Introduction to VEX Robotics

Transcription

1 Using the VEX Robotics System Introduction to VEX Robotics Archbishop McCarthy High School Robotics Team

2 Types Of Control Remote Control Wireless using some type of joystick Uses radio frequencies to communicate Autonomous Performs without human guidance A computer program tells it what to do Has sensors to respond to its environment Tethered Remote but wired control

3 Power Our primary power source will be a battery Portable Heavy Steady DC voltage Needs to be recharged or replaced May need multiple batteries with different voltages One for propulsion and microcontroller and one for the controller (joystick)

4 Movement Wheels and pulleys use DC motors A DC motor continuously rotates (360⁰) Speed is controlled by the amount of DC voltage Direction is controlled by polarity of DC voltage Arms and grippers can use servo s A servo goes to a position and holds there Typically minus 90 degrees to plus ninety degrees Position is controlled by an electronic signal

5 DC Motor Voltage amount given by pulse width modulation Longer on time means higher voltage Higher voltage equals higher speed Direction of rotation controlled by polarity

6 VEX Motor 2 wire motor connects directly to the Cortex ports 1 and 10 2-Wire Motor 269 Requires a motor controller to connect to any 3 wire port Motor Controller 29 3 wire ports produce a servo type RC signal output Ports 2-9 on the VEX Cortex

7 Motor Specs Free Speed: 100 rpm Stall Torque: 8.6 in-lbs Stall Current: 2.6A Free Current: 0.18A All motor specifications are at 7.2 volts Custom designed to connect to the VEX structural system Square drive shaft 2 screw connections Note that screw connections are 6-32, not the more common 8-32

8 Servo A servo is a motor connected to a built-in electronic control unit The control unit coverts the input signal to a position The input signal is a form of pulse width modulation

9 More Servo s Pulses are always 20 ms apart 50 pulses per second Pulse width varies between 1 and 2 ms ms of dead time A DC motor getting this signal would spin very slowly, if at all The pulse width determines the servo position 1 ms = full ccw (usually - 90⁰) 1.5 ms = middle (or null) position 2 ms = full cw (usually + 90⁰)

10 VEX Servo 3 wire servo connection Orange wire is +5 VDC power ALWAYS the middle wire Black wire is ground (0 VDC) White wire is PWM signal Connects directly to ports 2-9 on the VEX Cortex

11 Servo Specs Rotation: 100 degrees Stall Torque: 6.5 in-lbs Voltage: Volts Motor life will be reduced operating outside this range Current Draw: 20mA to 1.5 A per Servo 2 screw connections Square drive shaft Requires a clutch so gears don t strip

12 VEX Cortex Controller More powerful than the PIC Advanced STMicroelectronics ARM Cortex-M3 microprocessor Programmable with EasyC V4 VEXnet wireless technology Ethernet communications protocol b/g USB Adapter Keys

13 Cortex Controller Specs Built-in VEXnet Technology Wireless driving, wireless debugging, and wireless program downloading (8) standard 3-wire Motor or Servo ports (2) high current 2-wire Motor ports (8) high-res Analog Inputs, (12) fast Digital I/Os All can be used as interrupts Support for two 75 MHz transmitters and receivers Rx1 and Rx2 Ports I2C Smart Sensor Port Will connect to multiple new smart sensors in the future

14 VEXnet Joystick Joystick communicates with Cortex controller via wireless g Two X/Y joysticks plus 12 programmable buttons Ports on the back are: - Partner phone cord to another Joystick shares control (buddy system) - Program programming cable from PC USB port - Competition port On/Off power switch Adapter Top view Back-side view

15 Cortex M3 VEXnet Controller Adapter 8 Analog ports Two UART (data) ports One 12C (sensor) port 12 Digital I/O ports 2 built-in speed controllers 2 external speed controllers 10 motor/servo ports Backup power port (9V battery) Rx 2 Rx1 7.2 V battery port On/Off Switch

16 Cortex Controller Wiring Plan Black, - Gnd Red, +5 White, control/signal - Gnd + 5 V Rx (clock for 12C Tx (Data for 12C Black, - Gnd Red, + White, Control/Signal Two Wire Black Red +

17 Gears Gears are used for several things: To increase the speed of rotation To increase the torque, or the rotating force applied to a load Gears trade one for the other If you use gears to increase speed, torque will decrease If you use gears to increase torque, speed will decrease

18 More Gear Info Gears use teeth to transmit torque Teeth must be the same size, even on different size gears The number of teeth varies for different size gears A smaller gear has fewer teeth A larger gear has more teeth A big gear driving a small gear increases speed A small gear driving a big gear increases torque

19 Gear calculations

20 Structural System The structural subsystem of the robot is responsible for physical support. Holds everything in place The durable skeleton of the robot to which all the other subsystems are attached. The Structure and Motion subsystems are tightly integrated to form the chassis of the robot.

21

22 Additional Info 2 types of screw 6-32 and 8-32 Keps nuts Square drive shaft Bearing flat Spacers and friction reducers Metal sized by number of holes 5 X 15 1 X 25

23 Programming To program the robot you need both software and hardware The software is the computer program we use to write the program that goes into the VEX The hardware has two pieces: The VEX controller itself The cable that connects the computer to the controller so you can download the program you write into the microcontroller

24 Programming The VEX Cortex is programmed with easyc V4 easyc uses graphics based drag and drop programming Includes a full C text editor for advanced programming Download to the robot wirelessly over VEXnet or directly using USB

25 EasyC V4 The programs you write are a form of user code called project files A robot only does what the program tells it to do Select new project to create a brand new program Select open project to open an existing project VEX includes a couple of programs built in to EasyC The default code and the test code These programs will set up or restore your robot to an out of box condition

26 Opens IFI/Intelitek Loader window Screenshot of easyc V4 startup window

27 C Code Window Shows code in text format Function Block Window Drag and drop these into the programming window Block Programming Window Shows your code in a graphic block diagram format

28 Mapping Your Robot This is the full range of speed control for both motors and servo s 127 = full ccw (servo) or full speed reverse (motor) -127 = full cw (servo) or full speed forward (motor) 0 = null (servo) or off (motor)

29