1. ROBOTC for VEX Online Professional Development

2. Homework Questions
Thoughts?
Questions?

3. Troubleshooting
Student: My loop should only be running for 1 minute, but it never stops.

4. Student: “My program runs when the Cortex is connected to the computer, but when it’s not connected it just sits there doing nothing.”

5. Student: “My program runs when the Cortex is connected to the computer, but when it’s not connected it just sits there doing nothing.”

6. Student: “My motor should spin forward for 3
Student: “My motor should spin forward for 3 seconds, stop for 2 seconds, then reverse for 3 seconds, but it never stops in the middle.”

7. Sensor Information: Touch Sensors

8. Touch Sensors Touch Sensor Check How they work Two Types
Plugged into Digital 6 on the Cortex
How they work
Digital sensor - Pressed or Released
1 = Pressed, 0 = Released
Watch out for “bouncing”
Two Types
Limit Switches (top)
Bumper Switches (bottom)
Setting them up
ROBOTC Motors and Sensors Setup window
Using them
The SensorValue[] command
untilTouch(), untilRelease(), until Bump()

9. Move Forward until Pressed

10. Natural Language - Until
Commands that allow you to create behaviors where the robot acts “until” a certain event
untilTouch()
untilRelease()
untilBump()

11. Touch Sensors Other Properties Limitations
Limit Switch arm can be bent to create a more ideal “hit area”
Both sensors spring back to “open” position
Limitations
Watch out for “bouncing”. As the sensor is pressed or released, it may bounce between 0 and 1 very briefly and quickly.
A very brief wait can be inserted as part of the untilBump() command, or after the untilTouch() and untilRelease() commands to reduce the bouncing effect:

12. Natural Language
Move Forward until Pressed

13. Touch Sensors Start Button
Remember how we used the Remote Control button to start the timer portion of the program?
How would we implement the same thing with the limit switch?

14. Additional Resources

15. Sensor Information: Potentiometer

16. Potentiometers Potentiometer Check How they work
Analog Port 6 on Cortex
How they work
Analog sensor
Measures rotation of a shaft between 0 and ~265 degrees
Cortex returns values 0 - ~4095
Using them
The SensorValue[] command
untilPotentiometerGreaterThan, untilPotentiometerLessThan NL commands

17. Potentiometers Other Properties Limitations
Internal mechanical stops prevent the potentiometer from turning a full revolution.
Limitations
Caution: Excess torque against the internal mechanical stops (can be caused by hand or by a VEX motor) will cause them to wear away. The potentiometer will continue to function, but will have a “dead zone” where the mechanical stops were, where no new values are sent.
Switching the direction the potentiometer is facing will also switch the direction it “counts”. For example: counter-clockwise turns will count 0 to 4095 on one side; on the other counter-clockwise turns will count 4095 – 0.

18. Potentiometers

19. Natural Language - Until
Commands that allow you to create behaviors where the robot acts “until” a certain event
untilPotentiometerGreaterThan()
untilPotentiometerLessThan()

20. Natural Language
Autonomous Arm Control

21. Potentiometers Variable Speed Program
Use the rotation of the potentiometer to control how fast the robots motors spin

22. Advanced Arm Control
Use the Touch Sensor and Potentiometer to control the minimum and maximum values of the arm. Follow videos in the VEX Cortex video Trainer.

23. Sensor Information Ultrasonic Rangefinder

24. The Ultrasonic Rangefinder
Ultrasonic Rangefinder Check
Input into Digital Port 8 (Always lower port number)
Output wire plugged into Digital Port 9
How they work
Similar to how bats and submarines work
Digital sensor – but returns distance values between 0 & 648 cm
(Can also return values of -1 or -2)
Cortex resolution can be in inches, cm, or even mm
Using them
Be careful not to use them immediately as your program starts – they take time to initialize and will return negative values
The SensorValue[] command
untilSonarLessThan(), untilSonarGreaterThan()

25. Ultrasonic Rangefinder
Other Properties
The Ultrasonic Rangefinder is able to detect objects in a “cone” field of view. As objects get further away, the sensor is able to detect them further away from the center of the sensor.
The sensor bases distance calculations off of sound waves, which means that some objects may not be detectable: soft objects that absorb sound, sharp objects that deflect sound, etc.
Do not use the ultrasonic sensor as the very first command in your code. Until the first sound echo returns to the sensor, it will have a value of -1. A simple delay at the beginning of your program solves this.

26. Forward until Near

27. Natural Language - Until
Commands that allow you to create behaviors where the robot acts “until” a certain event
untilSonarGreaterThan()
untilSonarLessThan()

28. Natural Language
Forward until Near

29. The Ultrasonic Rangefinder
Forward/Straight until Near
Move straight forward until the robot is near an object, then stop
Follow along with videos in VCVT

30. Straight until Near

31. Sensor Homework VCVT Videos Homework Assignments:
Sensing > Limiting the Arm
(Optional) Movement > Shaft Encoders
(Optional) Movement > Automated Straightening
Sensing > Behaviors and Functions
Sensing > Forward until Near
Homework Assignments:
Minefield Removal Level 2 Challenge
The Speed of Sound
Quick-tap Challenge