Solenoids are electromagnetic coils wrapped around a tube with a metal plunger inside. When the electricity is turned on, the magnetized coil attracts the plunger and pulls it in. If you attach a permanent magnet to the plunger, then the electromagnet can also repel the plunger when it is turned on and push it out.
Solenoids are used in many mechanisms such as car door locks. In robots, they can be used instead of a motor to push or pull an effector in a straight line. They can also be used to hit objects, like the keys in a robotic xylophone. This model shows how a solenoid uses electricity to move a plunger back and forth.
This project is adapted from my book Robotics: Discover the Science and Technology of the Future, published by Nomad Press.
Step 1: Materials
To make your demo solenoid, you will need:
- plastic drinking straw
- electrical tape
- 6 feet (2 meters) very thin insulated wire -- size 32 magnet wire works best
- 1.5 volt battery (AAA works fine)
- flat head nail thin enough to fit in straw
- super-strong (rare earth) disc magnet
If you don't have, or don't want to use, a magnet, you can make a solenoid using a pin instead of a nail.
Step 2: Wrap the Wire for the Electromagnet
Cut a straw about 4 inches (10 centimeters) long. Cut a piece of tape about 3 inches (7.5 centimeters) long. Fold one end over a couple times, sticky side out. Attach the sticky folded part to the straw, about 1/2 inch (1 centimeter) from one end so it hangs off like a flag. Then wrap the rest of the tape around the straw, sticky side out.
Take the wire and let out about 6 inches (15 centimeters). From that point, take the wire and start wrapping it around the straw over the tape. Start at one edge of the tape and go to the other edge, making a neat line of tight coils. Then, still coiling the wire in the same direction, make a second row on top of the first, going from the edge where you stopped back to the first edge.
Keep making layers of wire until you only have 6 inches (15 centimeters) left. You should have
at least 100 coils.
Step 3: Add the Battery
Take the battery and tape it across the other end of the straw to form a "T." If you are using magnet wire, take the sandpaper and rub off about 1/2 inch (1 centimeter) of the shiny coating from either end. If using regular wire, remove about 1/2 inch (1 centimeter) of insulation. Tape one end of the wire to one end of the battery.
Step 4: Test Your Solenoid
Hold the straw upright about 1 inch (2 centimeters) from your work surface. Take the super-strong disc magnet and let it attach itself directly to the flat head of the nail.
Briefly touch the loose wire end to the other terminal of the battery. The nail should be pulled up into the straw. When you disconnect the battery, it should drop down again.
If your solenoid doesn't work, try flipping the magnet over the other way so the positive and negative ends are reversed.