Introduction: (Initial Observation)
Electric motors are among the most widely used machines that convert electrical energy to mechanical energy. Electric motor is the main element of many household equipment such as mixers, hair dryers, electric fans, vacuum cleaners, drills, and many more. Dissecting an electric motor can give us some clue and understanding of how these machines work.
Visit your local library and get a book about electric motors. Also read the following information and follow the links for on-line information.
To start Click Here to see the principles of electric motor. Try to perform the experiments suggested in this section. If you like to make an electric motor as a part of this project, Click here to see how you can make an electric motor. Or you can Click here to see another method for making a very simple electric motor.
In this project we will only study the electric motors that use direct current electricity also known as DC. Direct current electricity is like electricity that we get from a battery. Electricity that comes to the homes is Alternative Current electricity also known as AC. The reason that they call it alternative is that it constantly changes. You can think of that like an electricity that comes and goes about 50 times per second. So the fluorescent light that you have at home is actually turning off and on about 50 times per second. Our eyes can not easily detect such a fast blinking, but it is really blinking 50 times per second.
Many household equipment that we plug them to the electricity, may actually have DC motors. In this case an internal or external power adapter usually converts the AC electricity to DC electricity.
Motor Can: The motor can is the body of an electric motor and holds all other components. The motor can is manufactured out of steel and holds the armature, the magnets and brushes.
Magnets: The magnets are glued to the motor can and are what produces the magnetic field that causes the motor to work.
Endbell Mounting Key: DC motors are fixed with 24 degrees of timing. A key on the endbell fits into the slot on the motor can to insure this timing is maintained and that you can only fit the endbell on one way. Endbell is the bottom part of an electric motor that holds brushes.
Bushing: The bushing holds the end of the motor and is what the spinning armature uses as a bearings. Some motors use a ball bearing instead of bushing. You should put one drop of oil on each bushing every few runs to make sure it is properly lubricated.
The armature is what spins in the motor. Some may shorten the name of this piece to just “arm”.
Electricity flows through the brushes into the commutator, the slotted commutor then passes this electricity into the windings. Since the windings are wrapped into a coil, they create a magnetic field when current is passed through them. This magnetic field is repelled and attracted to the magnets in the can causing the armature to turn.
Armature Stack: The armature stack is constructed of laminated steel. It holds the windings of the motor and helps increase the magnetic force created by the windings when current is passed through them.
Commutator: Many times this is called the “comm”. The comm takes current from your brushes which ride on this part of the armature and sends it to the windings. The comm is not one solid piece, but is actually made up of 2 separate pieces and this allows the current to be switched to the different windings on the armature as it spins. Because it rubs against the brushes as the armature spins, the comm needs to be cleaned after a while. You can purchase comm cleaning sticks from your local hobby shop.
Balancing Holes: Armatures are balanced when they are manufactured so they run smoother. This is needed since it is almost impossible to get exactly the same amount of wire on each armature pole. Without balancing, your motor would not run as fast, may vibrate and would wear out quicker.
Windings: Each pole of the armature was wire wound around it. This lacquer coated (for insulation) wire is what the battery current passes though and creates a magnetic field so the motor will run. Small motors have about 27 wraps (or turns) of 22 gage wire. You may hear some refer to this as “winds or turns”. Less winds generally means a faster motor and the smaller number of the gage means bigger diameter wire. You may see small motors with as few as 8 “winds or turns” and as many as 35 or more.
Here is an “exploded” view of a DC motor. You can use this as a guide in case you need to find out how to reassemble your motor once you have taken it apart to clean or rebuild.
End Bell: This is the end of the motor that holds brushers and takes care of the electrical connections to your motor. The wires from your speed controller connect to it and through the brushes passes the electricity from your battery to your motor. End Bell is made of a non-conducting material, on it is mounted the brush hoods, an armature bushing and capacitors. In a motor that can be rebuilt, two screws hold the end bell to the motor can.
Brushes: The brushes are what actually pass the battery power to your motor and makes it go. They are generally made out of a graphite compound and can have mixtures of silver added for better conductivity. With use, brushes do wear out and will be one of the items that need to be periodically replaced.C
The purpose of this project is to know, display and introduce the parts of an electric motor.
You do not identify variables for display projects like this.
No hypothesis is required for display project.
Experiment Design (Activity, Procedure):
Use the links in the information gathering of this project and build a small electric motor. Following is also another design for a basic electric motor that you can make at home.
This is a classic design from the 1938 book “Things a Boy Can Do with Electricity” by Alfred Morgan. You can make this simple model electric motor with the following materials:
- Block of wood, 6 x 4 x 3/4 inches (app. 152 x 101 x 19 mm)
- Three 20-penny nails
- Glass tubing (short piece)
- Magnet wire, No. 20 to No. 24
“Using a hacksaw, cut the heads off two twenty penny nails 2 3/4 inches (70mm) from the point. Drill two small holes in the base on centers 4 3/8 inches (111mm) apart. Drive the cut nails into these holes until they stand 2 1/4 inches (57mm) high above the base. These nails form the cores of the field magnets. The field magnets supply the magnetic field in which the armature revolves.
The motor armature is 20-penny nail pushed into a hole in a large cork. The cork is provided with a bearing made of glass tubing which has been closed at one end by holding in a flame. The piece of tubing should be about 1 3/4 inches (44 mm) long and 1/4 inch (6mm) in diameter.
A nail, driven through from the underside of the base exactly halfway between the two field cores is the pivot upon which the armature turns. Adjust the glass tubing in the cork until the ends of the armature (nail) are level with the upper ends of the field core (nails).
You can modify this design based on the material that you can find.
Each field core is wound with four layers of No. 20 to No. 24 magnet wire. Both coils are wound in the same direction.
The armature is also wound with four layers of wire (of the same size as that used for the field). The armature winding is divided into two sections, one on each side of the cork. Both sections are wound in the same direction. The nail should be wrapped with two or three layers of thin paper before the wire is wound in place.
The terminals of the armature winding are scraped bare of insulation and fastened to the glass tube so as to form what is known as the commutator. It is by means of the commutator that electrical connection is established with the revolving armature coils. The wires are fastened to the tubing with thread or narrow strips of adhesive tape.
The outside terminals of the field windings should each be connected to a binding post. The inside terminals are scraped bare of insulation and used as brushes. The brushes are fastened in position by wrapping each one around a small nail or brad driven into the wooden base.”
Connect several dry cells to the binding posts. Make certain everything is wound and connected correctly, and that the brushes are in the right position. Give the armature a twirl with your fingers, and the motor should turn.
Materials and Equipment:
Can be extracted from the experiment or links that you use for your working model.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Not needed for this project.
Summery of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.