| |
OBJECTIVE
The objective of this lesson is to introduce the students to how
gears work so they can use them in their final projects. The students
will also be introduced to orthographic and isometric drawings in
this lesson. These two topics will assist them in creating their
final projects as well as documenting their work.
BACKGROUND FOR THE TEACHER
Gears
Gears are used in many mechanical devices. Gears are a simple machine
that can give you a mechanical advantage (the ratio of the force
exerted by a machine to the force applied to it). The components
of any mechanical devices could be broken down into simple machines.
There are six basic simple machines: lever, pulley, wheel and axle,
inclined plane, wedge, and screw. The gear is considered to be within
the wheel and axle category of simple machines. Gears (1) transmit
motion, (2) increase/decrease speed, and (3) increase/decrease torque
(power).
Gears are used in hand-mixers or eggbeaters to
increase the slower rate the user is able to rotate the hand crank
into a very high rate of rotations for the beaters. Without such
assistance, a person couldn’t turn cream into whipped cream.
The gears in your bike can help you to transmit more torque to your
wheels. When you go up a steep hill, you have to shift down to a
larger or “higher gear”. In a “higher gear”,
you have to pedal more, but without as much force. A “higher
gear” is when the chain on the bicycle shifts onto a larger
gear on the rear wheel such that the gear you pedal with is smaller
than the gear connected to the wheel’s axle. This increases
the torque to the wheel.
ORTHOGRAPHIC DRAWINGS
A picture is worth a thousand words. It may be a bit cliché,
but it certainly rings true in the field of engineering. Orthographic
drawings are crucial to communicating ideas, products, solutions,
etc. Drawings can effectively communicate the design of a complex
system or product. For example, an engineer could design something
and then send the drawings to a machine shop to construct a prototype,
to marketing to decide on the colors and logo placement, to purchasing
to purchase the materials, and to their boss to get a pat on the
back (or approval).
Engineers most commonly use orthographic drawings to communicate
their designs. An orthographic view of an object is just one side
of it. There are six orthographic views of an object. Imagine putting
an object inside a box. Then looking at each side of the object
through the six sides of the box. The different views would include
the front view, the top view, the rear view, the bottom view, the
left side view, and the right side view.
STANDARDS ADDRESSED
2.2 Describe different ways in which a problem can be represented,
e.g., sketches, diagrams, graphic organizers, and lists.
6.3 Identify and describe three subsystems of a transportation vehicle
or device, i.e., structural, propulsion, guidance, suspension, control,
and support.
MATERIALS
Lego Team Challenge kit: 1 per group
Foldable
box for projections demo
Gearbox
drawing handout: 1 per group
Client
letter: 1 per group
SETUP
Photocopy gearbox drawing handouts and distribute one set to each
group
GUIDING THE ACTIVITY
“One of your clients who bought one of your motorized wheelchairs
has sent a letter saying that the wheelchair is unable to make it
up steep inclines/hills. They also thought the wheelchair moves
much too fast to be safe.”
“How might you be able solve this problem for your customer?”
If someone mentions gears, probe intow how gears would help. If
no one mentions gears ask:
“Does anyone know what gears can be used for?”
If someone mentions a bicycle (if no one mentions it bring it up),
discuss further with the class how gears on a bicycle help you go
up/down a hill.
“Today you are going to use gears to make a wheelchair that
will move slow, but also have the power to go up a ramp.”
“In a minute you will receive an orthographic drawing of a
gear train. You will use this to construct the gear train and then
you will have to find a way to construct it into a wheelchair.”
“I just used a new word, ORTHOGRAPHIC drawing. Does anyone
know what that is?”
Hold up the gearbox drawing handout.
“This is an orthographic drawing of the gearbox you will be
building.”
“What do you think these different pictures represent?”
Point to the three orthographic projections on the handout.
Demonstrate foldable cube representation of projections
“Why do you think engineers would make drawings of objects
or designs?”
Discuss with students
Pass out envelopes with handouts and distribute the LEGO kits
“Read the challenge and go ahead and build!”
“Don’t forget after you build the gear train you will
have to connect it to a motor and the RCX.” (Note: it may
be easiest to build the gear train and motor assembly separately
from the RCX and then just connect the motor to the RCX with a long
wire. This way the students have a little more freedom to design
a wheelchair around the gearbox.)
Walk around and assist students with any questions they have. For
most of the questions they have regarding building the gearbox,
you should direct them to look closely at the drawings. If the drawing
doesn’t answer the question, have them inquire further.
Give them time countdowns every 5 minutes. Figure the time remaining
based on leaving you 20 minutes to wrap up the lesson and end.
Remind them to attach the gear train to a motor, wheels and the
RCX.
“OK wrap it up!”
Have the students put everything back into their kits except for
their design.
Have the students come to the front of the room as a group and test
their design on the ramp. For designs that don’t work, have
them discuss why they think it didn’t work.
DISCUSSION
Direct the students to look at their Engineering Design Process
handout. Ask them:
“What steps of the Engineering Design process did you all
work with today? ”
Take answers and discuss how/why they used that step of the process.
“How do you see you could use what we learned today to help
you with your final design project (making an assistive device)?”
Discuss
END
|
]