Introduction to Sensors

Sensor Basics

Aptly named, sensors are integral to how your robot understands the world around it. For instance, maybe you have noticed your teammates lunch box is green, a color sensor would allow your robot to notice the same thing. Color isn't the only sense your robot has! Robots use sensors to collect various types of information about their environment. The following list is just some of the scenarios where sensors are needed.

Scenarios where a sensor is needed:

  • The robot needs to autonomously move to a specific location and stop there.

  • The robot needs to move forward at a green signal and stop moving at a red signal.

  • The robot has an arm that needs to be prevented from rotating too far or it may damage other parts of the robot.

  • The robot needs to stop 1 meter away from an opaque wall.

  • The robot needs to be able to tell how many game objects it is currently holding inside it’s hopper.

Different Sensor Types and Uses

In The REV Robotics Control System, sensors are classified as beginner, intermediate, or advanced. This division among sensors is based on programming complexity. Beginner sensors can typically be coded using an if/else statement. Intermediate sensors, like the IMU, require a higher level understanding of programming. Advanced sensors require advanced knowledge of programming. Visions sensors and encoders are considered advanced.

Beginner

In the REV Robotics Control System, both Analog and Digital sensors are considered beginner sensors. Analog and digital sensors log changes in state as changes in Voltage. Digital sensors, like the touch sensor, report voltage changes along a binary. With digital sensors the voltage is typically 0v or 3.3v. Whereas analog sensors are similar to an adjustable resistor and they report a range of voltages between 0v to 3.3v.

Some sensors in the REV Control System are capable of running up to 5v. To learn more about sensor voltage visit the pages of the individual sensors!

The table below gives the basic usage scenarios for analog and digital sensors

Digital

Analog

Gives feedback as either on or off. This type of sensor is ideal for setting limits of a mechanism.

Gives feedback as a proportional voltage range. This type of sensor is ideal for knowing exactly where a mechanism is, like a dial on a radio.

Digital Sensors

  • Touch Sensor : A sensor with a button. The button press can be used to trigger actions like stopping motors.

  • Magnetic Limit Switch: A sensor that detects magnetic fields. When there is sufficient field strength of either magnetic pole detected the sensor is triggers and a limit of movement can be established.

Analog Sensors

  • Potentiometer: The Potentiometer senses the angular position of a shaft.

Intermediate

I2C sensors are considered intermediate because they give feedback through two-way communication with a robot controller. These types of sensors allow for more complex data to communicate to the robot, such as color values of an object.

  • IMU: The IMU incorporates three sensors: a 3-axis accelerometer, a 3-axis gyroscope, and a 3-axis geomagnetic sensor. This sensor can be used to determine orientation and location of the robot.

  • Color Sensor: A sensor capable of sensing colors and proximity of objects.

  • 2m Distance Sensor: It is typically used to detect the distance from the sensor to other opaque objects.

Advanced

The two types of advanced sensors in the REV Control system are Vision sensors and Encoders.

Vision

Encoders

Gives feedback as images to the robot controller. These types of sensors require the use of image processing software, like VuForia, to use to their full potential.

An Encoder, in the context of robotics, is a type of digital sensor that converts rotary motion into digital signal. These type of sensors require “decoding” to get this information into a usable form. The Control Hub and Expansion Hub have built in decoding through the “Encoder Ports” under the motor ports.