ROBOTC Software
EV3 Robot
Workshop
Lawrence Technological University
Course Overview
• 2015 Robofest competition RoboGolf
• SPbot introduction
• Using the SPbot to solve the RoboGolf
challenge
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2016 Robofest competition
•
•
Video overview
– My Youtube Channel
– This channel is not complete,
but will have videos about
using RobotC.
Key tasks
– Find the edge of the table
– Follow the edge of the table
– Find a putting green
– Find the golf ball
– Aim for the hole
– Mathematics to locate the center hole
– Rotate the robot to putt
– Putt the golf ball
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2016 Robofest competition
• Please note that putting the golf balls is
beyond the scope of this workshop
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LEGO EV3 robot used – SPbot
Right Motor: C
Touch Sensor
EV3 Computer
Sonar Sensor
Color Sensor 1
Left Motor: B
Color Sensor 2
Remember the connections!
• Left Motor connects to B
• Right Motor connects to C
– If your motors are upside down forward will be
backwards in your program
•
•
•
•
Color sensor 1 connects to port no. 1
Color sensor 2 connects to port no. 2
Touch sensor connects to port no. 3
Sonar sensor connects to port no. 4
Please note that the retail version of EV3 uses an infrared sensor, not a sonar sensor.
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ROBOTC Versions Used
• ROBOTC Version 4.52
• Build Date Dec 7, 2015
• PowerPoint and all example programs are
available at robofest.net under Tech Resources
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Setting Up The ROBOTC Environment
• Opening the source
codes files for the
workshop will assist in
setting up the ROBOTC
environment
• Once the source files are
loaded the EV3 motors
and sensors should be
assigned
Setting Up The ROBOTC Environment
• The first step in using ROBOTC is connecting to
your EV3 robot
– Robot -> LEGO Brick -> Communication Link Setup
– Select your EV3
– Hit the Close button
Setting Up The ROBOTC Environment
• The first time you use an EV3 robot with
ROBOTC, you need to download the ROBOTC
kernel
– Robot -> Download EV3 Linux Kernel -> Standard
Kernel
Brick Overview
Setting Up The ROBOTC Environment
Under Robot Menu
Compiler Target
• Physical Robot
Platform Type
• LEGO Mindstroms EV3
• Uncheck Natural Language
Motors and Sensor Setup
• Reviewed on the next slide
Firmware Download
12
Motors and Sensors Setup
• Select Custom Configuration
13
Motors and Sensors Setup
• Set left and right motors
**Check these boxes if your motors are
upside down or if your robot moves the
wrong direction.**
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Motors and Sensors Setup
• Set up sensors
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Code generation
• Once the motors and sensors at set up,
ROBOTC will generate code to configure them
• We will use this code in all programs we write
in this course
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Task 0
Find the edge of the table
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Task 0: Example Solution
Set up a Threshold of 20
Turn on motors forward.
Wait until the edge of the
table is detected.
Stop the robot.
Program: findTableEdge.c
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YouTube: https://youtu.be/Nq7mPQIY4pE
Reading sensors values
• One method of monitor the sensor values is to
use the ROBOTC debugger window
– Download program to your robot
• This opens the Debugger and Debugger
windows
Debugger Windows
• ROBOTC offers many debugging options
Reading sensors values
• We can write a program to display the sensor
values on the EV3 LCD screen as well
Program: sensorValues.c
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Task 1
Follow the edge of the table
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Left Edge
• Use the zig-zag method
to follow the edge of the
table
• Edge following is also
referred to as line
following
• We need to determine
when the robot is on or
off the table
Right Edge
Follow The Edge Of The Table
Table
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Follow The Edge Of The Table
• Get color sensor values to determine when the robot
is on or off the table and putting green. We will use
the color sensor in Reflective Light Intensity mode.
• We can use the sensorValues.c program to assist or
use the Sensor debugging window.
• Color Sensor 1
Color Sensor 2
– Off table = ______ (10)
– On table = ______ (60)
On green = ______ (20)
On table = ______ (60)
Color
Sensor
Readings
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Follow The Edge Of The Table
• Light sensor settings example
– Off table = 10
– On table = 60
– Median threshold = (10+60)/2 = 35
• Two cases
– Light sensor reading > 35. On table.
– Light sensor reading < 35. Off table.
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Simple Line Following Algorithm
Set the threshold value.
Loop forever – the robot will
not stop.
Based on color senor
reading, determine which
direction to travel to line
follow.
Program: LineFollowZZ.c
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YouTube: https://youtu.be/8ZhOBW_ofk4
How to improve our line following
algorithm
• Zig-zag method can cause a bumpy response
• To improve the response, you can use a 3-level
line follower (concept shown below)
Off Table
On Table
Off Table
On Table
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Task 2
Find a putting green
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Find A Putting Green
• One method of finding a putting green
requires two color sensors
– Sensor 1 used to follow the edge of the table
– Sensor 2 used to locate the putting green
• General idea
– Follow the edge of the table until the second color
sensor detects a putting green
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Find A Putting Green
• Let’s modify the previous program to stop
when the robot reaches the putting green
Currently the program will
line follow until we stop the
robot.
Let’s change the outer loop
to stop when the green is
reached.
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Find A Putting Green
Here we modify the while
loop conditional statement
to use the second color
sensor to detect when the
putting green is reached.
Once putting green is
reached, we exit while loop
and stop the robot.
Program: LineFollowZZStop.c
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YouTube: https://youtu.be/8ChSq_KQk5Q
Task 3
Find the golf ball
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Find The Golf Ball
• General idea
– Let’s assume we located the putting green and we
know where the golf ball is on the green relative
to the edge of the green
– How can we begin to position our robot to putt?
36
Find The Golf Ball
• Example
• Follow the edge of the
putting green a
distance “m”
• This will position the
robot in line with the
golf ball
m
Robot
m = 11 cm for the Junior Division. What about the Senior Division?
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Find The Golf Ball
• How to find “m” given n/m
– From the diagram of the putting green we have
𝑛 + 𝑚 = 22 cm
– Let’s assume that n/m = X (X is known)
– Now we can solve for m
𝑛
=𝑋 → 𝑛 =𝑚∗𝑋
𝑚
𝑛 + 𝑚 = 𝑚 ∗ 𝑋 + 𝑚 = 𝑚 𝑋 + 1 = 22 cm
22 cm
𝑚=
𝑋+1
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Find The Golf Ball
• One solution
– Follow the edge of the putting green until we
reach the position of the ball
• Approach
– Let’s modify LineFollowZZStop.c to stop at the
location of the ball
• Tools needed
– Line following
– Measure distance traveled
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Measure Distances
• Determine how far the robot travels moving
forward for 2 seconds
Compute distance traveled
by measuring the number
of rotations of the wheel
Distance
40
Measure Distances
• Use the wheel geometry
PI = 3.14
Radius
How can use this
information?
41
Measure Distances
• For each rotation of the wheel, the robot will
travel (Wheel Diameter) x (PI)
• Distance = (Wheel Diameter) x (PI) x (# Rotations)
• Distance = (5.5 cm) x (PI) x (# Rotations)
• Distance = (17.28 cm) x (# Rotations)
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Measure Distances
Here we reset the a motor
encoder.
The encoder outputs the
rotation of the motor in
degrees so we convert the
output to rotations.
Code added to wait until the
touch sensor is pressed to
keep the information visible
on the robot screen.
Program: measureDistance.c
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Aligning The Robot With The Golf Ball
• Proposed method:
– Compute the distance to travel along the edge of
the putting green
– Compute the number of rotations required to
travel that distance
– Find the edge of the putting green
– Reset motor rotation sensor
– Follow the edge of the putting green
– Stop the robot when the desired number of
rotations is reached
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Aligning The Robot With The Golf Ball
• Example
– Putting green dimensions
• m = 11 cm, n = 11 cm
– Number of rotations
• Distance = (Wheel Diameter) x (PI) x (# Rotations)
• Solve for (# Rotations)
(# Rotations) =
(# Rotations) =
Distance
(Wheel Diameter) x (PI)
11 cm
(5.5 cm) x (PI)
= 0.64 rotations
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Aligning The Robot With The Golf Ball
Here we define some
variables.
Loop until the desired
distance is traveled.
Compute the distance
traveled.
Program: lineFollowDistance.c
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Task 4
Aim for the hole
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Aim for the hole
• We will review a few methods to aim for the hole
• Method 1: Search for the flag pole
– Scan using the sonar senor
• Method 2: Compute the location of the hole
– Mathematically determine the location of the hole
• Step 1
– Determine the angle we must rotate to aim the robot towards the golf hole
• Step 2
– Rotate the robot the determined amount
• Method 3: Determine the location using trial and error
– Here we find the hole by rotating the robot different amounts in an attempt to
find the correct orientation
Method 1: Scan For Hole
• Here we are going to have the robot spin until
it “sees” the center hole flag with the sonar
sensor
This empty loop with allow
the robot to spin until an
object is detected by the
ultrasonic sensor.
Program: spinSearch.c
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Method 2: Mathematical Approach
• Using this approach we can calculate how far
to rotate the robot to face the center hole
• We complete this in two steps
– Step 1
• Determine the angle we must rotate to aim the robot
towards the golf hole
– Step 2
• Rotate the robot the determined amount
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Determine The Rotation Angle
• We can use geometry to determine the
location of the hole
r
s
t
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Determine The Rotation Angle
• We can use trigonometry to determine the
location of the hole and aim the robot
𝑟
si𝑛 𝜃 =
𝑡
𝑠
𝑐𝑜𝑠 𝜃 =
𝑡
𝑟
tan 𝜃 =
𝑠
r
s
𝑟
𝜃 = atan
𝑠
θ
t
Determine The Rotation Angle
• Use an advanced math block to compute the
necessary rotation angle
40
– Assume the following
• r = 40 cm
• s = 30 cm
36.87°
30
53.13°
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Program: trigMath.c
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Rotate The Robot To Putt
• We need to rotate the robot θ degrees to aim
the robot at the golf hole
Starting Position
Robot
Rotated Position
90° - θ
Rotate The Robot To Putt
Robot
• We will use the spin feature to turn the robot
θ degrees
• When the robot spins, the wheel path is a
circle centered between the wheels
• The diameter is the track width of the robot
Rotate The Robot To Putt
• For an example, let’s spin the robot 90 deg
– Robot track width = 16.2 cm
– The circumference of the robot’s path
• C = PI * D = 3.14 * 16.2 cm = 50.87 cm
– The circumference of the robot’s wheel
• C = PI * D = 3.14 * 5.5 cm = 17.27 cm
• 90 degrees is ¼ of the circle. The robot travels
– D = ¼ x 50.87 cm = 12.72 cm
• How rotations to travel 12.72 cm?
– # Rot = Distance / (Wheel Circumference)
– # Rot = 12.72 cm / 17.27 cm = 0.74
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Rotate The Robot To Putt
• Spinning robot example
– Robot width = 16.2 cm
– Wheel Diameter = 5.5 cm
• Circumference = 17.27cm
• Number of rotations
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑇𝑟𝑎𝑣𝑒𝑙𝑒𝑑
# 𝑅𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑠 =
𝑊ℎ𝑒𝑒𝑙 𝐶𝑖𝑟𝑐𝑢𝑚𝑓𝑒𝑟𝑒𝑛𝑐𝑒
12.72 𝑐𝑚
# 𝑅𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑠 =
= 0.74 𝑟𝑜𝑡𝑎𝑡𝑖𝑜𝑛𝑠
17.27 𝑐𝑚
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Rotate The Robot To Putt
• We can use one block to spin the robot
Set motor targets to the
degrees they need to turn,
or #Rotations * 360
Speed of 20 for leftMotor
and a speed of -20 for
rightMotor so they spin in
opposite directions.
Program: spin90.c
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YouTube: https://youtu.be/icAw-SnjIes
Whew that’s A LOT of math!!!
Task 5
Putt the golf ball
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Putt The Golf Ball
• Again, this task is beyond the scope of this
course
• However, your robot should be in position to
putt the ball in the center hole
• Remember, you can only hit the golf ball once
and only with the wooden block putter
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Functions
• Solving the Robofest Game challenge will
typically require a fairly large EV3 program
• Very large programs can be difficult to
understand, navigate and use
• To alleviate this issue, ROBOTC allows the use
of functions group and reuse sections of your
program
Functions
• For example, let’s assume
you have a section code
that completes the
following:
– Move forward until the
edge of the table is found
with color sensor 1, then
stop
– After stopping, rotate the
robot 90 degrees
• Here is an example…
Functions
• Let’s create a function called findEdgeAndTurn
Now can call the function from our
main task program
Program: findEdgeAndTurn.c
Putting It All Together
• In this course we learned how to
– Find the edge of the table
– Follow the edge of the table
– Find a putting green
– Find the golf ball
– Aim for the hole
– Putt the golf ball
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Little Robots, Big Missions
Questions?
Email me at
Bjb01234@gmail.com
chung@LTU.edu
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