Unit 2 - Gears
How can I use gears to change speed, torque, or direction of rotation?
What Am I Learning and Why Learn This Now?
Time for your "Baby" bot to start moving around! Most robots use gears to increase speed or torque, or to change the direction of a motion. In this unit, you'll be investigating how different gear combinations work. (This unit is about rotational motion. In a later unit, you'll investigate mechanisms for changing rotary motion to linear motion or vice versa.)
By the end of this unit, you will have "met" competency 4, and you will have a summative grade for your engineering journal on competency 1.
Robotics Learning Project: Hill Climb (or Tractor Pull)
Create a Hill Climb bot. It needs to make it up the defined "hill" as fast as possible; the "hill" is usually a board placed at a given angle.
Alternatively, you could create a Tractor Pull bot that is able to pull the most mass possible across the given "course." (The tractor pull "course" is usually a specific floor tile in the room or marked distance on a flat board. The "sled" for the mass must have a flat bottom without wheels.)
For this unit, the "robot" just has to be a machine you can turn on & off. In the next unit, you will program your machine to respond to other inputs.
Minimum Hill Climb / Tractor Bot Expectations
Robot:
Robot climbs the defined "hill" or pulls at least 500 grams in the sled (at least twice in every three tries).
Engineering Journal:
Entries for every section
Initial brainstorm sketches include at least three structures and at least three distinct gearing possibilities (ie, worm, compound, simple... not just one setup with three different ratios)
Parts Analysis has about three system parts (one of which may be the simple "program")
Test-Result-Change cycle includes at least four different gearing combinations and at least four different tread, mass or mass distribution tests. Results include TIMES if the robot climbed the hill.
How to Navigate this Unit:
KNOW YOUR GOAL: READ the competency 4 rubric. Ask for clarification of expectations as needed.
PLAN and LEARN: Investigate gears and gear ratios. You can schedule some direct instruction, or use Internet resources. Check in with your teacher as you go! ( http://auto.howstuffworks.com/gears.htm is a great place to start. If you want something more like a textbook, try the VEX Robotics unit on gearing.)
As you learn, record your notes and questions in your engineering journal, in a "notebook" format. Call the journal "Gearing."
Build some LEGO gear trains and count the number of rotations of the driver vs the driven gear. Record your observations in your engineering journal.
Vocabulary words you should understand:
Driver / Driven / Idler Gears; Axle
Simple vs Compound Gear Trains
Gear Ratio; Mechanical Advantage; RPM
Types of gears: Pinion, Crown, Rack, Worm
LEARN: Construct a 10:1 compound LEGO gear train, and document how you can calculate the gear ratio based on the number of teeth on the gears. Be sure you include a photo or LEGO CAD diagram of the gear assembly. Be sure to keep the gear assembly to show your teacher at your formal check-in.
LEARN: Construct gear assemblies that use each of the following: worm gear, crown gear, gear chain (you could do a friction wheel assembly instead). Be sure to document assembly, observations of how they work, and how to calculate the mechanical advantage/gear ratio. This means PHOTOS, not just words on the page.
DEMONSTRATE READINESS: Schedule a formal check-in with your teacher to show that you are ready to begin your Hill Climb (or Tractor Pull) bot. (see #2-4)
LEARN: Work with your teacher to set the specifics for your bot's task. Complete your bot, remembering to document your process in your engineering journal. Be sure to check-in with the teacher AS you work, especially right before you begin your test-result-change cycles. Formally check-in with your teacher at least twice BEFORE you complete the bot.
DEMONSTRATE READINESS: When you have completed your hill climb bot and feel you meet the requirements for competency 4, schedule a formal conference with your teacher. At the conference, you will demonstrate your robot, answer teacher questions about your project, and turn in your engineering journal.
ASSESS: If your teacher agrees that you are ready, schedule a time to take your gearing exam. Your gearing exam will require you to calculate the gear ratio for diagrammed gear assemblies, calculate the RPM / torque of the driver or driven gear given RPM or torque of the other gear, and design/construct gear assemblies from given gears to achieve a specified ratio.
Resources:
Be sure to check the resources folder for notes on the structure of your engineering journal and other resources on 2 - GEARS.