Electrical SafetyBasic Electrical Practices andTips for Passing Inspection

George MellorsTeacher Engineering former Industrial Engineer

Electrical Safety (Hazards)Electrical ComponentsSystem Design/PlanningResourcesQuestions

Agenda

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.

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.

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

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

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.

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)

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

Electrical Control System & Components

Robot (PLC) Rio, Robo Rio

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

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

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

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

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.

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

Control Table for Software EngineeringOutput from

What does it control and how Special Considerations

▪ Servos (6V)▪ Speed

Diagram if possible

What kind of control?▪ CAN▪ PWM▪ On-Off

▪ Feedback ? If so from were▪ Build in software ?▪ Labels

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

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

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

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

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

Acceptable Wire Gages

Signal light proper operation + visibility

Battery Terminal Lugs need electrical tape

Voltage monitoring improperly wired

Easily accessible 120A breaker/Dump Valve

Common Inspection Failures

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

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

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

Questions?

Thanks for attending!