Robotics Workshop

At this stage, you should have all the main components for your robot including actuators, motor controllers, a microcontroller, sensors, and communication systems.

Image credit: zatalian

You are now approaching the integration stage where you will put all these parts together in what will likely be a custom robotic frame. For this, you will need to get your workshop/laboratory/bat cave ready with the appropriate tools.

Robotics Workshop

We have set up three possible robotic-oriented labs scenarios. Choosing which parts to add to your lab depends on how many robots you plan to make, and how involved in robotics you would like to get. We have outlined three broad categories for labs, but don’t assume the three labs are exclusive; in the real world, you will undoubtedly find robot builders who have tools from more than one section, and can give you a list of other tools which they have found useful.
The Essential setup is intended for first time robot builders who foresee building a few inexpensive robots for fun or have a single project in mind. It is the least expensive setup at less than $100, but don’t be fooled by the price tag. In the right hands, a workshop such as this can be used to create professional robots too.
The Intermediate setup is intended for builders who are not quite “professional” but are willing to invest a bit more in tools and equipment in order to ease fabrication, assembly, testing and troubleshooting.
The Ultimate setup is intended for users who plan to make many advanced robots and prototypes, using a variety of parts and materials. This type of builder wants the finished prototype to look as professional as possible and may even want to produce some small production runs of the finished design. This is the type of setup would likely find at a small robotics company. We cannot cover all the tools required at this level but can give some general suggestions.
As always, it is very important to have the right tool for the right task and only you know your needs best. Below, you will find the various tools and materials suggestions for your workshop classified by level and type.

Mechanical Tools

• Essential
  • Small screwdriver set
    These small screwdrivers are necessary when working with electronics. Don’t force them too much though – their size makes them more fragile.
  • Regular screwdriver set
    All workshops need a multi-tool or tool set which includes flat / Phillips and other screwdriver heads.
  • Needle nose pliers
    A set of needle nose pliers is incredibly useful when working with small components and parts and is a very inexpensive addition to your toolbox. These are different from regular pliers because they come to a point which can get into small areas.
  • Wire strippers/cutters
    If you are planning to cut any wires, a wire stripper will save you considerable time and effort.  A wire stripper, when used properly, will only remove a cable insulation and will not produce any kinks or damage the conductors. The other alternative to a wire stripper is a pair of scissors, though the end result can be messy.
  • Scissors, ruler, pen, marker pencil, exacto knife (or other handheld cutting tool)
    These are essentials in any office.
• Intermediate
  • Rotary Tool (Dremel for example)
    Rotary tools have proven to be incredibly versatile and can replace most of the conventional power tools provided the work that needs to be done is at a small-scale. They can cut, drill, sand, engrave, polish, etc.
  • Drill
    A drill is very useful especially when creating larger holes or using stronger / thicker materials. If you are prepared to make the investment, a drill-press allows you to reliably create perfectly perpendicular holes.
  • Saw
    A saw of some type is beneficial at this stage to cut thicker materials or make long straight cuts. You can use a hand saw (although you may need to finish the edges), a bandsaw, table saw, etc.
  • Vise
    As your work become more complex, you will need to hold materials and parts firmly in place while you work on them. A vise is essential for this and allows to go further in terms of precision and quality.
• Ultimate
  • Tabletop CNC mill
    A tabletop CNC machine allows you to precisely machine plastics, metals and other materials and creates three dimensional, intricate shapes.
  • Tabletop lathe
    A (manual) tabletop lathe allows you to create your own hubs, shafts, spacers, adapters and wheels out of various materials. A CNC lathe tends to be overkill since most builders only need to change the diameter rather than create complex shapes.
  • Vacuum Forming Machine
    Vacuum forming machines are used to create complex plastic shells that are moulded to your exact specifications.
  • Metal Benders
    When making robotic frames or enclosures out of sheet metal or metal extrusions, using a metal bender essential in order to obtain precise and repeatable bends.
  • Other Specialized tools
    At this stage, you will be very aware of your machnining needs and will probably require more specialized tools such as metal nibblers, welding machines, 3D printers, etc.

Electrical Tools

• Essential
  • Breadboard
    This has nothing to do with slicing bread. These boards are used to easily create prototype circuits without having to solder. This is good in the event that you have not fully developed your soldering skills or want to quickly put together prototypes and test ideas without having to solder a new circuit each time.
  • Jumper wires
    These wires fit perfectly from hole to hole on a solderless breadboard and not only look pretty but also prevent clutter.
  • Breadboard power supply
    When experimenting with electronics it is very important to have a reliable and easy to use power source. A breadboard power supply is the least expensive power supply offering these features.
  • Soldering tool kit
    An inexpensive soldering iron kit has all the basic components needed to help you learn how to solder and make simple circuits.
  • Multimeter
    A multimeter is used to measure voltage, resistance, current, check continuity of connections and more. If you know you will be building several robots and working with electronics, it is wise to invest in a higher quality multimeter.
  • Wall adapter
    Standard voltages used in robotics include: 3.3V, 5V, 6V, 9V, 12V, 18V and 24V. 6V is a good place to start since it is often the minimum voltage for DC gear motors and microcontrollers and is also the maximum voltage for servo motors. A wall adapter can also be a good replacement for batteries since they can be very expensive in the long run. A wall adapter can allow you to use your project without interruption whereas even rechargeable batteries need to be recharged.
• Intermediate
  • The Intermediate electronics lab builds upon the essential lab by adding the following:
  • Adjustable temperature soldering station
    A basic soldering iron can only take you so far. A variable temperature soldering iron with interchangeable tips will allow you to be more precise and decrease the risk of burning or melting components.
  • Brass sponge for solder
    In combination with the more traditional wet sponge to wipe away excess solder, a brass sponge can help clean the soldering iron tip without cooling it down, allowing you to spring back into action quicker and solder like a ninja.
  • Variable power supply (instead of wall adapter)
    Having a powerful and reliable power source is very important when developing complex circuits and robots. A variable power supply allows you to test various voltages and currents without the hassle of needing several types of batteries and power adaptors.
• Ultimate
  • Oscilloscope
    An oscilloscope is very useful when dealing with analogue circuits or periodic signals.
  • Logic Analyser
    A logic analyzer is like a “digital eye” when working with digital signals. It allows you to see and store the data produced by a microcontroller and makes it simpler to debug digital circuits.

Miscellaneous

• Essential
  • 22 gauge hook-up wire
    The most common wire diameter (gauge) used in robotics is 22 (0.0254 ” or 0.64 mm). Although there are advantages to multi-strand wires, single strand (solid core) allows you to easily plug them into pin headers and breadboards.
  • Third hand
    When soldering, having a helping hand that is impervious to heat is extremely useful. A third had is an incredibly helpful tool since it holds the PCB and components in place while you solder.
  • Hot glue gun
    A hot glue gun is incredibly useful no matter what your level of expertise and will only set you back a few dollars. The glue which comes out of a hot glue gun sets rapidly and provides a good bond. Unlike normal glue, this glue is three-dimensional, which means you can use it as a spacer; glue; filler; bridge etc.
  • Tape
    The most popular types of tape used in robotics are duct and electrical. Electrical tape is best suited for electrical components (since it does not conduct) while duct tape is best for structural elements.

• Intermediate
  • Thicker wire
    As you build larger robots, DC motors will require higher current and therefore larger diameter wires. The lower the gauge, the thicker the wire and the more current it can handle.
  • Vernier calliper
    In addition to a regular ruler, a vernier allows you to more precisely measure parts as well as diameters (both inside and outside).

Software

• Essential
  • CAD
    Google SketchUp is a free program which can be used to create your robot in 3D, to the proper scale, complete with texture. This can help you ensure that parts are not overlapping, check dimensions for holes and change the design before it is built.
    Autodesk 123D is another free 3D CAD (Computer Aided Design) software aimed at hobbyists. While it shares many of the same features as Google Sketchup, it has some interesting features such as solid-based part design, assemblies, parametrized transforms and other functionalities that are usually seen in higher end CAD programs.
  • Programming software
    Your first programming software should correspond to whichever microcontroller you selected. If you chose an Arduino microcontroller, you should choose the Arduino software; if you chose a Basic Stamp from Parallax, you should choose PBasic and so forth. In order to use a variety of microcontrollers, you may want to learn a more fundamental programming language such as BASIC or C.
  • Schematics and PCBs
    There are many free programs available on the market, and CadSoft’s EAGLE is one of the more popular. It includes an extensive library of parts and helps you convert your schematic to a PCB.

• Ultimate
  • CAD
    SolidWorks is the CAD program of choice for many when doing mechanical design but it is certainly not the only one available. Whet working at this level (i.e. using programs worth several thousands of dollars) you should have a good idea of your needs in order to choose the right tool (Unigraphics, Catia, ProE etc.).
  • CAM
    If you are using a CNC machine, you will need a proper 3D CAD program such as ProE, AutoCAD, SolidWorks or other similar program. In order to convert your CAD model to useable code to send to the CNC machine, you need  a CAM program. Often you can purchase a CAM program specifically for the CAD software you selected, or find a third-party supplier.

Raw Materials

• Essential
  • Thin sheet metal
    This material can be cut easily with scissors and can be bent and shaped as needed to form the frame or other components of your robot without necessarily having to do machining.
  • Cardboard
    The right cardboard (thick but can still be cut using hand tools) can easily be used to make a frame or prototype. Even basic glue can be used to hold cardboard together.
  • Thin plastic
    Polypropylene, PVC about 1/16” thick can be scored or sawed to create a more rigid and longer lasting frame for your robot.
  • Thin wood
    Wood is a great material to work with if you have the means. It can be screwed, glued, sanded, finished and more.
• Intermediate
  • Polymorph
    Polymorph allows you to create plastic parts without the hassle of having to create custom moulds.
  • Sheet metal
    If you have thicker metal-cutting sheers, sheet metal makes an excellent building material for a robot frame because of its durability, flexibility and resistance to rust.
  • Plastic sheets
    Plastic sheets are fairly rigid and resist deformation. If you are cautious and slow when cutting or drilling most plastics, the results can look professional

Practical Examples

Essential Workshop: Ard-e

Ard-e, the Arduino based robot , is an example of what you could do achieve with a simple workshop including only essential tools.

Intermediate Workshop: POLYRO

POLYRO is a very advanced robot that can be built with an intermediate workshop. It has most of the features professional robotic platforms used in research laboratories have. Although it has many complex parts, mostly all of them can be put made using simple hand tools.
For the standard practical example included at the bottom of every lesson, only an intermediate level lab would be needed to put the robot together. We will go into more detail in the following lesson.

Ultimate Workshop: BaR2D2

The BaR2D2 is a good example of what can be achieved with such an advanced robotic workshop. It has many intricate custom-machined parts and requires good tooling abilities

Robot Sensors

Unlike humans, robots are not limited to just sight, sound, touch, smell and taste. Robots use a variety of different electromechanical sensors to explore and understand their environment and themselves. Emulating a living creature’s senses is currently very difficult, so researchers and developers have resorted to alternatives to biological senses.

What can humans sense that robots can’t?

Robots can “see” but have a hard time understanding what they are looking at. Using a camera, a robot may be able to pick up an image made up of millions of pixels but without significant programming, it would not know what any of those pixels meant. Distance sensors would indicate the distance to an object, but would not stop a robot from bumping into it. Researchers and companies are experimenting with a variety of different approaches to permit a robot to not only “see” but “understand” what it is looking at. It may be a long time before a robot is able to differentiate between objects placed before it on a table, especially if they do not appear to be exactly the same as what is in its database of objects.
Robots have a really hard time tasting and smelling. A human may be able to tell you “this tastes sweet” or “this smells bad” whereas a robot would need to analyze the chemical composition and then look up the substance in a database to determine if humans have marked the taste as being “sweet” or the smell as being “bad”. There has not been much demand for a robot that can taste or smell, so not much effort has been put into creating the appropriate sensors.
Humans have nerve endings throughout their skin and as such, we know when we have touched an object or when something has touched us. Robots are equipped with buttons or simple contacts placed in strategic locations (for example on a front bumper) to determine if it has come into contact with an object. Robot pets may have contact or force sensors placed in their head, feet and back, but if you try to touch an area where there is no sensor, the robot has no way of knowing it has been touched and will not react. As research into humanoid robots continues, perhaps an “electromechanical skin” will be developed.

What can robots sense that humans can’t?

Although a robot cannot tell you if a substance tastes good or if an odour smells bad, the steps involved in analyzing the chemical composition can give it far more information than a normal human could about its properties. A robot, equipped with a carbon monoxide sensor, would be able to detect carbon monoxide gas which is otherwise colorless, odorless to humans. A robot would also be able to tell you the Ph level of a substance to determine if it is acidic or basic and much, much more.
Humans use a pair of eyes to get a very good sense of depth, though for many, accurately gauging distance is not easy. A human might tell you “the tree looks to be about 50 feet away”, but a robot, equipped with the right distance sensors, can tell you “the tree is 43.1 feet away”.
Additionally, robots can not only sense but give accurate values of a variety of environmental factors that humans are otherwise unaware of or incapable of sensing. For example, a robot can tell you the precise angular or linear acceleration it is subjected to, while most humans would only tell you “I’m turning”, or “I’m moving”. A human can tell you based on experience if they think an object will be hot or cold without actually touching it, whereas a thermal camera can provide a 2D thermal image of whatever is in front of it. Although humans have five main senses, robots can have an almost infinite number of different sensors.

Which sensors do my robots need?

So, what types of sensors are available and which ones does your robot need? You need to first ask yourself “what do I want or need the robot to measure?” and refer to the appropriate category below. There is a good chance what you have in mind will not fall “nicely” into one of these categories, so try to break it down into its basic elements.

Contact

Push button / Contact switch

Switches,  buttons, and contact sensors are used to detect physical contact between objects and are not just restricted to humans pushing buttons; bumpers on a robot can be equipped with momentary push buttons, and “whiskers” (just like an animal) can be used to sense multiple distances.

• Advantages: very low cost, easy to integrate, reliable
• Disadvantages: single distance measurement

Pressure sensor

Unlike a push button which offers one of two possible readings (ON or OFF), a pressure sensor produces an output proportional to the force that is being applied to it.

• Advantages: allows gauging how much force is being applied
• Disadvantages: can be imprecise and are more difficult to use than simple switches.

Distance

Ultrasonic Range Finders

Ultrasonic range finders use acoustics to measure the time between when a signal is sent versus when its echo is received back. Ultrasonic range finders can measure a range of distances, but are used specifically in air and are affected by the reflectivity of different materials.

• Advantages: medium range (several meters) measurement.
• Disadvantages: surfaces and environmental factors can affect the readings.

Infrared

Infrared light, which as we saw is used in communication, can also be used to measure distance. Some infrared sensors measure one specific distance while others provide an output proportional to the distance to an object.

• Advantages: low cost, fairly reliable and accurate.
• Disadvantages: closer range than ultrasonic

Laser

Lasers are used when high accuracy, or long distances (or both) are required when measuring the range to an object. Scanning laser rangefinders use spinning lasers to get a two dimensional scan of the distances to objects

• Advantages: very accurate, very long range.
• Disadvantages: much costlier than regular infrared or ultrasonic sensors.

Encoders

Optical encoders use mini infrared transmitter/receiver pairs and send signals when the infrared beam is broken by a specifically designed spinning disk (mounted to a rotating shaft). The number of times the beam is broken corresponds to the total angle travelled by a wheel. Knowing the radius of the wheel, you can determine the total distance travelled by that wheel. Two encoders give you a relative distance in two dimensions.

• Advantages: assuming there is no slip, the displacement is absolute. Often comes installed on the rear shaft of a motor
• Disadvantages:  additional programming required; more accurate optical encoders can be ~$50+ each

Linear Potentiometer, resistive band

A linear potentiometer is able to measure the absolute position of an object. A resistive band changes resistance depending on where a force is applied.

• Advantages: position is absolute. A resistive band requires pressure to be applied at a given position.
• Disadvantages: range is very small

Stretch and Bend Sensors

A stretch sensor is made up of a material whose resistance changes according to how much it has been stretched. A bend sensor is usually a sandwich of materials where the resistance of one of the layers changes according to how much it has been bent. These can be used to determine a small angle or rotation, for example how much a finger has been bent.

• Advantages: useful where an axis of rotation is internal or inaccessible
• Disadvantages: not very accurate, and only small angles can be measured

Stereo Camera System

Just like human eyes, two cameras placed a distance apart can provide depth information (stereo vision). Robots equipped with cameras can be some of the most capable and complex robots produced. A camera, combined with the right software, can provide color and object recognition.

• Advantages: can provide dept information and a good feedback about a robot’s environment
• Disadvantages: complex to program and use the information

Positioning

Indoor Localization (room navigation)

An indoor localization system can use several beacons to triangulate the robot’s position within a room, while others use a camera and landmarks.

• Advantages: excellent for absolute positioning
• Disadvantages: requires complex programming and the use of markers

GPS

A GPS uses the signals from several satellites orbiting the planet to help determine its geographic coordinates. Regular GPS units can provide geographical positioning down to 5m of accuracy while more advanced systems involving data processing and error correction thanks to the use of other GPS units or IMUs can be accurate down to several cm.

• Advantages: does not requires markers or other references
• Disadvantages: can only function outdoors.

Rotation

Potentiometer

A rotary potentiometer is essentially a voltage divider and provides an analog voltage corresponding to the angle the knob is rotated to.

• Advantages: simple to use, inexpensive, reasonably accurate, provides absolute readings.
• Disadvantages: most are restricted to 300 degrees of rotation

Gyroscope

An electronic gyroscope measures the rate of angular acceleration and provides a corresponding signal (analog voltage, serial communication, I2C etc.). Integrating this value twice will give you an angle.

• Advantages: no moving “mechanical” components
• Disadvantages: the sensor is always subjected to angular acceleration whereas a microcontroller cannot always take continuous input, meaning values are lost, leading to “drift”.

Encoders

Optical encoders, as explained above, use mini infrared transmitter/receiver pairs to signal when the infrared beam is broken by a spinning disk (mounted to a rotating shaft). The number of times the beam is broken corresponds to the total angle travelled by a wheel. A mechanical encoder uses a very finely machined disk with enough holes to be able to read specific angles. Mechanical encoders can therefore be used for both absolute and relative rotation.

• Advantages: accurate
• Disadvantages: for optical encoders, the angle is relative (not absolute) to the starting position.

Environmental Conditions

Light Sensor

A light sensor can be used to measure the intensity of a light source, be it natural or artificial. Usually, its resistance is proportional to the light intensity.

• Advantages: usually very inexpensive and very useful
• Disadvantages: cannot discriminate the source or type of light.

Sound sensor

A sound sensor is essentially a microphone that returns a voltage proportional to the ambient noise level. More complex boards can use the data from a microphone for speech recognition.

• Advantages: inexpensive, reliable
• Disadvantages: more meaningful information requires complex programming

Thermal Sensors

Thermal sensors can be used to measure the temperature where it is on a particular component or the ambient temperature.

• Advantages: they can be very accurate
• Disadvantages:  more complex and accurate sensors can be more difficult to use.

Thermal Camera

Infrared or thermal imaging allows you to get a complete 2D thermal image of whatever is in front of the camera.  This way it is possible to determine the temperature of an object.

• Advantages: differentiate objects from the background based on their thermal signature
• Disadvantages: expensive

Humidity

Humidity sensors detect the percentage of water in the air and are often paired with temperature sensors.

Pressure Sensor

A pressure sensor (which can also be a barometric sensor) can be used to measure atmospheric pressure and give an idea of the altitude of a UAV.

Gas sensors

Specialized gas sensors can be used to detect the presence and concentration of a variety of different gases. However, only specialized robotic applications tend to need gas sensors.

• Advantages: These are the only sensors which can be used to accurately detect gas
• Disadvantages: inexpensive sensors may give false positives or somewhat inaccurate readings and should therefore not be used for critical applications.

Magnetometers

Magnetic sensors or magnetometers can be used to detect magnets and magnetic fields. This is useful to know the position of magnets.

• Advantages: can detect ferromagnetic metals.
• Disadvantages: some times the sensors can be damaged by strong magnets.

Attitude
(roll, pitch and heading)

Compass

A digital compass is able to use the earth’s magnetic field to determine its orientation with respect to the magnetic poles. Tilt compensated compasses account for the fact that the robot may not be perfectly horizontal.

• Advantages: provides absolute navigation
• Disadvantages:  greater accuracy increases the price

Gyroscope

Electronic gyroscopes are able to provide the angle of the tilt in one or more axes. Mechanical tilt sensors usually determine if a robot has been tilted past a certain value by using mercury in a glas capsule or a conductive ball.

• Advantages:  electronic tilt sensors have a higher accuracy than mechanical ones
• Disadvantages:  can be expensive

Accelerometers

Accelerometers measure the linear acceleration. This allows to measure the gravitational acceleration or any other accelerations the robot is subject to. This can be a good option to approximate distance travelled if your robot cannot use the surrounding environment as a reference. Accelerometers can measure accelerations along one, two or three axis. A three-axis accelerometer can be used also to measure the orientation a

• Advantages:  they do not require any external reference or marker to function and can provide absolute orientation with respect to gravity, or relative orientation.
• Disadvantages: they only approximate the traveled distance and cannot precisely determine it.

IMU’s

An Inertial Measurement Unit combines a multi-axis accelerometer with a multi-axis gyroscope and sometimes a multi-axis magnetometer in order to more accurately measure roll

• Advantages: it is a very reliable way of measuring the robots attitude without using external references (besides the earth’s magnetic field)
• Disadvantages: can be very expensive and is complex to use.

Miscellaneous

Current and Voltage Sensors

Current and voltage sensors do exactly as their name describes; they measure the current and/or voltage of a specific electric circuit. This can be very useful for gauging how much longer your robot will operate (measure the voltage from the battery) or if your motors are working too hard (measure the current).

• Advantages: they do exactly what they are intended to do
• Disadvantages: can disturb the voltage or current they are measuring. Sometimes they require the circuit being measured to be modified.

Magnetic Sensors

Magnetic sensors or magnetometers detect magnetic objects and can either require contact with the object, or be relatively close to an object. Such sensors can be used on an autonomous lawn mower to detect wire embedded into a lawn.

• Advantages: usually inexpensive
• Disadvantages: usually need to be relatively close to the object, and sadly cannot detect non-magnetic metals.

Vibration

Vibration sensors detect the vibration of an object by using piezoelectric or other technologies.

RFID

Radio Frequency Identification devices use active (powered) or passive (non-powered) RFID tags usually the size and shape of a credit card, small flat disc or addition to a key chain (other shapes are possible as well). When the RFID tag comes within a specific distance of the RFID reader, a signal with the tag’s ID is produced.

• Advantages: RFID tags are usually very low cost and can be individually identified
• Disadvantages: not useful for measuring distance, only if a tag is within range.

Practical Examples

1.      “I want my robot to follow a person”

There is no “person following sensor” available (yet), so you would need to see which categories above may apply and which don’t need to be considered.

• Q: Are you looking to detect, measure distance to  (or contact with) an object?
  • Immediately the answer should be yes and this first category of sensors will likely give the best results.
• Q: Are you looking to measure rotation?
  • Perhaps, but you really don’t need to know if the robot is rotated (that’s a different aspect entirely) or if the human is rotated with respect to the robot.
• Q: Are you looking to measure environmental conditions?
  • Not really. You might consider tracking a human based on their thermal signature, but differentiating between humans and animals (or even a microwave) would be difficult.
• Q: Are you looking to measure position, orientation, or angle?
  • GPS is the first sensor which immediately stands out.

Having gone through the main categories, we should be considering sensors related to distance, contact and detection, and also considering GPS. Taking a closer look at the types of sensors in this category:

• Contact: irrelevant since the robot will be following the human at a distance.
• Distance: 
  • Ultrasonic, infrared and laser: measuring the distance is useful when combined with other sensors.
  • Camera: This may be the best option and we will look into it.
  • Stretch: This would require the human to be physically connected to the robot, which is something we do not want.
• Rotation: irrelevant
• Positioning:
  • GPS: placing a GPS unit on both the robot and the human would allow the robot to easily follow the human within a certain radius.
• Environmental conditions: irrelevant
• Attitude:
  • Accelerometer: not very useful since it does not give the robot an idea of where the human is.
  • IMU: not very useful since it does not give the robot an idea of where the human is.
• Miscellaneous:
  • RFID:  An RFID reader can locate a tag placed around it, and although some sort of RFID option may be possible, it would require quite a bit of research.

Therefore out of the options available, the most appropriate sensors to allow a robot to follow a human may be ultrasonic or infrared distance sensor(s), a camera and GPS. A camera may be used to pick up a specific pattern placed on the shirt of the individual to follow while GPS units mounted on the robot and on the human would help the robot find the human if she cannot be seen visually. Distance sensors would ensure the robot does not get too close to the human. Therefore when choosing sensors to help your robot follow a human, the sensors listed above would be a good starting point.

2.       “I want my robot to stay within the boundaries of our lawn”

There is no “neighbour’s grass” sensor available (that we are aware of), so you will need to devise another sensor-based solution.

• Q: Are you looking to detect, measure distance to  (or contact with) an object?
  • Yes, we are looking to detect a boundary
• Q: Are you looking to measure rotation?
  • Not really
• Q: Are you looking to measure environmental conditions?
  • Not really, but we’ll keep an open mind since the robot is outdoors.
• Q: Are you looking to measure position, orientation, or angle?
  • Not really

Applicable categories therefore include measuring distance, feel contact, detect an object, and perhaps environmental conditions. Out of the list of sensors in this category, we can see that the following may be useful:

• Contact: Detecting collisions in order to avoid obstacles.
• Distance: 
  • Ultrasonic, infrared and laser: These will help the robot to avoid hitting objects, and when several placed facing downwards, will help the robot avoid falling into openings such as pools.
• Rotation:
  • Encoders: Encoders: these will help position the robot in two dimensional space based on a starting position.
  • Positioning:
    • GPS: Ideal, the robot could be instructed to remain within certain coordinates.
• Environmental conditions:
  • Humidity sensor: This is not an “intuitive” solution and was creatively used on the Lawnbott Spyder lawn mower to differentiate between grass and “non-humid” surfaces such as concrete and pavement.
  • Magnetic sensor: Magnetic sensors are used both indoors and outdoors to mark boundaries. The perimeter is marked with a strip of conductive wire and the robot is equipped with a few magnetic sensors.
• Attitude:
  • IMU: this may make the data obtained from the encoders more accurate, especially if there are slopes or uneven terrain.
• Miscellaneous: irrelevant

Controlling thr Robot

The definition we have chosen for a “robot” requires the device to obtain data about its environment, make a decision, and then take action accordingly. This does not exclude the option of a robot being semi-autonomous (having aspects which are controlled by a human and others which it does on its own). A good example of this is a sophisticated underwater robot; a human controls the basic movements of the robot while an on-board processor measures and reacts to underwater currents in order to keep the robot in the same position without drifting. A camera onboard the robot sends video back to the human while onboard sensors may track the water temperature, pressure and more. If the robot loses communication with the surface, an autonomous program may kick-in causing it to surface. If you want to be able to send and/or receive commands from your robot, you will need to determine its level of autonomy and if you want it to be tethered, wireless or fully autonomous.

Tethered

Direct Wired Control

The easiest way to control a vehicle is with a handheld controller physically connected to the vehicle using  a cable (i.e. a tether). Toggle switches, knobs, levers, joysticks and buttons on this controller allow the user to control the vehicle without the need to incorporate complex electronics. In this situation, the motors and a power source can be connected directly with a switch in order to control its forward/backwards rotation. Such vehicles usually have no intelligence and are considered to be more “remote controlled machines” than “robots”.

Advantages

• The robot is not limited to an operating time since it can be connected directly to the mains
• There is no worry about loss of signal
• Minimal electronics and minimal complexity
• The robot itself can be light weight or have added payload capacity
• The robot can be physically retrieved if something goes wrong (very important for underwater robots)

Disadvantages

• The tether can get caught or snagged (and potentially cut)
• Distance is limited by the length of the tether
• Dragging a long tether adds friction and can slow or even stop the robot from moving

Wired Computer Control

The next step is to incorporate a microcontroller into the vehicle but continue to use a tether. Connecting the microcontroller to one of your computer’s I/O ports (e.g. a USB port) allows you to control its actions using a keyboard (or keypad), joystick or other peripheral device. Adding a microcontroller to a project also may require you to program how the robot reacts to the input. Instead of using a laptop or desktop computer, netbooks are often a desirable choice because of their low price, small size and low weight.

Advantages

• Same advantages as with direct wired control
• More complex behaviours can be programmed or mapped to single buttons or commands.
• Larger controller choice (mouse, keyboard, joystick, etc.)
• Added onboard intelligence means it can interface with sensors and make certain decisions on its own

Disadvantages

• Cost is higher than a purely tethered robot because of the added electronics
• Same disadvantages as with direct wired control

Ethernet

A variation on computer control would be to use an Ethernet interface. A robot that is physically connected to a router (so it could be controlled via the Internet) is also possible (though not very practical) for mobile robots. Setting-up a robot that can communicate using the internet can be fairly complex, and more often than not, a WiFi (wireless internet) connection is preferable. A wired and wireless combination is also an option, where there is a transceiver (transmit and receive) connected physically to the internet and data received via the internet is then sent wirelessly to the robot.

Advantages

• Robot can be controlled trough the Internet from anywhere in the world
• The robot is not limited to an operating time since it could use Power over Ethernet (PoE).
• Using Internet Protocol (IP) can simplify and improve the communication scheme.
• Same advantages as with direct wired computer control

Disadvantages

• Programming involved is more complex
• The tether can get caught or snagged (and potentially cut)
• Distance is limited by the length of the tether
• Dragging a long tether adds friction and can slow or even stop the robot from moving

Wireless

Infrared

Infrared transmitters and receivers cut the cables connecting the robot to the operator. This is usually a milestone for beginners. Infrared control requires “line of sight” in order to function; the receiver must be able to “see” the transmitter at all times in order to receive data. Infrared remote controls (such as universal remote controls for televisions) are used to send commands to an infrared receiver connected to a microcontroller which then interprets these signals and controls the robot’s actions.

Advantages

• Low cost
• Simple TV remote controls can be used as controllers

Disadvantages

• Needs to be line of sight
• Distance is limited

Radio Frequency (RF)

Commercially available Remote Control (R/C) units use small microcontrollers in the transmitter and receiver to send, receive and interpret data sent via radio frequency (RF). The receiver box has a PCB (printed circuit board) which comprises the receiving unit and a small servo motor controller. RF communication requires either a transmitter matched/paired with a receiver, or a transceiver (which can both send and receive data). RF does not require line of sight and can also offer significant range (transmission distance). Standard radio frequency devices can allow for data transfer between devices as far away as several kilometres and there is seemingly no limit to the range for more professional RF units.
XBee and Zigbee modules use RF for communication, but allow the user to vary many of the communication parameters involved. These modules have a specific footprint (layout) and are only produced by certain companies. Their main advantage is that they provide a very robust easy to set up link and take care of all of the communication protocol details.
Many robot builders choose to make semi-autonomous robots with RF capability since it allows the robot to be as autonomous as possible, provide feedback to a user and still give the user some control over some of its functions should the need arise.

Advantages

• Considerable distances possible
• Setup can be straightforward
• Omni directional (impeded but not entirely blocked by walls and obstructions)

Disadvantages

• Very low data rate (simple commands only)
• Pay attention to the transmission frequencies – they can be shared

Bluetooth

Bluetooth is a form of RF and follows specific protocols for sending and receiving data. Normal Bluetooth range is often limited to about 10m though it does have the advantage of allowing users to control their robot via Bluetooth-enabled devices such as cell-phones, PDAs and laptops (though custom programming may be required to create an interface). Just like RF, Bluetooth offers two-way communication.

Advantages

• Controllable from any Bluetooth enabled device (usually additional programming is necessary) such as a Smartphone, laptop, desktop etc.
• Higher data rates possible
• Omnidirectional (does not need line of sight and can travel a little through walls)

Disadvantages

• Devices need to be “paired”
• Distance is usually about 10m (without obstructions)

WiFi

WiFi is now an option for robots; being able to control a robot wirelessly via the internet presents some significant advantages (and some drawbacks) to wireless control. In order to set up a WiFi robot, you need a wireless router connected to the internet and a WiFi unit on the robot itself. For the robot, you can also use a device that is TCP/IP enabled with a wireless router.

Advantages

• Controllable from anywhere in the world so long as it is within range of a wireless router
• High data rates possible

Disadvantages

• Added programming required
• Maximum range is usually determined by the choice of wireless router

GPRS / Cellular

Another wireless technology that was originally developed for human to human communication, the cell phone, is now being used to control robots. Since cellular frequencies are regulated, incorporating a cellular module on a robot usually requires added patience for programming as well as an understanding of the cellular network system and the regulations.

Advantages

• Robot can be controlled anywhere it has a cellular signal
• Direct satellite connection is possible

Disadvantages

• Setup and configuration can be complex – NOT for beginners
• Each network has its own requirements / restrictions
• Cellular service is not free; usually the more data you transmit/receive the more money you will need to pay.
• System is not (yet) well setup for robotics use

Autonomous

The next step is to use the microcontroller in your robot to its full potential and program it to react to input from its sensors. Autonomous control can come in various forms: pre-programmed with no feedback from the environment, limited sensor feedback and finally complex sensor feedback. True “autonomous control” involves a variety of sensors and code to allow the robot to determine by itself the best action to be taken in any given situation.
The most complex methods of control currently implemented on autonomous robots are visual and auditory commands. For visual control, a robot looks to a human or an object in order to get its commands. Getting a robot to turn to the left by showing a piece of paper with arrow pointing left is a lot harder to accomplish than one might initially suspect. An auditory command such as “turn left” also requires quite a bit of programming. Programming a variety of complex commands like “get me a drink from the fridge” or “get my shoes, they’re near the front door” is no longer fantasy but requires a very high level of programming, and a lot of time.

Advantages

• This is “real” robotics
• Tasks can be as simple as blinking a light based on one sensor readings to landing a spacecraft on a distant planet.

Disadvantages

• It’s only as good as the programmer; if it’s doing something you don’t want it to do, the only option you have is to check your code, modify it and upload the changes to the robot.

Practical Example

For our project, the goal is to create an autonomous rover capable of making a decision based on external input from sensors. Should the robot “misbehave” it will be physically close and shutting it off will not be an issue. However having the option of semi-autonomous (wireless) control to allow us the option of making a remote-controlled vehicle is also attractive. We will not have the need for tethered control.

The microcontroller chosen in the previous lesson uses what are called “shields” which are essentially ad-on boards specific to the Arduino’s pin layout. There are many shields, including ones that allow for Ethernet, Xbee, or Bluetooth communication. There is even a shield that allows for GPRS (i.e. cellular) communications. The basic robot will therefore have no additional modules, though it is important to note that it does have wireless communication capability.