Science and Technology of Everyday Life
Hope College GEMS 151-01, Spring 1999
The Electric Motor
Introduction
In this laboratory we will be building an electric motor. The electric motor is extremely common in our everyday lives. While often hidden from view, the electric motor is an essential component in many familiar devices. Electric motors are found in such diverse objects as: blow-dryers, washing machines, fans, power drills, blenders, mixers, computer disk drives, tape players, VCRs, Camcorders, CD players, computer CD ROM drives, sewing machines, dishwashers, copy machines, laser printers, car starter motors, elevators, escalators, refrigerators, and vacuum cleaners. The electric motor is a device that converts electrical energy into mechanical energy. Electric current is used to create rotary motion.
Building the Motor
The electric motor that we will be building is from a kit. The kit is based on the model number 10-135 Toy Motor Kit made by Science First, 95 Botsford Place, Buffalo, New York 14216.
Throughout the room, there are several finished motors that you can examine to see how your motor should look. If you have any questions, ask for help. In building the motor you will finish sooner if you get help on steps for which you are unsure. Getting help, even if you need to wait a few minutes, will be faster than having to take-apart and redo steps that are not done correctly. Some steps are tricky, difficult, and frustrating: do not hesitate to ask for help.
Even if the figures seem clear, please READ the accompanying text to avoid missing important information.
There are three times during the assembly when you should obtain a check from the instructor or a TA before proceeding. These signatures go on the last page.
The write up is due in lab next week. Note that there are questions to be answered outside of the lab! Answering these questions will require some thought and effort.
There should be a sample motor available on your table. Examine the sample motor. This is what you will be building. You can keep the motor that you build.
Initial setup
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1.)Open the kit.Carefully open the kit and empty the parts into the round plastic tray. Fig 1 shows all of the parts and they are identified in the given table. Refer to Figure 1 throughout the lab to help locate and identify the parts needed for a particular step.
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Part Name |
Figure 1 |
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2.) Tools.Open the tool kit and locate a cardboard sanding surface for your use. To build the motor the following tools should also be in your kit: Scissors, Screwdriver, Knife, Diagonal Wire Cutters, Needle-Nose Pliers, a Ruler and Sandpaper. A drill and soldering iron will also be used.
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3.) Battery wires.Cut about 3 inches of wire off one of the coils. Then cut about 4 inches of wire off the other coil. Set these aside for later use.
Constructing the Field
In this portion, the part of the motor known as the "field" will be constructed. These motor components establish a stationary magnetic field that interacts with the rotating part of the motor. In this motor, the field magnet is an electromagnet. That is, a magnetic field is not created until an electric current flows through the coil of wire.
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1.) Winding the field coil.Locate the field pole (part F), and the mounting bracket (part H). Place the field pole on top of the mounting bracket so that the flat mid portion of the field pole rests on the raised mid portion of the mounting bracket. See figure 3. Using a piece of tape about 2 inches long, tape these together.
Now take one of the coils of wire and wrap it around the middle section of both parts. Leave 2 inches of wire free at both ends. It is important to wind the coil evenly. The turns do not have to be precisely side-by-side but there should not be a big bump of wire in the middle of the space. If the wire is concentrated in the middle, the spinning part of the motor will hit it and stop turning.
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2.) Preparing the ends of the wire.The wire is coated with an orange varnish-like material that ensures that the electric current in the wire flows along the wire (the way we want it to go) and not between the wires. This coating is called the insulation. Later we will want to make electric current flow between the coil and other parts of the motor. Electrical current only flows when contact is made between conducting materials. We must therefore remove some of the orange varnish insulation from the ends of the wire. Sandpaper is used to accomplish this.
Fold the sandpaper with the rough side in. Place one end of the wire in the fold of the sandpaper. Squeeze the sandpaper and gently pull the wire out. This will scrape off some of the coating on the wire. Repeat several times, twisting the wire or repositioning the sandpaper each time until about 1 inch at the end of the wire is bare, shiny copper all around, and there is no trace of the orange coating. Another way to do this is to lay the wire on a cutting surface and sand off the insulation. Do not sand directly on the table. This will scratch the table. Keep rotating and sanding until all the orange coating is sanded off.
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3.) Attaching the field assembly to the base.Locate the two screws and two hex nuts. Hold the mounting bracket (H) on the plastic base and insert the screws through the holes marked 1 on the base and through the bracket. This is shown in figure 4. The head of the screws should be underneath the plastic base and the nut should be on top. Using a screwdriver and needle-nose pliers tighten the nut.
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Figure 3 |
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Figure 4 |
The Armature
The armature is the part of the motor that spins. Like the "field" the armature is a magnet. In all motors, the armature is an electromagnet. It must be an electromagnet because during operation the north and south poles must switch. This is accomplished by reversing the direction of the current flowing through it.
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1.) Armature wire.Locate the second coil of wire. Unwind the coil.
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2.) Armature pieces.Locate the two halves of the armature (A) and the Motor shaft (M). Fit the two halves of the armature together and insert the motor shaft through the center as shown in figure 5. Tape the two halves together as in figure 6.
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Figure 5 |
Figure 6 |
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3.) Wrapping the armature.Using the coil of wire, straighten out 2" and tape it to the shaft as shown in figure 7. This will hold it so it is easier to wrap. Wrap about 6 turns around one of the flat parallel lengths (or wings) of the armature. Then cross over to the other wing and wrap six turns in the same direction. See figure 8 and 9 on the next page. Cross back and forth wrapping six turns on each wing until there is only 2" left of the wire. When wrapping, be sure that it is always in the same direction. As you cross back and forth from one side to the other the wire should form an "X" in the middle space between the armature wings.
Be sure that the two wings are balanced, meaning that the same amount of wire is on each wing.
Avoid wrapping too close to the ends of the wings, otherwise the wire might fall off later.
When finished untape the wire and adjust the motor shaft until it projects about 7/8 inch on one side of the armature.
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Figure 7 |
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Figure 8 |
Figure 9 |
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4.) Preparing the tubing spacers.The black insulating tubing (K) is used to make spacers. Using the knife cut one piece of tubing 5 mm and another piece that is 15 mm. Note that these pieces are measured in millimeters not inches. The extra tubing should be kept for later use.
When cutting the tubing make sure that the ends are cut square. It is very important in the performance of the motor that the pieces be cut square. Figure 10 shows the correct and incorrect way to do this.
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Figure 10 |
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5.) Installing the spacers.Slip the 5 mm piece over the long end of the motor shaft to rest against the armature. (The short end is the end that is projecting 7/8 inch.)
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6.) First check.Before proceeding have the parts you have finished, the armature and the field coil, checked by an instructor or TA and initialed on the last page.
The Commutator
Building the commutator is both the most important and most difficult part of assembling the motor. Do not hesitate to ask for help if you have the slightest problem. Ask for help and clarification before you get frustrated. It might be a good idea to take a short break before continuing.
The commutator is the portion of the motor where electric current enters and exits the electromagnet of the armature. The commutator causes current to flow in one direction through the armature for half of a complete rotation and then reverses the flow direction for the other half of the rotation. The reversal of current changes the poles of the armature: North becomes a South and South becomes a North. This switching keeps the motor spinning.
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1.) Securing the wires.Locate the armature assembly you just finished. The armature wires are to be secured to the motor shaft. Wrap each wire once around the 5 mm piece of tubing that is on the shaft. Make one complete rotation. After the wires have been wrapped around the shaft straighten them out so that they are perpendicular to the armature wings. See figure 11.
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2.)Remove insulation.Using the sandpaper remove the insulation from the wires. Remove all of the insulation to within 1/8 inch of the motor shaft to expose the bare copper. It is very important to thoroughly remove every trace of the insulation but not any closer than 1/8 inch. After the insulation has been removed, make sure the wires are straight and in the position shown in fig 11
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3.)Bending the wires.THIS IS A KEY STEP. The wires will now be bent in a direction parallel to the motor shaft. Using the pliers, grip a wire at the base of the shaft. Bend the wire so that it is parallel to the shaft but still perpendicular to the armature. The wire should be just above the shaft. See figure 12.
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4.)Commutator insulator installation.To install one of the commutator insulators (L) slip the motor shaft through the large middle hole and the two armature wires through the two smaller holes. The smooth side of the insulator should face away from the armature. Slide the insulator along the shaft until it is pressed firmly against the insulating tubing.
After the commutator insulator is installed check the alignment of the wire to the armature wings. When looking at the shaft the wires should remain perpendicular to the wings as shown in figure 13. This is important so if there is any uncertainty ask the instructor or TA for clarification.
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Figure11 |
Figure 12 |
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Figure 13 |
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5.)Installing the 15 mm tubing.Locate the 15 mm piece of tubing. Install the tubing on the motor shaft. It should rest tightly against the commutator insulator.
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6.)Commutator insulator installation.Install the second commutator insulator as was done in step 4.
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7.)Aligning the insulators.Check to make sure that both commutator insulators are still aligned so that the wires are at right angles (perpendicular) to the armature wings. It should look like figure 14.
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Figure 14 |
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8.)Bend the wires to hold the commutator together.Gently tug the two wires and bend outward away from the motor shaft to hold the commutator together. Clip off each wire about ¼ inch from the commutator insulator. See fig 15.
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Figure 15 |
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9.)Finishing touches on the commutator.Using the needle-nose pliers, squeeze the commutator wires so that they are pressed tightly against the tubing on the motor shaft. This will tighten everything and make the motor run much better. Make sure that everything is still aligned correctly, i.e. the wires are still at right angles to the armature wings as in step 7.
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10.)Have armature and commutator checked.Have the instructor or a TA check the armature and commutator assembly. Have them sign the last page.
Installing Armature on Base
The armature will now be installed on the black plastic base. Locate the two shaft supports (J) and the remaining portion of black insulating tubing.
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1.)Cutting the tubing.Carefully cut a 2 mm piece of tubing. This must be cut square. Now cut a piece that is 10 mm long. This one must also be cut square.
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2.)Inserting the tubing.Now slip the 10 mm piece onto the motor shaft. It is to be put on the end opposite of the commutator. Slide it tightly against the armature wings. The 2 mm piece is to be slipped onto the end of the motor shaft that has the commutator. It should rest tightly against the commutator insulator.
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3.)Installing shaft supports.Twist the support shafts to separate them from the plastic connecting piece. Now insert the shaft supports into the holes marked two and three in fig 2. It does not matter which support goes into which hole. The supports should be inserted so that the smooth side of one support faces the smooth side of the other.
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4.)Installing the armature.Now the motor shafts must be inserted into the supports. Take the commutator end of the motor shaft and insert it into the shaft support located in hole number three. Insert the other end of the motor shaft into the slot of the other support.
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5.)Adjustments.The armature should be between the field magnet poles as shown in the figure 16. The armature should spin freely and not scrape on anything. If necessary the field poles can be bent out slightly to give more clearance for the armature. Also, if the assembly is too tight between the shaft supports then the tubing on the non-commutator end of the shaft may be trimmed. (At least 1 mm will probably have to be trimmed off.)
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Figure 16 |
Constructing the Brushes.
The brushes bring current to the commutator. One is always connected to the positive (+) side of the battery and the other is always negative (-). A key aspect of the brush assembly is that the brushes must make contact with the commutator so current can flow into the armature magnet.
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1.)Locate the brushes.Make sure you have two strips of 0.004 inch brass (note: these are NOT pictured in figure 1. The strips are 50 mm long by 8 mm wide. Notice, again, that these dimensions are in mm not inches. Set these aside for now.
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2.)Prepare the base for brushes.Locate two of the T-type paper fasteners (I) and the two pieces of wire cut earlier. Using the sandpaper, scrap off 1inch of the insulation from both ends of each wire. Now using the needle-nose pliers, make a loop in the end of the 3 inch piece of wire large enough that the T-type paper fastener will fit through. Next, take the paper fastener and put it through the wire loop and then into hole 5a from fig 2. This is shown in figure 17. Bend the prongs out on the underside of the base to hold the wire in place. Try to get it as tight as possible. Make sure there is bare copper touching the fastener.
Take one of the 2 inch wires from the field magnet and attach that in hole 5b using the same method as above. Make sure that it is tight and that there is bare copper touching the paper fastener. When finished it should look like figure 18.
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Figure 17 |
Figure 18 |
Installing the battery holder. r
Locate the black plastic battery holder. It has a red and black wire. The red wire should be connected to the wire from the field coil. Make a loop in the end of each wire and attach to the base using a T-type paper fastener. This is shown in figure 22. Use a sample motor as a guide. Ask the instructor of TA for assistance if needed.
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2.)Attaching last copper wire.Attach the remaining free copper wire to the base using a T-type paper fastener. This is shown in figure 22. Use a sample motor as a guide. Ask the instructor of TA for assistance if needed.
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Figure22 |
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Figure 24 |
Installing the brushes. r
Locate the two strips of brass. Take one and slide it through one of the fasteners that are in the base. Now very carefully flex it up so that it rests on the commutator as in figure 23 or figure 24. Do the same with the other side. The brushes need to rest against the shaft but not so tightly as to restrict rotation of the armature. Also, it is very important that the brushes do not touch each other. This will create a short circuit and the motor will not work.
Running your motor.
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1.)Starting the motor.Insert the batteries into the battery holder. The negative side (flat side) goes against the spring. Put the black wire from the battery holder under the T-type fastener (The one without the red wire). This is shown in Figure 25. Give the motor shaft a little twist and the motor should start.
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2.)Perfecting your motor.If your motor does not work or is not running very well see the list of things to check. If it still does not work see the instructor or TA.
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3.)Secure brushes.Once the motor is running, tape the bottom of the each brush to the black plastic base. If not taped, the brushes could slip out of position.
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4.)Get motor checked.After the motor is running show it to the instructor or TA and have them sign the last page.
Figure 25
If Your Motor Does Not Work
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1.)Make sure that the switch is in the on position.r
2.)Check all electrical connections to be sure that the insulation is scraped off completely.r
3.)Make sure that the motor shaft can spin freely. If it can not, then some of the tubing from the non-commutator end must be trimmed off.r
4.)Check to make sure that the field pole does not interfere with the armature movement. If it does, then gently bend it out. Talk to the instructor or TA if you need assistance.r
5.)Make sure that the commutator and armature are aligned correctly. See figure 15.r
6.)Adjust the brushes. Even if the motor runs, it may run better if the brushes are in a different position. Use trial and error to get the best performance.r
7.)Be sure that the battery is good.r
8.)The commutator wires and the brushes may corrode after a long running time. If this happens then remove the armature and clean the wires and brushes with sandpaper.Improving the Performance of the Motor (Optional)
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Figure 26 |
Name:_________________________
Science and Technology of Everyday Life
GEMS 151-01, Spring 1999
Write-up Questions
The Electric Motor
Use this sheet as acover sheet for your answers to the questions below. PLEASE Do Not turn in the other 15 pages of assembly instructions. Please Do Not try to squeeze your answers to the questions into the spaces on this cover sheet.
1.) Instructor or TA signatures:
Armature and Field Coil Checked: ________________________.
Armature and Commutator Checked: ________________________.
Operation of motor verified: ________________________.
Extra Credit Fan: _______________________.
2.) Explain how the motor works. Use drawings or diagrams to aid in your explanation. This question will require some thought and effort.
3.) Explain a fundamental difference in the operating principle of a car engine and an electric motor. If they both produce rotation are they not operating on the same underlying principle?
4.) Choose any 5 of the items using an electric motor listed in the beginning of the laboratory. Describe the function of the motor in each device. For example: What does a motor do in a blowdrier? Answers can be short: a few sentences should be sufficient for each device. (In a blowdrier, a motor to spins the blades of a fan that blows air over the heating coils) You may find some useful information in the textbooks. Other sources of information are available in VanWylen Library such as:
McGraw-Hill, Encyclopedia of Science and Technology, REF Q121 M3 (1992).
How Products are Made, N. Schalger, REF TS 146 .H67 V.1
Simon and Schuster, "The Way Things Work," REF T 47 .W3913. (A book with the same title as our text, but with a more traditional format)
