The Mars Rover

By contrast, the Mars rover robots use wheels instead of legs, since stabilizing a wheeled robot is far simpler, and there is less that can go wrong:

The front and rear wheels on the Mars rover shown in Figure 1.4 each have a motor to steer them. All wheels have a motor to drive them. The wheels are arranged to provide maximum grip and stability, in order to tackle Mars's rocky terrain and lower gravity. For more information about this rocker bogie system see https://mars.nasa.gov/mars2020/spacecraft/rover/wheels/. A design predominantly being a platform on wheels like this is known as a rover.Mars rovers are designed to work on a different planet, where there is no chance of human intervention if it breaks down. They must be robust. Updated software can only be sent to a Mars rover via a remote link as it is not practical to send up a person with a screen and keyboard. The Mars rover is headless by design.The Perseverance rover is deployed with its 23 cameras folded up. After landing, some cameras get unfolded. The head like cluster of cameras can positioned with motors, in a pan and tilt mechanism, which is used to send back the pictures of Mars.Beside Perseverance is a helicopter, Ingenuity. This has links back to the hobby robotics scene, which we’ll see more of later in this chapter.Like the Mars robots, the robot you'll build in this book uses motor-driven wheels. Our robot has also been designed to run without a keyboard and mouse, being headless by design. As we expand the capabilities of our robot, we'll also use servo motors to drive a pan and tilt mechanism with a camera to send back pictures of our test space.

Robots in industry

Another place robots are commonly seen is in industry. The first useful robots have been used in factories and have been there for a long time, with designs from 1956!

Robot arms

Robot arms range from tiny delicate robots for turning eggs, to colossal monsters moving shipping containers. Robot arms tend to use stepper or servo motors at their joints. Most industrial robot arms (for example, ABB welding robots) follow a predetermined pattern of moves. However, for a more sensor-based smart system, take a look at this robot named Yumi from ABB:

Robot arms can be unsafe to work around, requiring cages or warning markings around them. This robot Yumi is a collaborative robot or cobot , designed to be easy to train and work safely alongside people. Arm sensors and soft joints also allow Yumi to sense and react to collisions. Image credit: At the Science Museum (12) by Anthony O'Neil, CC BY-SA 2.0, via Wikimedia Commons.Yumi has a training and repeat mechanism for workers to adapt to tasks, using arm joint position sensors when being trained or playing back motions. Our robot will use encoder sensors to precisely control wheel movements.

Warehouse robots

Another common type of robot used in industry is those that move items around a factory floor or warehouse.There are giant robotic crane systems capable of shifting pallets in storage complexes. They receive instructions on where goods need to be moved from and to within shelving systems.Warehouses also have fleets of smaller mobile robots as shown in the next figure:

The preceding figure shows the Ocado fleet of warehouse robots, working together to store and retrieve grocery items in a vast warehouse. They sense when they are aligned with storage boxes, and as well as driving can act by lifting or lowering items.Figure 1.6 image credit: Techwords, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons.Humans tend to interact with them through a central system, so each robot is headless, as our robot will be.We’ve seen robots in space and in industry, what about those closer to home?

Robots in the home

Many robots have already infiltrated our homes but are often overlooked as robots. However, they are more sophisticated than they appear.

A washing machine might be considered a robot with sensors (like temperature and water level, water transparency), outputs (like motors, heaters, pumps, door locks, and displays) and processes to control the wash time, temperature and water level. Some washing machines use sophisticated algorithms to automatically detect the stop conditions.

Smart fans use sensors to detect room temperature, humidity, and air quality, and then output through the fan speed and heating elements. Other machines in the home, like a microwave, for example, may have only timer-based operation, they do not make decisions and are too simple to be regarded as robots.

The robot vacuum cleaner

Perhaps the most obvious home robot is a robot vacuum cleaner:

The wheeled mobile robot in Figure 1.7, is like the one we will build here, but prettier. Robot vacuum cleaners are packed with sensors to detect walls and dust levels, and as this one is doing, navigate back to their charging station. This robot is autonomous and mobile.Let’s take a closer look at its systems:

Figure 1.8 shows a robot vacuum cleaner as a block diagram. The robot’s controller connects to many sensors, inputs, and outputs.Some are for user interaction, like a remote connection to a smartphone, indicator light, beeper, and user button. Some ensure things are working normally like the cover sensor, battery charge sensor and dust collector sensor. It has outputs for brush motors and the vacuum suction motor.The motors have encoders, so the vacuum knows how far it has moved or turned. It has floor sensors, so it won’t drive off edges, distance sensors to avoid walls, and IR sensors to locate its charging sensor. When it is driving, feedback loops are formed between some of these sensors and wheel motors.As we build our robot, we will explore how to use its camera to navigate to and track objects like this robot finds its charging station, we’ll use encoders to measure wheel movement, and distance sensors to avoid walls.Now we’ve examined robots we use our homes, what about the robots people build in their homes?

Discovering competitive, educational, and hobby robots

The most fun robots are those created by amateur robot builders. This is an extremely innovative space.Robotics always had a home in education, with academic builders using them for learning and experimentation platforms. Many commercial ventures have started in this setting. University robots are often group efforts, with access to hi-tech equipment to create them.Hobby robotics is strongly linked with the open-source software/hardware community, making use of sites such as GitHub (https://github.com) for sharing designs and code, leading to further ideas. For example, searching Github for topic: robotics org: orionrobots would show you my robotics work.Hobbyist robots can be created from kits available on the internet, with modifications and additions. The kits cover a wide range of complexity, from simple three-wheeled bases to drone kits and hexapods. They come with or without the electronics included. An investigation of kits will be covered in Chapter 2, Exploring Robot Building Blocks – Code And Electronics, Choosing a chassis kit.The following robot was built using a kit:

I used a hexapod kit to build SpiderBot (Figure 1.9) to explore the walking motion with 6 legs. It uses an esp8266 controller and an Adafruit 16 Servo driver for the motors.Another way that hobby robots are built is via toy hacking, taking a moving toy, for example a remote-control (RC) vehicle, or a device like a hoverboard, and converting it into a robot. This can be fun, but also needs some confidence in electronics problems. An example is the robot pictured in Figure 1.10:

Skittlebot, pictured in Figure 1.10 was built using toy hacking, repurposing a remote-control excavator toy into a robot platform. It was made for the 2018 PiWars competition. It uses the motors, tracks, and base of the RC toy with a Raspberry Pi controller similar to what we will use in this book.

Pi Wars is an autonomous robotics challenge for Raspberry Pi-based hobby robots, with both manual and autonomous challenges. It welcomes entries with decorative cases and resourceful engineering.

Skittlebot uses three distance sensors to avoid walls. We will investigate this kind of sensor in Chapter 8, Programming Distance Sensors with Python. Skittlebot also uses a camera to find colored objects, as we will see in Chapter 13, Robot Vision – Using a Pi Camera and OpenCV, in the section Colors, masking, and filtering – chasing colored objects.Some hobbyist robots are built from scratch, using 3D printing, laser cutting, vacuum forming, woodwork, CNC, and other techniques to construct the chassis and parts, like this robot, Apex:

Apex, the robot shown in Figure 1.11, was built by Rowan Hansard of Onydus Robotics in 2023, with the design inspired by the Mars Rover’s rocker bogie, a camera on a mast, and a camera beneath to detect and align itself over screws. It has been built using a junction box, and some plywood, with a Raspberry Pi 3b+. Apex was made to apply sealant to screws. This robot uses principles from previous editions of this book, including vision with the camera, headless via a remote-control web app and build around a Raspberry Pi.Some robots combine techniques, like scratch building and kits:

I built the robot “ArmBot” shown in Figure 1.12, combining materials I had cut and shaped with a robot arm kit, for a London robotics group in 2009. It was based on a small laptop but now uses a Raspberry Pi.In this book, we will use a chassis kit to get started and experiment on. We will cover some of the communities where robots are being built and shared, along with starting points on using construction techniques to make them from scratch.Having seen a few robots, let’s see what the parts inside them are!

Hobbyist robot parts

Figure 1.14 shows a hobbyist rover robot in its disassembled form:

The component groups in Figure 1.14 include ten types of components:

1. The chassis or body forms the main structure of the robot; other parts are attached here.
2. A castor wheel, ball or skid balances a 2 wheeled robot.
3. Two drive wheels. Other robots may use more wheels or legs here.
4. The drive motors are essential for the robot to move.
5. The main breakout bridges between a controller and connected components. These often include motor drivers.
6. A controller, here a Raspberry Pi, runs instructions, takes information from the sensors, and processes this information to drive outputs, such as motors, through the main breakout.
7. All robots must have power, usually one or more sets of batteries.
8. Sensors provide information about the robot's environment or the state of its physical systems.
9. User interaction devices let the robot communicate with the user, or the user control the robot.
10. Many robots have some articulated parts. These can be robot arms, pan and tilt mechanisms or grabbers.

We will examine these components in more detail in this chapter.We can visualize a robot as a block diagram (Figure 1.15) of connected parts. Block diagrams use simple shapes to show a rough idea of how things may be connected:

The block diagram in Figure 1.15 does not use a formal notation, but has a sensible key to identify sensors, outputs, and controllers. It could be as simple as a sketch on some scrap paper. The critical factor is that you can see blocks of functionality in the hardware, with the high-level flow of data between them.It is from this diagram that you can develop more detailed plans, plans containing details in terms of electrical connections, power requirements, the hardware, and how much space is needed. Sketching a block diagram about a robot you'd like to create, is the first step towards making it.

A block diagram is not a schematic, nor a scale drawing of a finished robot. It doesn't try to show the actual electronic connections. The picture ignores details, such as how to signal an ultrasonic distance sensor. The connection lines give a general idea of the data flow. This block diagram considers the type and number of motors and sensors, along with additional controllers they may need.

This brief overview of robot components shows a robot like the one you’ll build disassembled into parts and a simple robot block diagram. In the next section, we will take a closer look at each of the robot's components, starting with motors.

Types of actuators

Actuators are the parts of a robot that act on the world. Actuator power can be modulated with signals to control movement. Our primary actuators are motors, output devices that rotate when power is applied. Other examples of actuators are solenoids, valves, and pneumatic rams.Linear actuators, like those shown in Figure 1.16, are devices that convert electrical signals into motion along a single axis. These can be a stepper motor driving a screw in a fixed enclosure, or use arrays of coils and magnets:

A solenoid is a simple linear actuator using an electromagnetic coil with a metal core that is pulled or pushed away when powered. A common use of this type is in hydraulic or pneumatic valves. Hydraulic and pneumatic systems generate powerful motions like those seen in excavators. A smaller solenoid-based actuator is that used in a doorbell, pulled to hit one tuneful bar and released to hit another.Another type are rotary actuators. The output of these rotates, with speed or power depending on the input power. While there are hydraulic and pneumatic types, the most common are electronic motors, since we will be using those in our robots, let’s take a closer look at them.

Types of motors

There are a number of different kinds of motors that robots commonly use. Let's take a look at what each one of them does and how we might use them for different types of motion:

To identify what each of these motors do, let's look at them in detail:

1. DC motor Figure 1.17 (A): This is the simplest motor in robotics and is the basis of gear motors. It uses Direct Current (DC), which means it can be driven by a continuous voltage, with the direction and speed controlled by the direction and magnitude of that voltage. The motor speed is proportional to the voltage versus the torque required to move. A motor like this can spin too fast to be useful. It will not have much torque and stall easily.

   Torque is a rotating/twisting force, for example, the force a motor will need in order to turn a wheel. If the torque increases, a motor will require more power (as current) and will slow down while trying to cope. A motor has a limit, the stall torque, at which point it will stop moving.

2. DC gear motor Figure 1.17 (B): This is a DC motor fitted with a gearbox. This gearbox provides a speed reduction and increases the torque it can handle. This mechanical advantage increases the motor's ability to move a load. We will use gear motors such as this on our robot in Chapter 6, Building Robot Basics – Wheels, Power, and Wiring, and Chapter 7, Drive and Turn – Moving Motors with Python.
3. Servo motor (or servomechanism) Figure 1.17 (C): This type of motor combines a gear motor with a position sensor and a built-in controller as shown in Figure 1.18:

The motor is coupled through a gearbox to the sensor in a feedback loop. The controller compares the intended position with the actual position feedback, outputting the power needed for the motor to reach the intended position. Servo motors are used in pan and tilt mechanisms, robot arms and limbs. We will connect and program servo motors in Chapter 10, Using Python to Control Servo Motors. Some servo motors provide feedback as an analog signal from the position sensor. There are also smart servo motors that use a data signal, over which can provide more feedback to a controller.

1. Stepper motor Figure 1.17 (D): These have coils powered in a sequence to let the motor step a certain number of degrees. Where exact motions are needed, engineers use steppers. Stepper motors tend to be slower and generate a lot of heat compared with DC motors or servo motors. They are used in fine-control applications, such as 3D printers and high-end robot arms. They are heavier and more expensive than other motors.
2. Brushless motor: These can be more precisely controlled than DC motors, operating like fast stepper motors. They can be capable of ranges of very low to very high speeds, and high torque but require Electronic Speed Controllers (ESCs). They run quieter and are popular in drones and hoverboards. They may require a gearbox to reduce speed depending on the motors magnet arrangement.

IMPORTANT NOTE

All but servo motors require hardware for a controller such as the Raspberry Pi to drive them. This hardware allows the Pi to control power-hungry devices without destroying them. Never connect DC motors, stepper motors, or solenoids directly to a Raspberry Pi!

Let's look at some other types of actuators next.

Status indicators – displays, lights, and sounds

Another helpful output device is a display. A single LED (a small electronic light) can indicate the status of some part of the robot. An array of LEDs could show more information and add color. A graphical display can show some text or pictures, like those found on a mobile phone.Speakers and beepers can be used for a robot to communicate with humans by making sounds. The sound output from these can range from simple noises through to speech or playing music.Many robots don't have any displays and rely on a connected phone or laptop to display their status for them. We will use a phone to control and see the status of our robot throughout the book.

Types of sensors

One of the most important parts of a robot is sensors, for it to respond autonomously to its environment. Let’s see some of the robot sensor types:

Figure 1.18 shows a collection of sensor types used in robotics. They are similar to those that we will explore and use in this book. Let's examine them and their uses. We will add some of them to the robot and cover in more detail.Let's understand each sensor from Figure 1.18 in detail:

1. Optical interrupt sensor (Figure 1.18 A): These detect light(infrared or visible) passing through a gap between two posts, sensing when the beam is broken. When used with notched wheels, like the one pictured, they can detect rotation and speed by counting notches making them encoders. We will use encoders in Chapter 10, Programming Encoders with Python.
2. Ultrasonic distance sensor (Figure 1.18 B): The HC-SR04 is a distance/ranging sensor that uses sound pulses, similar to the way bats navigate. It is affected by the types of material an object is made from. It requires precise timing in the controller. We will be programming distance sensors in Chapter 8, Programming Distance Sensors with Python.
3. Inertial Measurement Unit (Figure 1.18 C): This sensor can detect the orientation of a robot, using gravity, magnetic and rotational forces. We will look at one of these in Chapter 12, IMU Programming with Python.
4. Solid-state LiDAR (Figure 1.18 D): This sensor (an LD-07) uses an infrared laser array to sense the distance of many points over a 90-degree range. These produce lists of distance points. The LD-07 is hard to get hold of, with most LiDAR (Light Detection and Ranging) sensors being large and expensive.
5. Raspberry Pi Camera module (Figure 1.18 E): This module lets a Raspberry Pi capture pictures and video sequences. We'll use it for visual processing in Chapter 13, Robot Vision – Using a Pi Camera and OpenCV. It can generate a lot of data quickly, which is one of the problems associated with robot vision. It is sensitive to lighting conditions.

There are many more sensors, including ones to detect positions of limbs, light, smoke, heat sources, and magnetic fields. These can be used to make more advanced robots and add more exciting behavior.