Connecting VEX and ROBOTC
Electrical Engineer Responsibilities
Developed in collaboration with
Electrical Engineer
Responsibilities:
1. Keep batteries charged
2. Work with Mechanical Engineer to attach the
battery, motors and sensors to the model and
the Cortex.
3. Work with the Computer Engineer to complete
Motor and Sensor Setup
4. Complete the Motor and Sensor Schematic on
Automation Through Programming Summary
Cortex
The VEX Cortex Microcontroller
coordinates the flow of information and
power on the robot. All electronic
system components must interface to
the Microcontroller.
The Microcontroller is the brain of
every VEX robot.
Power
1. Keep batteries charged – In order for a robot to operate,
it needs a power source.
• A 7.2V NiCd rechargeable battery is
used with your VEX robot.
• Attach a battery strap to your model.
• When your team is ready to test your
model, retrieve a battery from the
container of charged batteries. Attach
the
battery to the model using the strap
and plug in to the Cortex.
• At the end of class put your battery on the VEX
charger so it will be ready for the next class.
Motors
2. Attach Motors to the model and Cortex
• Motors are devices that can transform electrical
energy into mechanical energy.
• They take electrical power and create rotary motion.
Use motors to power the robot’s drive wheels. The
wheels need to make continuous full rotations, which is
exactly the kind of motion provided by the motors.
Rotation for forward motion is shown.
Motors
• 2-wire motors can be connected directly to
ports 1 and 10 on the VEX Cortex
• The VEX Motor Controller 29 allows you to
connect the VEX 2-wire Motors to any of the
standard 3-wire ports on the VEX Cortex.
• To use the VEX Motor Controller 29, plug the
3-wire end into one of the MOTOR ports (29) on your VEX Cortex Microcontroller.
Motors
• Connect the other end of the VEX Motor Controller
to the 2-wire Motor. Be sure to align the black and
red wires.
• To prevent the 2-wire Motor and Motor Controller
wires from accidentally separating while the robot is
running, use the supplied wire ties to secure the
two ends, along with any excess wire.
Claw
• Notice the motor used to open and close the claw.
• How many motors are needed for this project?
Sensors
2. Attach Sensors to the model and Cortex
• 4 Sensors:
• Touch /
Bumper Switch
• Limit Switch
• Line Tracker
• Potentiometer
Bumper Switch Sensor
Signal: Digital
Sensor Values: 1 = pressed, 0 = released
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.
Type: SPST switch (“Single Pole, Single
Throw”) configured for Normally Open
behavior.
Signal Behavior:
Limit Switch Sensor
Signal: Digital
Sensor Values: 1 = pressed, 0 = released
Description: The limit switch sensor is a
physical switch. It can tell the robot whether
the sensor’s metal arm is being pushed in
or not.
Type: SPDT microswitch, configured for SPST
Normally Open behavior.
Signal Behavior:
Line Tracker
Signal: Analog
Sensor Values: Range from 0-4095
Description: A line follower consists of an
infrared light sensor and an infrared
LED. It works by illuminating a
surface with infrared light; the sensor
then picks up the reflected radiation
and, based on its intensity,
determines the reflectivity of the
surface. Light colored surfaces will
reflect more light than dark surfaces.
This allows the sensor to detect a
dark line on a pale surface, or a pale
line on a dark surface.
Line Tracker
The line followers are an analog sensor,
meaning that its output covers a range of
values (in this case, from zero to five volts)
rather than being only high (five volts)
or low (zero volts), as is the case for a
digital sensor.
You can use the line trackers to
help your robot navigate along a
marked path. A typical application
uses three line follower sensors,
such that the middle sensor is
over the line your robot is
following.
Line Tracker
You can use the line trackers to
discern the boundary between
two high-contrast surfaces as
well.
The optimal range for the line
tracker to read a value is ¼ in.
In this elevator model, the line
tracker sensor is used to
determine if the elevator is at the
correct floor.
Paper – ¼ in from sensor
Line Tracker
Potentiometer
Signal: Analog
Sensor Values: Range from 0-4095
Description: The Potentiometer is used to measure the
angular position of the axle or shaft passed through
its center. The center of the sensor can rotate roughly
265 degrees and outputs values ranging from 0-4095
to the Vex Microcontroller.
Mounted Potentiometer
CAUTION! When mounting the
Potentiometer on your robot, be sure that the
range of motion of the rotating shaft does not
exceed that of the sensor. Failure to do so
may result in damage to your robot and the
Potentiometer.
ROBOTC - Programming
3. Work with the Computer Engineer to complete
Motor and Sensor Setup
Allows you to configure and name all of the motors
and sensors connected to your robot.
Motor and Sensor Setup
Type a name to describe
the motor location.
Remember Ports 1 and
10 can be used for 2 –
wire motors, or use a
Motor Controller 29 to
plug into ports 2-9.
Check reversed if you
want the motor to turn in
the opposite direction.
Motor and Sensor Setup
Type a name to describe
the sensor.
Choose the type of
sensor – the only analog
sensors for GTT are Line
Follower and
Potentiometer.
Motor and Sensor Setup
Type a name to describe
the digital sensor
location or purpose. Both
the limit and bumper
switches are Touch Type.
LED’s can be plugged in
to Digital Ports 1-12, the
type is VEX LED.
Motor and Sensor Schematic
4. Complete the Motor and Sensor Schematic on
Automation Through Programming Summary
This information should match
the motor and sensors setup
done in ROBOTC
Resources
Carnegie Mellon Robotics Academy (2011). VEX Cortex
Video Trainer. Retrieved from
http://www.education.rec.ri.cmu.edu/products/teaching_r
obotc_cortex/index.html
VEX Cortex Video Trainer
–http://www.education.rec.ri.cmu.edu/products/t
eaching_robotc_cortex/index.html