gears

Gears – Two toothed wheels fit together either directly or through a chain or belt so one wheel will turn the other. Some gears may have a screw or a toothed shaft in place of one of the wheels. A gear may also be a combination of toothed wheels that produces a certain speed (such as a bicycle’s top gear which makes the bike go fast, and the low gear for slow speed.)

• Mechanical gears in Nature – gear mechanisms previously thought to be solely man-made have an evolutionary precedent. Scientists say this is the “first observation of mechanical gearing in a biological structure”. Discovered in 2013.

Gears are wonderful things that are used in many different ways in many different industries. See what happens when gears are rotated and how their size and number of teeth affects the outcome of rotation. Enjoy this great gears introduction video (10:59) that aims to deliver the basics of ratio, rotation, mechanical advantage and more.

Using gears to change direction and rate of motion

• bevel gear – used to change the axis of rotational motion. By using gears of differing numbers of teeth the speed of rotation can also be changed.
• cardan gear (animation) – a way of converting rotary motion into straight line motion.
• rack and pinion (animation) – The rack is the flat, toothed part, the pinion is the gear. Rack and pinion can convert from rotary to linear of from linear to rotary. Rack and pinions are commonly used in the steering system of cars to convert the rotary motion of the steering wheel to the side to side motion in the wheels.
• worm gear (animation) – the axis of rotation is turned by 90 degrees. Unlike ordinary gears, the motion is not reversible, a worm can drive a gear to reduce speed but a gear cannot drive a worm to increase it.

Some amazing examples of gears in use

• Clock
• Automobile
• Drill
• These little LEGO walking bots seem to have great personality. The gears in each one determine the way they move. The particular motions and speed create a pattern of movement that we interpret as a personality.
• The Writer Automaton (video) – A 240 year old doll that can write, a clockwork creation by Pierre Jaquet-Droz – using only mechanical cams and gears driven by springs (circa 1770)

Gears and Gear Ratios
Bicycle gearing is a great introduction to the subject or gearing and gear ratios. They are exposed and big. There are plenty of cyclists, bike shops, books, magazines and [/web%20sites web sites] that provide information.

• Multi-speed gears allow you to climb hills comfortably that might force you to stand up and “pump” or even get off and push if you were riding a one-speed. They also allow you to go faster downhill or with the wind at your back.
• “Higher” gears put more resistance on the pedals. If you select a gear that is too high for the conditions, it will force you into a slower cadence. Pedaling slower than your ideal cadence is wasteful of energy. You also run a higher risk of muscle strains and joint damage, particularly to the knees and hips.
• “Lower” gears make the pedals easy to turn, so it becomes easier to spin to a fast cadence. Pedaling faster than your ideal cadence can allow you to generate an extra burst of speed, but you will tire yourself out too soon if you try to maintain an excessively fast cadence.
• Gear ratios – diagram shows several different gear ratios that can be used on this robot, depending on the need. The size of each gear and the number of teeth on each determine the power and speed differences.

Determining the appropriate personalized gearing follows the steps in the [/Engineering%20Design%20Process Engineering Design Process].

• Ask – How would having gears make the biking experience better? What’s wrong with bikes without gears?
• Imagine – What are some ways to improve bike performance? How can the bike be modified to make it easier to match the effort of pushing the petals to the speed of the bike?
• Design, Build – How many different gears are required? How many different gear ratios are enough for most bicyclists? How are the bike gears arranged? How are the gears manufactured?
• Improve – What changes can be made for bikers with special needs? For cycle racing like the Tour de France, the bikes are custom made for each racer. Races even have special bikes for different parts of this long race. A bike that is good for riding up steep mountain roads is not very good for sprinting across flat countryside.

That’s engineering

• alloy – a uniform mixture made up of two or more chemical elements, at least one is a metal. An alloy has properties different from the metals it is made of. Most alloys are made by melting the metals, mixing them while they are liquid to form a solution, then leaving them to cool and turn solid again.
• worm gear (animation) – used to reduce speed. For each complete turn of the worm shaft the gear shaft advances only one tooth of the gear. As the speed is reduced the power to the drive increases correspondingly. Worm gears are a compact, efficient means of substantially decreasing speed and increasing power.

Engineering ideas

• mechanical advantage, gear, gear ratio, cam, deraillieur, force, motion, alloy, plastic, speed, power

Do it
Here are some challenges for you to work on…

• gear ratios – show what you learned about gear ratios. Include types of machines that use them and how they work
• Design an automated hand-stamping machine – design, build, and test an automated hand-stamping machine by borrowing concepts from existing designs and modifying them to fit your needs. Gain experience using gears and pulleys to explore concepts such as mechanical advantage, changing from rotary to linear motion, and altering timing in a machine. Modify your design so that the stamp leaves a clearer image, to adjust the stamping mechanism to different hand sizes, or to allow more time to slide a hand underneath before the next stamping.