Introduction to VEX Robotics - Maverick Robotics Websitemaverickrobotics.weebly.com/uploads/1/3/7/3/13730295/intro_to_vex.pdf · Introduction to VEX Robotics ... •A DC motor getting

Introduction to VEX

Robotics

Using the VEX Robotics System

Archbishop McCarthy High School

Robotics Team 2013-2014

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

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)

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

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

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

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

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

More Servo’s

• Pulses are always 20 ms apart

• 50 pulses per second

• Pulse width varies between 1 and 2 ms

• 18-19 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)

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

Servo Specs

• Rotation: 100 degrees • Stall Torque: 6.5 in-lbs • Voltage: 4.4 - 9.1 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

VEX Cortex Controller

• More powerful than the PIC

• Advanced STMicroelectronics ARM

Cortex-M3 microprocessor

• Programmable with EasyC V4

• VEXnet wireless technology

• Ethernet communications protocol

802.11 b/g

• USB Adapter Keys

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

VEXnet Joystick

•Joystick communicates with Cortex controller via

wireless 802-11g

•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

Back-side view

Top view

802.11 Adapter

Cortex M3 VEXnet Controller

10 motor/servo ports

12 Digital I/O ports

8 Analog ports Two UART (data) ports

One 12C (sensor) port

Backup power port

(9V battery) Rx 2 Rx1 7.2 V battery port

On/Off Switch

802.11 Adapter

• 2 built-in speed

controllers

• 2 external speed

controllers

Cortex Controller Wiring Plan

Black, - Gnd

Red, +

White, Control/Signal

Two Wire

Black –

Red +

Black, - Gnd

Red, +5

White, control/signal

- Gnd

+ 5 V

Rx (clock for 12C

Tx (Data for 12C

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

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

Gear calculations

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 sub-

systems are tightly integrated

to form the chassis of the robot.

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

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

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

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

Screenshot of

easyC V4 startup

window

Opens IFI/Intelitek

Loader window

Function Block Window Drag and drop these into the

programming window

Block Programming

Window Shows your code in a graphic block

diagram format

“C” Code Window Shows code in text

format

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)