robot design workshop: vex hardware & robot building basics elliot eid minnesota best robotics...

Robot Design Workshop:

VEX Hardware

& Robot Building Basics

Elliot Eid

Minnesota BEST Robotics

Copyright © 2010 BEST Robotics, Inc. All rights reserved. 1

BasicsBasics Only use parts supplied in the consumable and

returnable kits, or on the approved optional items list

Do not modify returnable parts No paint, tape (except non-residue tape), glue, etc.

may be placed on these parts

Robot must fit into a two-foot cube (initially) and weigh less than 24 pounds Arms may extend outside two-foot cube after game

starts

All machines will be inspected for compliance prior to competing


Servos

Controller

Analog

Motors/Servos

Battery

Digitali/o

WiFi key USB/Tether

Serial

Joystick

(2)

Servo Horns

Return Kit ItemsReturn Kit Items


(2)(2)

Servo Extensions

(2)

USB A-A cable

AAA Battery Charger

(4)

(2)

(2)

(2)

Motors

Drive Components

Return Kit ItemsReturn Kit Items


MotorController (4)

Screw TerminalMotor i/f Cable (4)

Screw TerminalSensor i/f Cable (8)

7.2V Battery

7.2V Battery Charger

Battery Adapter

(2)

VEX Cortex Battery ConnectionVEX Cortex Battery Connection

Robot Design Workshop 2011 Copyright © 2010 BEST Robotics, Inc. All rights reserved. 5

leave connected hereconnect/disconnect here

VEXnet Control SystemVEXnet Control System


• VEX Cortex Microcontroller• Dual ARM Cortex CPUs• Programmable• WiFi Radio Technology

VEXnet Cortex M3 ControllerVEXnet Cortex M3 Controller


System StatusIndicators

WiFi 802.11Proprietrary Comm8 Analog

inputs

12 DigitalInputs or Outputs

10 Motor/Servo Ports(Built-In ESC on 2 ports)

Standard Serial Interfaces(UART, I2C)

SpeakerOutput

VEXnet JoystickVEXnet Joystick


2 XY Analog Joysticks

8 Buttons on Top

Plug-in USB/ WiFi Key

4 Buttons on Front-Side

Programming Interface

“Playstation” Game-Style Controller

3 Axis Accelerometer(XY Tilt, XYZ Accel, Shake)

Power Switch6 AAA

RechargeableBatteries

VEX Cortex ConnectorsVEX Cortex Connectors


USB

AnalogIn

DigitalIn/Out

2-wire motor

Standard Serial Interfaces(UART, I2C)

SpeakerOut

1

12

1

8

SP

12

910 2-wire motor

3-wire PWMServo/Motor Ctrl

Gnd(Blk)

+5v(Red)

Sig(Wht)

Sig(Wht)

+5v(Red)

Gnd(Blk)

VEX Cortex ConnectorsVEX Cortex Connectors


Backup Battery Port for WiFi Communications (9V)

75MHz Crystal Interface Ports (not used by BEST)

On/Off Switch

Main Battery Port (7.2V)

Configuration Switch (used for special

procedures)

VEX Cortex PinoutsVEX Cortex Pinouts


Ground

+ 5V

Signal/Control

+ Battery Power

+ Battery Power

(for + control input)

+ Battery Power

(for – control input)

DC MotorsDC Motors

Four Motors are Supplied in the Kit Two large motors and two

small motors Motors can be used to

power wheels, lifting arms or mechanisms, grippers, etc.

Motors may be mounted using the Brackets and Screws supplied in the Consumable Kit.


Mounting DC MotorsMounting DC Motors Use of motor mounting plates to mount the motors is

no longer required. HOWEVER, if they are not used when face mounting the small motor, it is easy to damage the internal gear plate.


DC MotorsDC Motors


Four External Motor Controllers Supplied this YearConnect via 3-wire external motor controller and

2-wire screw terminal cable (red/black) Use motor ports 2 thru 9 only!

Do NOT Use the Built-In Motor Controllers Motor ports 1 and 10 Motor amperage may damage circuitry


DC MotorsDC Motors

Servo/Motor Ports are Divided into 2 Banks Bank 1 = Ports 1 - 5 Bank 2 = Ports 6 – 10 Use only ports 2 – 9 Each bank can support a maximum of 4 amps of current BEST large motor stall current can reach 3.5 amps

For Power Reasons, Spread Motors among Ports No more than 2 motors plugged into ports 2 – 5 No more than 2 motors plugged into ports 6 – 9 Otherwise you risk overcurrent and shutdown of the processor

Sheet Metal Shield around the Large Motors IS Needed and Should NOT be Removed

DC MotorsDC Motors


Connect Wires to Motor Terminals Quick-disconnect terminals (Strongly Preferred!) Solder

Polarity is NOT Marked on Motors: positive (+), negative (-) Wiring (and Programming) will Determine Clockwise or Counter

Clockwise Rotation for Positive Stick Movement Its recommended that you mount motors using supplied Brackets

and 8-32 Machine Screws

Machine screwsmust be cut to

proper length toavoid motor damage(use screws supplied

in kit)!

Max screw depth=~1/8” (small motor)~1/4” (large motor)

3-Wire Motor Connection3-Wire Motor Connection


External MotorController Standard 2-wire

Motor Cable

Standard 3-wirePWM connector

Suggest using a 4” wire tie, heat shrink tubing, or RESIDUE FREE painter’s tape here

Screw Terminals for attaching motor leads

3-Wire Motor Connection3-Wire Motor Connection


Connectors are not keyed Connect red to red, black to black

ServosServos Servos produce a

specified rotational movement when activated

Possible Uses Activation of micro-

switches Operation of grabber

mechanisms Release of a spring-

loaded latch


ServosServos


Futaba S3003 or S3004 Series Maximum 120 Degree Rotation (+60, -60) Connection to Cortex Controller

Via 3-wire Servo Power Adapter Cable Prevents damage to servos

Use motor ports 2 thru 9 only

Servo Horns may be Modified

Servo Horns

(2) (2)

(1)

Do not overtighten mounting screws!

Example HookupExample Hookup


Servo

Motor Controller

DC Motors

Battery

Motor Screw Terminal

Cortex Controller

There are 3 things

wrong here


Motor/Servo ConnectorsMotor/Servo Connectors Placement of Servo Connectors

VEX motor controller can be placed adjacent to a Futaba servo or extension connector

1) Keyed differently; will work but a tighter fit.

2) Recommend keeping motor controller in a higher numbered port; may lose one servo port due to this.

Futaba servo & extension connectors ARE keyed BUT they will still fit in backwards. Pay attention to the keying and wire orientation (white wire to the inside).

1 2

Digital Input ConnectionsDigital Input Connections


Use for Limit Switches, Microswitches Connect to Cortex Digital Inputs using 2-wire Sensor Screw

Terminal Cables (white/black wires)

Sensor Screw Terminal Cable

Connect to Switch

Connect to CortexDigital Input Port

Digital Input ConnectionsDigital Input Connections


Must program Digital Port for proper direction (input) Open = reads as ‘1’ ; Closed = reads as ‘0’

Use Digital Ports1 thru 12

Sensor CableConnector is keyed

Analog Input ConnectionsAnalog Input Connections New last year: POTENTIOMETERS!


5V Pin

Signal Pin

Ground Pin

Signal Terminal on CK Pot

Re-Syncing (Pairing) VEXnetRe-Syncing (Pairing) VEXnet


If VEXnet does not connect, you may need to re-sync thejoystick/controller pair by simplyconnecting a USB cable and powering on both units.

Out of the Box ConfigurationOut of the Box Configuration


Cortex Controller comes pre-installed with a default program.

Allows a team to hook up the Cortex and have it work without having to program it.

Referred to as the “BEST default” program. This is NOT the only configuration for the

Cortex! Good for initial checkout, but we want teams

to load a unique configuration.

BEST Default ProgramBEST Default Program

Motor/Servo

Port

Joystick

Channel

Motor Limits

Positive Direction

Negative Direction

Motor 1

(Arcade Right)

Channel 1 (Lt, Rt)

Channel 2 (Fwd/Rev)

None None

Motor 2 Channel 1 Digital Input 1 Digital Input 2




Motor 6 Channel 3 None None

Motor 7 Channel 3 Inversed None None

Motor 8 Channel 4 None None

Motor 9 Channel 4 Inversed None None

Motor 10

(Arcade Left)

Channel 1 (Lt, Rt)

Channel 2 (Fwd/Rev)

None None


BEST Programming OptionsBEST Programming Options


Three different programming environments available easyCv4 http://www.intelitekdownloads.com/easyCV4 RobotC http://www.robotc.net/download/cortex Mathworks MATLAB/SIMULINK http://www.mathworks.com

easyC is a block programming environment (similar to software for Lego Mindstorms)

RobotC programs in C with a text editor, but it has runtime debugging (can step through program line by line and see what the results are)

SIMULINK is graphical programming/modeling environment with simulation capability (see what your program will do before you download it to the Cortex)

Direct USB DownloadDirect USB Download


Downloading a ProgramDownloading a Program

Uses only the A-A USB cable.

Battery is notneeded


Testing TipsTesting Tips Ensure your robot is ‘safe’ to operate:

Can’t move or fall off table (use a jack-stand) All team members clear of moving parts

Connect either WiFi keys or tether cable between the joystick and the Cortex controller.

Make sure Cortex switch is in OFF position. Attach a charged battery. Turn on joystick (if not using tether). Turn Cortex switch to ON position. For WiFi comm, link should establish in ~10 sec. Test robot operations with transmitter.

LED Status LightsLED Status Lights


Joystick Battery Status

Robot Battery Status

Communication Link Status

Game Status (not used by BEST)

• Green Battery – good charge• Yellow Battery - dying• Red Battery – dead

• Green VEXnet – communication established• Yellow VEXnet – searching• Lights on the controller and the joystick are

the same

Team TipsTeam Tips Use quick-disconnect terminals to attach wires to motor

terminals (preferred). If using solder, tin motor wires before attaching to screw terminals since frayed stranded wires can cause a short.

Do NOT solder wires to Cortex connectors! Sensor cables, servo wires, and servo extensions are all keyed

in correct orientation; insert and remove carefully to avoid destroying connectors (pin connectors are very delicate).

Tighten screws on motor and sensor connector cables so that wires are not loose and do not pull out.

Mount Cortex to robot using #8 screws through holes provided; be careful not to over tighten.

Avoid “hot insertion” of USB Keys. You may operate tethered by removing the USB WiFi key and

connecting a USB A-A cable between joystick and Cortex.


Joystick CalibrationJoystick Calibration If the motors hum or creep (sticks not returning to zero), the

joystick may need to be recalibrated Calibration procedure (as extracted from the easyC help file):


1) The Joystick must be "Linked" to the Cortex Microcontroller using the VEXnet Keys.

2) Hold the "6U" Back Switch depressed.

3) While the "6U" Back Switch is depressed, use a small Allen Wrench (1/16" or smaller) or similar small straight tool to depress and hold the CONFIG Switch.

4) Hold both Switches depressed until you see the Joystick LED Flash RED and GREEN - you can now release both Switches.

a. There is a 10 second time limit to complete the following steps 5 and 6.

5) Now move both Joystick Pots to the maximum position desired in all 4 directions - Up, Back, Left, and Right.

a. If a movement is not detected in all 4 directions, a timeout will occur after about 10 seconds and the Cal Mode will be discontinued and the VEXnet LED will briefly Flash Red.

b. The Joystick LED will continue to Flash RED and GREEN during the calibration process.

6) After movement is detected in all 4 directions, the Joystick LED will be ON and Solid GREEN.

a. To "Save" the Calibration, depress and release the "8U" Top Switch Button.

b. If the calibration is accepted and Saved, the Joystick LED will start Flashing Fast GREEN for a few seconds.

c. If the Calibration is not Saved, a timeout will occur after about 10 seconds and the Cal Mode will be discontinued and the VEXnet LED will briefly Flash Red.

d. To cancel a calibration, depress and release the "7U" Top Switch Button. The Cal Mode will be discontinued and the VEXnet LED will briefly Flash Red.

e. If the Cal Mode is discontinued or saved, the Joystick LEDs will resume their normal function after the VEXnet LED briefly Flashes.

Design Basics: ChassisDesign Basics: Chassis

Use plywood or PVC to create a chassis. Other components will be mounted to the chassis.

Two large motors can be used to power drive wheels. Robot will move forward, backward, or turn by varying relative speed and direction of each motor.

Allow non-drive wheels to pivot to make robot maneuverable.


Chassis (plywood or PVC)

Wheels

Motors

Wheel AttachmentsWheel Attachments Some proven techniques for mounting drive wheels

to motor spindle. Other techniques can be used.


Wheel SizeWheel Size

Experiment with size of wheels.


• Large wheels:• Faster robot• More difficult to control

• Small wheels:• Slower robot• Easier to control

Lifting MechanismsLifting Mechanisms

Many mechanism designs can be created to lift or retrieve objects.


Belt and Pulley

Slide and Rail System Scissors Lift Parallel Arm Linkage

Linear Drive MechanismLinear Drive Mechanism


Rotational motion of motor can be used to create a linear drive using belts and

pulleys.

Grabbing MechanismsGrabbing Mechanisms

Simple grabbing mechanism can be operated by a servo, allowing motors to

be used for lifting mechanisms.


Servo with Servo Horn

Wires attach armsto Servo Horn

As Servo rotates, grabber arms open and close

Pivot

RemindersReminders

Read Generic Kit Notes Read Generic Game Rules Read Game-Specific Rules Re-read all of the above!



Where to find help?Where to find help? Online documentation (BRI Site)

http://www.bestinc.org

BEST Public Message Board (for anyone) http://tech.groups.yahoo.com/group/bestinc/ Must register for login account Share ideas, resolve issues, …

Official Q&A “Control System” Category http://www.bestinc.org/cgi-bin/bestqna Use “Official Q&A” page during contest for “rules specific” questions Is this legal?

VEX Forum http://www.vexforum.com/forum.php Technical questions about VEX equipment easyC and RobotC dedicated forums included here

Robotevents BEST Forum http://forum.robotevents.com/forumdisplay.php?f=51 Dedicated user forum for BEST Robotics Must register for a login account

robot design workshop: vex hardware & robot building basics elliot eid minnesota best robotics...

Documents

best onoff

cortex connectors copyright

cortex pinouts copyright

small motors motors

kit items copyright

control input slide

vexnet joystick copyright

signalcontrol battery