Petoi Bittle Robot Dog Assembly and Servo Calibration Guide

Degrees of freedom (DOF) define the independent movements a mechanical system can perform. In three-dimensional space, any free object has six DOF: three linear movements along x, y, and z axes, and three rotational movements (yaw, pitch, roll). Linear movements include forward/backward, left/right, and up/down motions. Rotational movements are named from aviation: yaw (rotation about z-axis), pitch (rotation about x-axis), and roll (rotation about y-axis). Different joint types constrain motion differently: revolute joints allow rotation about one axis (1 DOF), prismatic joints permit linear movement along one axis (1 DOF), cylindrical joints combine rotation and translation along the same axis (2 DOF), spherical joints enable rotation about all three axes (3 DOF), and universal joints allow rotation about two perpendicular axes (2 DOF). Grubler's criterion calculates DOF using the formula: DOF = 6n - (j + 1) + Σf_i for 3D mechanisms, or DOF = 3n - (j + 1) + Σf_i for planar mechanisms, where n is the number of links, j is the number of joints, and Σf_i is the sum of DOF permitted by each joint.

Degrees of Freedom (DOF) is the number of independent coordinates needed to describe a body's position in space. A free body has six DOF: three linear translations along X, Y, Z axes and three rotations about these axes. Fixed objects have zero DOF. Each link initially has three DOF before connection. When connected by a turning pair, DOF reduces to one. The Kutzbach Criterion calculates DOF as F = 3(L-1) - 2J - H, where L is total links, J is lower pairs, and H is higher pairs. Each lower pair removes two DOF, while each higher pair removes one. When multiple links join at a point, additional lower pairs must be counted for each extra link.

Degrees of freedom represent the number of independent movements an object can perform. In 3D space, a rigid body has six degrees of freedom: three translational (x, y, z) and three rotational movements. In 2D space, only three degrees of freedom are needed (two translations and one rotation). For open kinetic chains with one end fixed to ground, degrees of freedom equal both the number of joints and links. A joint link variable is an independent variable defining link motion at each joint. Manipulators typically require six degrees of freedom: three for positioning (x, y, z coordinates) and three for orienting the end effector. A manipulator with exactly six DOF is called a spatial manipulator.

A mechanical linkage is a contact relationship between pieces in a mechanism, enabling specific functions. Three contact types exist: point, line, and surface. A body free in 3D space has 6 degrees of freedom: 3 translations (Tx, Ty, Tz) and 3 rotations (Rx, Ry, Rz). Fixed linkages (liaison encastrement) allow zero degrees of freedom, preventing all relative motion. Revolute linkages (liaison pivot) permit one rotational degree of freedom around a single axis, while prismatic linkages (liaison glissière) allow one translational degree of freedom along a single axis.

Degrees of freedom (DOF) in robotics refers to the number of independent variables needed to describe a robot's position and orientation. A typical robot requires six DOF: three for positioning (x, y, z coordinates) and three for orientation (wrist-like motion). These are divided between the arm (positioning) and wrist (orienting). Adding any independent joint increases the system's DOF. Robots are classified into spatial manipulators (full 3D movement, 6 DOF), planar manipulators (2D plane movement, 3 DOF), and redundant manipulators (more DOF than necessary for basic tasks, enabling obstacle avoidance).

Arduino boards are microcontrollers that don't run operating systems, executing single pieces of code with kilobytes of RAM. The Arduino platform simplifies development by abstracting hardware complexity into standardized functions. Arduino-compatible boards include Uno, Nano, Mega, and clones from manufacturers like Adafruit (Feather, ItsyBitsy, Metro). Modern microcontrollers like SAMD51 support interfaces including SPI, I2C, CANBUS, Ethernet, and I2S. Arduino shields and module systems (STEMMA QT, Grove) add functionality like motor controllers and displays. The Pico, designed by Raspberry Pi, represents the microcontroller approach with GPIO pins for I/O control.

Arduino boards (Uno, Nano) are based on the AT Mega 328 microprocessor with USB connectivity and extensive community support. The modular shield system allows adding functionality through plug-in modules for relays, Ethernet, and other features. The Nano variant offers the same functionality in a compact form factor. Peripheral modules include display types (seven-segment, dot matrix), communication interfaces (Ethernet ENC28J60, Wi-Fi MRF24, RF nRF24L01 for wireless up to 1 km), motor control (stepper motors with ULN2003 drivers), and RGB LED modules (Neopixels). Advanced displays require more powerful microcontrollers. This ecosystem enables rapid prototyping and easy expansion without redesigning circuits.

Embedded systems are computer systems programmed to perform specific tasks, consisting of hardware and software components. They are embedded within products like automobiles, industrial machinery, robots, traffic systems, and household appliances. A microcontroller is a small electronic component that stores executable instructions internally. The integrated circuit (IC) was invented in 1958 in the United States, containing thousands of electronic components on a single silicon chip. The first complete microcontroller was developed by Intel in 1980 (801), with the real breakthrough coming from Microchip's PIC 16X84 in the mid-1990s. A microcontroller consists of a Central Processing Unit (CPU), ROM and RAM memory, Input/Output ports, time control units, communication units, and Analog-to-Digital Converters. The Arduino project began in 2005 in Ivrea, Italy, initiated by Massimo Banzi and collaborators. By 2013, over 700,000 Arduino boards were shipped worldwide. Arduino is an open-source programmable electronic board containing a Microchip ATMEGA 328P microcontroller. It can communicate with various sensors and control motors. The Arduino IDE is open-source and free. The Arduino Uno uses an ATMEGA 328P microcontroller running at 16 MHz, costs less than $10, and can be used by both professionals and beginners.

Microcontroller selection depends on project requirements and form factor constraints. Arduino Uno serves as an excellent test platform with built-in USB programming. Nano and Pro Mini offer smaller form factors suitable for final installations but require external FTDI programmers. LilyPad versions feature circular pin arrangements for wearable applications. For custom PCB designs, individual ATmega328 chips can be soldered with minimal supporting components. Higher-performance options include Arduino Mega for more I/O pins and memory, ESP8266/ESP32 for Wi-Fi connectivity, and STM32 for advanced processing. Programming interfaces include ISP programmers, FTDI adapters, and dedicated programmers. Interfacing modules expand functionality: DFPlayer modules play MP3 files from SD cards, audio amplifiers drive speakers, microphone preamps capture audio, and Bluetooth modules enable wireless audio transmission.

Microcontrollers contain various peripherals for interfacing with external components: GPIO (General Purpose Input/Output for LEDs, switches, relays), UART (Universal Asynchronous Receiver Transmitter for serial communication), SPI (Serial Peripheral Interface), I2C (Inter-Integrated Circuit for sensors), ADC/DAC (Analog-to-Digital and Digital-to-Analog converters), memory interfaces (SDRAM, Flash), CAN (Controller Area Network for automotive), LIN (Local Interconnect Network), Ethernet (wired networking), USB (Universal Serial Bus), HDMI (High Definition Multimedia Interface), VGA (Video Graphics Adapter), PWM (Pulse Width Modulation for motor control), DMA (Direct Memory Access), and timers. Understanding these peripherals enables connection of various sensors and actuators.

Building autonomous robots requires understanding three core electrical concepts: voltage (electrical pressure, measured in volts), current (electron flow, measured in amperes), and power (energy transfer rate, measured in watts). The fundamental relationship P = V × I governs all power calculations. In practical systems, voltage remains constant while current varies with load. Critical safety principle: power supply ratings indicate maximum safe output, while component ratings indicate maximum safe input—exceeding either causes failure, overheating, or fire. Robot systems require multiple voltage levels: 5V for microcontrollers (Raspberry Pi, Arduino) and USB devices, and higher voltages (typically 12V) for motors. Since pure 5V batteries don't exist due to chemistry limitations, voltage regulators convert higher input voltages to stable outputs. Two regulator types exist: linear regulators (simple, cheap, but inefficient at high currents) and switching regulators/buck converters (more efficient, recommended for demanding applications). Current analysis drives critical design decisions—list all components and estimate maximum draw, then select regulators and power supplies accordingly.

This segment teaches essential electrical safety principles through a relatable story about a child charging a robot truck. Key lessons include: never use electrical equipment with wet hands as water conducts electricity and can cause shock; never unplug devices by pulling cables as this damages insulation and exposes live wires; always grip plugs firmly when disconnecting; and avoid overloading power outlets as excessive devices can cause overheating and fires. The narrative demonstrates these principles through practical scenarios, making safety education engaging and memorable for young learners.

Modern mining relies on electricity for equipment operation, requiring respectful handling due to accident risks. Low voltage (650V or less, commonly 120-240V) causes more deaths than high voltage. Key concepts include: Voltage as electrical pressure (like water pressure in pipes), Current measured in amperes causing damage (20mA can be fatal), Resistance measured in ohms indicating conductivity. Good conductors (copper, aluminum) allow easy flow, while insulators (rubber, plastic) prevent it. Electricity always flows from high to low voltage, seeking ground (zero volts) through the path of least resistance.

Some robotic systems may be powered by biological processes, such as the natural decomposition of organic matter. This creates a unique relationship between the robots and their environment, as they derive energy from the very substances they are designed to handle. According to Ohm's Law, electrical current flows through conductive materials when there is a potential difference. To avoid electric shock, one should never touch conductive parts while they are connected to a power source. The only safe situation to touch conductive parts is when they are not connected to any power source. This principle is fundamental to electrical safety and applies to all electrical systems.

This segment addresses power management and safety in robot construction. Robots require multiple voltage levels: +12V for motors and +5V for logic circuits. Power distribution should include dedicated outputs for each voltage level. The +5V can be generated from +12V using a voltage regulator circuit. Critical safety warnings emphasize that connecting components to incorrect voltage levels can cause permanent damage—servo motors require +5V while motors require +12V. The Arduino Servo library must be included in programs for servo motor control. Additional voltage regulation may be necessary for motor drivers to prevent damage from voltage fluctuations.