Offers a kid-friendly design that is heavy on eye-popping graphics Focuses on basic projects that set your child on the road to further exploration Boasts a small, full-color, accessible package that instills confidence in the reader Introduces basic robotics concepts to kids in a language they can understand If your youngster loves to tinker, they'll have a whole lot of fun while developing their creative play with the help of Building Your Own Robots.
I want you to love building robots, too. It took me a while to learn about many of the tools and parts in amateur robotics. Perhaps by writing about my experiences, I can give you a head start. This book continues its aim at teenagers and adults who have an avid interest in science and dream of building household explorers. No formal engineering education is assumed. The robot described and built in this book is battery powered and about the size of a lunchbox.
It is autonomous. Learn robot building from the ground up, hands-on, in full color! Love robots? Start building them. John Baichtal has helped thousands of people get started with robotics. He knows what beginners need to know.
He knows your questions. He knows where you might need extra help. Hundreds of full-color photos guide you through every step, every skill. Wondering just how much you can really do? Baichtal shows you 30 incredible robots built by people just like you!
Learn how to program a voice agent to communicate with and control the actions of your robot. Using sensors, allow your robot to see its surroundings and avoid obstacles. Learn about the basics of AI action including speech recognition and visual processing.
Wi-Fi is used to monitor AI robots. If you need steady, long-term power, then purchase a voltage-adjustable DC power supply see Figure That way, even if the circuit breaker fails to trip, you can quickly cut power without having to touch the rampaging device. Unlike circuit breakers that detect too much total power, GFCI outlets disable power when not all of the electricity being sent out from the outlet is returning.
This is more likely in wet conditions, where the water provides an electrical path from the device to your body. Like circuit breakers, GFCI outlets can be lifesavers. Another place to consider a fuse or circuit breaker is on the robot itself.
The portions of the circuit with regulated power go through a voltage regulator chip. So, check their datasheets to make sure your regulator chips have built-in thermal and current overload mechanisms most do.
For circuits on the robot that connect directly to the battery, such as the motors, use a fuse or circuit breaker to prevent damage or fire. A few seconds after the fault is corrected, they cool down and automatically reconnect the power. A classic single-use fuse left versus PPTC self-resetting circuit protection devices right Saving the Ground Prong Never cut off the third prong from a power cord see Figure Grounded three-prong plug With the advent of the third prong, the metal case can safely dispose of the electricity back into the outlet instead of into the person touching the device.
A trip to the hospital is going to be a lot more expensive. Rooms with just a few two-prong outlets are becoming a thing of the past. Disconnecting Power Always physically disconnect power from the robot's circuits before working on it. On larger robots, not only should the batteries be disconnected, but they also should be literally removed from the robot during maintenance.
This is safer for the builder and it prevents physical damage to power sources. Either way, use test probes to ensure no power remains. Large, charged capacitors are one of the reasons that television sets and computer power supplies can be so dangerous to service.
Never touch a live circuit with both hands—you want to avoid creating a path through your heart. You should also wear rubber-soled or other insulating-soled shoes. An electrical path from a hand through your chest and out a foot can be deadly. Ground paths work because the electricity makes its way through the path of least resistance.
One last point: human skin is much more conductive when wet. That includes rain or sweaty hands gross! Sorry about your arm. Even if intended for good purposes, moderate-sized motors can produce significant force. Wonder why? Motors and power components tend to get hot during use. Think about the amount of electrical work being performed by each piece and the amount of current it is receiving.
Every electronic or mechanical part wastes a portion of the power it receives as heat. Additionally, bright lighting makes it easier to spot mistakes, especially in circuit boards. If the workpiece is easy to see, it reduces the likelihood of leaning way into the piece or squinting. Whenever possible, purchase fluorescent lights see Figure Not only are they energy efficient, but they run cooler.
Hmm, are those two factors related? A nice desk-mounted adjustable table lamp is a must. Desktop adjustable lamp with fluorescent bulb Staying Rested and Level-Headed Fatigue and frustration can cost you and your robot. Plan ahead to finish your robot well before a competition. Relax, take breaks, and enjoy your hobby. Multimeter features are broken into groups: must-have, nice-tohave, and optional.
The chapter concludes with an analysis of three multimeters. A multimeter is a required tool for robot building. You will need a multimeter to perform the experiments and build the projects in the chapters that follow. See Figure for an example of a multimeter.
What follows are brief descriptions of the features available on multimeters. Digital multimeter with test probes Digital Digital meters display measured values on an LCD liquid-crystal display similar to a calculator see Figure No guessing or interpretation is needed. Analog meters have a needle that swings back and forth, with line markings underneath see Figure Every digital multimeter meets this requirement.
A range of 0. Every basic multimeter meets this requirement. Needle display of an old-fashioned analog multimeter DC Current Measured in amps, DC current indicates how many electrons are speeding by per second.
Resistance Measured in ohms, resistance indicates how much something opposes electricity going through it. Probes or Leads The meter should come with the cables see Figure needed to connect it to the parts to test. Ironically, really expensive pieces of equipment, such as many oscilloscopes, require probes that are sold separately. Test probes or test leads Figure Many multimeters have this feature, but the range is usually less broad. This is an important feature because it can help classify different diode types and test and identify transistors.
It can even light up LEDs. Most multimeters have this feature. Continuity Measured in ohms, continuity indicates whether an electrical connection exists between two points. Frequency Measured in hertz, frequency indicates how many times something is occurring per second. If the meter has a frequency function, get one that at least measures up to 45, Hz 45 kHz. Some multimeters have this feature, but the range is usually less broad.
Meter displaying kHz frequency measurement Duty Cycle Measured in percentages, duty cycle indicates how often a measurement is high as opposed to how often a measurement is low. This turns out to be an important measurement in robotics, as it is the key to PWM pulse-width modulation. Only some multimeters have this feature, which often appears in frequency mode. Autoranging automatically determines the range and subsequently bumps it up or down as necessary, which is nice. Autoranging can be annoying if the measurement is occurring on the border between two ranges, because the device will keep switching between the modes unless the multimeter also has some sort of range-hold button.
Only the mid-range and high-end multimeters have the autoranging feature, which you can easily identify by uncluttered dials see Figure Luckily for the battery, my meter has auto power off. The bipolar type of npn or pnp is usually determined by the user inserting the transistor into different socket holes see Figure See Chapter 16 for detailed steps on testing with a transistor socket or diode feature.
Dual Display A dual display includes a small, second set of digits in a corner of the display so that other measurements or calculations can be displayed at the same time as the ongoing value. This is almost a requirement for maximum, minimum, and the other calculated features, since the ongoing value is otherwise not displayed. Many meters have this feature. Maximum A maximum mode displays the maximum value measured.
While the meter continuously measures, you can exercise the various parts of a circuit, pausing every so often to view the maximum value read by the meter. Many multimeters have this feature. Transistor test socket Minimum A minimum mode displays the minimum value measured. See the Maximum feature, previously described. Stand Most meters have a foldout piece to prop the meter up at an angle on the desktop see Figure This makes it easy to read the display while working on the robot.
Optional Features Here are some bonus features that are available on some multimeters, but not absolutely necessary to have: Inductance Measured in henries, inductance indicates the amount of opposition to changes in electrical flow.
Very few multimeters have this feature; otherwise, it would have made the nice-to-have list. This can be very useful for generating test logs. If available separately, consider purchasing the software at the same time as the multimeter, just in case the software becomes unavailable when that multimeter model is discontinued.
Only some multimeters have the data interface feature. This can be an extremely useful feature for examining the quality and grouping of data pulses and timing signals. Unfortunately, the resolution and maximum speed limit of multimeter-based scopes is rather limited at this time.
A true, high-speed oscilloscope with a generous display is a different beast. Few multimeters have a scope feature, and their price is greatly increased. Useful at night or in dimly lit areas. Mainly higher-end or graphic-intensive units have backlighting. It can be useful for checking circuit timing or servo commands. Few multimeters have this feature.
Temperature Measured in degrees Celsius or degrees Fahrenheit, a temperature mode indicates how hot or cold something is. Sound Measured in decibels, a sound mode indicates how loud or quiet something is. It could be useful for motor, speaker, or microphone volume testing. Count A counter measures the number of times something occurs, regardless of length of time.
Instead, they average their readings over a short period of time and update the display only a couple of times per second analog-nostalgic supporters point to this weakness. So, some digital multimeters supplement their display with a bar graph, which is a rapidly updating single-axis line see Figure Digital bar graph allows DMMs to approach responsiveness of analog meters Data Hold Data hold prevents the screen from changing from the currently displayed value. Most meters continue to display the current measured value but place the held value somewhere else on the screen.
Data Auto A data-auto mode periodically moves the measured value to the smaller portion of the dual display. Most multimeters have this logic mode feature. Meter transitioning through logic states Memory Similar to the memory feature available on most calculators, memory mode on a multimeter can store one or more measured values.
When only a single value is frozen and stored elsewhere on the display, this feature is simply another name for data hold. This shows the change in value, rather than the absolute value. Some multimeters have this feature. Offset An offset mode shows the difference between the value stored in memory and the current value being measured.
The meter is almost always operated with the boot installed, unless space is a serious issue. Rubber boot edge cover for meter If a rubber boot is available but not included with the meter, it might be best to purchase the boot at the same time as the meter. The boot may no longer be available when the meter is discontinued. Most multimeters have a boot available.
Because of the danger from the higher voltage and current capacity of household outlets, this book only involves DC. Sandwich, the line-following robot A line-following robot usually contains the same building blocks that are universal to all robots. Only after understanding the individual components, circuits, and techniques will you be ready to combine them into a robot.
This chapter introduces the project goals. The following chapters walk you through component parts in detail. The line-following robot acts as a context for discussing many of the parts and circuits, but the part-specific information applies to all robots.
Surface Materials The terrain must be flat and smooth, like a linoleum floor. Also acceptable is short, solid carpeting like commercial or non-patterned Berber loop-pile. On the other hand, sidewalk concrete quickly grinds down parts. Course Lighting Indoor lighting conditions without heavy shadows are essential. Although you can make a robot to handle both indoor and outdoor driving, you would need additional electronics.
Defining the Line The width of the line to be followed should average from 1. The line must contrast well with the floor. Both the line and the floor should be solid colors, not patterns. In fact, solid white on solid black would make the robot happiest see Figure The line and floor must remain the same color throughout the course.
Picking Line Marking Material How should you make your line? Painting the line can work very well. With paint, there is a wide variety of colors and glosses to choose from and you can control the line width. Some long-term upkeep may be necessary, but generally a painted line tends to be very durable. However, painting entails preparation time and is permanent. A course made with ordinary masking tape on a flat, dark surface Alternatively, wide-head marker pens work well on poster board.
Make sure the lines are wide enough and cover the background thoroughly. Spotty, faded, or broken lines can cause the robot to drive off course. For household courses, most people prefer tape lines. You can create, adjust, and remove nonpermanent tape courses quickly.
Tape rolls are easily obtained and come in the desired range of widths. Glossy shiny white cloth tape or flat non-shiny black cloth tape provides the highest contrast and thus is easiest for the robot to follow. Ordinary semi-translucent masking tape may not adequately cover the color and pattern of the floor underneath it. Watch out for glossy dark materials. Tape lines can leave a sticky residue when removed. This is especially true in hot conditions or if the tape remains in place for too long.
Blue masking tape see Figure or other low-adhesion varieties are much cleaner than ordinary off-white masking tape. For this reason, I use blue masking tape most often. Warning: A mother contacted me regarding the difficulty of removing old tape from new hardwood flooring. She recommended the book include a warning.
Now it does. The upside to this is that blue masking tape can be followed as a light line when placed on a dark background and a dark line when placed on a light background. The downside is that the maximum contrast is less than an actual white or black line. There are two disadvantages to blue masking tape.
First, the blue color reflects very little infrared, and therefore is not suitable for use as a light line for robots with infrared emitters.
Second, unless firmly applied, blue tape can catch on the robot and get pulled up. Very-low-adhesion tape often suffers from this problem. Sharp turns, however, can derail even a competent robot. However, for the example robot, limit turn angles to Lines should always be contiguous.
Feel free to experiment with increasingly difficult arrangements. After all, the worst thing that can happen is that the robot wanders away. Many designers fret over line crossings or line splits in the course see Figure Summarizing Course Conditions In summary, the Sandwich robot follows a moderately thick, easy-to-see line around an obstacle-free flat floor.
The course should feature gradual turns on a high-contrast surface illuminated evenly by indoor lighting. Maybe one that fits into the palm of your hand see Figure Unfortunately, very small robots are difficult to assemble and work on. Like a miniature dollhouse, all of the parts on a small robot need to be equally small. This limits part choices and options. A palm-sized line-following robot At the other extreme, large robots are usually heavy, requiring larger motors to move.
Large motors need a lot of power, which leads to a bigger battery. To support all the weight, the body must be constructed of stronger materials, which are harder to cut and drill. Perhaps the best size for an amateur robot is around the size of a lunchbox. Plenty of parts fit those dimensions, standard consumer batteries provide enough power, and plastics and soft metals have enough strength for the forces exerted.
Topping it all off, lunchbox-size robots fit well within the home. With the successful completion of a few moderate designs, you can expand your work into the dimensions you desire. Seeing Sandwich There are many possible designs for a line-following robot. However, you can choose to make a couple of the pieces yourself from raw materials.
This robot is named Sandwich because its body is based on a sandwich container. Even if you choose a different shape, you can still apply the same circuit and techniques. Depending on the motors and containers you have lying around, your robot may turn out looking very different but with approximately the same line-following capabilities.
Blinking lights, colorful wires, production-quality wheels, metal screws, and a rounded case all add sophistication without adding much real work. Half of the battle is showmanship. This robot breaks down into smaller modules that are easily recreated. The next sections of this chapter describe the modules and switch functions. Line-Following Switch At the rear of the robot is a toggle switch see Figure This switch has three positions: left, center, and right.
Rear-mounted line-following toggle switch in center motors off position When the switch is in the left position, the left motor is connected to the left sensors and the right motor is connected to the right sensors. This allows the robot to follow dark-colored lines. When the switch is in the right position, the motor wires are crossed.
The left motor is connected to the right sensors and the right motor is connected to the left sensors. This allows the robot to follow light-colored lines. Believe it or not, switching the motor connections is all that it takes to follow different line brightnesses.
No fancy algorithms or circuitry! Power Source and Power Switch Also at the rear of the robot is a battery and a power switch see Figure The battery is an ordinary 9 V consumer battery.
The headlights allow the robot to drive in darkness. By lighting the floor evenly, the headlights help prevent the robot from thinking a shadow is a dark line. Front-mounted sensors and headlights The four sensors are arranged in pairs: two sensors for the left side and two sensors for the right side.
Technically, each side only requires a single sensor, but the leftmost and rightmost sensors act as safety nets in case the line sneaks by the middle sensors on a sharp turn. Placing the Robot on the Center of the Line When positioning the robot, the sensors should be centered over the line see Figure This way, the amount of light received is equally balanced between the left and right pairs of sensors.
It then applies power to either the left or right motor to turn itself until the brightness is balanced again. Adjusting Sensor Balance At the front of the robot is a small hole leading to a sensor adjustment dial see Figure A tiny screwdriver fits into the hole to turn the dial.
Front-mounted sensor adjustment dial There are a number of reasons why a sensor adjustment dial is necessary. First, it would be very difficult to find four perfectly matched brightness sensors. Second, during soldering, one sensor is inevitably placed a little bit higher than another. Third, as the parts age or become soiled with dirt or dust, they may no longer provide the same sensitivity that they did originally. With the adjustment dial, you can balance the left pair of sensors against the right pair.
Since adjustments need to be made when the robot is already in place on a track, the dial must be accessible with the robot assembled. An internally mounted dial with an access hole ends up being the solution. Fine-tuning dials are wise features to have. Also, it would be impossible to properly adjust the sensor balance dial without some feedback from the robot as to which pair of sensors was seeing more light.
Three yellow LEDs light up on the right side when the right sensors see more brightness than the left sensors. Conversely, three green LEDs light up on the left side when the left sensors see more brightness see Figure When completely balanced, both sets of LEDs light up or blink off and on.
Three LEDs are used so that the indication is visible from any angle. It simply turns on a motor and indicator light if one set of sensors is brighter, or turns on the other motor and indicator light if the other set of sensors is brighter.
To accomplish this feat of genius, a chip called a comparator is used see Figure It compares two signals and flips a switch one way or another. So, transistors provide power to each side of the robot as the comparator directs. The Muscle The motors are fixed in a forward position without the ability to swivel for steering.
Tiny steering columns are tricky to make at home and difficult to obtain in the sizes desired for a robot. However, the robot can control its direction by varying the amount of power applied to each motor. Power to both motors drives the robot forward. Power only to the left motor causes the robot to turn right, pivoting around the right wheel. Power only to the right motor causes the robot to turn left, pivoting around the left wheel.
Sandwich has two wheels. If the robot had four wheels, it would be very difficult for it to pivot. Mainly the robot would go straight. On the occasions that it did turn, it would make a horrible vibrating noise as one pair of wheels was dragged horizontally rather than in the forward direction they want to roll. There are other wheel arrangements possible, such as a single caster or ball roller on the front or rear, making a three-wheel robot.
There are even omni-directional wheels available, containing multiple sets of perpendicular rollers. Although not a critical factor for small, lightweight robots, wheel formation becomes more significant with heavier or faster robots. Mounting the two wheels toward the rear causes the front lip of the robot to drag on the ground.
Generally the plastic slides quite well in any direction. This makes for reasonably smooth forward movement and agile turning. Sometimes the front of Sandwich skips and hops due to uneven or gritty terrain.
With fresh batteries and tall wheels, Sandwich occasionally stands up on its rear and pops a wheelie! The prices are reasonable and no one produces higher-quality parts. Most wheels consist of a tire the outer rubbery part and a rim with hub the inner hard part. It turns out that you can make such as part, called a coupler see right side of Figure With a coupler, you can quickly slide different wheels on and off the robot, without needing tools.
This is great for experimenting. It can also save you from a disaster if you suddenly discover the wheels you originally planned to use are too short or too wide.
The earlier model see Figure is good, but is more difficult to build. It has an aluminum base and bracket that have to be cut to size.
Also, the sensors are exposed in front and bend every time the robot smacks into something. The electronics, wires, and gears are also exposed, which makes picking up the robot a delicate endeavor. Wavy, the predecessor of Sandwich Using a consumer storage container solves all of those problems.
Plastic containers are lightweight, inexpensive, easy to drill, and available at local grocery stores. Most disposable food storage containers are made from polypropylene thermoplastic. Polypropylene is highly resistant to chemicals and moisture. It can resist boiling heat, although it will become brittle in freezing temperatures. Ziploc brand square 2. Many hobbyists overuse these fastening methods, resulting in a sloppy or fragile robot. Physical Connections Whenever possible, use ordinary screws to connect parts to the body see Figure You can buy fasteners of all shapes and sizes at your local hardware store, or online at MSCDirect.
Common round slotted machine screw To whatever extent you can, use the same type and the same size screws throughout your robot.
This makes for a strong connection, though nearly permanent. For electrical connections coming into the board, such as the power switch or motors, use a removable connector see Figure Not only is servicing a breeze, but you can pull parts for testing or even interchanging them with other robots. Wires connect to a circuit board with Molex KK connectors Obtaining a Kit Suppliers of individual parts are listed throughout this book, in the relevant chapters.
However, you can save money and get a head start on the Sandwich robot by purchasing a kit see Figure This ensures that you have the correct components and reduces the time it would have taken to track down pieces from various vendors. Of course, you still have the option of modifying the kit as desired, by substituting your own parts or decorations. In any case, you will need to supply a piece of plastic or container to hold the robot together.
Building Up You should now understand the line-following course requirements and the basic functional anatomy of Sandwich. The coming chapters break down each element, telling you what to buy, how to test, and how to prototype the line-following circuit.
Although Sandwich forms the framework for each topic, the subject matter and techniques taught are applicable to all robots. In fact, most of my robots use 9 V batteries because the batteries are so small and lightweight.
Alkaline 9 V battery How many volts in a nine-volt battery? A pump with more pressure can spray water harder than a pump with less pressure. Likewise, a battery with more voltage can spray electricity harder than a battery with less voltage. The unit for voltage is volts or simply the letter V. So, 9 volts and 9 V mean the same thing.
Robot builders measure battery voltage quite often. Setting Up a Multimeter for Voltage Testing 1. Connect the black-colored test lead to the multimeter terminal hole marked COM see Figure Connect the red-colored test lead to the multimeter terminal marked V. Common and voltage test lead terminals on multimeter If your meter is manually ranged has several ranges in the V section of the dial , choose a number above 9 see Figure Since you expect to see a little more or less than 9 volts on a 9 V battery, pick a range a little more than 9.
Do not touch the metal tips of the probes to anything at this point. The meter should now be displaying zero see Figure The number on the display may bounce around a little, but it should be near zero. Meter displays no voltage 5. Probe tips touching battery terminals Interpreting Test Results If the multimeter display shows a negative number see Figure , then something has gotten reversed.
Check that the test leads are connected to their proper terminals on the battery and on the meter. Switch the probes if necessary.
Make sure the leads are fully inserted into the meter terminals. Make sure the metal tips are touching the metal portion of the battery terminals. Depending on the type of battery and the capacity remaining, a valid voltage of a 9 V battery should be between 5 and 10 volts.
A positive number indicates a proper measurement When you remove either probe from either battery snap terminal, the meter will display zero again. Somehow the name for the size got mixed up with the voltage. The Fresh column in Table is approximately the voltage you may find when you test a brandnew or newly recharged battery not connected to a circuit.
Voltage always reads a bit lower when testing a battery attached to other electronic parts. A fresh battery settles down to the officially rated voltage with age or after a short amount of use. In all cases except rechargeables, the manufacturers state the batteries are designed to provide approximately 9 V. The Halfway column was generated by taking the total number of hours the battery lasted until the discharged voltage was reached, and then looking at the voltage at half that time.
This gives a sense of the voltage when half of the battery capacity has been used up. In the Discharged column, the manufacturer arbitrarily picks this voltage number. Realistically, many consumer devices stop performing adequately when their 9 V battery falls below 7 V.
Referring again to Table , the Mass column reflects the differences in battery masses due to differences in chemical makeup and case materials. For example, a plastic case weighs less than a steel or aluminum case. These differences also suggest a potential opportunity to shave a little weight from a robot by the choice of battery. The Capacity column is stated in mAh. Basically, the capacity value indicates how much electricity can be circulated for an hour.
If the device uses less electrical current, the battery will last longer than an hour. If the device uses more electrical current, the battery will last less than an hour. Rechargeable batteries are called secondary batteries. Unfortunately, rechargeable batteries have a lower run time total capacity compared to nonrechargeable batteries.
Also, every day they lose some percentage of their electricity, even when not in use. However, because you can recharge them, simply top them off immediately before a robotic demonstration.
Nickel-metal hydride rechargeable 9 V batteries. Left: low-end 8. Right: high-end 9. For most uses, you want to purchase 8. You may want to have a 9. But, be aware that the A higher-capacity mAh battery outlasts a lower-capacity battery of similar chemistry.
It also retains a higher voltage for a longer period of time during usage. The batteries are advantageous to the robot builder, as you can have a stock of nearly charged batteries without constantly keeping them in the charger.
Lithium-Polymer Li-poly lithium-polymer rechargeable batteries see Figure are similar to li-ion lithium-ion batteries used in laptops. You can recharge them hundreds of times, they retain their charge better than NiMH, are lightweight, can provide high current, and have capacities that nearly match alkaline batteries.
As such, I switched from NiMH to lithium-polymer during robot competitions. The disadvantages of lithium-polymer batteries are that they are more expensive and that you must use a charger specifically designed for lithium-polymer batteries.
Lithium-polymer rechareable 9 V batteries Alkaline Alkaline batteries see Figure are the most common and are readily available. These batteries retain their charge for years when not in use , have a high starting voltage, and tend to keep a reasonable voltage during use. For medium or high-current electrical draw, alkalines are the longestlasting non-rechargeable consumer batteries.
This practice can get very expensive. So, these batteries might be good for a high-altitude balloon robot or a multi-year test project. These minuses make lithium unsuitable for most motor-driven robots. The rechargeable varieties offer higher current bursts without the same caveats. The greatest benefit I could come up with is they are the least expensive to buy for a single use.
This might make a good choice for a robot that dives off cliffs or unsuccessfully explores lava pits. Despite their low initial cost, the total lifetime price of carbon-zinc, magnesium-carbon, and zincchloride batteries see Figure is much higher than rechargeable batteries. This is because the rechargeable batteries can be recharged, but the carbon and zinc batteries cannot. Classic and super heavy-duty 9 V batteries Heavy-duty battery capacity is seriously eroded at higher discharge rates, so the respectable mAh rating is hideously reduced in power-hungry robots.
Older-technology carbon and zinc batteries have a short shelf life they self-discharge faster. Carbon and zinc battery voltage slopes down steadily during use, which decreases the useful battery life if the device requires a higher voltage. Ironically, the sloping voltage turns out to be useful for predicting remaining capacity.
The major brands no longer make NiCd batteries. These enhancements are basically marketing gimmicks. The companies charge a notably higher price for an unnoticeable change in performance. Nickel-cadmium rechargeable 9 V battery Figure Instead of brand name, pay attention to battery chemistry alkaline, NiMH, and so on , price, and freshness date.
Watch out for batteries with a voltage rated at less than 8. For example, some NiMH rechargeable 9 V-size batteries are only 7. The cause? Instead of seven internal cells, those batteries contain only six cells and some filler see Figure Although a lower voltage is detrimental to many applications, it does provide a lower-weight and a lower-power battery in a standard form factor case style. The motors were too fast for sharp turns. So, I switched from a fresh 9.
The lower voltage produced lower motor speed. The slower speed had a dramatically positive effect on the line following. Alternatively, another robot was a little too slow and a little too weak in a robot Sumo contest. The motors were nominally rated for 12 volts, so it was safe to upgrade to a fresh By using a standard-size battery in your robot, regardless of whether it is 9 V, AA, AAA, C, D, or whatever, you can switch between battery chemistries to adjust performance.
It is a lot easier and faster to switch batteries than to rebuild your robot or alter the software five minutes before a competition. Mounting Batteries Batteries tend to be one of the heavier parts in a robot. For this reason, the battery in Sandwich is mounted near the wheel axle see Figure That way, most of the battery weight is on the tires adding traction rather than on the front part which drags.
I made a mistake in my mini-Sumo robot, Bugdozer. The batteries are stored underneath the wires and circuitry see Figure , requiring most of the robot to be disassembled to swap in a fresh power source.
Spot the copper tops! There are two batteries hiding inside this robot. Your job: find them. There are a number of ways to physically connect a 9 V battery to a device. Most consumer products have specifically designed compartments formed into their cases. Unless you have access to some wonderful tooling or injection-molding machinery, custom compartments are not viable options for your robots. At the opposite end of the spectrum, masking tape is ugly and unreliable.
Rubber bands are okay for securing batteries, though not ideal. The only problem with hook and loop fasteners is that one fastener strip needs to be permanently adhered to the battery. A new fastener strip needs to be attached to each replacement battery thereafter. Preformed metal clips are available Jameco or Mouser or They have a screw hole in the middle see Figure that makes it easy to secure against a frame.
The damage is purely superficial, and a little masking tape around the ends of the clip eliminates the problem. Molded plastic parts can cradle a battery and provide an electrical connection. With a little bit of thought given to battery location, you can find it a spot in your robot. Looking ahead, the 9 V battery will supply power to each of the upcoming experiments.
But what do you do if you want to make a quick connection for a simple experiment? This chapter covers a simple method for making a few temporary connections.
It also describes a multimeter test that you can perform to check if an electrical connection has been made. When you let go of the clip, the mouth closes and can hold onto things. Alligator clip with insulated shroud Alligator clips are friendly.
They have a lighthearted name and you can pinch their mouths open and shut like they are eating or saying hello. A pair of clips attached by a wire is called a jumper lead or clip test jumper see Figure The wire itself is usually flexible copper surrounded by an insulating colored plastic casing. A jumper lead is alligator clips with a connecting wire. Obtaining Hook Clips Clips are available in many sizes and colors see Figure Close-up of hook Sometimes the end of a hook bends flat during use.
Bend it back. When the hook retracts, it should fit into the hole in the end notch. Purchase at least five medium alligator and five mini IC hook jumper leads see Table They are available in a variety of colors. Try to obtain red, black, and at least one other color. As always, connect the black test lead to the COM terminal of the multimeter. Most likely the test leads will be in the same places they were when you were testing the voltage of the 9 V battery. If your multimeter has a continuity feature, turn the dial to that see Figure A continuity test checks to see if a continuous unbroken connection exists between the two probe tips.
This measures resistance. A short wire like the jumper lead should have almost no resistance to electricity flowing through it. Do not touch the metal tips of the probes to anything at this point see Figure Multimeter probe tips not touching A meter with a continuity feature should now display open and should not be beeping. Check your meter manual.
Touch the probe tips together see Figure Touching the probe tips together to make an electrical connection A meter with continuity should now display short see Figure and should beep annoyingly. The electricity from the meter goes out of one probe and then directly into the other! Testing an Alligator Connection Shorted 6. Instead of touching the multimeter probe tips together directly, connect them with an alligator jumper lead see Figure Using a single jumper, attach one alligator clip to the tip of the black probe and the other alligator clip to the tip of the red probe.
Making a connection with alligator jumper leads You should get the same value displayed on your meter whether you touch the probe tips together directly or whether you connect them with a jumper.
The alligator clips and wire are just as good at allowing electricity to flow through them as touching the probes together directly. During use, alligator clips may become loose or grimy and fail to make a solid connection. The wire between the clips may rip and detach. In those cases, if the jumper lead no longer conducts a continuous connection, you can test for it on your multimeter. Think of the wire in the alligator jumper lead as electrical pipe. Electricity flows through the copper wire or any metal like water flowing through a pipe.
Discovering Unintended Connections The continuity mode and also the ohm mode of a multimeter has a very beneficial use in robotics. It can detect if an unintentional electrical connection exists between various robot body parts and circuits. Although you won't perform these steps now, here are some example steps you might take to test a robot.
Remove all of the batteries, if possible. Connect the black test probe of the multimeter to one piece of the robot. If you prefer, you can use an alligator clip to connect the probe tip to the piece being tested. Doing so is a lot easier than holding the black test probe in place. Also, a hook clip may be able to reach spots that would be awkward for a test probe.
Touch the red test probe tip to each metal part throughout the robot, as thoroughly as desired. One of my line-following robots, Sweet, uses a metal candy container for a body. When I proudly powered on the robot, the circuits went crazy. Exposed metal on drill holes causes unintended electrical connections I should have probed the robot a bit with the continuity mode of my multimeter before powering up.
Plumbing with Jumpers In the last chapter, you learned that a 9 V battery works like an electricity pump. In this chapter, you learned that alligator clip jumper wire or any other piece of metal acts as electrical pipe. All you need now is something worth hooking up to the pipe. These resistors are so vital that Sandwich could not operate without them. But the pipe leading to your showerhead is a lot smaller. Obviously, the smaller pipe saves some space, but it also acts to decrease the amount of water delivered to that location.
You would not be pleased to begin your day with a shower blasting you with the full force of your water main! Besides the displeasure of getting overwhelmed by a watery blast, a lot of water would get wasted. Resistors limit or divide up the flow of electricity. In doing so, they prevent waste and deliver the specifically requested amount of electricity to each part.
The Jameco includes a cabinet, which is nice. Those are too small to experiment with see Figure Many of the high-precision resistors have more than four color bands, which makes it more difficult for a beginner to decipher the value. Cut It Out Components often arrive connected together by tape bands see Figure This is because most components are manufactured in long reels so that they can be fed into robotic part-placement machines. A reseller purchases a full reel and then cuts off lengths according to your order.
The residue can prevent a clean metal-to-metal connection when prototyping.
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