Aula 3 - Atuadores

Name: Aula 3 - Atuadores
Uploaded: 2025-03-12T12:08:21.000Z
Duration: 3 h 40 min 1 s

What Defines a Robot?

Understanding the Basics of Robotics

The discussion begins with defining what constitutes a robot, emphasizing its existence in the physical world and its ability to sense and act upon its environment to achieve specific objectives.

Key components of robots include actuators and effectors, which are essential for interaction with the physical environment. Actuators enable movement while effectors perform actions that create effects in the world.

Effectors and Their Role

An effector is described as a component that creates an effect on the environment; for example, wheels on a wheeled robot serve as effectors for locomotion.

Manipulators also utilize effectors, such as robotic arms equipped with tools like welders or grippers. These tools differ from human hands in terms of degrees of freedom.

Actuators: The Driving Force Behind Robots

Functionality of Actuators

Effectors require actuators to function since they do not have independent movement capabilities. Actuators are mechanisms that enable effectors to perform work by creating motion.

The importance of actuators lies in their role in allowing robots to manipulate or interact with their surroundings effectively.

Types of Actuation

Traditional actuation often involves electric motors due to their compactness, ease of use, and affordability compared to other types like hydraulic or pneumatic systems.

Exploring Alternative Actuation Methods

Passive vs. Active Actuation

Passive actuation can utilize potential energy sources instead of traditional motors; for instance, a pendulum can create movement through gravitational forces without active motor assistance.

Limitations and Innovations

While electric motors are common due to their practicality, there are ongoing research efforts aimed at miniaturizing hydraulic and pneumatic systems for robotics applications.

Challenges in Robotic Design

Maintenance and Safety Concerns

Hydraulic and pneumatic systems pose challenges such as size constraints and maintenance issues due to fluid pressure reliance; leaks can lead to failures or safety hazards.

Emerging Technologies

Research is being conducted into alternative materials that react to light or temperature changes (e.g., photo-reactive materials), although these typically yield limited movement capabilities.

The Importance of Electric Motors

Motor Functionality

Understanding Motor Functionality in Robotics

Overview of Motor Operation

The explanation of motor functionality is intentionally simplified, omitting detailed electrical circuit and electromagnetism concepts, focusing instead on robotics.

Conversion of Energy

Motors convert electrical energy into kinetic energy (motion) using electromagnetic principles involving magnets and coils. When electric current passes through the coils, it generates a magnetic field that rotates the motor's shaft.

Practical Application with Microcontrollers

The speaker prompts participants to reflect on their experiences using motors in projects with Arduino or microcontrollers.

A participant shares their experience connecting a motor directly to a battery and mentions using a relay for control.

Current Requirements and Control Circuits

Directly connecting a motor to a microcontroller can lead to failure due to high current demands; motors require significantly more current than microcontrollers can provide.

Small motors typically draw between 100 mA to 1 A, while simple microcontrollers average around 5 mA. This necessitates an external power source capable of supplying sufficient current.

Amplification Techniques

To manage the power requirements for motors, circuits such as MOSFET transistors or H-bridges are used. These components amplify signals from the microcontroller while allowing an external power source to drive the motor.

Types of Motors Used in Robotics

Characteristics of Brushed Motors

The simplest type discussed is the brushed DC motor, which has two terminals and uses carbon brushes for contact within its structure.

Mechanism of Motion Direction Change

To reverse the direction of rotation, one must switch the polarity by changing connections at the terminals. This requires special circuitry since direct inversion isn't possible with standard microcontroller outputs.

Circuit Design for Motor Control

An H-bridge circuit connects between the microcontroller and motor terminals, enabling electronic control over direction by configuring transistor states appropriately.

Motor Specifications and Project Considerations

Voltage Compatibility

Selecting an appropriate motor involves ensuring compatibility with project voltage specifications; either choose a suitable motor or adjust project voltage accordingly.

Operational Voltage Range

Motors have operational voltage ranges rather than fixed voltages; higher voltages increase potential current flow according to Ohm's Law (current = voltage/resistance).

Understanding Motor Torque and Power

Relationship Between Voltage, Current, and Torque

The relationship between voltage and current is directly proportional; higher voltage results in higher current, which increases the torque produced by the motor when no load is connected.

When a load (mass) is attached to the motor running at 5V, it requires more energy to maintain operation compared to running without a load. This situation deviates from Ohm's Law due to non-linear behavior.

To handle increased loads at the same voltage, motors must draw more current to generate additional torque necessary for movement.

If the motor shaft is completely locked while powered, excessive current can flow through it, risking damage or overheating of the motor.

Power Generation in Motors

Torque is proportional to current; thus, the energy generated by a motor correlates with its torque output.

The power available for work done by a motor combines both torque and rotational speed (frequency), emphasizing that electrical power (voltage times current) differs from mechanical power used for motion.

Conversion of Power Units

Mechanical power can be expressed in different units such as CV (horsepower), which can be converted into watts for consistency in electrical contexts.

Electric vehicles often specify their power output in watts rather than horsepower because it's more relevant for electric systems.

Efficiency of Energy Conversion

Supplying 10W of electrical energy does not guarantee that all will convert into mechanical movement due to inefficiencies; some energy dissipates as heat during conversion processes.

Motor Specifications and Applications

Small motors typically operate between 3,000 to 9,000 RPM. Specific performance depends on individual motor specifications regarding maximum and minimum speeds.

Understanding Gear Mechanics

Basics of Gears and Torque Conversion

The discussion begins with the fundamental concept of gears, which are used to convert torque into rotation or vice versa. This conversion is essential for altering the output torque or speed of a motor depending on how the gears are connected.

Gear Relationships

The relationship between a larger gear and a smaller gear is introduced, emphasizing that there is a proportional relationship based on their sizes. The input gear connects to the motor while the output gear connects to the load.

Input and Output Dynamics

A visual representation of a motor's setup is described, where an input gear (connected to the motor) drives an output gear (connected to the load). This setup illustrates how motion transfers from one component to another.

Speed and Torque Proportions

It’s explained that both speed and torque are proportional to the ratio of radii between two gears. A smaller gear rotates faster than a larger one due to this ratio.

Teeth Count and Gear Ratio Calculation

The example provided includes specific teeth counts: 20 teeth for the small gear and 60 for the large one. This establishes a ratio of 3:1, indicating that for every turn of the small gear, it takes three turns of the large gear.

Torque vs Speed in Gears

Understanding Gear Ratios

Clarification on how fewer teeth in an input gear results in higher rotational speed compared to an output gear with more teeth. This principle underlines basic mechanical advantage concepts in physics.

RPM Calculations

If an input rotation speed (RPM) is set at 60 RPM for the smaller gear, calculations show that due to their ratio, the output will be at 20 RPM.

Implications of Reduced Speed

While lower speeds may seem disadvantageous, they come with increased torque. As speed decreases by a factor related to their ratios, torque increases inversely.

Practical Applications in Robotics

Torque Enhancement through Gear Reduction

In robotics applications, reducing motor speed while increasing torque allows machines to lift heavier loads effectively—contrasting with bicycles where higher speeds are desired.

Energy Conversion Limitations

It’s noted that energy conversion from electrical power into kinetic energy isn’t perfect; losses occur due to factors like play between gears which can affect precision in positioning tasks.

Understanding Gear Mechanics in Robotics

The Impact of Gear Friction

Reducing the gap between gears increases friction, which opposes the applied torque and converts some energy into heat, leading to energy loss.

In robotics, motors must generate sufficient torque for movement; however, a significant portion of input energy is lost as heat due to gear friction.

Gear Ratios and Torque Conversion

To achieve a desired RPM reduction (e.g., from 3000 RPM to 100 RPM), a substantial gear ratio is necessary—specifically, a ratio of 30:1.

Larger gear ratios complicate design and manufacturing; thus, using multiple gears in series can simplify this process.

Series Gear Configurations

By grouping gears in series, one can achieve higher overall gear ratios without needing excessively large or small individual gears.

For example, combining two sets of 3:1 gear ratios results in an overall ratio of 9:1 between input and output.

Servo Motors in Robotics

Servo motors are commonly used for precise control over rotation direction and speed; they often contain multiple internal gears to manage torque effectively.

Unlike standard DC motors that primarily control speed, servo motors allow for position control essential for robotic applications.

Position Control Mechanisms

Positioning mechanisms utilize sensors (like potentiometers) linked to the motor's axis to determine its current position accurately.

The sensor provides feedback to an electronic circuit that adjusts motor rotation until the desired position is reached.

PWM and Servo Control in Robotics

Understanding PWM and Servo Mechanics

PWM (Pulse Width Modulation) is discussed as a method for controlling devices like LEDs and motors, emphasizing its slower nature compared to standard PWM applications.

The concept of servo control is introduced, where the pulse width corresponds to the angle of output. A 20 ms interval with varying pulse widths determines the servo's position.

Standard servos typically operate within a range of 180°, with specific pulse widths indicating positions: 1 ms for 0°, 1.5 ms for 90°, and 2 ms for 180°.

Continuous rotation servos are mentioned, which can rotate beyond the typical limits of standard servos, allowing for ongoing motion rather than fixed angles.

The advantage of using servos lies in their closed-loop control system that corrects errors by adjusting output based on feedback from the current position versus desired position.

Closed-loop Control Systems

A closed-loop control system involves monitoring output to minimize error; if a servo is commanded to reach an angle but detects deviation, it compensates accordingly.

An example involving an aeromodel demonstrates how servos adjust against external forces (like wind), maintaining stability through corrective torque application.

The actuator's role is highlighted as it performs movements while counteracting external forces to maintain desired positions effectively.

Testing with a servo connected to Arduino illustrates its firmness in resisting external pushes, showcasing its ability to compensate dynamically during operation.

Torque vs. Position Control

Two types of control are discussed: position control (most relevant in robotics), which maintains specific angles or positions, and torque control, which focuses on maintaining consistent force without regard for position changes.

Degrees of Freedom in Actuators

The concept of degrees of freedom (DoF) is introduced as essential for understanding actuator movement capabilities; each actuator has unique characteristics affecting its movement range.

A simple wheel actuator can move forward or backward along one axis (x-axis), illustrating basic DoF principles within a two-dimensional plane.

Degrees of freedom are defined mathematically as the minimum number of coordinates needed to specify movement within mechanical systems; this concept helps clarify robotic mobility constraints.

Understanding Degrees of Freedom in 3D Space

Introduction to Degrees of Freedom

The concept of movement in three-dimensional space is introduced, highlighting the ability to move along the X, Y, and Z axes.

A discussion on how an object with mass (e.g., a cell phone) also possesses three degrees of freedom for movement in these dimensions.

Additional Movements and Rotational Degrees

Beyond translational movements, objects can also rotate around their axes, adding three more degrees of freedom: roll, pitch, and yaw.

The term "free body" is defined as an object not constrained by external forces or attachments, emphasizing its six degrees of freedom in 3D space.

Types of Motion Explained

Translational movements are categorized into X, Y, and Z directions while rotational movements include roll (around Y), pitch (around X), and yaw (around Z).

An example using a helicopter illustrates how it can navigate through all six degrees of freedom effectively.

Actuators and Control Mechanisms

The importance of actuators is discussed; typically one actuator controls one degree of freedom.

For a robotic system to achieve multiple degrees of freedom, multiple actuators are necessary—one for each degree desired.

Practical Example: Car Movement

In an ideal scenario where a car operates on a flat surface with a low center of gravity, it exhibits only three degrees: two translational (X and Y) and one rotational (yaw).

The limitations in lateral movement are highlighted; cars cannot move perfectly sideways due to design constraints.

Understanding Car Maneuvering and Degrees of Freedom

The Challenge of Parking

Parking between two cars requires more than just sliding into the space; it involves understanding the car's movement capabilities.

While lateral movement is limited, drivers can maneuver by combining forward/backward motion and orientation adjustments to navigate tight spaces.

Ideal vs. Realistic Movement

In an ideal scenario, a car has three degrees of freedom (x, y, z), but only two are controllable: forward/backward and orientation.

Real-world factors like weight distribution affect how a car behaves during turns or sudden stops, complicating parking maneuvers.

Continuous Trajectories in Parking

Effective parking requires maintaining a continuous trajectory without leaving the plane of movement; this means moving back and forth rather than lifting the vehicle.

The concept of "discontinuous speed" arises as drivers must stop and reverse multiple times to align correctly in a parking space.

Degrees of Freedom in Robotics

Similar challenges exist in robotics where uncontrolled degrees of freedom make precise movements difficult.

Systems with equal controllable degrees of freedom to total system degrees are termed "holonomic," while those with fewer controllable freedoms are "non-holonomic."

Redundancy in Robotic Systems

A non-redundant system like a car has limited control over its movements compared to redundant systems found in nature, such as human arms.

Human arms possess seven degrees of freedom within three-dimensional space, allowing for versatile movement options when reaching for objects.

Implications for Motion Planning

When moving from one position to another, redundancy provides multiple pathways for achieving desired positions through various combinations of joint movements.

Trajectory Calculation and Degrees of Freedom in Robotics

Understanding Actuators and Movement

The challenge of calculating trajectories for robotic systems involves increasing the number of possible solutions, which requires more processing power, making calculations slower.

A vehicle's movement is limited; it primarily controls the X-axis (forward/backward), while a helicopter can maneuver in multiple directions due to its six degrees of freedom.

Helicopters can perform various movements such as ascending, descending, or rolling sideways, illustrating their complex control capabilities compared to simpler vehicles like cars.

Degrees of Freedom Explained

Players familiar with video games that involve piloting helicopters can easily grasp the concept of controlling multiple degrees of freedom.

Calculating a car's trajectory is complicated by its lack of lateral movement capability; having this ability would simplify trajectory calculations significantly.

Actuator Requirements

Each degree of freedom typically requires an actuator; for cars, this includes motors connected to wheels for directional control.

In addition to electric or combustion motors, human input also acts as an actuator for controlling vehicle direction.

Types of Movements: Locomotion vs. Manipulation

Movements are categorized into locomotion (moving from one place to another) and manipulation (interacting with objects).

Locomotion involves using limbs or wheels; however, biological systems do not utilize wheels but rather legs and fins which complicate computational requirements due to increased degrees of freedom.

Stability Challenges in Movement

Biological systems face challenges maintaining stability during locomotion; unlike machines that use wheels, natural organisms rely on limbs which require more complex computations.

Stability is crucial for effective movement; it refers to maintaining balance without falling over. This concept applies both in robotics and human biology.

Defining Stability

Stability can be defined as the ability not to tip over or fall easily. Static stability relies on having sufficient points of support.

For example, humans have two points (feet), while insects may have six legs providing them with greater stability through more points of contact with the ground.

Center of Gravity Considerations

Understanding Insect Stability and Human Balance

The Concept of Support Polygons

The support polygon is defined as the area formed by the points of contact (legs) with the ground. The insect's body mass is centered within this polygon, indicating that its center of gravity is stable.

An insect maintains stability when all six legs are on the ground, preventing it from falling even if the surface is inclined. This stability arises from having a large support polygon.

Center of Gravity in Humans vs. Insects

Unlike insects, humans have a smaller support area when standing on two feet. If a human's center of gravity shifts outside this small polygon due to an incline, they risk losing balance.

A hypothetical scenario illustrates that if a person leans forward while standing straight, their center of gravity may extend beyond their base of support, leading to potential falls.

Challenges in Maintaining Balance

Infants struggle with walking because their disproportionate head size causes their center of gravity to be high and unstable, making it difficult for them to maintain balance.

The concept emphasizes how maintaining equilibrium can be challenging due to an unbalanced center of gravity in relation to body proportions.

Static vs. Dynamic Stability

Static stability refers to maintaining balance while stationary; dynamic stability involves movement without losing equilibrium during locomotion.

During static walking, lifting one leg has minimal impact on the overall center of gravity due to its relatively low weight compared to the rest of the body.

Dynamics of Walking and Movement Efficiency

While static walking is stable, it’s not efficient since it requires excessive energy expenditure for movement without significant progress.

Dynamic stability allows for more efficient movement as compensatory actions occur throughout the body while legs are lifted and moved forward.

Robotic Movement and Stability Concepts

Robots mimicking human or animal movements must achieve dynamic stability by coordinating leg movements with adjustments in other body parts for balance maintenance.

The inverted pendulum effect illustrates how balancing mechanisms work: as one part moves outwards, compensatory movements must occur elsewhere to maintain equilibrium.

Key Elements for Effective Locomotion

Successful locomotion—whether in nature or robotics—requires five key elements: stability, speed, efficiency, robustness (ability to recover from failure), and simplicity in operation.

Robotic Locomotion Techniques

Common Robotic Examples

The speaker discusses common examples in robotics, specifically mentioning the Atlas robot from Boston Dynamics, which is bipedal and mimics human movement with two points of support.

Introduces the concept of alternating elements in robotics, highlighting the tripod gait used by insects as a simple and efficient method for locomotion.

Stability in Robotic Movement

Emphasizes that one point of support is unstable, while two points do not guarantee stability due to center of gravity issues; three points provide good static stability.

Describes how a tripod gait maintains three legs on the ground at all times, ensuring stability through alternating movements.

Alternative Gait Patterns

Discusses the undulating gait for six-legged robots, comparing it to centipedes. This method is less efficient than the tripod gait but demonstrates another approach to robotic movement.

Concludes that while tripodal gaits are effective for locomotion, wheeled robots are generally more efficient but require specific designs for uneven terrain.

Design Considerations for Wheeled Robots

Highlights challenges faced by wheeled robots on irregular terrain, such as needing a low center of gravity or suspension systems similar to cars or tank treads.

Explains that building a statically stable wheeled robot typically requires at least three wheels (a tricyle design).

Mechanisms for Stability and Control

Discusses achieving static stability with three points of support and why two wheels on an axis can lead to instability akin to an inverted pendulum.

Suggests using passive caster wheels alongside independently controlled drive wheels to enhance maneuverability and control during turns.

Practical Applications in Robotics

Understanding Differential Traction and Robotic Manipulators

Differential Traction in Robotics

The concept of "differential traction" is introduced, which refers to the mechanism that allows wheels to turn based on the difference in speed between them.

In small robots, such as vacuum cleaners, differential traction is commonly used with one wheel driving while another steers.

Components of a Robotic Manipulator

A robotic manipulator consists of an end effector designed to interact with objects; it includes rigid parts and joints for movement.

The end effector's role is crucial as it directly affects the environment; examples include tools like welding or cutting devices.

Movement and Degrees of Freedom

The goal of the manipulator's links and joints is to position the end effector accurately within a three-dimensional space, typically requiring six degrees of freedom.

Achieving a desired trajectory involves multiple movements and sequences, constrained by joint limits and obstacles in the environment.

Types of Joints in Manipulators

Two main types of joints are discussed: spherical joints (allowing rotational movement) and prismatic joints (providing linear motion).

Spherical joints enable rotation similar to a ball, while prismatic joints function like pistons for extending or retracting movements.

Kinematics and Position Calculation

Each joint contributes a degree of freedom; anthropomorphic arms often have multiple joints mimicking human anatomy for complex tasks.