Alright, now let’s get the tickets for the game

“Don’t worry about the tickets for the game”, my friend said. Next thing we know, the tickets were all sold out to season ticket holders. Our other friend found some tickets on viagogo, BUT, we didn’t know if they were fake. We needed a new plan. “It’s OK, we can buy tickets off scalpers on the black market”, my friend says. The black market sounded all well and good until the news reported armed robberies occurring where scalpers were robbed of their legitimate tickets which were now worth a couple hundred US dollars, a value that is a large chunk of a typical local’s monthly salary. We could now only rely on the viagogo tickets being legitimate. Then there is me, the clueless foreigner in his country and doesn’t speak any Spanish, who can only helplessly watch events unfold without knowing at all how to help.

In our already not-so-good situation, a representative from viagogo calls us and said that the tickets can only be picked up at 5pm close to downtown. The problem was that the stadium is on the edge of the city and the game starts at 6pm. There was no way to go to the pickup location for the tickets AND get to the game on time because traffic on game day would be terrible. My friend calls the viagogo representative and tells him the situation and guilts him into letting us pick up the tickets earlier by saying how we trusted the company with these tickets and whatnot and the rep agrees to let us pick up the tickets earlier. Whether or not the rep was sincere in that offer we didn’t know. We needed a plan B in case we really had to pick up the tickets at 5pm. This is where our plan got SUPER elaborate. We spent a good hour brainstorming a good plan and this is what we came up with:

The guy who bought the tickets (the American), would have to ride a motorcycle to the ticket pickup location, pick up the tickets, and go to the stadium, while the rest of us would get to the stadium early with a van so that when the bike arrived with the tickets, we could hide the bike inside the van. When his dad heard the plan, he began to scold him saying how crazy it was, and in his scolding, I heard a word come up over and over again. When I looked it up, I found out it was profanity. Awesome! My Mexican friend called all of his connections that he had to see how we’d get our hands on a van and a motorcycle. According to him, “he knows a lot of people, people owe him favours”. The problem with that plan was that the guy who had the van got into an accident (whether or not that was true, we’ll never know), which suddenly broke our whole plan.

Okay, so what if he rode a bicycle to pick up the tickets? He’d have to ride 12km from the pick up location to the stadium in terrible traffic. Not to mention the person riding the bike isn’t familiar with traffic in Mexico (traffic that does not respect bikers), and that most streets don’t have stop signs or lights. Throw in some lack of sleep – the guy would be flying in that morning in an overnight flight from LA. He was up to the challenge. My Mexican friend summarized the whole plan into a PowerPoint, calling it “the story to be told about this amazing adventure”. We wouldn’t be able to execute this plan until the day of the game. In the meantime, my Mexican friend showed me around.

Lake Chapala

Lake Chapala is Mexico’s largest freshwater lake, and for whatever reason, there is a substantial population of Canadian and American retirees here.

Tequila

Got to see some Agave fields (and eat some Agave too!) on a tour at the Jose Cuervo Distillery in a town called Tequila (where the name of the alcohol comes from). I made the tour guide speak English because I was the only guy on the tour who didn’t know Spanish.

Driving in Mexico?!

At one point, my friend’s brother asked me if I wanted to drive. I thought to myself, “okay, so there are no stop signs anywhere, I have no idea where to stop, and based on the driving I’ve seen, nobody really follows the rules on the road”. I drove anyway!

Knowing that I was a complete newb on the road in Mexico, my friend and his brother were both very watchful to make sure I was stopping at the right times. They had practically memorized all the places where cars should and shouldn’t stop. I had no clue whatsoever. I stopped and went when they told me to.

Later on, we saw police cars stopped on the side of the street in front of us. My friends just told me to play it cool and just drive normally. I also realized I didn’t have ID on me, so if I had gotten pulled over or something, I would have had to pay $100 USD just to get out. But luckily, nothing happened.

Picking up the tickets

Now it was time to execute the plan. My friend called the Viagogo rep in the morning and he says that we can pick up the tickets at noon. Okay, so no problem. We went and picked up the tickets while in the back of our minds we were still wondering if the tickets are fake. If the tickets were fake, then our whole plan would be meaningless.

We meet the rep and he gives us the tickets. We closely inspect them, and everything looks good. We were in a bit of a disbelief. Everything seemed too easy. But we wouldn’t know if the tickets were real for sure until we actually go to the ticket counter. At this point, we wouldn’t have to execute our crazy bike plan, and could only wait and see when we got to the stadium. With the couple of hours until the game, we spent some time walking around the city center of Guadalajara.

Touring the city center

Lots of people out and about on a hot day. We went in May, statistically the hottest time of year in Guadalajara.

The local boy/girl scouts were running a recycling campaign or something.

Game time

After lunch, my friend’s dad drove us to the game. As expected, the traffic was real bad. On the way there, as my friend’s dad drove, he says to us that he’s going to break a bunch of traffic rules and not learn from him. He then proceeds to cut a bunch of lanes, crossing the hatched areas on the road, and cuts in in front of people. He even made use of an handicapped sign on his car to get into the parking lot quicker even though he wasn’t handicapped at all (seniors just get those because they’re above a certain age). With his epic driving, we got to the stadium right on time.

Now, the moment of truth. The guard checking the tickets would be the one to tell us if the tickets were real or not. As we got closer, we got more and more nervous. The guard scanned our tickets and waved us through. What a relief. We didn’t need any of our contingency plans after all. Logically, everything went smoother than we could have possibly imagined. Now it was time to enjoy the game!

The entire crowd pretty much supported the home team, and there was a small section of Tigres fans, probably about 50-100 people only. Tons of people waved Chivas flags, and some even waved the French flag because it had the same colours as the Chivas jersey. We all bought jerseys for the game too!

As the game went on, the crowd cheered and chanted, “dale dale dale rebaño!”, which roughly means “let’s go herd [of goats]” (chivas means goats). At one point, when it looked like the Tigres were making a comeback, the crowd cheered even harder. With an amazing 2-1 finish (4-3 aggregate), the Chivas had beaten the Tigres to win their 12th championship!

Celebration

That night, large crowds gathered at the Minerva statue in the city to celebrate the team’s big win. My friend’s dad said he’s never seen the crowd this big in a long time. To celebrate, the dad made us all tequila cocktails (there was probably 3-4 shots worth of tequila in that) before we headed out and had a great time. As the only Asians in the city (my American friend is of Japanese descent), we stood out a lot and people occasionally said random phrases to us in different Asian languages. I guess that’s what happens when two Asians show up with Chivas jerseys!

Last, but not least, the food

My first meal when I arrived in Mexico: Menudo. My friend thought my stomach wouldn’t be able to handle it, because the meat in the soup was tripe. But, nope! Chinese people eat tripe all the time!

Not exactly a meal that I had, but there is a running joke that a guy can take a girl out with roses and a can of Jack Daniels. Once that joke caught on, the store intentionally started putting roses next to the Jack Daniels in the store.

Tacos with carnitas and guacamole? Sign me up!

Lonches. Basically a sandwich with meat inside served with a dipping sauce on the side (can also just be poured onto the plate to let the bread soak). The bread used is a kind local to Guadalajara (birote/bolillo).

Then there are tortas ahogadas. Very similar to lonches. It has a the same bread, but this one is way meatier and the sauce is a tiny bit of spice.

Ceviche! A dish with raw fish cured in lemon/lime with added spices. Can’t say no to seafood!

My friend’s mom also cooked food for us and I totally wish I had taken some pictures of that food. She cooked a pork stew and I wish I knew what was in the sauce! Both parents encouraged me to eat so much and they showed so much hospitality! They kept offering me more and more food until I was super stuffed. Good thing my friend’s brother taught me “estoy bien”! This was definitely one of the best trips I ever had – full of excitement and not just doing touristy things. Having a local show you around really helps!

Link to photo album: here

The tour took us to various locations in the camp, where prisoners were experimented on, suffered in standing cells, etc. The guide also explained how the Germans ran the camps day to day, how they used certain prisoners to oversee other prisoners (Kapos), and of course the extermination. One of the most impactful exhibits here was a room full of just shoes – shoes of many who died at the camp. It’s one thing to be told a bunch of numbers of how many died, but it’s another thing to see thousands of shoes just laid out in front of you.

The camp was split into two: Auschwitz I and II, where the main purpose of Auschwitz I was for political prisoners while Auschwitz II was for extermination and forced labour. Originally, Auschwitz I had many one story buildings, but an additional floor was added to increase capacity.

Guardtowers and electrified barbed wire fences prevented escapes. They really thought of everything.

The death wall is where people were lined up to be executed by firing squad.

The next part of the tour took us to Auschwitz II. Railway tracks efficiently brought prisoners directly into the camp. It’s impressive how efficient they were – that’s what made so scary.

As the Allies closed in on the camp, the Germans destroyed many of the buildings to try and hide what they did. But nonetheless, the truth came to light at the end and many of those responsible were tried and executed.

It was really hard to imagine millions of people were killed in this one place alone. People didn’t talk much during the tour as if to informally have a moment of silence for all the victims. There was nothing to be said. Everyone felt the aura of sadness just by being there.

Link to photo album: here

1.0 Motors

The chosen motors are:

• Finger grasping – Cytron IG32E-264K at a cost of USD $57.03 from RobotShop
• Finger sliding – Cytron MO-SPG-30E-20K at a cost of USD $22.58 from RobotShop

Both motors meet the torque speed requirements for this project.

1.1 Finger Grasping Actuation

From the initial budget, the budget set for actuators was set at $325.  The torque requirement needed for gripping was also calculated and each finger would require 4 Nm at its output to lift a 4 kg object using only the fingertips.  The evaluation criteria states that the device grasp as fast as possible and that the client would have the highest satisfaction if the device cost was less than $700.

Looking on several websites that sold motors, the following DC motor was chosen: Cytron IG32E-264K at a cost of USD $57.03 from RobotShop.  The specifications are as follows:

At 12 V with gearing included, the stall torque would be 20.7 Nm (without consideration of mechanical efficiency).  A motor with a high stall torque is also beneficial because it lowers the gear ratio required, which leads to the use of less space for gearing.  The motor also comes with its gearing, which contributes to its high torque.  Given the high stall torque of this motor addition gear reduction is not required.  During grasping, the motor will be exerting high torque at low speeds and therefore, the motor will be operating near the stall torque.  The torque here is more than sufficient even with mechanical efficiency losses accounted for.

For finger actuation before grasping occurs, there is a low load and therefore the motor will be operating closer to the no load speed.  The no load speed with gear reduction is 27.7 rpm (without consideration of mechanical efficiency).  Split among three output shafts, the speed would be 9.21 rpm.  Even with the load of the fingers accounted for, this is still acceptable. based on requirements and evaluation criteria.

While the torque is a lot higher than required, this motor was only more expensive than a motor of one size smaller by less than three dollars.  The electrical characteristics were also identical.  With a higher motor torque, the grasper would be comfortable in lifting objects even heavier than 4 kg, which is another benefit based on the evaluation criteria.

1.2 Finger Sliding Actuation

The motor required here does not require a large torque since motion in this degree of freedom is not expected to handle heavy loads.  This motor only requires enough torque to overcome the friction of the finger on the power screw that it is mounted on.  Therefore, a low-cost motor (relative to the grasping motor) will suffice.  The DC motor of choice is the Cytron MO-SPG-30E-20K at a cost of USD $22.58 from RobotShop.

The specifications are as follows:

The consistency of the stated specifications do not match the previous motor because the information that was provided by the manufacturer was not consistent.

An initial estimate of two 200 g fingers sliding on a 1/2” diameter power screw with a steel-steel sliding interface (friction coefficient of 0.8) shows that only 20 mNm of torque is required.  Therefore, this motor meets the requirement.  The power screw also has 13 threads per inch, and at the rated 185 rpm, the power screw would slide linearly at 6 mm/s.

1.3 Motor Type

DC and servo motors are motors that are suitable for the project.  An investigation between DC and servo motors showed that many manufacturers of motors did not provide the necessary specifications for choosing a servo motor in terms of the values of the no load, stall torque, and stall current.  While servos generate a lot of torque relative to their size when compared to DC motors, it is not feasible to use a servo motor because of the unknowns in the specifications.  It is possible to buy several servos and test them, but this is costly and time consuming.  At this stage in the project, the team is not able to commit the time to investigate further.

Comparison of the cost of the grasping motor relative to motors from Maxon Motor, a supplier of motors for UBC Thunderbots, shows that the price of a motor of the same power output costs approximately the same amount.  However, a fundamental difference is that the motor from Maxon does not include a gearbox, while the chosen motor for this project does.

2.0 Microcontroller

The microcontroller of choice is the Arduino Diecimila.  The primary motivator for using this board is because the UBC Thunderbots team already has this board and is currently unused.  The Thunderbots team has generously provided the board for use on this project.

The MCU will allow the turning the motors on and off, changing motor direction, changing motor speed, and reading encoder feedback.

3.0 Voltage Regulation for Encoders

Since the power supply is likely going to be run at 12 V, the encoders will require voltage regulation down to 5 V (the operating voltage of the encoder for the motors).  The chosen voltage regulator is the MC78L05A at a cost of USD from Digikey.  According to the typical application diagram of the datasheet, two capacitors will also be required (0.33 μF and 0.1 μF).  The cost of these are less than $1.

The voltage regulator will be wired up in this way as the datasheet shows:

The input will be from the 12 V source, and the output will be to the encoders.

4.0 Motor Driver

To control the motors, an H-Bridge is to be used.  However, due to the different current flows for each motor, one motor driver will require a high current capacity while the other one will not.  The high current capacity motor driver consists of a driving circuit using two half-bridges.  The low current capacity motor driver is made up of 1 IC.

4.1 Finger Grasping Motor Driver

To design the H-Bridge for controlling the motor, an L6205 motor driver will be used.  Each of them costs USD $11.36 from Digikey and can withstand a continuous current of 2.8 A and a peak current of 5.8 A and can be interfaced with the microcontroller with PWM inputs.  The driver can also be run in a parallel mode to double the current ratings by using both of its full bridges together.  The datasheet provides an application circuit as follows:

Output pins from the Arduino can turn the motor on and off through the enable pins.  Direction is controlled by adjusting the voltage polarity between IN1 and IN2.

There are also two output pins for current sensing.  By using it to measure the current draw, the microcontroller program can determine what the torque is through the use of the motor curves provided in the motor specifications.

4.2 Finger Sliding Motor Driver

The motor driver of choice is the L293D and each one costs $2.50 from Digikey.  Bidirectional control of a DC motor can be achieved by adapting the application circuit from the datasheet:

The 1A and 2A pins determine the direction of the motor or the motor deceleration.  A truth table is provided in the datasheet.

5.0 Power Supply

To power the grasper, a power supply plugged into the wall will be used.  It is expected that the future robot will have a power source of its own which will power the hand as well.  Therefore, for the purposes of testing the grasper for this project only a wall power supply will be required.

Looking at the maximum electrical power consumption of the two motors, the total comes to ~65 W (12 V * 5 A + 12 V * 0.41 A).  The other components also consume power and so the final power consumption will be higher.  To compensate, a 12 V power supply with a maximum wattage and current of 84 W and 7 A was selected.  The part number is CENB1090 and each costs USD $70.48 from Digikey.

6.0 Power Supply Connector

The power supply chosen has one port that uses a Molex Mini-Fit Jr. Receptacle.  Therefore, a proper receptacle must be used so that proper wire routing can power all the circuitry.  This also means that the future robot will also require a matching plug for this receptacle.

7.0 Fuses

Fuses will also be used as a redundant mechanism to stop the motor in case the current draw is too high.  The primary method of stopping the motor is through the current sense pins on the motor driver.

Link: http://en.m.wikipedia.org/wiki/List_of_common_misconceptions

Full article here (http://www.personalitypage.com/ISTJ.html)

This is what the letters stand for:

I – Introvert
S – Sensing
T – Thinking
J – Judgment

Quote #1

As an ISTJ, your primary mode of living is focused internally, where you take things in via your five senses in a literal, concrete fashion. Your secondary mode is external, where you deal with things rationally and logically.

That’s exactly what I do.  I have huge troubles with metaphors and anything abstract.
Quote #2

ISTJs tend to believe in laws and traditions, and expect the same from others. They’re not comfortable with breaking laws or going against the rules. If they are able to see a good reason for stepping outside of the established mode of doing things, the ISTJ will support that effort. However, ISTJs more often tend to believe that things should be done according to procedures and plans. If an ISTJ has not developed their Intuitive side sufficiently, they may become overly obsessed with structure, and insist on doing everything “by the book”.

I do not like breaking tradition because there was always a reason why they are set.  If I’m able to identify this reason and agree with it, I would be very comfortable living with those traditions.  It’s also true I like doing this by the book, but at the same time, I see a lot of things as situational, meaning that my actions are based on whats happening around me.

Quote #3

The ISTJ is extremely dependable on following through with things which he or she has promised. For this reason, they sometimes get more and more work piled on them. Because the ISTJ has such a strong sense of duty, they may have a difficult time saying “no” when they are given more work than they can reasonably handle. For this reason, the ISTJ often works long hours, and may be unwittingly taken advantage of.

Total truth.  I remember always agreeing to take on more work at my Co-op job if it was needed of me.  I also totally remember working on homework or other work for 15 hours straight.

Quote #4

Under stress, ISTJs may fall into “catastrophe mode”, where they see nothing but all of the possibilities of what could go wrong. They will berate themselves for things which they should have done differently, or duties which they failed to perform. They will lose their ability to see things calmly and reasonably, and will depress themselves with their visions of doom.

Totally, and that makes me a pessimist

Concept

I was given the circuit shown below (from Microelectronic Circuits 6th Edition by Sedra and Smith):

I was asked for the voltage of the output terminal and the current flowing through the diode.  Finding the current was easy, but I didn’t quite get the voltage.  I thought to myself, “from what two points do I measure the potential difference?”, because after all, voltage measurements are always taken relative to two points.  It took me the longest time before I could just use ANY two points and the measure the voltage.

What I figured is that, for part a, since the diode is in forward bias, the diode will act as a short circuit.  I then can say that V – (-5) = 0, since the voltage difference along a short is 0.  From there, I can easily determine that V = -5.  I can apply that same logic to the other three.

Nodal Analysis

I was given the circuit shown below (from Microelectronic Circuits 6th Edition by Sedra and Smith):

From class, I remember the professor saying that since we cannot tell right away which diodes are on and off, we can only make an assumption about the states of the diodes and then apply the usual analytical techniques.  In the event that the result is unreasonable, we know that our assumption wrong.  I made my assumptions, but afterward, I didn’t know where to go next.  I had forgotten how to analyze these circuits.

Later, I realized that I could use nodal analysis.  Since I assumed the two diodes in part a were both on, I replaced them with short circuits.  I used the intersection right before the current splits as my node.  For part a, the current into the node was 3 V/5 kΩ = 0.6 mA.  The current leaving was some unknown current for diode 1, and a current for diode 2.  I could determine the current of diode 2 by taking the potential difference between the node and the -3 V output and dividing that by the resistance in the path.  The result was (0 – (-3))/ 10 kΩ = 0.3 mA.  From the nodal analysis equation 0.6 mA = current from diode 1 + 0.3 mA, the current from diode 1 is 0.3 mA.  And as for the voltage V, the potential difference between V and the -3 V output is equal to the voltage across the resistor, (0.3 mA)(10 kΩ) = V – (-3).  Therefore, V = 0.  Alternatively, I can use the potential difference between the node and the output, which equals zero, thus yielding the same result.

Boolean Logic

The next issue I had was determining the Boolean outputs of a diode logic circuit.  Again, the picture below is from Electronic Circuits 6th Edition by Sedra and Smith.

The issue I had here is that I did not know current sources have no voltage if there is no current running through them.  Looking back that sounded pretty intuitive.  Finding all possible combinations of inputs A and B for this logic circuit, we get the truth table below:

A B X Y
0 0 0 0
1 0 0 1
0 1 0 1
1 1 1 1

The outputs of X reveal an AND gate.  Setting A or B to a logic 0 in (a) will cause current to flow through that path.  The potential difference X – A or X – B (depending which one was set to 0), will yield 0, thus the output X will be zero as well.  When A and B are both set to logic 1, it causes the diodes to go into reverse bias, and node X will be powered by the current source.

The outputs of Y reveal an OR gate.  Setting A or B in (b) to have different inputs, either 1,0 or 0,1, will cause the diode to be in forward bias for the input that has the logic 1.  For the input with logic 0, the diode will in reverse bias.  Since one of the diodes is on, current will flow and output Y will yield a logic 1.  In the case of both diodes being off, no current will flow, thus causing output Y to yield logic 0.

Other Notes

In the case of multiple parallel diodes in the same direction, if one of them is on, chances are they are all on (provided that the voltage across them is positive).  However, there may be a case where one parallel diode will want to flow into the other because of a greater voltage difference.  For example, if there were two parallel diodes, one with a 3V input and the other with a 2 V input both going to the same node, current from the 3 V input will want to flow into the diode connected to the 2 V input.  This will cause a reverse bias in the diode connected to the 2 V input, thus turning it off.

There is also another case where there are parallel diodes with different output voltages.  If current is flowing toward it, they will all be on, so they will all be a short circuit.  Which path will the current go to?  The path with the larger current.