Transcript Lesson 06 - STEM Learning

Project Overview
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Introduction
Frame Build
Motion
Power
Control
Sensors
Advanced Sensors
Open design challenges
Project evaluation
LESSON 06
LESSON 06 STARTER
Sensor exploration Quick task:
In groups, discuss each sensor and try to
decide which description card matches which
sensor.
Bumper Switch
Limit Switch
Line Tracker
Ultrasonic Range Finder
Optical Shaft Encoder
Light Sensor
INTRODUCING SENSORS
Learning objective: Develop an understanding of how inputs such as sensors help robotics to function.
Work with a range of sensors to achieve a desired level of control and functionality.
Consider – In the scenario shown right, the robot
begins in the start zone (red) and needs to navigate
towards an object, then needs to stop and change
direction, continue forward, stop again, change
direction, and move forward once more to navigate to
the end zone (blue)
With human interaction, we could use a controller to
achieve this. But robots are not just human operated,
but autonomous as well.
Using sensors, we can achieve this outcome.
INTRODUCING SENSORS
Solving this scenario
It is actually very easy to achieve this goal, and in many different ways. Here is the best way…
Ultrasonic range finder method
1. Fit an ultrasonic range finder to the front of the robot.
2. Create a programme (code) that informs the range finder that once it receives a signal back
from an obstacle close to it, the robot will stop.
3. Once stopped, the code can instruct motors to move in opposite directions so that you
achieve a zero radius turn (see right).
4. Repeat this code but instructing the robot to stop and rotate left instead.
5. Launch the robot autonomously and watch it drive!
Easy!!!
INTRODUCING SENSORS
Analog vs Digital
Among sensors, there are two main electrical “languages”
spoken: Analog and Digital. You’ll have seen these on your
cortex.
Analog sensors communicate with the Microcontroller by
sending it an electrical voltage along a wire. By measuring where
the sent voltage falls between zero and a maximum voltage, the
Microcontroller can interpret the voltage as a numeric value for
processing. Analog sensors can therefore detect and
communicate any value in a range of numbers.
A line follower sensor, for instance, can communicate how
bright a surface is by sending a zero voltage for total darkness,
sending maximum voltage for a very bright light, or sending an
in-between voltage for any other amount of light, depending on
exactly how bright the surface is.
INTRODUCING SENSORS
Analog vs. Digital
A weakness of analog sensors is that it is very difficult to send and maintain an
exact, specific voltage on a wire in a live circuit. Digital sensors, on the other
hand, can send signals very reliably, even in electrically “noisy” conditions.
However, they do so by sacrificing the ability to indicate the entire range of
values. Digital signals can only have one of two values: either HIGH or LOW.
A digital sensor sends a voltage, just like an analog sensor, but instead of sending
a voltage between zero and maximum, it will send only zero OR maximum. If the
Microcontroller detects a voltage that is above a guaranteed Low or below a
guaranteed High the results cannot be determined, it can be reported as a High
or Low. It may seem like a terrible loss to only be able to indicate two values
rather than a whole range, but in many situations, this is preferable.
For instance, the Bumper Switch Sensor is a digital sensor. Since the purpose of the
sensor is to detect whether something is pushing the bumper in or not, two values are
all it needs to do its job.
INTRODUCING SENSORS
“Bump” – this robot has been fitted with two bump sensors at the front and back of the robot.
They are mounted onto two 3 inch stand-offs and wires are slotted into the cortex.
Task: Propose what you think Bump does? Discuss at your table and write down your answer.
Bumper Switch Sensor
Signal: Digital
Description: The bumper sensor
is a physical switch.
It tells the robot whether the
bumper on the front of the
sensor is being pushed in or
not.
Technical Info:
Type: SPST switch
(“Single Pole, Single Throw”)
configured for Normally Open behaviour.
INTRODUCING SENSORS
“Switch” – this robot has been fitted with two limit switches to the underneath of the robot chassis.
These sensors brush the surface and trigger when pressed.
Task: Propose what you think Switch does? Discuss at your table and write down your answer.
Limit Switch Sensor
Signal: Digital
Description: The limit switch
sensor is a physical switch. It
can tell the robot whether the
sensor’s metal arm is being
pushed down or not.
Technical Info:
Type: SPDT micro switch,
configured for SPST
Normally Open behaviour.
INTRODUCING SENSORS
“Line-o” – this robot has been fitted with a pair of line sensors under the front of the
robot chassis. They lie side by side and will pick up changes in the surface colour and
adjust the movement of the robot accordingly.
Task: Propose what you think Line-o does? Discuss at your table and write down your
answer.
INTRODUCING SENSORS
“Sonic” – this robot has been fitted with two ultrasonic range finders, one at the front and one at the rear. Again they
are fitted using 3 inch stand-offs, but this time wires from the sensor fit into the cortex labelled input and output.
Task: Propose what you think Sonic does? Discuss at your table and write down your answer.
INTRODUCING SENSORS
“Buzz-Light” – this robot has been fitted with a light sensor, on the front of the robot. Again it is fitted using a 3 inch
stand-off, and a single input is plugged into the digital port.
Task: Propose what you think Buzz-Light does? Discuss at your table and write down your answer.
INTRODUCING SENSORS
Design Challenge – design a Tumbler (on paper) that can do one of the
following challenges. To do this challenge successfully you need to draw the
sensors carrying out the task on the robot, including where they will be
positioned to be triggered or to receive information.
Challenge 1
A robot that can drive down a tunnel until it hits a blockage, then return back to
the entrance of the tunnel, provide a measurement.
Challenge 2
A robot that can detect gaps in very long (miles) animal zoo perimeter fence,
stop at the opening, and sound an alarm to attract the zoo keepers to repair it.
Challenge 3
A robot that when loaded up with lit fireworks, can drive quickly to safe
distance, stop, then let the fireworks go off, then return to the owner once the
fireworks have stopped.
Challenge 1
Challenge 2
Challenge 3
CONSIDER YOUR SENSORS
Which sensors?
Here is a new scenario for you to consider.
“The robot needs to travel across into the blue zone.
There are buried landmines which will go off if driven
over too fast in its way. It needs to get to the blue zone
in the quickest time possible.”
First of all, what does the robot need to do to stay in one piece?
Answer: It needs to drive slowly over the land mines
Which sensor(s) are appropriate?
What information would the sensors take in?
How would the robot change its output?
Answer: The limit sensors underneath would trigger by the landmine, which could single to the cortex to reduce the
motor speed until the switch turns off again. The sensors would pick up the raised surface off the ground. The output
would be slower motor drive.
LESSON 06 PLENARY
As a class, let us consider the following questions?
A. What do sensors do? (describe in detail)
B. What can sensors not do for a robot?
C. How do all sensors work?
D. In the following areas, consider what sensors might be used for:
- nuclear power plant
- distribution of products across the UK using automation
- the study of animals
- sea rescue helicoptors
- the farming industry
- the military
- in the kitchen
SUMMARY
Learning objective: Develop an understanding of how inputs such as sensors help robotics to function.
Work with a range of sensors to achieve a desired level of control and functionality.
Today you have:
 Explored different types of sensors and how they create different forms of input.
 Worked with different sensors to prepare for control of a robot.
 Developed a wider knowledge of sensors and how they can be used in other contexts beyond
robotics.