ROBOTC for VEXOn-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