ROBOTC for VEX
On-Site Professional Development
Troubleshooting
• Student: My robot won’t stop turning.
Troubleshooting
• Student: I used the auto straightening code, and it
compiles, it isn’t working, it’s just being weird.
Troubleshooting
• Student: One of my encoders is counting
down even though it’s spinning forward.
Troubleshooting
• Student:
My code
won’t
compile.
Radio Control
Radio Control
• An out-of-box VEX Microcontroller comes with
basic built-in Radio Control functionality
– The Radio Control Transmitter can be configured to allow some
customization of that built-in functionality
– Still very limited customizability and usefulness!
• The ROBOTC firmware enables full
customization of how the Radio Control
Transmitter signals controls the VEX
– By default ROBOTC turns off reception from the transmitter to
save battery life during autonomous programming
– One line of code turns it back on
Radio Control
• One Transmitter continuously sends out 6
separate values over 6 separate channels
– Values range from -127 to 127
– Doesn’t something else have values that range from -127 to
127?
• The “crystal” number must match on the
transmitter and receiver
– The crystal is what controls the frequency of the transmission
– One transmitter can control multiple robots, so be careful in your
classrooms
– 13 different crystals/frequencies are available
Radio Control Reset
• Since the Radio Control Transmitter can be
configured, there’s the possibility that it’s
configured inappropriately for our purposes.
– Watch the Radio Control Setup and Values and Axes (Part 1)
Videos in TRC4V, found in Radio Control > Control Mapping
– Be sure to follow along with the Radio Control Setup Video!
Radio Control Signals
Radio Control
• Direct Value Mapping
– Values from the transmitter are directly used to control the
motors (1:1 ratio)
• Program Flow Tracing
– Radio Control with Wait States
– Radio Control with a Loop (real-time control)
• Indirect Value Mapping
– Values from the transmitter are modified before being used to
control motors
– Can make the robot easier to control
– Appropriate in situations that require more “delicate” movements
– Notice: the robot reads the right side of the equal sign first
Advanced Radio Control
• Attach the Arm!
• Use the Transmitter buttons to control the arm
– The Transmitter buttons send values of -127, 0, or 127
– Would direct mapping or indirect mapping be most appropriate for
controlling the arm? Why?
• More loop control please?
– Is remote controlling the robot forever always appropriate?
– Question: Where would the wait statement go if we wanted the robot to
be remote controlled for a controlled amount of time?
– Answer: Nowhere! We need something else.
• Solution: Timers
– Can be thought of as internal stopwatches (4 available)
– Like encoders, timers should be “cleared” anytime before they are used
• Watch where you clear them!
Advanced Radio Control
• Wasting Time?
– The time it takes to turn on the VEX and start Radio Control is
wasted time.
– Could we make the robot wait to start it’s timer until we were
ready? Any ideas?
• Wait for a Transmitter Button press
–
–
–
–
The robot won’t start the timer until we say so
The robot also can’t move until we says so
Program Flow Trace
Could this idea also be used to make a “more friendly” start
button on a non-radio controlled robot?
• Other ideas of how to improve radio control?
– Use the buttons to initiate common actions
• Turn 90 degrees, move straight forward, ect
Advanced Radio Control
• Assigning a function to a button press
– Auto pickup
Radio Control Challenges
• TRC4V Videos
(recommended)
– Watch remaining Control
Mapping videos 3-5
• Race to the Finish
– Remember to Journal
– Remember to Pseudocode
• Shut off your transmitter when it’s not in use!
– Drastically saves the battery life (and your ears)
• The transmitter is always transmitting, even if the robot isn’t on
Advanced Radio Control
Challenges
• TRC4V Videos (recommended)
– Watch remaining Radio Control Videos (Control Mapping,
Timers, Buttons sections)
• Minefield Level 1 Challenge
– Remember to Pseudocode
– Remember to Journal
• RoboDunk
– First try it
Tele-Operated,
then Autonomously
Competition Templates
• VEX Competitions have a “Field Management
System” in place
– Manages when robots are enabled/disabled
– Determines whether the robots are in autonomous/tele-operated
mode
• A Competition Template is available that can be
programmed in to work with the Field
Management System
– Contains autonomous and tele-operated sections
– Found in the Sample Programs > Competition folder
Troubleshooting
• Student: My loop should only be running
for 1 minute, but it never stops.
Touch Sensors
• Touch Sensor Check
– Front sensor plugged into A/D 1
– Rear Sensor plugged into A/D 4
• How they work
– Digital sensor - Pressed or Released
– Watch out for “bouncing”
• Two Types
– Limit Switches – on Squarebot 3.0
– Bumper Switches
• Setting them up
– ROBOTC Motors and Sensors Setup window
• Using them
– The SensorValue[] command
Touch Sensors
• Start Button
– Remember back to how we used the Transmitter button to start the
timer portion of the program. How would we implement the same thing
with the limit switch?
• Fine-tuned arm control
– Using the limit switches to tell the robot when it has reached it’s
minimum and maximum points
Touch Sensor Challenges
• Quick-tap Challenge
– Incorporating Sensors, Variables, Loops, If
Statements, Timers, Boolean Logic, Pseudocoding,
and FUN all into one activity
• Addition & Subtraction
– Everything you just learned, but with another twist
The Ultrasonic Rangefinder
• Ultrasonic Rangefinder Check
– Input wire plugged into A/D Port 5
– Output wire plugged into INT Port 1
• How they work
– Similar to how bats and submarines work
– Digital sensor – but returns distance values between 0 & 255
• (Can also return values of -1 or -2 if used improperly)
– Resolution is in inches (a value of 5 = 5 inches away)
• Setting them up
– ROBOTC Motors and Sensors Setup window
• 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
The Ultrasonic Rangefinder
• Forward until Near
– Move forward until the robot is “near” an object, then
stop
– Thresholds
• Automatic Pick-up
– Forward until Near + picking up the mine
– Assign to a button
Sensor Challenges
• TRC4V Videos (recommended)
– Watch Remaining Sensing Section Videos
• Minefield Level 2 Challenge
– Remember to Pseudocode
– Remember to Journal
– The two are not mutually exclusive!
• The Speed of Sound
• Sonic Scanner Level 2 (Start)
Potentiometers
• Potentiometer Check
– Sensor plugged into A/D 1
• How they work
– Analog sensor
– Measures rotation of a shaft
between 0 and ~265 degrees
– Returns values 0 – ~1023
– Internal mechanical stop
• Setting them up
– ROBOTC Motors and Sensors Setup window
– Using Analog and Digital Sensors
• Using them
– The SensorValue[] command
Potentiometers
• Variable Speed Program
– Use the rotation of the potentiometer to control how
fast the robots motors spin
• Arm Control
– Instead of using the limit switches, use the
potentiometer to control how far the arm is allowed to
swing up and down
Servo Motors
• Very similar in appearance
to the normal motor
• Very different in operation
– Rotates between 0 and 120 degrees
– Where the motor is set to a “power value” the servo is set to
a “position value”
– -127 = 0 degrees, 0 = 60 degrees, 127 = 120 degrees, ect
– Servo motors are programmed exactly the same way as
normal motors in ROBOTC, so the programmer must know
the hardware and intent
Pneumatics
Pneumatics
• Solenoids operate as Digital Outputs
• Are plugged into Analog/Digital Ports
– Are set to open by setting them to 1
– Are set to close by setting them back to 0
• Demo in ROBOTC
End of Day Challenge
• Minefield Level 2
– Incorporate an autonomous scoring behavior
before your tele-operated code begins
– One “mine” should always be in the same place,
near the goal