Adafruit Learn Guides
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Adafruit's free library of thousands of step-by-step electronics tutorials covering microcontrollers, sensors, motors, servos and CircuitPython. Each guide includes wiring diagrams and code, so learners can assemble, wire and program working robot and maker hardware projects.
More resources on Robot Hardware
Design of Electromechanical Robotic Systems (MIT 2.017J)
Design, construction and testing of field robots, with ocean waves and marine structures as the central theme. Covers electronics, instrumentation, statistics, linear systems, Fourier transforms, random processes and extreme-event design. Provides lecture slides, the open course text, problem sets and example projects.
Pololu Robotics & Electronics
Top supplier for robot motors, drivers, sensors
Underactuated Robotics (MIT 6.832)
Nonlinear dynamics and control of underactuated systems such as walkers, swimmers and flyers: motion planning, partial feedback linearization, energy shaping, optimal control and reinforcement learning. Includes 23 lecture videos, problem sets with solutions and projects, preparing learners to design controllers that exploit natural dynamics.
Introduction to Autonomous Mobile Robots
Standard textbook on mobile robotics by Siegwart, Nourbakhsh and Scaramuzza covering locomotion, kinematics, perception and sensors, probabilistic localization, mapping and path planning. Readers learn how wheeled and legged robots sense their environment, estimate their position and navigate autonomously.
arduino.cc
Arduino's official site for learning and building with microcontroller-based projects. It provides boards and the Arduino IDE, tutorials, example projects, reference docs, and community resources for beginners to advanced users.