Electromagnetic Launcher Instructor Materials

INSTRUCTOR

OVERVIEW OF THIS PROJECT AND WHAT TO EXPECT

This project involves the design, fabrication, and testing of an electromagnet that will accurately launch a ferrous metal projectile. The launchers are constructed from a list of simple materials by student teams of two or three. The project helps students understand magnetism, electromagnets, and projectiles.

SPECIFIC PURPOSE OF THIS PROJECT

This project gives students the opportunity to learn about solenoids and switches and creative ways to use them. By doing the project, students will acquire knowledge necessary to help them understand more complex applications of electromagnetism. They will also gain an understanding of the process of design in which compromises are made so as to maximize performance while satisfying practical constraints.

THE REAL-WORLD PROBLEM RELATED TO THE PROJECT

Solenoids are used in practice for tripping safety mechanisms, operating regulating devices, opening and closing valves, and many other applications. Many times, designers use a solenoid (a coil of wire that looks like a spring, has electric current passing through it, and has an iron cylinder that moves inside the coils) when they need a compact, efficient, and reliable way to move something a small distance. In this project, the students will use the principles involved in the solenoid with some creative switching to move something a large distance. The switch is the most difficult to design component of the launcher even though its function is simply to open and close a circuit. You will soon discover that students who design a good switch will be more consistent and not have to rely on quick taps of the wire to the battery terminal to test their launcher.

SPACE AND TIME REQUIRED

Each team should have about nine square feet of area to work on. The minimum time required for this project is about five hours. Five one-hour segments or some other combination of two, three, or one-hour blocks will also work.

MATERIALS AND EQUIPMENT REQUIRED

In this project, the students are limited to a small set of materials. They are

• One non-Aluminum Soup Can

• Fifty Feet of Insulated Copper Wire (30gauge)

• One 12in piece of Scotch Tape

• One cardboard Cereal Box

• Two 9 volt Batteries

• One Large Nail

• One Small Nail

• Two Plastic Coffee Stirring Straws

• One Strip of Tacky Stick

• Three Paper Clips

Scissors, wire cutters, sheet metal sheers, and possibly a metal cutting saw make it possible for the students to utilize all the listed materials. Choose nails that can be easily cut with the wire cutters or provide a small hacksaw. For testing, a yard stick or carpenter's tape measure and large flat surface are necessary.

SUGGESTIONS REGARDING STUDENT TEAMS

This project works best with teams of two or three students.

PREPARING FOR THIS PROJECT- WHAT TO DO IN ADVANCE

The first thing to do is understand solenoids. Read the student materials for this project and anticipate questions from students. Perform the demonstrations pictured in figure 2 and figure 3 of the student materials. Obtain some solid magnets for students to play with. Most importantly, build a launcher.

Most of the materials for this project can be obtained by the students during the week or two before the project. Copper, telephone or magnet wire can be obtained in most hardware stores. Fifty feet of telephone wire with four single-stranded wires (200ft total) costs approximately four dollars. If the wire is obtained this way, the four strands should be separated and wrapped on individual spools before the project starts. Fun-Tack helps make winding the wire around the electromagnet easier. Hot glue can be substituted if sufficiently available. Each design team should start with a complete set of materials as listed above.

IMPORTANT STEPS IN MANAGING THIS PROJECT

1. Divide the class into teams of two or three students.

2. Distribute the Student Project Description.

3. Present the project to the students (20-30 minutes).

4. Let the students read the materials, discuss it among themselves, ask questions, and generate design ideas (20-30 Minutes).

5. Give the students the working materials.

6. Let the students work on a prototype and experiment (60 Minutes).

7. Test the working prototypes. Slower teams or teams that cannot get anything to launch will benefit from the preliminary testing and the excitement that it generates. Discuss the possible reasons for successes or failures during testing (30-60 Minutes).

8. Let the students improve their prototypes or redesign and reconstruct (60 Minutes).

9. Test the final designs (30 Minutes).

10. Summarize the results of the project and tie the concepts together in a

11. positive closure (30 Minutes).

TESTING THE DESIGNS

The Launchers may be tested individually or in groups of four or five. Each individual or group testing requires a flat area about three feet wide and ten feet long. At one end mark a line behind which all launchers must remain. Allow the students to demonstrate their launchers five times.

The Basic Performance Index is satisfied by launching the projectile any distance. The Extra Performance Index involves launching the projectile several feet. Calculate the EPI with the following formula.

IMPORTANT PRINCIPLES INVOLVED

Figure 1. Magnetic field around conducting wire. Field is strongest very close to the wire.

Electromagnetic things operate by making magnetic fields with wire that is conducting electricity. Magnetic fields are invisible, but can be felt if two solid magnets are held close together but not allowed to touch. You will feel either attraction or repulsion. This works well in a demonstration. The magnetic field that is induced around a single, current carrying wire is shown in Figure 1. When a single strand of wire is connected to a battery, a current flows through the wire, and at the same time a magnetic field is produced right around it. Figure 2 shows what would happen if that single strand of conducting wire was placed close to a magnet. This also can be incorporated into your demonstrations. A nail with wire wrapped around it can be magnetized, or made into an electromagnet by connecting the wire to a battery. The wire of an electromagnet is often wrapped around many times to intensify the magnetic field. The more wire that is wrapped around the nail, the stronger the electromagnet will be. So, the electromagnet is actually a circuit with a voltage source and a coil of conducting wire.

Figure 2. When a piece of copper wire is placed close to a magnet, there appears to be no magnetic interaction (A). But when a current is allowed to flow in the wire, the magnetic field induced around the wire interacts with the magnetic field of the magnet and causes it to be pushed away from (B) or attracted toward (C) the magnet.

A simple solenoid, and the magnetic field produced when an electrical current flows through the conductor coils is shown in figure 2. If an iron containing material was placed inside the coil of figure 2, a magnetic field would be induced in it and it would act just like a common magnet with north and south poles. You could use a nail with a current carrying wire wrapped around it just as you would use any solid magnet.

Because the current carrying coils will set up a magnetic field in any iron containing material that is placed inside or near them, you can use the opposite poles that are produced to move the material (Fig. 3).

Figure 3. Cut away view of a typical solenoid with a voltage source and switch (A). When an iron containing material is placed near one end, a magnetic field is set up in it. The interactions of N and S poles of the material and with those of the nearby coils cause an acceleration of the material (B). As the material moves toward the center, the effect of the opposite poles equalizes (C). If the circuit is opened quickly, the momentum of the material will carry it out the other end (D).

PROVIDING SUCCESSFUL CLOSURE

In particular we encourage you in this project to emphasize that effective design is the application of suitable principles to achieve specified goals. Reviewing the principles listed above should prove helpful to the students. Finally, please make a special point of reminding the students that this kind of creative activity is at the heart of engineering and that, if they found the project enjoyable, they should consider engineering as a profession.

SAFETY CONSIDERATIONS

If your students were to take a small piece of wire, say 3in long, and hold it to both ends of a nine volt battery, the wire would heat up quickly. If the wire is very thin, like the wire they will be using during the project, it may heat up enough to cause a burn. Encourage them to be very cautious with the circuits they design and test them to assure that there is enough wire windings in the circuit so that it will not heat up enough to burn someone or cause a malfunction with the device. Also, be sure that when you test the final launcher or launching prototypes there is no one in the direction of the projectiles path. A good practice would be to make sure everyone is behind a vertical plane that is perpendicular to the nail's path during launching. Finally, if students decide to cut out pieces from the soup can, make sure they are very careful with the sharp edges.

This project was developed by Eddie Richert.