Technology Enrichment Session 4: Electronics

Technology Enrichment Session 4: Electronics
Technology Enrichment
Session 4: Electronics
10/23/2015
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Today’s Agenda
● Electricity primer
● Safety
● Control Systems
● Common Tools and Techniques
● Common Robotic Components
● Cable Management
Electrical Basics
● Electrical Power Source
●
Most often a battery
●
Electrcity flows from positive to negative- the terminals on a
battery
●
This is called “polarity”
● An electrical “circuit” works only when it forms a loop
starting from the + terminal and ending at the - terminal
Electrical Circuit
● A very simple circuit where a battery is driving a motor
Voltage and Current
● Voltage - Potential difference of charge between two pts.
● Current - The rate at which charge flows through a
section of the circuit
● Voltage is cause and current is its effect
Resistance & Ohm’s Law
Wiring – Types of Wire
● Solid Core Wire
● Contains continuous length of solid metal/conductor
● More rigid- can fail due to bending
● Preferred for permanent installations and soldering
● Stranded Wire
● Contains multiple strands of metal
● More flexible
Wiring
● Wires are measured by gauges (AWG)
● Determines how thick the wire is
● Lower number is thicker, and can carry more current
● Common wire sizes for FRC ● 6 AWG for battery in FRC (very high current connection)
● 10-14 AWG usually for connecting motors
● >26 AWG for connecting sensors
Connectors
● “PWM” Pin header
● “Male” pins, and “Female” casing with a connection
● Mostly for PWM and I/O connections
Connectors
● WAGO Connector
● A class of connectors that secure cables generally through snap
connects
● Found on the Power Distribution board in FRC
● Usually needs a screwdriver to open
Connectors
● Lugs and Ring Connectors
● Connects cable to a device by bolting it together
● Often used to connect the battery or motor controllers
Connectors
● Anderson Powerpole Connector
● Connects power cables usually to batteries
● Quick connect allows for easy replacement
Tools & Techniques: Crimping
● Crimp Tool
● Crushes a metal connector around wire
● Most often used to attach a connector to a wire
Tools & Techniques: Soldering
● Soldering Iron
● Solder- Specially formulated metal
● Soldering Iron is used to quickly melt metal to join metal
wires, pins, and points on a circuit board
Tools and Techniques- Wire Strippers
● Removes insulation from a wire, so that you can access
the conducting metal
Tools and Techniques- Multi-Meter
● Measures the current, voltage, and connectivity of an
electric circuit
● Uses probes to measure into the circuit.
● Measure voltage in parallel to the circuit
● Measure Current, and connectivity in series
Techniques- Measuring Voltage
● Measure voltage in parallel to the circuit
● Example:
Techniques- Measuring Current
● Measure voltage in parallel to the circuit
● Example:
Electrical Safety
● Always wear Eye Protection: Goggles
● Do Not Complete a circuit with YOURSELF! Use plastic
gloves if needed.
● When Soldering, remember to unplug it and let it cool
down before putting it away. Do Not Play around with
it!!!
● Replace any damaged wires and Secure any loose wires
● Always be cautious of your surrounding and other people
● Do not wear any metal hand jewelry while working on
circuits
Electrical Components
● Battery
● Power Distribution
● Radio
● Controller
● NXT Brick, RoboRio, Vex Cortex
● Motor Controller
● Sensors
The Battery
● 12 Volt DC Battery
● Connects through the breaker to turn on the robot 120
Volt breaker
● Discharges over time
● Even faster if under use, like driving the robot
● Make sure to keep it charged
Power Distribution Panel
● Allows other parts of the robot to use the battery
power safely
● Contains connectors for:
● 12 Volt connection to motors
● 12 Volt to supply the VRM, RoboRio, and
Pneumatic Module
● Fuses to prevent high current draw from damaging
your robot
● CAN connection to get diagnostics on RoboRIO
Voltage Regulator Module and Pneumatic
Module
● The VRM Supplies regulated 5V power to
important devices
● Radio
● Camera
● The Pneumatics Module provides power pneumatic
hardware
● Solenoid drivers to drive the pneumatic valves
● Circuit to power compressor, with pressure switch cutoff
● Controlled over CAN
Radio
● The radio communicates to the field and driver
● Allows the competition to enable the robot to play
● Is a normal wireless router that you might find in your
house
● Connects to the RoboRio over ethernet
● All communication is over internet protocols
● New Radio for 2016, not sure about power
Pneumatics
● Solenoid Valves drive open a valve when a signal is applied,
and allows air to drive cylinder
● Either 12 or 24 Volt solenoids, controlled by jumper on Pneumatic
Module
● Compressor charges pneumatic storage tanks with
compressed air
● Runs off of 12v from the Pneumatic Module
● Wired into a pressure switch to turn off when a certain pressure is
reached for safety
Motor Controllers
● Takes in 12V from the PDP, and outputs between 0-12V
to the motor based on signal from RoboRio
● 2 Options for motor controllers Talon SRX and Victor SP
● PWM is most common, allows for control of the motor
voltage with PWM signal
● CAN allows control of the motor over the CAN bus and
allows for more advanced controls and feedback, but is
much harder to utilize
● Only available on the Talon SRX
The Controller
● FRC Controller is the RoboRio and runs the software to control the robot
● The Robot Signal Light is attached to show the state of your robot during
the match
● Manages the input and output for the motors and sensors
● PWM pins to drive motors
● Digital I/O pins for sensors
● Analog Input Pins for sensors
● I2C,CAN,SPI bus pins
● USB, and Ethernet ports
FRC Wiring Diagram
Sensor Basics
● Sensors are useful to determine what state your robot is in,
and make more reliable programming
○ Allows you to know where you are instead of guessing
● Many types of sensors that allow you to know specific things
about your robot
Sensor Types
●
Switches and Buttons
●
Acceleration and Motion Sensors
●
○
Accelerometer
○
Gyro
Rotational Sensors
○
Digital Encoder
○
Potentiometer
●
Hall Effect Sensor(Magnetic Sensor)
●
Rangefinder
○
Ultrasonic Rangefinder
●
IR Sensor
●
Camera
Switches and Buttons
● Completes or breaks a circuit when a condition is met
○ Usually a lever or button, but can be something like
pressure or a magnet in the area.
● The signal is high either or low when the switch is closed
○ If the signal is high when closed that means the
switch is normally open
○ If it is low then it is normally closed (Pneumatic
pressure switch)
○ Keep track what type of switch it is, especially if you
are connecting it to hardware (like the pneumatic
pressure switch)
● Uses:
○ Setting limits for an arm
○ Pneumatic pressure switch
Accelerometer
● Measures acceleration- how fast an object changes
velocity
● Constantly measures gravity downward
● Possible to measure position over short distances
by double integrating the reading
● Uses:
○ Knowing if the robot is tilted
○ Measuring movement over small distances
Gyroscope
●
●
●
●
Measures changes in orientation or angular velocity
○ Pitch: tilt up and down
○ Roll: tilt side to side
○ Yaw: tilt around the upwards axis
Yaw is hopefully the only measurement needed for a FRC robot
Gets noisy readings and becomes inaccurate over time
Uses:
○ Keep constant heading while moving
○ Get field centric control for a holonomic drive
Potentiometer
●
●
●
Changes voltage as it turns, due to the variable resistor
○ 0 at minimum rotation and 5V at fully rotated
Only limited degree of motion (usually 180-270°)
○ Some can wrap around, but the voltage resets
○ Good for when there is only one rotation being
measured
Uses:
○ Measure position of an arm
Encoder
●
●
●
Counts the marks on a disk as it spins by, the count tells how many
fractions of a rotation there has been
○ The fraction depends on the number of marks, or cycles per
revolution
Since it is just a count the rotation is continuous, and doesn’t reset
after a revolution
○ Does require a starting point to start from
○ This is usually done with a limit switch
Uses:
○ Distance driven by the robot
○ Height of an elevator lift
Magnet Sensor
●
●
●
Measures the magnetic field around the sensor
Functions most often as a switch or an encoder
○ The encoder functions by counting every time a magnet on
a rotating disk passes under the sensor
Uses:
○ Track rotational motion by counting the magnet on a wheel
○ Put setpoint positions on an arm
Ultrasonic Rangefinder
●
●
●
Produces an ultrasonic sound, and measures the time to
hear a reflection
○ By knowing the speed of sound you can measure
distance
○ This is often done in the software libraries or onboard
the sensor
Can cause inaccurate readings at close distance or certain
jaggy geometry (such as corners)
Uses:
○ Measures the distance to a goal
○ Check if you are close to a wall to prevent a collision
Infrared Sensor
● Measures infrared radiation
○ Can measure pulses, or radiant heat
● Uses:
○ Use IR pulse and wait for reflection to
use as a rangefinder
○ Locate IR targets in FTC, but not used
often in FRC
Camera
●
●
●
Creates an computer readable image
This image can be manipulated and analyzed to provide
additional information
○ Use image processing and computer vision
techniques
○ This is very difficult to do well, especially in teleop
Uses:
○ Give the human driver another view of the field
○ Perform computer vision to target a goal
○ Score when a certain visual signal is given in auto,
this usually gives bonus points
Cable management tips
Use zip ties to hold wires in
place.
Label wires properly. Ideally,
you should be able to unplug
all wires and know where they
go from the labels.
Plan ahead when it comes to
your electronics board layout.
Cut wires to correct lengths.
Needlessly long wires only get
in the way.
Wire management Ideas
Cable Carriers
● Protects wiring and allows
maneuvering of wires easily
when wires need to extend to
high heights on robot
Tubing
Sleeves
Velcro Wraps/Fasteners
● A good substitute for zip ties,
and can be taken off easily if
needed to access those wires.
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