Electrical Principles

�OFF SEASON TRAINING

Volts vs Amperes vs Watts

• Volts (Power), V
• the potential difference in charge between two points
• the size of the force that sends the electrons through a circuit
• Amperes (Current), Amp, I
• the unit used to measure electric current
• The number of electrons flowing through a circuit.
• Watts, W
• A measure of the rate of energy transfer of an appliance
• The rate of energy generated or consumed
• Ohms (Resistance), 𝝮
• A measure of the opposition to current flow in an electrical circuit

What is Electricity

Series v Parallel

A closed loop of conductive material.

Continuously flow of electric current. Positive to negative or ground. (+, -)

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Series: Components are chained together from positive to negative to positive etc.

Parallel: Negative to Negative and Positive to Positive

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Circuits

Electrical Safety

General:

• Power off before doing any electrical work
• Finish what you start
• Always check for exposed conductor

Battery:

• Check wires and breaker, make sure robot is ready to be turned on

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Etiquette:

• Once power is involved, listen to instruction if instruction is being given
• No mistake is a singular person’s fault, we are a team
• If you are bored, do not play with tools on the table

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COMPONENTS

What makes up the Electrical system?

System Overview

Power Distribution Part 1

12V Lead Acid Battery

Nominal Voltage: 12V

Capable of over 180 amps

120 Amp Breaker

Used to disconnect and connect the battery and prevent the system from drawing too much power.

Power Distribution Part 2

PDH

Distributes power from battery to all components plugged into it

• Breaker limits current to the component. ( 5 amp - 40 amp options)
• The mini-fuse is not resettable ( 5 - 20 amps)

Power Distribution Part 3

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VRM

Regulates voltage directed from PDH to smaller devices

(limelight, etc)

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RPM

Supplies PoE (Power over Ethernet) for the radio.

Radio

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Communicates with the driver’s station via it’s own WiFi network

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Connects to PDH

and RPM for power and RoboRio with ethernet cable

Smaller Components Part 1

RSL

Controlled by the RoboRIO

Flashes whenever the robot is enabled

Stays solid when disabled.

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CANcoder

Precisely measures the

rotation of a shaft or wheel

Integrated within CAN chain

Smaller Components Part 2

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CANivore

Separates different CAN bus chains.

Ex. one for drive and one for upper shooter

RoboRIO

The brain

Any device that needs info must be connected here

CAN bus chain

Electrically, the FRC CAN network is a two-wire bus, designed to allow dozens of devices to talk to each other with a single network.

• Needs two 120 ohm resistors to terminate the ends of the bus.

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(The daisy chain is an example of a series circuit (if it breaks in once place, the whole circuit is useless).

Speed Controllers

• “smart motor controller” for more advanced things like encoder positioning, software limit switches, and feedback loops

• Regulates the speed and power of a motor
• Communicates via the CAN bus

DISCUSSION

What is the RoboRio?

What is the RPM?

What is a CAN chain?

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Pneumatics

How to move things with air.

• Compressor

Charges air for components on the robot.

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• Pressure Switch

Works with a controller to tell the compressor when to shut off.

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• Solenoid Valves

Electronically controlled valves.

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Pneumatic Controllers

PH/PCM

• Controls the compressor and up to 8 solenoids.
• It gains input for a pressure sensor to control the compressor when needed.
• Can based communication

Electrical Solenoid Valve(s)

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Actuates the different sides of a pneumatic component such as a shifter or piston. Can be single or double action.

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Compressor

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Charges air for components such as pistons and shifters on the robot. FRC-legal amount of air is 120 psi.

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Emergency Relief Valve

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Keeps the air under 125 psi if the compressor or pressure switch is working incorrectly

Pressure Switch

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Manages amount of pressure in the robot

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Acts as “go-between” for the PCM and compressor.

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Dump Valve

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Releases (or dumps) all air out of the robot.

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Questions

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DISCUSSION

What is the compressor?

What keeps the system from overcharging?

How do you release the air?

Sensors

How the robot knows things about its surroundings

Analog Signals and Digital Signals

Analog Signals

• Smoothly and continuously go through a range of values
• Accelerometers create analog signals

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Digital Signals

• Blocky and steps between two values 1 or 0
• Limit switches create digital signals

Limelight

A smart camera that makes giving the robot vision simpler.

Used for april tag or retro reflective tape detection for targeting scoring elements.

Gyros and Accelerometers

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Pigeon

What angle the robot is at on the X, Y, Z axis

Critical for autonomous or balancing

Able to tell how fast the robot is moving

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Encoders

Both types are used to measure the rotation of an axle

Absolute encoders know their angle on startup while Incremental need to be zeroed

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Limit Switches and Magnetic switches

Hitting the top button interrupts or starts the flow of electricity depending on how it’s wired. Good for hard limits

Detects when a magnet is close to the sensor, good for when you don't want something physically touching

Beam Breaks and Proximity Sensors

Uses light to tell if there is an object between the emitter and receiver

Tells how far away an object is by bouncing light off it and recording the time it takes to sense the light

Uses a change in resistance as the shaft rotates or slider moves to indicate position or adjust voltage levels

Linear and Rotary Potentiometers

Discussion

How does a optical encoder know its rotation?

Which signal type is smooth and which is blocky?

What switch requires contact?

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Questions