Introduction

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

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 => lower current, vice versa

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)

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 Must use battery, wire, lugs, connector from KoP

18. Securing the Battery

19. Main 120A Circuit Breaker Must be accessible, this is the �on switch� for your robot

20. Power Distribution Block Breaks circuit apart to go to fuse panels Ground everything through the ground side of block Do not use chassis as ground

21. Circuit Breaker Panels ATC fuse panel for 20/30A Maxi-style fuse block for 40A

22. Diagram

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.pdf 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/