Chapter 4
Safety First (and Always)

Robotics is a safe and sane hobby, but only if you practice it with caution and respect. It can involve working with soldering tools that can burn, saws that can remove bits of flesh, and household current that can electrocute.

Any dangers involved in robot building are easily minimized by taking a few simple steps to practice safe working habits. Take your time and think things through; you may never have to burn yourself with a soldering iron, cut yourself with a knife or saw, or shock yourself with an exposed electrical wire.

Project Safety

If you plan on constructing the bodies and frames of your robots, you’ll need to work with saws, drills, and other building tools. Use all tools according to the manufacturer’s instructions. Use tools only in well-lighted and well-ventilated areas. Wear proper clothing and shoes.

Power saws are especially dangerous, even those with safety guards and mechanisms. Never defeat them! Don’t allow children in the work area. More:

Wear eye protection at all times, especially when cutting and drilling material. The glasses or goggles should wrap around your temples to prevent stray debris from striking your eyes from the side.

Make sure that saw blades and drill bits are sharp. If they’re dull, sharpen or replace them.

Some project plans require the use of sharp knives for cutting—making robot bases out of foamboard, for example. Use a sharp knife, and cut on an appropriate surface. Don’t use your free hand to hold down the board; if the knife slips, you could get badly cut. Hold down the board with a straightedge.

Wear ear protection when using saws or any other power tools.

Battery Safety

Batteries used in robots may produce only a few volts, but they can generate lots of current—so much current that if the terminals of the battery are shorted, the battery could get very hot. If you’re lucky, the battery terminals will only melt. But exploding batteries that cause fires are not unheard of.

Never short out the terminals of a battery just to see what’ll happen. Store charged batteries so that the terminals will never come into contact with metal objects. Always be sure to recharge batteries in a recharger meant for that type of battery.

Soldering Safety

Soldering electronic circuits requires that you use a very hot iron or pencil. Temperatures exceed 600°F, which is enough to give you third-degree burns after only momentary contact with the tool. This temperature is equivalent to an electric stove burner set at medium-high heat, so you can imagine the dangers involved.

If you plan on doing any soldering, keep the following safety tips in mind:

Always place your soldering tool in a stand designed for the job. Never place a hot soldering tool directly on the table or workbench.

Mildly caustic and toxic fumes are produced during soldering. Maintain good ventilation to prevent a buildup of these fumes in your workshop. Avoid inhaling the fumes produced during soldering.

If your soldering tool has an adjustable temperature control, dial the recommended setting for the kind of solder you are using, usually about 650° to 700° for standard 60/40 rosin-core solder.

Always use rosin-core solder designed for use on electronics. Other kinds of solder could damage the circuit or your soldering tool.

Do not attempt to solder on a “live” circuit—a circuit that has voltage applied to it. You run the risk of damaging the circuit, the soldering tool, and, most of all, you!

Fire Safety

Fire is a potential hazard during the construction and use of any electrical device. A hot soldering tool can ignite paper, wood, and cloth. A short circuit from a large high-current battery can literally melt wires. Although not common for the type of projects presented in this book, an electric circuit may develop too much heat, and could melt or burn its enclosure and surroundings. Proper construction techniques and careful review of your work will help prevent these kinds of mishaps.

If your project operates under house current, keep an eye on it for the first several hours of operation. Note any unusual behavior, including arcing, overheating, or circuit burnouts. If a circuit breaker trips while your project is on, you can bet that something is amiss with your wiring.

For obvious reasons, you should always build and operate your projects away from flammable objects, including gasoline, lighter fluid, welding and brazing equipment, and cleaners. Always keep a fire extinguisher near you, and don’t hesitate to use it if a fire breaks out.

Melting plastic can release highly toxic chemicals and gases. After you put out the fire be sure to ventilate the area thoroughly. Melted PVC plastic can release hydrogen chloride gas. Seek medical attention if you’re not feeling well.

Avoiding Damage by Static Discharge

The ancient Egyptians discovered static electricity when they rubbed animal fur against the smooth surface of amber. When the materials were rubbed together they tended to cling to one another. While the Egyptians didn’t comprehend this mysterious unseen force, they knew it existed. Today we fully understand static electricity and know it can cause damage to electronic components.

As a robo-builder, you must take specific precautions against electrostatic discharge, otherwise known as ESD. Damage from static discharge can be all but eliminated by taking just a few simple steps to protect you, your tools, and your projects from static buildup.

THE PROBLEM OF ELECTROSTATIC DISCHARGE

Electrostatic discharge involves very high voltages at extremely low currents. Combing your hair on a dry day can develop tens of thousands of volts of static electricity. But the current (akin to the force of the electricity) is almost negligible. The low current protects you from serious injury.

Many electronic components that are manufactured with semiconductor material are not so forgiving. These include transistors and integrated circuits, especially those that use what’s known as a metal oxide substrate. These include:

MOSFET transistors

CMOS integrated circuits (ICs)

Just about any microcontroller

Any module (digital compass, sensor) that contains one or more of the above

Don’t worry if the names of these electronic devices are alien to you. You’ll know a static-sensitive device when it comes to you in an antistatic plastic pouch or on antistatic foam. You should keep these devices in their pouch or stuck into their foam until you use them.

Figure 4-1 An antistatic wrist strap draws static electricity from your body, helping to prevent damage to sensitive electronic components. Be sure to use the wrist strap according to the manufacturer’s instructions.

Just to be on the safe side, you should treat all semiconductors as delicate. You don’t need to go overboard; things that aren’t (usually) sensitive to ordinary static discharge include resistors, capacitors, diodes, motors, or any mechanical device, such as a switch or relay.

USING AN ANTISTATIC WRIST STRAP

If you live in a dry climate or where static is an ongoing problem, consider using an antistatic wrist strap whenever you work with sensitive electronics. This strap, like the one shown in Figure 4-1, grounds you at all times and prevents static buildup.

To use, put the strap around your wrist, then connect the clip to any grounded or large metallic object. A nearby computer (plugged in) or the frame of a metal desk or bookshelf are good choices. If you have an antistatic desk or floor pad it will likely have a metal stub on it that you can connect the wrist strap to. Even if the pad is itself not grounded, the idea here is that it dissipates the static because of its large surface area.

Though you may read otherwise, it’s not a good idea to go sticking your wrist strap into the ground hole of an electrical wall socket. It’s too easy to accidentally plug yourself into one of the other holes and receive a shock.

STORING STATIC-SENSITIVE DEVICES

Plastic is one of the greatest sources of ESD. Bench-top storage containers are often made of plastic, and it’s a great temptation to dump everything into these containers. Avoid that. Invariably, static electricity will develop and a sensitive part could become damaged.

Unfortunately, there’s no way to tell if a component has become damaged by ESD just by looking at it. You won’t know anything is wrong until you actually try to use the component.

Static-sensitive electronics are best stored using one of the following methods. All work by connecting (grounding) the leads of the component together, thereby diminishing the effect of a strong jolt of static electricity. Note that none of the storage methods is 100 percent foolproof.

Antistatic mat. This mat looks like a black sponge, but it’s really conductive foam. Be sure to save your antistatic foam! You can use it to make pressure sensors, as described in Chapter 42, “Adding the Sense of Touch.”)

Antistatic pouch. Antistatic pouches are made of a special plastic coated on the inside with a metallic layer. Many are resealable so you can use them again and again.

Antistatic tube. Quantities of integrated circuits are most often shipped and stored in convenient plastic tubes. They’re treated with a conductive coating to help reduce static.

PROPER CLOTHING FOR STATIC REDUCTION

Avoid wearing polyester and acetate clothing, as these can develop static. A cotton lab overcoat can be worn to help reduce static electricity. Overcoats are available at many chemical and industrial supply houses. If nothing else, they’ll make you look like an important scientist!

Only thing about the overcoat: Don’t wear it when using power tools to cut or drill things. The long sleeves and dangling smock could get caught on spinning parts of the tool.

USE ONLY GROUNDED SOLDERING TOOLS

A common source of ESD damage when building electronic circuits is using an ungrounded soldering iron or pencil. Ungrounded tools have only two prongs on their power cord, instead of three. The third (round) prong is the ground connection.

A grounded tool not only helps prevent damage from electrostatic discharge, but lessens the chance of a bad shock should you accidentally touch a live wire. Be sure to use only a grounded wall socket; if you use an extension cord, be sure it, too, is grounded.

Working with House Current

None of the projects in this book directly use AC house current, but let’s cover the safety precautions just the same. A live AC wire can, and does, kill. Exercise caution whenever working with AC circuits. You can greatly minimize the hazards of working with AC circuits by following these basic guidelines:

Always keep AC circuits fully covered. Always.

Keep AC circuits physically separate from DC circuits. If necessary, construct a plastic guard within your project to keep the wiring separate.

All AC power supplies should have fuse protection. The fuse should be adequately rated for the circuit but should allow a fail-safe in case of short circuit.

Place your AC projects in a plastic box. Don’t use a metal project box.

Double-and triple-check your work before applying power. If you can, have someone else inspect your handiwork before you switch the circuit on for the first time.

First Aid

Despite your best efforts, accidents might happen. With luck, most will be minor, causing little or no injury. If injury does occur, be sure to treat it promptly. If necessary, see a doctor to prevent the condition from getting worse.

Consult a good book on medical first aid treatment for details on how to care for cuts, abrasions, and other minor injuries. You’ll want to keep a first aid kit handy at all times, preferably right there in your shop, or conveniently located in a washroom or lavatory.

Purchase a first aid kit, and keep it in your workshop. If you use an item from the kit, be sure to replace it. Every year inspect your first aid kit and replace anything that is past its expiration or use-by date.

EYE INJURY FIRST AID

Perhaps most serious of all is injury to eyes. Be sure to wear adequate eye protection at all times—when soldering, when using shop tools, the whole bit. Chips of solder and metal leads can fly off when they are cut with nippers. If these get into your eye, not only is it excruciatingly painful, but it could damage your eye, temporarily or even permanently.

Should you get something in your eye, especially a piece of glass, metal, or plastic, see a physician immediately. Trying to remove the object yourself can cause further injury.

ELECTRIC SHOCK FIRST AID

Should you get a nasty shock from a circuit or battery, check the area of skin contact for signs of burns. Treat it as you would any other burn.

Immediately after an electrical shock, stop what you are doing and consciously calm yourself down. Monitor your pulse to make sure your heart isn’t suffering from any aftereffects of the shock. If you feel anything is amiss, consult a doctor immediately.

Use Common Sense—and Enjoy Your Robot Hobby

Common sense is the best shield against accidents and injury, but common sense can’t be taught or written about in a book. It’s up to you to develop common sense and use it at all times. Never let down your guard. Don’t ruin the fun of a wonderful hobby or vocation because you neglected a few safety measures.