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And a specialized wheel called a gear.
Let’s have a crash course on gears so we can talk more meaningfully about mechanical advantage and torque.
I can’t wait to talk about torque.
But, first? Gears!
Types of Gears
Gears come in a variety of sizes with curved or straight teeth which occur in a variety of angles. They connect with other gears to transfer motion and force in machines.
Different gears have specific jobs depending on what you need them to do.
Gears can change the speed, torque, and direction of a power source. It’s what they do.
- Spur Gears– Or straight cut gears are the simplest type of gear. The teeth are straight and parallel to the axis of rotation.
- Bevel Gears– Designed to meet at 90* with another bevel gear. These gears are conically shaped allowing them to work at angles.
- Crown Gears– A type of bevel gear in which the teeth project at right angles to the plane of the wheel. They are typically meshed to other bevel gears though sometimes they mesh with spur gears.
- Worm Gears– These gears resemble screws. The worm is meshed with another gear. It’s an easy way to get a high torque, low speed gear ratio. The worm gear is the drive gear and it’s used when you want to hold load so that it can’t go back the other direction. More on gear ratios in a moment!
Where Do you Find Gears?
Maybe we could ask, where don’t you find gears? Chances are, if a machine has a moving part it could have a gear.
I can think of a few examples. Can you think of more?
- car engines
Find out How Gears Do Their Work
Let’s try a few examples to see how gears do work. Make sure you have the following on hand:
- Technic LEGOS– These are the LEGOS which are mostly beams and pegs. If your student has Star Wars or Bionicle themed LEGOS, they have technic pieces.
- Technic Gears– Our collection is from our Mindstorms kits, but gears are found in any LEGO set requiring non-brick construction. Go ask your LEGO fan- they’ll know!
- Three spur gears of the same size– for the first demonstration
- Three spur gears of various sizes– for the second demonstration
Set up your first demo like the picture above with three spur gears of the same size. Note that not all the gears size are able to sit on a beam and mesh like the ones pictured. These are 16 teeth gears and they work well.
- Rotate the outer gear– notice the direction each gear is going. What do you see about the direction of gears next to one another?
- Count the teeth– on each gear. If you are using technic gears, the larger gears will have the number on the gear. The number of teeth is the circumference of the gear. That will be important later on.
- Look at the gear speed– are the gears moving at the same rate? Another way to ask this is do they have the same number of rotations when you move them?
Gears which are the same size will move at the same rate and gears next to each other move in the opposite direction.
For the second demonstration, set up three different sized gears next to one another on the same beam. Then try these steps:
- Spin a gear– notice what direction the other gears are going. What do you see?
- Count the teeth in each gear– again, if you are using Technic gears, the number of teeth is stamped onto the gear if it is a large gear.
- Observe the rotations of each gear– do they move at the same rate? Does one gear rotate more than the other?
Resources for Learning about Gears
This is a simple demonstration of how gears interact with one another and what that means for mechanical advantage. If you need to get the Technic gears or want more information on how gears work, enjoy these titles.
- LEGO Crazy Contraptions Kit– This is a kit with Technic pieces for building all sort of little machines. It will contain what you need for these exercises.
- The Way Things Work Now– This book, by David Macaulay, has wonderful drawings and explanations about gears in addition to lots of machines which use them.
- Gears the Basics– a YouTube video that shows how to find the gear ratio between a large and small gear.
The next three books are photographic books showing how to build all sorts of machines and contraptions with Technic LEGO pieces. We use them with our students to teach them how to make a sturdy structure for use in robotics. We highly recommend them. If you are doing a unit on simple machines, Technic pieces are well suited for the task.
- LEGO Technic Idea Book Simple Machines
- LEGO Technic Idea Book Wheeled Wonders
- LEGO Technic Idea Book Fantastic Contraptions
Special things happen when you combine different sized gears to perform work. The ratio of the number of teeth from one gear to another allows you to choose between speed and torque.
Torque is our next lesson and we’ll be using Technic LEGOS for that too.