VEX and Robot C

Chris PattersonFrisco ISD CTE Center

Presented by

The VEX Kit

VEX Robotics Platform:Testbed for Learning Programming

VEX Motion Subsystem – Motors

• 2-wire motor 269– Two methods to connect to Cortex

• Motor ports 1 and 10• Motor port 2-9 using Motor Controller 29

• 2-wire motor 393

VEX Motion Subsystem – Servos

• Similar in appearance to the 3-wire motor• Very different in operation

– Rotates between 0 and 120 degrees– Motor is set to a “power value” – Servo is set to a “position value”– -127 = 0 degrees, 0 = 60 degrees, 127 = 120

degrees, etc.– Natural Language command

• setServo()

• Analog Sensors:-Light Sensor

-Potentiometer

-Line follower

• Digital Sensors:-Bumper Switch -Limit Switch

-Optical Shaft Encoder-Ultrasonic Range Finder

VEX Sensors Subsystem

Robot C and Natural Language

Step #1

Step #2

Step #3

PLTW Template

Natural Language

• In short, Natural Language is a form of C based programming that cuts down on coding and makes things a bit simpler.

• For Example,– What do you think startMotor(rightMotor, 127);

does?

Natural Language - Movement

Natural Language -Special

Natural Language - Until

• The program will wait at the “Until” line of code. Once the condition for that sensor is true, the program continues.

Natural Language - Until

• For example, what might you expect the following to do?

untilTouch(bumpSwitch);startMotor(leftMotor, 63);

Basic Output Programming

Behavior-Based Programming• A behavior is anything your robot does

– Turning on a single motor or servo• Three main types of behaviors

1. Complex behaviors – Robot performs a complex task (automated fan control)

2. Simple behaviors – Simple task performed by the robot (fan stops when sensor activated)

3. Basic behaviors – Single commands to the robot (turn on a motor)

• Complex behaviors can always be broken down into simple behaviors, which are then broken down into basic behaviors

Basic Output Programming

EXAMPLE 1 • Let’s turn on the rightMotor for 4 seconds and

then off for 4 seconds. Repeat this operation twice.

Basic Output Programming – Example 1

Basic Output Programming – Example 2

• Turn on a motor and then wait 5 seconds. Set servo to position 127 for 3 seconds and then position 96 for 4 seconds.

Basic Output Programming – Example 2

Programming with Sensor Feedback

Example 3

• A motor turns on once the bump switch is touched and then turns off once the limit switch is touched.

EXAMPLE 3

EXAMPLE 4

• A motor turns on clockwise at full power when the potentiometer is greater than 3000 and turns counterclockwise at full power when the potentiometer is less than 2000.

Example 4

Example 5 - What will this program do?

While and If-Else Loops

While Loops• While loop is a structure within ROBOTC• Allows a section of code to be repeated as

long as a certain condition remains true

• Three main parts to every while loop1. The word “while”2. The condition3. Commands to be repeated

The Condition• Condition controls how long or how many

times a while loop repeats– When condition is true, the while loop repeats– When condition is false, the while loop ends and

the remainder of the program executes

• Condition is checked once every time loop repeats before commands between curly braces are run

Revisit Example 1

EXAMPLE 1 • Let’s turn on the rightMotor for 4 seconds and

then off for 4 seconds. Repeat this operation twice.

• Instead of running it twice, let’s loop it continuously. (running it twice would require a variable, and we aren’t there quite yet)

While Loops – Example 1 Revisited

While Loops• The while loop has a true condition so it will

always run. If the condition is always true, you cannot leave the while loop.

• While loops can be based on a sensor condition as well. For example:

While Loops – Using a sensor condition

While Loops – Using Multiple Conditions

While Loop – Timers as ConditionsTimer T1 is used as the condition for the while loop, which will run for 30 seconds

If Statements• If statement in the program is evaluated by condition

contained in parentheses– If condition is true, commands between braces are

run– If condition is false, those commands are ignored

• Very similar to how a while loop works, but does not repeat the code

If-Else Statements

• If-else statement is an expansion of if statement– If checks condition and runs appropriate

commands when it evaluates to true– Else allows code to run when condition is false– Either if or else branch is always run once

If Statements Example

Let’s revisit Example 4• A motor turns on clockwise at full power when

the potentiometer is greater than 3000 and turns counterclockwise at full power when the potentiometer is less than 2000

Example 4 – While loop and If-Else Statements

This is just the beginning…

• You have been given enough tools to go out and EXPLORE on your own time.

• Use the lessons in the PLTW curriculums to try out some of the activities and projects.

Questions?