Electricity Fundamentals

Electricity is the lifeblood of modern robotics. Every motor, sensor, and microcontroller relies on the flow of electrical energy. To design reliable robotic systems, you must understand three fundamental electrical concepts: current, voltage, and resistance.

Voltage (V)

What is Voltage?

Definition: Voltage is the electrical potential difference between two points. It's the "push" that drives electrons through a circuit.

Voltage (V) = Energy per unit charge
Unit: Volts (V)

Physical Analogy: Think of voltage like water pressure in a pipe - higher pressure pushes water harder through the pipe.

Voltage in Robotics

Voltage Sources

Example: Battery Series Connection

Connect batteries in series to increase voltage:

2 × 3.7V Li-ion cells in series = 7.4V
3 × 3.7V Li-ion cells in series = 11.1V
4 × 3.7V Li-ion cells in series = 14.8V

Figure: XT60 connectors commonly used for battery connections in robotics

Current (I)

What is Current?

Definition: Current is the flow of electrical charge through a conductor. It measures how many electrons pass through a point per second.

Current (I) = Charge per unit time
Unit: Amperes (A)
1 Ampere = 1 Coulomb per second

Physical Analogy: Current is like the amount of water flowing through a pipe - measured in gallons per minute.

Current Direction Conventions

Two conventions exist:

For robotics, we use conventional current (positive to negative).

Current in Robotics

Typical current draws:

Ammeter Measurement

To measure current, use an ammeter connected in series with the circuit:

[+] Battery --> [Ammeter] --> [Load] --> [-] Battery

Resistance (R)

What is Resistance?

Definition: Resistance is the opposition to current flow in a circuit. It's caused by collisions between electrons and atoms in the conductor.

Resistance (R) = Opposition to current flow
Unit: Ohms (Ω)

Physical Analogy: Resistance is like friction in a pipe - it opposes water flow.

Resistivity and Resistance

For a conductor:

R = ρ × (L / A)

Where:

• ρ (rho) = resistivity of material (Ω·m)
• L = length of conductor (m)
• A = cross-sectional area (m²)

Key insight: Longer wires have more resistance; thicker wires have less resistance.

Wire Gauge and Resistance

Thicker wires (lower AWG number) have lower resistance:

Figure: Wire gauge comparison - thicker wires for power, thinner for signals

Resistor Types in Robotics

The Water Pipe Analogy

Understanding voltage, current, and resistance is easier with an analogy:

Energy and Power from V, I, R

Relationships

Power (P) = Voltage × Current
P = V × I

Power in resistor:
P = I² × R
P = V² / R

Example: 12V battery with 5A motor

P = 12V × 5A = 60 W

Energy Consumption

Energy = Power × Time

E = P × t
E = V × I × t (Wh - Watt-hours)

Example: 60W motor running for 2 hours

E = 60 W × 2 hours = 120 Wh

Summary

Key Relationships:

• ✓ Voltage = Electrical potential difference (pushes electrons)
• ✓ Current = Flow of electrical charge (electrons moving)
• ✓ Resistance = Opposition to current flow (friction-like effect)
• ✓ Power = V × I (wattage consumed)
• ✓ Energy = Power × Time (total consumption)

Practical Tips:

1. Understand typical voltage levels (5V, 12V most common)
2. Calculate current draw before designing power system
3. Choose proper wire gauge for current capacity
4. Use proper resistors for protection and control
5. Account for voltage drop in long wires