Wednesday, November 21, 2012

Bose Speakers!

About a month ago one of my professors invited me to be part of a speaker building seminar with Bose.  The purpose of this seminar was to expose us to the kind of stuff that Bose does, learn some basic acoustic theory and build some speakers!

The seminar was amazing, the guys from Bose explained some really cool features they put into their products. They showed us this "magic sound wand" which they could use to point at some location and make sounds seem like if it was coming from there. It was kinda spooky but awesome. We also learned a bunch about the use of crossover to give you better sound quality. One of the coolest things they showed was how they designed a new type of speaker cone which exhibits no parasitic harmonics under the audible range and thus was able to produce a pure note much better than a normal speaker cone. (I wish I had a video of this but they had a strobe going in the demo, so it was hard to film).

pink cone has parasitic modes, waffle cone (blue) gives you
 a much more pure note and no parasitics
bose dude holding the magic sound wand

The speaker building part was pretty fun too! We build two speaker cabinets out of PVC and MDF. At the end of the seminar we all put our speakers together and were able to play a 30 track piece in lobby 13!

speakers under construction


Sareena rudely interrupting my photo

Saturday, November 17, 2012

Tic Mag Toe v1.0

Hey guys!

As some of you know over the summer I became super interested in Magnetic Levitation. I started reading/learning about it and got super excited. I bought a maglev kit from Guy Marsden and it was super cool to see it levitate a pen.

Currently I am working on my own design using a switching mode converter and some analog feedback. Fun fact: it turns out that my Master's Thesis is going to be on modeling and control of Magnetic Bearings!

The previous examples I have mentioned are examples of active magnetic levitation, where a controller regulates the position of an object via feedback. Another kind of MagLev that exists is passive maglev which requires no active feedback. Turns out you can build a stable maglev system with no active control using Diamagnetic materials.

Diamagnetism is the property some materials have to repel magnetic fields. It is normally not a very strong effect but it is enough to make sheets of Pyrolytic Graphite levitate over strong neodymium magnets. My graduate advisor and I have been trying to think of uses of diamagnetism however given the forces involved are so low that we have not found any "real world" uses! I started to try and think of non-industrial non-real world uses and I thought it would be awesome to build a chess or checkers board with pieces made of pyrolytic graphite that levitate over the board. However given that the rare earth magnets are so expensive I decided to go with making a TicTacToe board first. I call this new creation Tic Mag Toe (im very proud of this name jajajaj...). I built a prototype this weekend:
tic mag toe v1.0
Getting the magnet in the checkerboard configuration was a little tricky cause they are crazy strong. We also had the world's first tic-mag-toe match:

I won it and became the undefeated world champion of Tic-Mag-Toe! However 10 minutes later Harry beat me twice... thus losing my glorious title to Canada.

My next step is to encase the magnet board into a nice laser cut frame and figure out a way to make nicer playing pieces. Then when I get enough money I'll go for the checkers board and maybe the chess board! For those of you wondering I got the supplies from the best source for strong magnets I could find online!

Tuesday, November 13, 2012

ThermoDynamic Bread!

Hey guys!

A lot of you have probably noticed that if you put 1 object in the microwave for X amount of time, then the temperature of the object goes up by some amount, however if you put two of the same objects for the same amount of time then each object will be individually less hot than in the first case. To me this was always an obvious fact that I learned from my early teenage years heating up tortillas in the microwave (I use tortillas as the example because it's funny cause I'm Latino).

At MIT I have learned that this is not an obvious fact for some people, one time during my junior year I had an argument with a freshman on the subject. He was convinced that if we put two sandwiches in the microwave for the same time as one, all three sandwiches will end up with the same temperature. I quickly tried to correct him but he gave me some stupid explanation on how the air will not heat up as much of you put two things instead of one thus making the efficiency higher blah blah blah... I tried to appeal to his inner scientist/engineer and talked about the first law of thermodynamics applied to microwaves but that did not work so then i just made fun of him which made him get kinda mad (sounds like I was being mean, but HEY! he asked for it! never mess with the FIRST LAW)

A couple of weeks ago I had the same argument with a friend who argued that formation of standing waves blah blah blah and that the temperature rise under the two conditions would be the same. (this case he was arguing that putting two Maruchan soups will heat each up the same as just putting one in. I tried to give my Thermo First Law speech AGAIN but it did not work so I was forced to do some late night experimenting: please enjoy!

 BAM! SCIENCE! I was right yet again, the single piece of bread exhibited a temp. rise that was 1.6 times greater than the two pieces of bread. However the question now is, why isn't that a factor 2? (half the mass means double temp. change for a same heat energy influx). That got me thinking on how the efficiency of the microwave varied with the properties of the food you cooked. (granted, the experimental set-up could be a total failure, thus I will be trying to repeat it in the next couple of days with cups of water instead of bread).

I started exploring the internets for answers I found some people that pretty much agreed with me (click here to see). Then some more people here. After this basic research it was obvious that the food properties (composition and geometry) and a lot to do with the linearity of the heating times, which adds an unknown for cooks in knowing how long to heat up things for. Interestingly fact: microwaves were initially unpopular because they were so "unpredictable" as far as heating times are concerned. (link to wikipedia microwave page

I will be conducting some more experiments of my own to check out how valid the linearity of heating times holds for things like water, bread and other random things.

Keep posted for the results! If you have any other "scientific experiments" or kitchen science questions that need to be answered please let me know and I'll do my best to address them in this blog!

Monday, November 12, 2012


Hey avid readers!

Sorry for the long delay, as a quick life update: in the last couple months I have started grad school at MIT (its going amazing!) and i joined the Electric Vehicle Team after my ex-roomie Victober infected me with the Electric Vehicle Fever. At the start of the school year, Victor and I worked on TinyCycle, after we finished it Victor and I took RailScooter and TinyCycle to the NYC Maker Faire, it was a day full of annoying delays (oversleeping, subway breaking down, forgetting to charge EVs etc etc) however it was a lot of fun and all the MIT folks raced their EVs around the power series track (Vicky and I also raced our EVs in the streets of Manhattan (not recommended) but that is another story...).

This whole experience left me really wanting a tiny electric motorcycle, just like TinyCycle. I looked around on craigslist and emailed/called/texted a couple of folks but never got an answer. Luckily for me  it turned out that one student group in 2.009 (MIT's Product Design Class) had taken apart a mini razor motorcycle as part of a class project and now it was sitting there alone in pieces. So i decided to do what every good samaritan would do... TAKE IT and give it a new home!. Thus my ChiquiCycle adventure started!

ChiquiCycle in Pieces
ChiquiCycle put together (no drive train or electronics)
It took me about a workday to put together all the parts I got from the 2.009 kids, it turns out they had lost the handlebars, the steering axle and most of the hardware. I eventually grabbed some scooter handlebars from MITERS, turned new steering axle pieces myself and grabbed some metric hardware from the shop. The motorcycle was now ready for its electronics! I started by procuring all the important parts: Motor, Controller and batteries. I had my ex-roomie victor help me with the battery pack (please see his excellent tutorial on how to assemble a Li battery pack!). The motor I used was this one and I decided to use a sketchy brushless motor controller from China that victor had laying around (in the near future Victober and I are planning to write a paper on sizing your motor and controller for your pocket bicycle).

We aimed to make the drive train assembly as simple as possible. I used an aluminum L-bracket to mount the motor. We took the driving sprocket out of the old motor the motorcycle came with. These sprockets normally come with a D shaped hole so it can transmit torque. I was lucky that the size of the sprocket bore was an M8 (same as my motor) this saved me the time it would take to machine an adapter. I pressed a spacer on the shaft then sanded the shaft to give it a D profile, put the sprocket on the shaft and finally machined a collar to constrain the sprocket axially.

my drive-train assembly
close up of driving sprocket mounting
The controller mounting was pretty easy (i just reused the mounting holes for the original brushless controller.

ChiquiCycle Frame with batteries, motor and controller! ALMOST DONE!

At this point ChiquiCycle was ready to roll!

We did some test runs (videos pending...) and it was obvious that we needed the controller to output more current to make our ride more exciting! With the help of Charles we hacked the motor controller to output more current and added hall effect sensors for motor startup. The scooter handlebars were making it impossible to ride chiquicycle semi-comfortably so I changed them to bicycle handle bars. I added a couple more pieces of the original plastic body and a Tesla decal and this was the "final" product:

ENTER CHIQUICYLE! (videos will be posted soon)

fun fact: I posted the above picture to the Tesla facebook page hoping that it would give me the opportunity to work at Tesla in the near future! I got over 130 "likes" from random people! My hope is that Elon Musk sees it and offers me a job in Tesla!

I'd like to thank the people that helped me out with this project, namely Victor, Charles, Lauren, Rango and Harry!

my awesome pit crew! (lauren and rango)
This project along with Victober's TinyCycle has pushed several friends to buy a tiny motorcycle! We are in the process of creating the Pocket Motorcycle Squad (PMS) and we aim to have a techfair booth in early 2013. Here's a picture of Lauren's chopper and future member of PMS!

UPDATE: Here is an instructable for Chiquicycle! It has almost 30k views and it won 2nd place in a "cars and motorcycles" contest winning me a bottle of "water spot remover"