Electrical System Presentation

1
Introduction

• Electrical System Presentation
• Minnesota Splash, Dec 8, 2007
• David C., of Team 1816, Edina Robotics

2
General Notes

• Overview
• Read the 2008 manual!
• Some things may change before next year

3
Safety

• Safety goggles
• Look before you touch
• Beware damaged batteries
• Follow wire size guidelines
• Don't leave batteries charging unattended
• Disconnect batteries from robot overnight, just
  in case

4
Tools and Supplies

• Basic
• Crimper
• Wire cutter
• Wire strippers
• Multimeter
• Optional/Advanced
• Extra terminals
• Extra wire/PWM cables
• Soldering iron
• Anderson connectors

5
Anderson Power Pole connectors
6
Battery and Voltage

• Stores energy as chemical energy
• Releases as electrical
• Voltage represents the pressure of the stored
  energy
• Measures differences in electrical potential

Water pressure height difference Electricity
pressure voltage difference
7
Current

• Rate of flow
• Water gallons per minute
• Electricity amount of charge per second
• Current moves through circuit due to pressure
  of voltage

8
Resistance and Ohm's Law

• Resistance restricts the flow of electricity
• Ohm's Law V I R
• If voltage is constant, higher resistance gt
  lower current, vice versa

Water closed valve restricts flow Electricity
high resistance restricts current
9
Energy in an electrical circuit

• Energy comes from the battery (chemical)
• Energy leaves through any source of resistance
• Ex resistors convert energy to heat
• Ex LEDs convert energy to light
• Rate of energy usage (a.k.a. Power) can be found
  with P I V

10
Power vs. Data

• Purpose is to provide energy to devices
• Higher currents, voltages
• Bigger wires
• More dangerous

• Purpose is to transmit information by turning the
  circuit on and off
• Lower currents, voltages
• Smaller wires

11
Data cont'd

• Analog varies continuously across range of
  voltages (i.e. gyro and accelerometer)
• Digital either on or off, represents a series
  of 1s and 0s (i.e. CMUCam2 and the radios)
• PWM Pulse Width Modulation changes between
  off and on at a fixed rate, but varies how much
  of the cycle is on (i.e. speed controllers)

0
1
0
1
0
0
0
1
0
1
Low value
High value
12
Crosstalk

• Due to noisiness from motor brushes
• Creates fields which can induce currents in data
  wires (erratic behavior)
• How to minimize
• Don't use too much excess wire
• Separate cable harnesses

13
Common Sensors

• Gyro
• Accelerometer
• Gear tooth sensor
• Optical encoder / shaft encoder
• Limit switch
• Potentiometer
• CMUCam2

14
FRC Electrical system

• Basic rules
• Copper only
• Minimum size rules
• Visibility/accessibility requirements
• Per-motor circuit breaker rules
• Color code wires

15
Wire sizing rules

• All wires have internal resistance depending on
  size
• Some motors require lots of current
• Current also has to flow through wires
• V I R and P V I ? P I2 R
• Large current through high-resistance wire ? heat
  generated quickly
• Melt insulation, start fire
• FIRST's rules limit both factors for safety's sake

16
Circuit Breakers

• Shorts or load faults - very low resistance,
  high current
• Circuit breakers detect high current, shut down
• (Bimetallic strip)

17
Wiring a Robot - Battery
Battery

• Must use battery, wire, lugs, connector from KoP

12V -
6 AWG
Battery Connector
6 AWG
18
Securing the Battery
19
Main 120A Circuit Breaker
12V -

• Must be accessible, this is the on switch for
  your robot

120 A
6 AWG
6 AWG
20
Power Distribution Block
12V -

• Breaks circuit apart to go to fuse panels
• Ground everything through the ground side of
  block
• Do not use chassis as ground

6 AWG
6 AWG
120 A
21
Circuit Breaker Panels

• ATC fuse panel for 20/30A
• Maxi-style fuse block for 40A

22
Diagram
12V -
120 A
6 AWG
6 AWG
14 AWG
14 AWG
Load
30 A
18 AWG
18 AWG
Load
20 A
6 AWG
12 AWG
12 AWG
Load
40 A
Load
40 A
23
Smaller Circuits

• Can use smaller wires (protected by circuit
  breakers with lower cut-off)
• 20A breaker 18 AWG or bigger
• 30A breaker 14 AWG or bigger
• 40A breaker 12 AWG or bigger
• Connect these to the different loads

24
DC Motors and Solenoid Valves

• Motors Brushed motors, use electromagnetic
  fields to spin a magnet
• Solenoid valves used in pneumatics, open or
  close to direct air flow
• Inductance
• Cannot use other solenoids, only solenoid valves
  (for safety reasons, prevent injury and shorts)

25
Victors and Spikes

• Speed controller
• Run a motor at any speed
• Rated for up to 40A
• Only use with motors

• Relay
• Switch between fwd/rev/off
• Rated for 20A
• Can't use certain motors with this
• Use these for compressor, solenoid valve

26
Custom Circuits

• Optional, if your robot needs it
• 20A breaker
• Commonly used to monitor subsystems or as a
  coprocessor

27
Troubleshooting and Common Pitfalls

• If using a compressor, you can replace the
  Spike's onboard fuse with a 20A breaker
• Never plug anything in backwards
• Check your backup battery often
• CMUCam2 and servos both run off of it, not main
  battery
• Servos tend to drain battery
• Optional onboard charger (use at own risk)
• http//ifirobotics.com/docs/first-backup-charger.p
  df
• If using gyro or accelerometer, connect both PWM
  headers to robot (to provide power)

28
Troubleshooting and Common Pitfalls

• If using a Gear Tooth Sensor, will have to make
  own power cable from PWM cable
• Communicate early and often with programmers
  about ports

29
Resources

• The manual
• Guidelines, Tips, and Good Practices
• Robot Power Distribution Diagram
• The Green Machine's forum http//www.edinarobotics
  .com/forum/
• ChiefDelphi http//www.chiefdelphi.com/
• The Blue Alliance http//www.thebluealliance.net/