Warm Up

1. What is the difference between Automation and Robotics?

2. What is a robot?

3. What are some of the types of robots we have studied so far?

4. What are the 4 D’s robots are used for?

Review

1. What is the difference between Automation and Robotics?

Automation involves a mechanical device that can imitate the actions of people or animals.

Robotics involves the design, construction, and operation of a robot.

2. What is a robot?

A robot is a machine that performs complicated tasks and is guided by automatic controls.

3. What are some of the types of robots we have studied so far?

Industrial

Medical

Assistive

Exploratory

Household

4. What are the 4 D’s robots are used for?

Robots are used to perform dirty, dull, or dangerous tasks, or to help someone with a disability.

Section 2.2: Mechanical Systems

• In this section we will:– Use ratios to solve mechanical advantage problems. – Use numerical and algebraic expressions and

equations to solve real-life problems, such as gear ratios.

– Use the characteristics of a specific mechanism to evaluate its purpose and applications.

– Apply knowledge of mechanisms to solve a unique problem for speed, torque, force, or type of motion.

Observing Mechanisms

Introduction• Think about a bicycle, an eggbeater, a sewing machine, a hand cranked drill, and a workshop vice.

• What do they have in common?

• All of them have at least one mechanism that provides movement.

• Some of the devices use human effort, while others use electricity.

• If the devices were taken apart, you would find a series of gears that redirect the applied force so they can accomplish their tasks.

• Gears come in all sizes. – Small gears are found in mechanical watches.– Very large gears are found in cranes that are

used to raise large bridge sections into place.

What is a Mechanism?A mechanism is the part of a machine which contains two or more pieces arranged so that the motion of one compels the motion of the others.

– A system of parts working together in a machine

Mechanisms

Generally used to:• Change the direction of

movement• Change the type of

movement• Change the speed of

movement• Change the amount of

torque or force available to do work

Mechanism Movement

Rotary

LinearReciprocating

Oscillating

Rotary Motion

Motion is around in a circle

Oscillating Motion

• To swing back and forth at a regular rate.

Linear Motion

• To move straight in one direction.

Reciprocating Motion

• Moving back and forth in a straight line.

In this class we will often use gear based mechanisms

• Gears come in all sizes. – Small gears are found in mechanical watches.– Very large gears are found in cranes that are

used to raise large bridge sections into place.

Gear Train• A gear train is a mechanism used for transmitting

rotary motion and torque. Gears transmit rotary motion through interlocking teeth.

• A gear train is made when two or more gears are meshed.– Meshed gears always turn in opposite directions.

Cannon: 1850’s Wool Mill: 1840’s

Gear Train

Energy input causes the drive gear to move

Energy is transferred to the driven gear called the output gear

Drive Gear, Driven Gear

• The drive gear is the input gear; the driven gear is the output gear.

Gear Ratio

1. Gear ratios compare the input drive gear to the output driven gear. The input gear transfers the energy to the output gear.

2. If the input (drive) completes one revolutions and for every two completed by the output (driven), then the gear ratio is 1:2.

DrivenDriven

Cra

nkC

rank

DriveDrive

Gear Ratio• Variables to know• n = number of teeth• d = diameter• ** Subscripts in and out are used to distinguish between

gears **

DrivenDriven

DriveDrive Nin: Nout 36:24 3:2  Din: Dout 10:5 2:1

Nin: Nout 36:24 3:2 Din: Dout 10:5 2:1

Calculating Gear Ratios# Teeth Input gear

# Teeth output gear

Gear

RatioExplanation

8 4040:8

or 5:1

The input (drive) gear must turn 5 times to move the output (driven) gear once. Torque increases.

36 4

6 48

16 20

Force & Torque

• A force is a push or a pull in a straight line.

• Torque is a push or pull in a circular direction.

Torque and Speed

• There is an inverse relationship between torque and speed:

-more torque = less speed

-more speed = less torque

ExampleA ten-speed bicycle has ten different gear selections. When you pedal up a hill, you use a gear train that provides more torque (turning force) but, in doing so, less speed. When you pedal on flat land, you use a gear train that provides more speed, but in doing so, less torque within the gear train. When pedaling up a hill, we trade off speed for torque. In other words a reduction in speed is a trade-off to increase torque and make pedaling easier.

Mechanical Advantage

• As the size of the driven gear decreases in relation to the size of the drive gear, output speed increases.

• •As the size of the driven gear increases in relation to the size of the drive gear, output torque increases.

Output BOutput BInput AInput A

This means: 

• bigger gear=more Torque

• smaller gear= more speed

• Which gear train provides more torque?• Which gear train provides more speed?• Which would you use to ride up a hill on

your bike?

Driven Gear

• To increase torque what happens to the size of the driven gear?

• To increase speed what happens to the driven gear?

List 5 different mechanisms in the Rube Goldberg picture above and predict the purpose of each. Does the mechanism change speed, force, torque, direction, or type of movement? Put a number on the picture to indicate location.