Electrical Engineer Responsibilities Connect VEX and ROBOTC Electrical Engineer Responsibilities Automation and Robotics VEX © 2011 Project Lead The Way, Inc.

Electrical Engineer Responsibilities: 1. Keep batteries charged Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Power 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. Battery life and batteries in general are well explained in the VEX Inventors Guide (Power). Page 4.9 describes how to revive batteries that appear weak due to “voltage drop” sometimes referred to as memory effect.

Motors 2. Attach Motors to the model and Cortex Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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 (2-9) on your VEX Cortex Microcontroller.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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 / Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Sensors 2. Attach Sensors to the model and Cortex 4 Sensors: Touch / Bumper Switch Limit Switch Line Tracker Potentiometer Sensors are used so the robot can sense its environment, and the robot can adjust its own behaviors based on that knowledge. A sensor will generally tell the robot about one very simple thing in the environment, and the robot’s program will interpret that information to determine how it should react. The Bumper Switch sensor, for instance, will tell the robot whether it is in contact with a physical object or not. Depending on how the sensor is set up, this can tell the robot a lot of different things. If the sensor is mounted on the front bumper, the robot could use this information to tell whether it has run into an obstacle, like a wall inside a maze. By making good use of sensors to detect the important aspects of its environment, a robot can make things much easier for its human operator. A robot can even operate completely independent of human control, autonomously.

Bumper Switch Sensor Signal: Digital Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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: Signal Behavior: When the switch is not being pushed in, the sensor maintains a digital HIGH signal on its sensor port. This High signal is coming from the Microcontroller. When an external force (like a collision or being pressed up against a wall) pushes the switch in, it changes its signal to a digital LOW until the switch is released. An unpressed switch is indistinguishable from an open port.

Limit Switch Sensor Signal: Digital Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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: Signal Behavior: When the switch is not being pushed in, the sensor maintains a digital HIGH signal on its sensor port. This High signal is coming from the Microcontroller. When an external force (like a collision or being pressed up against a wall) pushes the switch in, it changes its signal to a digital LOW until the switch is released. An unpressed switch is indistinguishable from an open port.

Line Tracker Signal: Analog Sensor Values: Range from 0-4095 Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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. This range of output from zero to five volts is sent to the microcontroller, which reads it as a range of integer values from 0 to 4095. For this particular sensor, sensor output will be low (around 0) when the infrared light bounces back to the detector – in other words, when the surface is pale or highly reflective – and high (around 4095) when the light is absorbed and does not bounce back. We can then set a threshold value in our code to act as a trigger for behaviors. From this basic premise, we can build more complicated behaviors. For example, if you have three line sensors on the front of your robot [hint: use the mounting bar included in your kit!], then you can program your robot to follow a white line on a black surface. LineFollower_Middle should always see white, and the other two — LineFollower_Left and LineFollower_Right — should always see black. If LineFollower_Left starts seeing white, then your robot needs to steer back to the left. If LineFollower_Right starts seeing white, then your robot needs to steer back to the right.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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. Line Tracker Paper – ¼ in from sensor

Potentiometer Signal: Analog Sensor Values: Range from 0-4095 Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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 Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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. Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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. Gateway VEX kits do not contain servo motors – so students should never choose Servo Style Motor

Motor and Sensor Setup Type a name to describe the sensor. Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Motor and Sensor Setup Type a name to describe the sensor. Choose the type of sensor – the only analog sensors for Gateway are Line Follower and Potentiometer.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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 Presentation Name Course Name Unit # – Lesson #.# – Lesson Name 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_robotc_cortex/index.html VEX Cortex Video Trainer http://www.education.rec.ri.cmu.edu/products/teaching_robotc_cortex/index.html