational motion; the mixing blades would travel continuously along the same path. That wouldn’t get the job done! If we were designing a hand-held electric mixer, we could expect the cook to introduce a more complex stirring path simply by moving the mixer around the bowl. But our stand mixer must be able to do the job automatically.

11. What You Should Know… The Marvelous Mixer… A good solution to our design problem would be to figure out a way for the mixing blades to revolve around the bowl while they rotate. Oh, and one more thing: if the direction of rotation (spin), is opposite to the direction of revolution (the path around the bowl), it would do a much better job of mixing. That’s a big design challenge. Fortunately, there’s a special type of gear that’s perfect for this job! It’s called a planetary gear. Direction of Revolution Direction of Rotation

12. What You Should Know… Planetary Gears… Planetary gears, also called epicyclic gears, are used in electric mixers, automatic transmissions and pencil sharpeners. Like many gear systems, their purpose is to transform rotational force to produce either more torque (turning force) or more speed. Unlike typical toothed gear systems, planetary gears travel around the inside of an outer gear called a hollow wheel (also called a ring gear or annulus) which may be fixed or rotating. Planetary gears consist of a central sun gear, planet gears and a hollow wheel. Each gear type can drive the system (provide the turning force), be driven (respond to the turning force) and be fixed or rotating. The planet gears are typically mounted on a planet carrier (not shown in this illustration) which can also be fixed or rotating. In this illustration, the directional arrows imply that the planet gears are fixed and the hollow wheel rotates. In our stand mixer, it is the opposite – the hollow ring is fixed and the planet gears revolve. Can you figure out which direction they would go in this drawing if the hollow wheel is fixed? Pencil Sharpener Planet Gears Sun Gear Don’t worry if the planetary gear doesn’t make much sense to you yet. It’s REALLY complex! You’ll understand it better once you’ve built one yourself! Hollow Wheel

13. Do It! Building a Planetary Gear… The planetary gear is a critical functional element of a stand mixer. So let’s build one first to see how it works. The planetary gear is found on page 28 of the Activity Booklet. Assembly instructions are on page 29 of the Assembly Instruction book. Planetary Gear Activity Booklet Assembly Instruction

14. Do It! Building a Bevel Gear… A bevel gear is a simple gear pair that changes the direction of rotation 90°. We’ll need one for our stand mixer. You can find plans for a bevel gear unit on page 29 of the Activity Booklet. Assembly instructions can be found on page 32 of the Assembly Instruction book. Bevel Gear If you’re pressed for time and feel like you understand how bevel gears work without building the model, you can choose to skip this step. Assembly Instruction Activity Booklet

15. Do It! Building the Stand Mixer… Now you’re ready to build the stand mixer. It’s called the kitchen appliance in the Activity Booklet and can be found on page 29. Assembly instructions can be found on page 33 of the Assembly Instruction book. Fischertechnik says that this project is for “real pros” so take your time and use the assembly instructions whenever needed. Assembly Instruction Activity Booklet Stand Mixer (Kitchen Appliance)

16. According to your fischertechnik Activity Booklet, you can actually use your stand mixer to mix a cup of ingredients. Be sure to ask your Facilitator first! Can you calculate the gear ratio of your stand mixer? Go online to learn more about Herbert Johnson and the invention of the stand mixer. Try building some of the other structures in the Mechanic + Static Assembly Instruction book. Or design one of your own. Try building one of the structural devices in the Mechanic + Static Assembly Instruction book. Go online and search for “fischertechnik projects”. Check out some of the amazing things people have built using this sophisticated modeling system. Extend Yourself…