High Torque Servo Control with Arduino Uno and ASME-03: 0-180 Degrees

The internal circuit of a servomotor interprets input signals lasting approximately 20 milliseconds. The position depends on the pulse width within this window: 0.5ms high state positions at 0 degrees, 1.5ms at 90 degrees, and 2.5ms at 180 degrees. PWM (Pulse Width Modulation) controls pulse width. The PWM frequency is set to 50 Hz, creating 20-millisecond pulses. Two methods control pulse width: duty_ns (measured in nanoseconds) and duty_cycle (16-bit resolution, 65,536 values). Values of 0 represent completely low state, while 65,535 represents completely high state. Specific duty cycle values: 500ns for 0 degrees, 1500ns for 90 degrees, and 2500ns for 180 degrees.

This section covers servo motor control using PWM (Pulse Width Modulation). Servo motors are used for precise angular control in applications like automatic gates and robotic arms. They have three wires: power (brown/red), ground (black), and signal (green/yellow/orange). The power wire connects to 3.3V or 5V, ground to ground, and signal to a microcontroller pin (e.g., D15). To control servos, you must import both 'pin' and 'PWM' from the machine module. Servo motors use PWM signals with a duty cycle range of 25 to 125, where 25 corresponds to 0 degrees and 125 corresponds to 180 degrees. The duty cycle determines how long the signal is 'on' within each cycle, controlling the servo's position. The duty cycle formula is: duty = min_duty + (angle / 180) * (max_duty - min_duty). For a servo with min_duty=25 and max_duty=125, this converts angles (0-180 degrees) to duty cycle values. A duty cycle of 50 means the motor receives power for 50ms, causing limited movement. A duty cycle of 100 means longer power duration, causing more movement. The duty cycle repeats continuously as the servo moves through different positions.

A servo is an electromechanical device that rotates an axis with high precision, consisting of a DC motor, electronic control circuit, position sensor, gears, and housing. Servos are classified by weight: micro (3-10g), mini (11-25g), standard (25-60g), and large (over 60g). PWM (Pulse Width Modulation) controls servos using two states: high (0.3V) and low (0V). Duty cycle represents the percentage of time the signal remains high, ranging from 0% to 100%. Standard 180-degree servos operate with duty cycles between 2% (0 degrees) and 12% (180 degrees). Frequency is measured in Hertz (typically 50 Hz for servos), and period is the reciprocal (20 milliseconds for 50 Hz).

A servo motor is a small DC motor with three terminals: positive (5V), ground, and a signal terminal. It is controlled using Pulse Width Modulation (PWM), a square wave signal where the 'on' portion width determines the motor's position. The PWM pulse width ranges from 0.5ms to 2.5ms with a 20ms total period. At 1.5ms, the motor is at 0 degrees (center); at 2ms, it moves to 90 degrees; at 1ms, it moves to -90 degrees. Servo motors come in two types: continuous rotation (direction controlled by PWM duty cycle) and position control (angle controlled by PWM pulse width).

This video explains how to control SG90 servo motors using a Raspberry Pi by generating Pulse Width Modulation (PWM) signals through Python programming; servos differ from regular motors in that they provide precise angular position control (0-180 degrees) via a feedback mechanism, where the angle is determined by the duty cycle of a 50Hz PWM signal (2% duty cycle = 0°, 12% duty cycle = 180°), and the Raspberry Pi's GPIO pins can generate these signals to control one or more servos simultaneously.

Motors require external power supplies because they draw much more current than the Arduino can provide. Connect the motor's positive terminal to the external battery pack's positive bus, and the motor's negative terminal to the transistor's Drain pin. The transistor then allows current to flow from the battery through the motor, through the transistor's Drain and Source pins, and back to ground. This keeps all high-current paths separate from the Arduino's low-current control circuit.

High-power DC motors like the 775 series require significantly more voltage and current than standard Arduino projects. These motors cannot be powered by the Arduino's 5V output or even by 7.5V from two 18650 batteries. They require external power sources because passing such high currents through the microcontroller would cause immediate damage. The key principle is that high-power components must be powered independently from the microcontroller to prevent system failure.

When a motor requires more current than the Arduino can provide, an external power supply must be connected to the L293D's Vcc2 pin (pin 8). The external power source (such as a battery or power adapter) provides the necessary current for motor operation, while the Arduino only provides control signals. The negative terminal of the external power supply connects to the circuit's common ground. This separation prevents the Arduino from being damaged by motor startup currents while ensuring the motor receives adequate power.

Arduino boards (UNO, MEGA, LEONARDO, DUE) require an external power supply of 12V DC with a current rating between 0.75A and 1.5A to operate safely; using a power supply with higher amperage can damage the board, while the voltage regulator ensures proper voltage distribution to the pinout for stable 24-hour operation.

Motor driver boards require an external power supply because stepper motors can draw substantial current that could damage the Arduino. The external power supply provides dedicated power to the motor, while the Arduino only handles data communication. This separation ensures the Arduino remains protected while the motor receives adequate power for operation.

Electrical circuits require proper grounding for safety, consisting of positive (live) and negative (neutral) wires with ground providing a safe path for excess current. Birds can sit on power lines safely because they only touch one wire, creating no complete circuit. Earth serves as the negative terminal, completing circuits when current flows from positive through devices back to ground. Insulators like rubber, plastic, and dry wood prevent current flow through unintended paths. The amount of current flowing through a person depends on voltage and resistance—higher voltage pushes more current through resistance. Materials with high resistance allow less current flow. Human perception thresholds vary: currents below 50-100 milliamperes may not be felt, while currents above 100 milliamperes cause painful shocks. Currents of 1000 milliamperes or more can cause cardiac arrest.

Electricity is moving charge (electrons) through wires that powers modern society. Current is the rate of charge movement (I = dQ/dt), measured in amps. Higher current means faster electrons and hotter wires, and can be dangerous (1 amp can kill). Voltage is the force pushing current through circuits, measured in volts. Ground is a reference point (0V) essential for circuit analysis and safety. Different electronics have different current tolerances (Arduino: 5-50mA, motors: 3+ amps). The human body has high resistance (10k-10M ohms), making even small currents dangerous.

This section explains why current matters more than voltage in electrical safety. Voltage represents potential difference or 'pressure' (measured in volts), while current measures actual flow (measured in amperes). Ohm's Law (V = I × R) describes their relationship through resistance. High voltage readings alone don't indicate danger—if resistance prevents sufficient current flow, no harm occurs. Standard grounding cords allow about 3.8 microamps of current, while filtered products dramatically reduce this flow, demonstrating how resistance protects against harmful electrical exposure.

This comprehensive section covers the foundational principles of electrical circuits and safety. Series circuits connect resistors end-to-end in a single path, with equivalent resistance calculated as R_eq = R1 + R2 + R3. Current remains constant throughout all components, while voltage varies according to Ohm's Law (V = IR). Parallel circuits maintain constant voltage across all branches while current divides among them. The section explains the relationship between charge, current, and time: Q = I × t, where one Ampere corresponds to approximately 6.25 × 10^18 electrons per second. Electrical safety thresholds are covered: currents below 10mA cause mild tingling, 10-15mA cause noticeable shock, and currents above 50mA can be fatal. DC current causes more severe shocks than AC current due to constant polarity.

An electrical circuit operates on the principle that current leaves the power source and returns to the same source through a closed path, applying to both DC and AC circuits. A critical misconception addressed is that electrons do not flow to ground during normal operation—they follow the intended circuit path back to the source. In parallel circuits, voltage remains constant across all branches, meaning a human body in parallel with a 120V circuit will experience the full 120V. Body resistance values are approximately 1000Ω for hand-to-hand and hand-to-foot, and 500Ω for hand-to-stomach. Using Ohm's Law, 120V through 1000Ω produces 120mA, exceeding the let-go threshold of ~1mA for most adults. The heart operates at ~40Hz, close to AC power frequencies of 50-60Hz, making it vulnerable to current disruption. As little as 50 microamperes through the heart can cause ventricular fibrillation—a chaotic rhythm preventing effective blood pumping. Research shows the let-go threshold is approximately 1mA per 10 pounds of body weight, explaining why children are more vulnerable than adults. The fundamental method to make electrical systems safe is to turn off the voltage source by opening circuit protection devices. To safely clear faults, an effective ground fault current path with low impedance must exist from the fault point back to the source. According to NEC Article 100, 'ground' is defined as the earth, and 'grounded' means connected to the earth or a conductive body extending to it. There are two types of grounding: system grounding (connecting one point of the electrical system to earth for overvoltage protection from lightning, resonant effects, and switching surges) and equipment grounding (connecting metal equipment parts to earth to reduce arcing and side flashes during lightning events).