Design and Build Your Own Robot


These are exciting times in the robotics hobby. Like all things electronic, the core technologies involved in building small autonomous robots continue to get more powerful and less expensive with each passing day. These improvements aren't limited to the computer circuits that serve as robot control systems. Hobby vendors now offer sophisticated sensors for sound, sight and touch, as well as mechanical components engineered specifically for robotic assemblies. Hobbyists of all ages and nationalities are building autonomous machines that can navigate new environments, find and move objects, accept voice commands, and more.

Getting started in hobby robotics involves a bit of pulling yourself up by the bootstraps. Designing and building your own robot requires you to be a jack of many trades. Ultimately you will need to develop a basic understanding of electronics, computer programming, and engineering, as well as the skills necessary to actually assemble your designs. However, you don't need particular expertise in any of these areas to get started - all you need is desire and the rest will fall into place.

It is important to view the robot design process as evolutionary and iterative. In order to be successful, at each step along the way you must not only have a clear idea of what it is you want to do, you must also have a clear idea of how to it. Make your first design as simple and as manageable as possible - perhaps a wheeled robot that wanders about a room, backing up and changing direction when it bumps into an obstacle. In completing this humble task you will have established a foundation to build on and you will have assembled the tools and knowledge necessary to take the next steps.

Remember always that you are standing on the shoulders of giants. Without the work and inventiveness of those that walked this road before us, there would be no robotics hobby. Read everything you can find, and study the plans, photographs and videos posted by others.

This tutorial provides an overview of some of the most common techniques and parts found in hobby robots with an emphasis on beginner projects.

Controllers

Every robot has some type of control system. There are some hobbyists who pursue very minimalist designs and create control systems using only switches and simple electronics. BEAM robotics is one such area. BEAM is an acronym for Biology, Electronics, Aesthetics, and Mechanics and BEAM Robots typically have analog circuits that mimic simple biological systems. Most often, however, the robot controller is computer based.

More than any other development, the availability of inexpensive, powerful microcontrollers drives the robotics hobby. Microcontrollers are a type of microprocessor (computer chip) designed for embedded systems. They typically integrate features like timers, memory and analog input that might require additional circuitry in systems based on other types of processors. They are engineered to be small, low cost, and use energy sparingly.

Frequently microcontrollers and microprocessors are packaged on small circuit boards known as controller boards and single board computers. These boards might offer extra circuitry to facilitate additional memory, connection to a power supply, and a computer interface for programming and data exchange. When building robots, circuitry for controlling motors is a particularly desirable feature on a single board computer.

There is a considerable variety of microcontroller platforms to choose from with a tremendous range of price, capability, and ease of use. You should expect some upfront expense for programming hardware, but once you are established, microcontrollers tend to be very inexpensive, with the smallest selling for as little as a dollar or two. The Microchip Pic and Atmel AVR are two popular families of microcontroller. Within the families, chips range in physical size and capability. These and similar processors are the workhorses of the electronic age - whether you know it or not you probably own several gadgets powered by either a PIC or AVR.

Controller boards are available with capacities up to and beyond those of a desktop computer, and it is also not unheard of to have a robot connected either directly or wirelessly to a laptop or desktop. However, the vast majority of robotic projects do not require this kind of horsepower. Cost, weight, and power consumption are all critical factors in a design. Choosing the optimal controller requires striking a balance between these real constraints and the capabilities required to do the job.

There are a number of microcontroller systems particularly geared toward students and hobbyists. If your computer programming experience is limited, or if you are brand new to programming, you will almost certainly want to choose from among these hobby-targeted systems. Some examples include the BASIC Stamp and the Propeller both manufactured by Parallax, the PICAXE manufactured by Revolution Education, and the Arduino which is an open platform available from many vendors. Each of the systems listed are popular with robot hobbyists and you can find enthusiastic help on forums and websites.

Locomotion

Robot locomotion is an area of tremendous creativity; some robots have wheels and some walk, while others drag, waddle, slither or roll.

A common technique for wheeled robots is the differential drive. The basic principle of the differential drive is to control two drive wheels independently and steer by either stopping or reversing one wheel while continuing to operate the opposite wheel in the forward mode. If the left wheel continues to move forward then the vehicle will turn to the right. If the right wheel continues to move forward then the vehicle will turn to the left.

Walking robots are more difficult to engineer than wheeled robots but have an obvious appeal. Stability is a major concern in legged robots. In two-legged bipedal robots it is often necessary to shift weight from one leg to the other in order to keep the robot from tumbling over, although some simple designs will overcome the balance problem by using extremely wide feet. The easiest and most common of the walking configurations is the six-legged hexapod. With hexapods it is possible to engineer a very stable walking gait in which there are always at least three feet on the ground.

Sensors

Sensors are the robot's connection to the outside world. They include switches, light and sound detectors, temperature sensitive devices, tilt and acceleration monitors, infrared and ultrasound object detection, cameras, and more. There are many manufactured sensors available; some were created for robotics while other are re-purposed from other applications. Sensors are also an area in which robot builders have exhibited a great deal of ingenuity. Homemade sensors for touch, light and motion abound.

The most important sensor, and one that is frequently overlooked, is the bumper switch. A bumper switch is a simple device that triggers when the robot strikes an object. Most robot and general hobby suppliers will have an appropriate device for a few dollars. It is also easy enough to engineer something to cause two wires to connect on impact.

The photoresistor, or light dependent resistor, is a simple component that passes more electricity in brighter light and less electricity in dimmer conditions. Photoresistors are very inexpensive and easy to use. The light seeking robot, or photovore, is a fun beginner robotics project. Photovores are usually made with two photoresitors mounted at an angle toward one another. When one sensor is "seeing" more light than the other the robot turns in the direction of the light until balance is achieved and then moves forward. The project sounds simple enough but calibrating the system and getting all the pieces working together is not easy. Photosensitive cells and light emitting cells are also used in systems that follow a black line or avoid falling off the edge of a table by detecting a sudden edge - again two fun and common early projects.

Range finding sensors are found in many autonomous robots beginner to advanced. Range finders detect an object and send a signal to the controller that is in some way proportionate to the distance to that object. Ultrasound rangers use the principles of sonar to time how long an echo will take to return from striking an object. Infrared rangers use prisms to make calculations based on the angles of reflected light.

Actuators

Actuators are the devices that give robots movement. With a few exceptions common actuators - like the simple DC motor - use the principles of electromagnetism to push, pull and spin.

Although motors are essentially simple, they are not that easy to interface with the electronics of a robot. Motors require more current than a typical microcontroller can provide and therefore additional components are required. Also, motors produce a disruption effect generally called "noise" in electronic circuits. This noise can cause microcontrollers to behave erratically. All but the most basic robots will need some type of filtering circuitry or other noise solution. It is not uncommon for a robot to use two power supplies - one for the electronics and one for the motors and other noisy components.

A straight DC motor can be difficult to control because the shaft will turn very quickly. Most robot drive systems would use a geared motor in which a sequence of gears will convert the rapid spinning of the shaft to a slower spin with more torque.

Servos are probably the most common actuator in hobby robotics. Rather than spin around, a servo is a motor with some additional circuitry added that allows the shaft to be positioned at a specific angles. This capability is useful not only for building arms and legs, but also for sensor mounts that pan and tilt.

Chassis and Physical Assembly

Regardless of function or form, the robot body is typically referred to as the chassis. The chassis is the frame on which the robot is built. The materials selected for the construction must be strong enough to do their job, yet light enough that the robot is not hampered by its own weight. Metals, plastics, and even woods are all used and intermixed successfully, each with their own pros and cons.

As with other areas discussed here, the skills and experience you bring to the table should be a big consideration in your choices for how to proceed with chassis design. For example, if you have the tools and the know-how to work with aluminum stock then this strong and light metal is ideal for many robotic applications. On the other hand, if you're all thumbs in the workshop then getting started working in aluminum is probably too difficult and too expensive to be considered for one of your first projects.

There are many different plastics that are inexpensive and easy to work with. ABS and HDPE are available in sheets of varying thickness and can be managed fairly well with a handsaw. Polymorph (a brand name) is a type of plastic that is hard at room temperature but melts at about 60 degrees Celsius making it easy to mold and form. Styrene is plastic used in craft modeling. It is not quite as tough as ABS or HDPE but extremely easy to work. Styrene can be cut with a hobby knife and when glued with model cement has a bond as strong as if it were molded.


A chassis assembled from off-the-shelf components is a viable alternative to building from scratch.

It is by no means necessary, or even recommended, to build the entire chassis from scratch. Robot suppliers offer various parts, platforms and even assembled chassis designed to be customized with a microcontroller and suite of sensors.

Next Steps

Hopefully this introduction has given you some inspiration and some ideas for where you would like to go in the robotics hobby. Hobbizine has plenty of resources to help you get off to a good start. Listed below are some other Hobbizine articles that you might want to read as well as links to pages with external resources including robotics and electronics vendors.

K'nexapod - A Hexapod Robot Built With K'nex and PICAXE

K'nexabeast - A Theo Jansen Style Octopod Robot

Introduction to the PICAXE Microcontroller

Flexinol and other Nitinol Muscle Wires

Flexinol Control Circuit Using PIC 16F690 and ULN2003A

Precision Flexinol Position Control Using Arduino

LaunchPad MSP430 Assembly Language Tutorial

Analog Sensors and the MSP430 Launchpad

An Arduino Neural Network

Robot Obstacle Detection and Avoidance with the Devantech SRF05 Ultrasonic Range Finder

Setting Up A Differential Drive For Your PICAXE Project

Basic PICAXE Servo Interfacing

Robotics Resources

Electronics Resources

Migrating to the 1284P

Getting Up and Running With a Tamiya Twin-Motor Gearbox


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