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Electrical SafetyBasic Electrical Practices andTips for Passing Inspection
George MellorsTeacher Engineering former Industrial Engineer
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Electrical Safety (Hazards)Electrical ComponentsSystem Design/PlanningResourcesQuestions
Agenda
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Electrical Hazards
Battery AcidElectron Flow CurrentShort Circuit
High current hazard Sparks
Electrical Fire(s) In competition, Moon rocks, a robot in
the Hartford competition was burned badly by an electrical fire.
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Amps .vs. Injury in electricution
Note on right, it only takes 0.1 AMP to 0.2 AMP for potential Death.
Batteries used in FIRST FRC competition are sealedLead-Acid batteries. They can produce a 50 AMP current.
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Battery Safety
Batteries used in FIRST Competition contain Sulfuric Acid
While handling, working, cleaning up from accidental situations with a battery
Wear Personal Protective Devices (PPD)▪ Safety Eyewear▪ Protective gloves, rated for battery acid▪ Apron, again rated for protection against
battery acid▪ No jewelry which could conduct electricity
Handling Upright and away from cloths and body
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Battery Safety(continued)
Do you have a Battery Spill Kit?▪ WWW example▪ http://www.uline.com/Product/Detail/S-19486/Sorbents-and-
Spill-Control/Battery-Acid-Spill-Kit?pricode=WY233&utm_source=Bing&utm_medium=pla&utm_term=S-19486Q&utm_campaign=Janitorial%2BSupplies
Do you have an emergency eye wash kit?▪ WWW example▪ http://www.wayfairsupply.com/Sperian-Safety-Wear-Saline-
Personal-Eyewash-Bottle-FND320004520000-L2389-K~ZHK1030.html?refid=MX2649490155-ZHK1030&device=c&ptid=1104000081468
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Battery Current OverloadsCommonly Called Short Circuits
A short circuit occurs when the resistance in the circuit is very low or zero.
Using Ohm’s Law this results in very high current.
It will be as high as the source allows.▪ In San Francisco in 2001, a electrical repair
crew on a sub station North of the city energized the sub station without removing the grounding strap. Put the entire city in darkness until the issue was resolved.
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What happens with a Current Overloads (continued)Commonly Called Short Circuits
How long is a short circuit?Possible dangerous outcomes
Sparks Current contact with, through, human
body Overheat wires and electrical
component(s)
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Electrical SafetyElectrical Fire
Class C fire extinguisherBattery Handling
Gloves, Safety Glasses, clear path for transportation
Battery Spill ResponseConnection
Using FIRST connectors and proper wire gauge
Tape, Tape, and more Tape… NO copper showing
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Electrical Control System & Components
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Robot (PLC) Rio, Robo Rio
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Robo Rio (continued) Robo RIO
Powerful computer Control System Interfaces with control computer and robot
system Programming
▪ Java, C++, Labview Module Order and placement matters
▪ Camera (x-over) = Port 1▪ Radio = Port 2
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Speed Controllers PWM Signal is sent to control motor
speeds One controller per motor Two types exist:
▪ Victor 884 Jaguars (black new for 2010) Advantages
▪ In the program for a long time▪ Easy to program
Disadvantages▪ Manual break/coast jumper▪ Hard to calibrate
Victor
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Black Jaguar Newer Technology
▪ Better low end control More features
▪ Read rules Unknown reliability Larger footprint
Victor 884 Older technology
▪ Well tested Very reliable May be phased out
in the next couple of years
Motor Control Workhorses
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Talon SRXAdvantages
CAN support Internal limit sensors Break/Coast Button Calibrate Button
Disadvantages Connection/Application of 10
pin connector Wires are short.
Challenge – Programming CAN
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New Victor SPAdvantages
PWM control Break/Coast Button Calibrate Button
Disadvantages No external input controls Wires are short.
Would be used on simple control high amperage control.
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Relay module Advantages
▪ Programmed easily▪ On or Off only▪ Outputs can be easily
reversed▪ Can control
▪ Compressor▪ Solenoids for cylinders▪ Small PM Motors
Disadvantages▪ Limited Amperage (fused)
Spike
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Control Table for Software EngineeringOutput from
What does it control and how Special Considerations
▪ Servos (6V)▪ Speed
Diagram if possible
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What kind of control?▪ CAN▪ PWM▪ On-Off
▪ Feedback ? If so from were▪ Build in software ?▪ Labels
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Step 1 Read the ENTIRE rulebook Think about the robot design
▪ How many motors?▪ Which speed controllers?
▪ How many sensors?▪ Safe wiring paths?
▪ How much space should be put aside?▪ One board or multiple locations?
Electrical System Design
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Step 2 Discover how much space is allocated
for the electronics once the robot is designed▪ Consider preparing an early schematic
Electronics should be protected, but easily accessible▪ Velcro panel, zip tied cover
Radio should not be enclosed, keep from noise
Electrical System Design
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Step 3 Get all components laid out nicely
▪ Non-conductive platform (wood/fiberglass/lexan)
▪ Think about wire paths (bend radius and #)▪ Leave room in case you need to add
something Try to group related components to
shorten wires▪ Use proper wiring color conventions
▪ Red/white/brown = Positive : Black/blue = Negative Labels!
▪ Assist troubleshooting and inspection
Electrical System Design
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Step 4 Bench top test the electronics if possible
▪ Basic control system & programming testing Mount into the robot when it is ready to
move Secure wires from motors/sensors to
frame▪ Chassis must be isolated, no ground return
Design a secure battery holder with quick access▪ Remember, Battery position matters! Help
your CoG
Electrical System Design
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Do inspections regularly during build Know the rules!
Don’t crowd the inspector 1-2 people interacting makes things
easierNeat wiring and accessibility
Make sure all components are securedHave charged battery ready + no air
pressure
Inspection Tips
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Acceptable Wire Gages
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Signal light proper operation + visibility
Battery Terminal Lugs need electrical tape
Voltage monitoring improperly wired
Easily accessible 120A breaker/Dump Valve
Common Inspection Failures
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Plan for sensor expandability Keep a log of parts used
Nice for keeping the budget for inspection Also keep a spec sheet of components for
reference With your log as reference you can form
your own schematic to assist in inspection/judging Schematics are great for debugging especially
when those who wired it aren’t around (off-seasons, future years)
Other hints
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Batteries, put someone in control of charging
Zip Tie/Velcro Anderson Battery connectors during the matches
Assign someone to preventative maintenance Make sure zip-ties aren’t breaking, battery
holder loosening, etcCheck that your radio is plugged into
the Robo RIO!
General Things
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Usfirst.org Get the Inspection Checklist and FRC
SuggestionsChiefdelphi.com
Great forums for asking anythingAndymark.biz
Purchase electronics/gearboxes/chassis/misc
Ifirobotics.com Purchase Victors/Spikes/Wheels
Resources
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Questions?
Thanks for attending!