Motors

History of the Motor
The basic ideas behind electromagnetic induction were discovered in the 1800's by Oerstead, Gauss, and Faraday. By 1820, it was discovered that an electric current produces a magnetic field. Soon a  simple DC rotary motor was invented. William Sturgeon invented the commutator and his motor was first to provide continuous rotational motion. His motor, built in 1826,  contained all of the elements present in modern DC motors.

Sturgeon's Motor

How Do Motors Work
Motors convert electrical energy into mechanical energy. An electromagnet is the basis of a motor. Motors use the basic principles of magnets: opposites attract and likes repel. A motor uses this principle to create rotational motion. Once the north end of the armature (the nail in the image below) reaches the north end of the field magnet it does a half turn downwards. At this point the magnet field flips causing another half turn motion and so forth.

Essentially, motors work by combining two electric fields so that they are opposite each other, which causes rotational motion. One electric field is created by wrapping two L shaped brackets with 14 gauge solid lamp wire. The second field is created by wrapping copper magnet wire around the armature. This attraction and repelling of the poles causes the armature to spin rapidly. 

Challenges with My Motor

If you have ever attempted to build something you are well aware that problems could arise. Especially when building something for the first time. When I built my motor I had three problems: creating successful brushes, attaching the copper contacts, and wrapping the copper magnet wire on the armature.

Copper Contacts
When I was building my motor, I chose to use a cork as the base on which to attach the copper contacts. I first tried taping them down with clear tape - it didn't stick. Then I attempted taping the copper down using heavy duty electrical tape - the copper stuck but this caused the gap between the two pieces of copper to become too big. I eventually tried hot gluing but the hot glue would not stick. Finally I decided to staple the pieces of copper to the cork.

Brushes

Brushes  

The brushes were by far the hardest component of the motor to get right. I ended up using the thin black lamp wire on the left of the photo for both of the brushes. When the brushes were made of the copper wire on the right they would always catch and stop the motor. By putting the thin black wire through the top they gently touched the motor and allowed it to spin.








Wrapping Copper Magnet Wire
For your motor to work the magnet wire must be wrapped nearly perfectly on the armature. It took three tries to wrap the armature perfectly. I ended up putting a thin layer of clear tape in between the first and second layer of wire to prevent cross-overs.

Building My Motor

A motor is essentially two magnetic fields - one stationary while the other one flips from north to south, which causes the armature to spin. A motor has a few parts: the field magnet, the armature, the brushes, the copper contacts.

Supplies:

• 24 gauge copper magnet wire 
• 14/16 gauge solid lamp wire 
• 14/16 gauge lamp wire 
• Thin copper (for contacts; foil may also be used) 
•  Base plank 
• Steel L brackets (2 large brackets and two small brackets) 
• 1/8 inch diameter metal rod - one long length and two shorter lengths 
• Scrap wood 
• Screws/Nails to attach scrap wood to base and screw in L brackets 

Steps:
1) Build the field magnet: take two L shaped pieces of steel ( steel conducts electricity well) and begin to wrap SOLID lamp wire around it. Five or six layers of wire should create a strong magnet. Be careful to not overlap the wire as this disrupts the magnetic field. The left side of the L will always be the north pole. Attach this to the base. Leave one end of wire free to attach to the battery later and leave one to attach to a brush.

2) Next you will need to create supports for your armature and the brushes. I choose to mount smaller L brackets onto scrap wood to hold the armature and I built a 'house' out of scrap wood with holes on top to push the brushes through.

4) Next take a thin metal rod, approximately 1/8 inch diameter, and tape two nails on either side so that a T shape is formed. Next begin to wrap magnet wire VERY neatly, working from one end of the metal rod to the nail head. Be sure to leave a little extra wire sticking out from the center of the armature. Then come back from the nail head to the rod and cross over to the other side - making sure to keep wrapping in the same direction. Repeat the process on the other side. In order to keep the wire smooth and prevent it from crossing over and disrupting the magnetic field, I chose to put a clear layer of tape in between the first and second layers of magnet wire. This is the armature.

5) Now it is time to create the copper contacts. Take a cork and drill a hole through the center so the metal rod is snug. Using either two pieces of foil or copper and (copper conducts electricity better and is more heavy duty) staple them to the cork. When attaching the two pieces make sure they do not touch - the gap is necessary in order to flip the magnetic field. On the flip side, do not make the gap too large otherwise there will not be enough surface area for the brushes to touch. If you chose to use copper, rub the outsides with steel wool in order to remove any enamel that could disrupt the motor later. Then proceed to scrape of the colored coating from the magnet wire left over from the armature. Tuck the stripped wire underneath the metal on the cork.

6) It is time to attach the brushes. Using two pieces of multi strand lamp wire, strip the wires and push them through the two holes you created in the top of the 'house'. At this point the copper contact should be under the roof of this house so that the brushes can make contact. Fan out the wire once you have pushed it through the holes - you may need to use tape in order to keep the brushes in the proper position. Remember to attach one of the brushes to the solid lamp wire from the field magnet. The second brush will attach to the battery later.

7) Your motor is complete - you just need to attach the circuit you have created to the battery. Attach one end of wire left from the field magnet to your 6 volt battery and attach one of the ends of the brushes to the other coil on your battery. This should complete the circuit and cause the motor to spin. Alligator clips can also be used if you did not save enough extra wire to reach the battery.

Here is the completed motor: 

In conclusion building a motor should be easy. As long as the wire is wrapped well, and the copper is attached and the brushes make contact, the motor will work. However, problems can arise. I will discuss some of the challenges I faced when building my motor in my next post.

My Bridge

The class was given 5 pieces of information:
1) The bridge must weigh less than 100 grams
2) The bridge must span a space of 16 inches
3) The bridge must be at least 3.5 inches wide
4) If the bridge is able to hold 120lbs, you will receive a 90%
5) The bridge can be made only out of balsa wood and adhesive

Based upon these criteria, I have chosen to build a Warren Truss Bridge. If, after I build this bridge, I have enough supplies to build a second or third bridge, I will. My bridge will be approximately 18 inches longs, 4 inches high, and 3.5 inches wide.

Here is an analysis of how the Warren truss distributes forces:

Each number represents a percent of the load applied to the bridge. My bridge will utilize equilateral triangles to spread the force out evenly across the bridge.

Bridges

We all depend on bridges. They are an easy way to get from point A to point B when there really was no path to cross at all before the bridge. Though there are many different kinds of bridges, including truss bridges, suspension bridges, and arch bridges, they all were made to accomplish the same goal - to spread out the forces (weight) acting upon it in such a manner that the bridge does not collapse or crumble. 

History of Bridges 

      The first bridges were made in Mesopotamia, the birthplace of modern society. These bridges were able to cover only short distances and became weaker with age due to environmental stress. Breakthroughs in bridge design first occurred in Ancient Rome. Roman engineers discovered that volcano rocks, if ground down, would become mortar. Mortar was much stronger than any other bridge 'glue' available at the time. Now bridges could become longer, carry more weight, and were becoming more efficient. The Romans also developed the arch bridge, a bridge that was able to hold a load of of its own weight. During the time of the Roman Empire, over 900  bridges were built. During the Middle Ages another critical development in bridges came about. They began to build bridges with living quarters on the bridge itself. Finally, in 1779 the first iron bridge was built. It was built by Abraham Darby and had a single span over 100 feet. As technology advanced, bridges became more and more efficient. 

Roman Arch Bridge 

Iron Bridge Built in 1779

Beam Bridges 

      A beam bridge, also known as a girder bridge, is one of the more simpler kinds of bridges. It is a flat, horizontal expanse supported by columns on either end, or throughout its length. These columns do all of the work in supporting the downward force applied by the weight of the bridge and the bridge's load. The columns push into the Earth and the Earth pushes back with an equal amount of force in order to keep the bridge from collapsing. Beam bridges utilize concrete or steel to build the vertical columns. The size and height of the column are directly related to the distance the bridge can span. When the height and size of the beam are increased, there is more space for the tension to spread out, allowing for a higher amount of tension before the beam snaps. 

Beam Bridge

Truss Bridges 

      Truss bridges are essentially beam bridges, but with added structural support. The trusses are built to create a bigger mass in which the tension can be spread throughout. There are many different kinds of trusses, including the Warren truss, the Pratt truss, and the Howe truss. A truss is essentially a latice that is used to disperse force. A famous example of a truss bridge is the Bollman Truss Bridge in Maryland. 

Bollman Truss Bridge,  Maryland

Arch Bridges 

      Arch bridges follow the same principle as a beam bridge. The arch directs the force into the Earth and the Earth pushes back, to keep the bridge from falling. As according to Newton's third law, every action has an equal and opposite reaction. 

Arch Bridge in the Japanese Tea Garden at Golden Gate Park, San Francisco 

Suspension Bridges  

      Suspension Bridges are the most recent development in bridge design. Suspension bridges spread the force out through hanging cables which in turn move the force into towers. These towers dissipate the force into the Earth. Suspension bridges may also have a truss support system in addition to the suspended cables; this is called the deck truss. It helps to prevent the roadway from swaying. A famous example of a suspension bridge is the Golden Gate Bridge in California.

Golden Gate Bridge, San Francisco

Static Equilibrium

Equilibrium is the point reached when all forces acting upon an object equal zero in all directions.
For instance, if there is 20 newtons acting upon a box from the right and 20 newtons acting upon a box from the left, that box is said to be in static equilibrium. Another example of static equilibrium would be a free body diagram.

These objects are in equilibrium because the net force in each direction is zero. 

In other words, equilibrium is the point at which an object is acting with an acceleration of zero. 

Static equilibrium has an added criteria. The object or system must be at rest; the object must be static. There are many objects in a state of static equilibrium. For example, a stationary table. Because this table has a constant 0 velocity (and therefore a 0 acceleration), it is not crumpling in on itself due to gravity, nor is it being pushed on the left or right, it is in a state of static equilibrium. The force of gravity is acting down upon the table, but as Newton's law states, every action has an opposite and equal reaction, meaning that the earth is pushing back up, mitigating the force applied downwards by gravity. Bridges are another example of static equilibrium. The bridge itself is unmoving, and if the bridge does not fail, it is in a state of static equilibrium. When a car drives along a bridge, a new force has been introduced to the bridge. The bridge dissipates this new force, so that it is constantly in a state of static equilibrium. Suspension bridges, arch bridges, and truss bridges all redistribute forces differently, but they all still remain in a state of static equilibrium.  

Suspension Bridge 

Above is an example of how a suspension bridge distributes force so that it maintains static equilibrium. Force is distributed into the columns and outwards into the far suspension cables. The Earth pushes up against the force downwards in each column, resulting in a net force of 0. The suspension cables, to the far left and right, push the force into the short columns where the Earth again pushes up, mitigating the force downwards. Because this bridge has a net force of 0, and it is stationary, or static, it is in a state of static equilibrium.