Project Overview  Introduction  Frame Build  Motion  Power  Control  Sensors  Advanced Sensors  Open design challenges  Project evaluation

LESSON 05

LESSON 05 STARTER Cortex Microcontroller Parts list Quick task: Discuss in pairs the cortex shown. Propose the function of the cortex for the Tumbler control, and write your description in your parts list.

CREATING CONTROL Learning objective: Learn how robotics are controlled and how this supports modern manufacture and industry. Work with a control programme to learn about how programming works. The VEX Cortex Microcontroller coordinates the flow of all information and power on the robot. All other electronic system components (motors, sensors, etc.) interface with the Cortex Microcontroller. The Microcontroller is the brain of every VEX robot. A robot is a very complex system of parts that must work together in order to achieve a desired goal. Electronic control provided by a programmable controller like the VEX Cortex Microcontroller allows the robot to coordinate the operation of the different components and achieve its goals.

How robots are controlled The VEX Sensor Subsystem provides information about the robot’s environment. It uses this data to make informed decisions about how the robot should behave. The actual behaviour that is activated when a sensor is triggered depends on which port the sensor is plugged into on the Microcontroller and the Code being executed. The code in this project is developed using Easy C, which establishes what happens in response to the signals moving in and out of the cortex. Micro Controller SensorsMotors A robot brain like a micro controller sends out and receives information in the form of signals (as voltage). Information is gathered in by sensors from the environment around the robot, and fed into the cortex, with this information, the cortex can then affect the motors by changing their output accordingly. In this way, robots have a level of intelligence, though limited by the functionality of the sensors and what can be achieved through changing signals to the motors. Worksheet for lesson 5 = CREATING CONTROL

A look at the cortex in detail Label your cortex worksheet accurately to create a reference document. UART I2C Smart Sensor Port: Will connect to multiple new smart sensors in the future. UART Fast Serial Ports: Connects to the VEX LCD Display (19,200 baud) and will have future support to Mbaud VEXNET Key Built-in VEXnet Technology: Wireless driving, wireless debugging, and wireless downloading Analog/Digital Digital/Analog Input Ports: (8) high-res Analog Inputs, (12) fast Digital I/Os that can be used as interrupts. Lights These signal information to the viewer including when connections are made to the controller, when battery is low, and when software needs updating. Fitting to metal A minimum of 2, maximum of 4 connections are required to fit a cortex to the metal frame of your robot. Motor Motor Ports: (8) standard 3-wire Motor or Servo ports. (2) 2-wire Motor ports. Config & Rx Rx1 and Rx2 Ports: Also support for two 75MHz crystal transmitters and receivers Power Battery Ports: Connect 7.2V power sources, such as the Battery Holder or the VEX 7.2V Robot Battery. Also connect a 9V Backup Battery to protect against communication losses CREATING CONTROL

Motor controllers Motor controllers are essential for controlling the motors that give you robot functionality. Positions 1 and 10 on the cortex already have motor controllers built into them. You can therefore connect motors to these to create movement. If motors are connected to ports 2-9, motor controllers are needed to ensure control is achieved. Connections (red and black) can be swapped on the two wire end of the motor controller to reverse the direction of the motor, though this is easy to programme in easyC. CREATING CONTROL

Use the Step by Step build guide – CONTROL Follow the instructions on page one of the build guide. Use the tools provided by your teacher and remember to check all the time that you are being accurate and working as a team! Key to getting it right… Tighten the cortex to the top of the chassis. Fit the wires in the correct place in the cortex, and neaten up the wires and motor controllers using cable ties to the chassis. Place a washer on the shaft before fitting the wheels. CREATING CONTROL

THE FINISHED TUMBLER The finished Tumbler without battery and sensors. [please note TD logo plaque not included) Cleaning up your build Once you have finished the Tumbler build, use cable ties to pull all the loose wires to the frame as neat as you can.

Quick Demonstration/quick behaviours Using the following guide, let’s have a look at how sensors can give you instant added behaviour. Try the following behaviour using your default code cortex (from the box) Adding limit switches Limit Switch Inputs: The Default Code on the Cortex allows jumpers or switches to be installed in the Analog Ports to limit certain motor directions. These are useful for stopping a motor when a moving arm hits the bottom of its safe movement. A limit switch plugged in to Analog 1 will stop Motor 6 from turning counter clockwise when activated. A limit switch plugged in to Analog 2 will stop Motor 6 from turning clockwise when activated. CREATING CONTROL

Connecting sensors and built in behaviours You can do quite a lot with a limit switch and a bump switch. Here are the pre programmed behaviours you can utilise. Quick bumper switch behaviours Quick limit switch behaviours CREATING CONTROL

Jumpers Jumpers are used to make changes to the default code on your cortex. They are plugged into the digital SP port of the microcontroller and automatically trigger behaviours in conjunction with the limit switch and bump switch. Connecting sensors and built in behaviours Normally sensors connect to the Analog/Digital port bank on the VEX Microcontroller. Some sensors must use an Interrupt Port on the Microcontroller using the Jumper. Different behaviours of the Default Code are activated depending on which port you plug the sensors into. The table right shows you behaviours that activate when Bumper Switch or Limit Switch Sensors are plugged into the indicated ports AND a jumper is placed in the SP port. CREATING CONTROL

Quick Sensor introduction: Tumbler obstacle detector Using ports you can create this primary behaviour for the Tumbler. Obstacle detection Sensor You must enable Autonomous Mode in order for these ports to work. Place a Jumper Clip in Analog/Digital Port 13 to enable Autonomous Mode operation. The robot should be set up in a 2-motor configuration for autonomous mode operation. The left motor should be plugged into Motor Port 3, and the right motor should be plugged into Motor Port 2. Attach a wheel to each motor for this demonstration to see the movement changes clearly. Plug Bumper or Limit Switch Sensors into Ports 11 and 12 to use this behaviour. You should use both ports (one sensor per port), because they perform different functions, both of which are needed for correct performance. If using Limit Switches, remember that these are fragile so use them carefully (without robust knocks). In Autonomous Mode both motors will drive forward. When the bumper switch on input port 11 is pushed in, the robot will interpret this as an indication that it has run into an immovable obstacle on the left side, and will turn to the right until the switch is no longer pushed in. The bumper switch on input port 12 does the same thing, but monitors the right side and makes the robot turn left when it is pushed. Suggested use: Autonomous Mode Obstacle Detector CREATING CONTROL

LESSON 04 PLENARY As a class, let us consider the following questions? A. What does the jumper do? B. Describe what sensors do to the cortex, and subsequently onto the motors. C. Why is a bump switch better for collision programming than the limit switch? D. How would you describe the term “behaviour” in the context of a robot?

SUMMARY Today you have:  Learnt about control when applied to a wide range of contexts, mainly robotics.  Observed how to connect simple control systems together and how they can be modified.  Developed knowledge of key terms and terminology used when describing control systems in industry. Learning objective: Learn how robotics are controlled and how this supports modern manufacture and industry. Work with a control programme to learn about how programming works.