Project Evaluation

David Mata

June 12, 2013

ENGR 44

Project Evaluation

     Earlier in the semester when the guidelines for the projects were handed out, Greg, Antonio, and I came up with the idea of building a combat robot. Out of all of the possible projects to choose from, we decided that the combat robot was easily the most interesting project and perhaps the easiest to construct. On the night when the PERT charts were due, Greg was absent, so Antonio and I were the ones who laid out the project plans and objectives to Professor Mason. But Greg certainly helped us out in the days prior by giving us some brilliant ideas on what to put on our chart. In the following weeks, we met about once or twice a week to work on our robot at Greg’s house. We all pitched in approximately $20 in the supplies needed to build our robot. We spent countless hours soldering the chassis and gluing on all the parts that was necessary to build a successful robot. We all contributed equally in this respect. I took primary responsibility in taking the photos for our group for the PowerPoint slides while we were constructing our robot. Greg did an awesome job as the leader of our group and even worked on the robot on his own free time when the group was not together. The three of us finally completed our robot and we discussed how we were to go about our presentation. Antonio, being the expert that he is in creating PowerPoint slides took charge in creating the slides while Greg and I continued giving him feedback and ideas regarding the presentation slides. In sum, we all worked hard on this project together, but Greg deserves extra credit for the leadership he brought to the table.

AC Lab

In this lab assignment, unlike in previous lab assignments, we performed an experiment with an AC source. Our objective was to analyze an an inductor with an inductive resistance in series, for which its impedance is given as Z = R + XLj.

Our first step was to determine the inductive resistance using a digital multimeter. We came up with a resistance of 3.2 ohms.

Step 2 required us to determine the inductance. In order to protect the function generation or the inductor from possible damage, we were instructed to create a test circuit shown below.

The resistor Rext in the photo above was the resistor we used to limit the drawn current. We were asked to use a theoretical value of Rext = 68 ohm. After choosing the appropriate resistors, we measured them with a multimeter and they came out to a total of 68.8 ohms.  Next we were to set up the function generator by energizing it and setting its frequency to 20.0 kHz and setting the RMS value to 5.00. We then energized the multimeter and connected it to the function generator. We achieved an experimental result of 4.91 ohm.

As shown in the photo above, we were required to build the circuit on the breadboard. We then took measurements of V in,rms and I in,rms which turned out to be 4.63 V and 69.1 mA, respectively. We were told that our V in,rms value should be less than 5.00 which indeed was the case. We did notice a difference in the voltage reading as compared to the function generator reading. We hypothesized that the internal resistance of the ammeter was the reason for the ammeter. Next, we were required to measure the corresponding value of the impedance from the above measurements. Here is what we obtained:

Next, we were required to rewrite the expression for the imput impedance. Here is what we obtained:

After that, we were asked to compute the magnitude of this impedance:

Then, we computed the angular frequency:

Finally, we used the equation the magnitude of the impedance in order to compute the value of the inductance:

Now we were ready to move on to Step 3 and analyze the following circuit below:.

To start off we were asked to compute the value of the capacitor using the values of the angular frequency and the inductor. Here is what we obtained:

Next we were required to set the capacitor box equal to this value and to modify the circuit to it's required values:

We were now to include the oscilloscope. After energizing it, we connected CH1 across the multimeter and CH2 to the inductor. After calibrating the oscilloscope, we obtained two cycles of a sinusoidal wave.

Setting the oscilloscope to a frequency of 20.0 kHz, we made the following measurements for Vpp,CH1, Vpp,CH2, and delta t:

The phase angle was computed to be 90 degrees out of phase.

Next, we were instructed to record the multimeter measurements for some selected frequencies. Here is what we obtained:

The laboratory procedures were now done with. We were now asked to answer some followup questions.

1.  The current is at it's highest value at 20.0 kHz because of resonance. The inductive and capacitive reactances cancel out and the circuit is the purely resistive.

2. The circuit looks more inductive at frequencies above 20.0 kHa because angular frequencies are directly proportional to inductive reactances.

3. The circuit looks more capacitive at frequencies below 20kHz because angular frequencies are inversely proportional to capacitive reactances.

This concludes our semester of circuit analysis lab assignments. It was such a fun semester solving circuit problems in lecture and reinforcing these concepts through experiments. I will definitely consider taking more electrical engineering courses in the future. I may consider taking a course in electronic devices in the near future.

MOSFET Lab

Purposes:

1. To investigate two circuits that can control the voltage across an electric motor.

2. To gain some insight into how DC brushed motors behave.

3. To control the power supplied to a motor with a MOSFET.

4. To regulate the behavior of a motor with a controller.

Materials:

N-type power MOSFET (IRF510 or NTE2382), 10kohm potentiometer, 2.2kohm resistor, 22-AWG wire, oscilloscope, 1N4007 rectifier 

Procedures:

Part 1: 

First we were required to construct the circuit shown in the schematic diagram shown below and to connect it to an oscillator. The second photo below shows the circuit itself. 

To begin, we were required to put the oscilloscope into storage mode and to set it for a single sweep. We made sure to set the vertical scale to 10 V/div as well as the time scale to 0.1mS/div. We adjusted the trigger level until we successfully started the motor. We indeed heard some off and on cycles. Next we attempted to neutralize the transients by putting a 1N4007 rectifier diode in parallel with the motor. We turned on the motor to investigate the effect of the diode onto the motor's cyclical sound. We did notice a longer cycle. 

Next we were required to construct the circuit in the diagram below which included the load resistor and the diode.  The photos below show both the schematic and actual circuits.

We noticed that the motor turned on at a gate voltage of 7.23 V. Next, we slowly increased Vgs from an initial value of zero. We noticed that with the increase in voltage, the motor begin spinning faster with the cycles being shorter. So I would definitely say that we were controlling the motor voltage well.  We measured the internal resistance of the multimeter and noticed that it had a value of 0.5 ohm. Then we were instructed to disconnect the motor from the circuit and to connect it onto the oscilloscope. We measured an induced back voltage of 8 V by hand.

Part 2: 

Now for the second part, we were to control the average voltage applied to the motor using pulse-width modulation.   

We were now required to replace the potentiometer with a 0-10 V square wave function generator and we set it to 10 kHz. We then used an oscilloscope to display the waveform of the voltage of the motor. Here is what we observed:

We now varied the duty cycle wave to 100% and noticed that the motor sped faster. The following photo shows proof that it sped faster. Notice how the cycles became shorter.

When then changed the DC source knob to 30% of maximum power and we made the following observation in the photo below:

Conclusion:

We considered this lab to be a success since we successfully completed all of our objectives. In all honesty, I thought that this was one of the most boring labs we've had all semester because it was based entirely on just observations without any data nor follow-up theoretical computations. 

Second Order Tutorial

The purpose of this assignment was to give ourselves an opportunity to supplement and reinforce what we've learned from our lecture and homework assignments regarding second order circuits. There were a total of 18 problems, plus an additional page summarizing our results. Please scroll down to view the screenshots of our results.

Problem #1

Problem #2

Problem #3

Problem #4

Problem #5:

Problem #6

Problem #7

Problem #8:

Problem #9:

Problem #10:

Problem #11: 

Problem #12: 

Problem 13:

Problem #14:

Problem #15:

Problem #16:

Problem #17:

Problem #18:

Problem #19:

As you can see, we were successful in our attempt to solve every problem correctly. I only wish our instructor would have shown us this tutorial page much sooner so that we could more easily familiarize ourselves with the mechanics of problem solving from previous chapters and sections. I really loved the fact that this tutorial gave us step-by-step guidance into solving the entire problem as a whole.