Before the first circuit, set up the bench. A little care here prevents the few accidents that hobby electronics has: burns from a soldering iron, and batteries that overheat.
Key idea
- Work only with low voltage: batteries and USB power, 3.3 to 12 volts. Never open, modify or wire anything that plugs into a wall outlet.
- Switch off or unplug the power before you move a wire.
- Do not let a battery's two terminals touch through a wire or a tool. A short circuit can make a large current, heat and even fire.
Lithium batteries
Most robots run on lithium-ion or lithium-polymer (LiPo) cells. They hold a lot of energy in a small, light pack, which is why they are popular and why they need care. A LiPo cell is about 3.7 volts in the middle of its range and 4.2 volts when full. A pack marked 3S has three cells in series: about 11.1 volts nominal and 12.6 volts full.
- Charge only with a charger made for lithium cells, set to the pack's cell count.
- Never leave a charging battery unattended. Charge it on a surface that will not burn, away from things that can.
- Never charge or use a pack that is swollen, punctured or damaged. Stop, and dispose of it as the maker directs, at a battery recycling drop-off, not in the trash.
- Do not leave packs in a hot car, and do not run them completely flat.
- For a first robot, AA cells or a USB power bank avoid most of this.
Soldering
Soldering joins wires and parts with a melted metal alloy. The iron's tip runs at about 300 to 400 °C. You can do a great deal of robotics with no soldering at all, using breadboards and plug-in wires; when you are ready, learn it with an experienced adult.
- The iron goes back in its stand every time you let go of it. Treat it as hot until it has been unplugged and cooled.
- Work with fresh air or a fume extractor, so the flux smoke is not breathed in.
- Wear safety glasses; clipped wire ends and solder can fly.
- Use lead-free solder. Do not eat or drink at the bench, and wash your hands with soap and water afterward.
- Keep paper and other things that burn away from the iron.
Moving parts
Motors and gears can pinch fingers and catch hair or loose sleeves. Test a new robot with its wheels off the table, on a block, and keep your hands clear until the power is off.
Worked example: Pack voltage
- Two cells in series add their voltages.
- $2 \times 4.2 = 8.4\ \text{V}$.
Answer: 8.4 V.
Common mistake