Saturday, October 12, 2013

The MEMS post

This summer I was fortunate enough to be selected to participate in the Lutchen Distinguished Fellowship Program. Essentially a more rigorous UROP, it allowed me to continue my MEMS resonator research with Professor McDaniel through the summer.

Rewinding a bit, I started working with MEMS in late 2012, applying for UROP for spring and fall 2013. The Lutchen Fellowship is offered to 10 students each year who have partnered with a university professor to work on a research project. The program ends with a presentation by the students to the other Fellows, their faculty mentors, and Dean Lutchen.

My first semester of research involved learning MEMS CAD software, called L-Edit, which is a delightful program that only runs in 256 color. To further show how much I love this program, I will also mention that the student version lacks the ability to include text on the design. Unfortunately, this is the software that MEMSCAP, the company that manufactures the dies, wants us to use. After slaving for hours, the final designs from L-Edit are submitted four times a year to MEMSCAP and the products are shipped back to you with just enough (not nearly enough) time for you to release, test, and redesign devices for the next production run.

All ~20 of my devices fit on one of those little squares, which are 2.5mm x 2.5mm
A few SEM images for your enjoyment:

Wide angle shot of whole die
A pair of double camped beams
coupled double-clamped beams
Close up of capacitive gap
I began my summer research by a frequency divider for lab use. Although I didn't end up using this extensively, I gained valuable experience in circuit and PCB design. I used CircuitLab to simulate and Eagle to design the board, which was cut by my friend Steve. Thanks, Steve!

Thanks, CircuitLab!

Green in, Yellow out.

Next came learning how to use the Network Analyzer. The HP 3577a Network Analyzer is a charming machine that looks, feels, and smells like the 1980s. Gradually learning the quirks of this particular machine, I wrote a delightful instructional manual which can be downloaded here. About twice as old as I was at the time, the NA had seen its fair share of wear and tear (talk about rhyming). Several of the buttons were sticky, the GPIB/LabView interface was essentially unusable, and the knob that moves the cursor on screen was... wait for it... totally broken. The silver lining of this situation is that I learned to perform the measurements I needed the hard way, which led me to find menus I didn't know existed, giving me a better understanding of what the machine could do.

After a few weeks of trial and error with the measurement methods and vacuum chamber, I eventually found a circuit that worked and found several resonances. The Qs of these resonators were not as high as we had expected, but we realized we were limited by design parameters. The main issue, we speculate, is that the minimum gap between the resonating beam and the driving pad is .75 microns, which forces us to have a large DC bias and drive voltage. This means that we are driving the beam really hard, which causes changes in the center frequency and reduction in quality.

My vacuum chamber
Wire Bonding (cell phone microscope picture)

The first resonance I could find in my pictures
What we established:

Resonant frequency is proportional to AC drive and inversely proportional to DC bias
Quality is inversely proportional to both AC drive and DC bias

Take a look at the hastily-constructed charts below for more details.

This research will continue through (at least) the fall semester and hopefully after that as well. Stay tuned for more updates and beautiful charts.

Saturday, May 18, 2013

It's Made of Wood... Yup.

Earlier in 2013, I started designing a version of Chibikart. Athought I knew I wanted my vehicle to be substantially larger and more comfortable to ride, the final goals for the project were not set in stone at the time and continue to evade me. I'm going to keep this post short because the project is not complete and this is basically just a photo dump with some words in between.

...just like all of my other posts.

The t-slot extrusions, known to me as 80/20 (supposedly 80% of the strength of aluminum at 20% the weight) will serve as the frame for this build and hopefully be adequate for any future four-wheeled vehicles I may feel the need to create in the near future. Special nuts can be inserted into the slots and removed without harming the extrusions, making them ideal for builds that are somewhat fluid in nature when it comes to component placement.

Thanks to the help of Evan Lane, I was able to cut sprockets from 1/8" 6061 Al using the mill in the BU Tinker Lab. <-- BU students, please come do things here so you will enter the job world with real engineering experience!

Test run on foam insulation

We made a fancy jig to hold it.

Number of end mils broken doing this: zero.

Done! Chamfer was added to the edges later, I promise.

The sprocket spacers were cut next.

A few tapped holes later, we've got drive wheels!

There was a small (big) snafu with materials and I was on a deadline for a competition (that I completely misunderstood the criteria for) so I was forced to lasercut all of the pieces that I needed so I could show the judges a thing that looked like a go kart and not a $800 pile of nuts and bolts...and a frame.

Here's a picture of the rolling chassis plus the throttle pedal, which I was overly excited to use, so I put it on as soon as I could.

The front wheels line up - cute.

The brakes were next

Then came the motors and chain.

Special thanks to Abominable Snowman Steering Systems.
A few hours later (in which I did not take pictures) a fully functional kart was completed. Not pictured: the seat, (arrived a few days later) the correct battery, and the sensors+boards (too lazy to put on before aluminum parts get here).

Please note comically large steering wheel. 
Current home:

Anti-grav comes standard in jasontrollers.

For the record, I did ride the wooden kart down the hallways of 44 Cummington for a few feet, but the wooden parts, especially the uprights, were very unhappy and were sagging from the weight of my huge ass. Stay tuned for when aluminum parts are cut and we do garage testing, hopefully by the end of the summer!

Tuesday, January 29, 2013

Phone Case Versions 1-3

Last winter, I designed a phone case for fun. When I designed it, I envisioned it out of aluminum. This idea was quickly scrapped as I thought about the effects on signal strength and how it was very easy to 'hold the iPhone 4 wrong,' according to Steve Jobs. In the summer of 2012, BU got a MakerBot Replicator and I decided to give my design a shot. 


There happened to be black plastic in the machine, so the case was black. It was a pretty good first try. The major things I didn't like about it were how flimsy it was, and how it didn't hold on to the phone as well as I wanted. It could be pushed side to side over the grooves on the iPhone 4 very easily. Additionally, the buttons were a bit tough to reach, despite the little recessions in the case.

At the time of the pictures, I didn't have any 1/2" 4-40 screws on hand, so this is the best I have. The screws were filed down and a hex nut was put on the back to hold it in place. This idea was scrapped because the nuts kept falling off and also placed unnecessary strain on the very thin corners of the first iteration of the case.

The next iteration came in late November. I had been using the first version for about a month after my 'real' case bit the dust. Props to Speck though, that case lasted me a year and a half. This second version had several modifications. The first was that the buttons were SUPER easy to reach, and the second was that everything was thicker. I did print one back piece with hexagonal cutouts for nuts just to entertain the idea again, but it felt forced and didn't look that great, given that I wanted to keep the case as compact as possible.

 This time the plastic in the machine was not black, but red!

After using the case for a few weeks and completing finals for fall 2012, I realized that I hadn't got any gifts for most of my friends for their respective winter holidays. Like any clever, financially broke engineer, I printed them iPhone cases with a little bit of personalization to make it seem like I put some effort into their gifts. (Boy, did I fool them...) Unfortunately, several weeks later one of them reported a four foot drop onto a tile bathroom floor which spawned a crack in the top. This quickly propagated inward and the upper left joint came loose. Just today, the other friend sent me a picture of his mutilated phone case, which had suffered similar failures. I'll take this time to say that my 'V2' case is perfectly fine and has survived several drops, albeit not onto tile floors. 

Tile floor: 1
  Case V2: 0

Bear attack.

Regardless, this motivated me to design version 3, which made the top piece significantly thicker and changed the structure of the side on the front only. The left side now appears to be whole from the front, but has a chunk cut out so that fingers can easily reach buttons from the back without sacrificing structural integrity.

So there you have it. We'll see how this iteration fares in the real world and I'll update the post with changes. Side note: several people have suggested that I try to mill this out of a stronger material, such as polycarbonate. This sounds like a good idea and wouldn't be too difficult to do in theory. This might happen. Hmmm.

Thursday, January 24, 2013

Noble Six Helmet

Wow, it's been a really long time since I've updated this, mostly because I've been busy recovering from an appendectomy and pretending to be musical. A few posts ago, I mentioned that I was making something for a friend's birthday. That thing was my short-lived adventure into the world of prop making. Basing my designs off of those from, I created laser cuttable files for Noble Six's helmet, from Bungie's Halo: Reach. I replicate the pepakura build in AutoCAD and cut the shapes out of 110 lb cardstock. The designs ended up on 11 sheets of the stuff, and took about two hours to cut, including setup. I still have most of the ream of cardstock. As a joke, I printed an essay on it, but have found no other use for it.

Guided by the original files in Pepakura Designer, I made a few of the major pieces, and then gradually glued them all together. 
Note to those thinking about doing this: hot glue is strongly advised because of the quick set time and the ability to heat it up again if you make a mistake. Keep plenty of glue on hand (I went through about a dozen of the small sticks in the process) and give your glue gun a break every so often - the handle on mine got pretty hot after a while.

Next in the process was the fiberglass and bondo. I used fiberglass mat and resin on the inside for structural integrity (bonus: itchy fingers) and bondo on the outside to smooth out the fairly wrinkly paper, add some bulk where needed, and hide errors.

Fiberglass. Note to self: use cloth next time; mat sucks.

I just realized that I don't have a picture of the helmet after I sanded down the whole thing. Oops. Anyway, the next step was painting the thing. The order of coats are 2X black matte, 2X silver, 2X blue, and finally black on the back and the visor perimeter. Painters tape was used to section off different areas that didn't need to be painted after a certain point, such as the visor. Vaseline was applied in 'swaths' to imitate scratches from battle.

Second coat of black. Nice and thick... and drippy.

First coat of silver.......... right.

2X silver.

Blue (as per Ben's character in the game)

It's a lion.


Bonus ALVIN.
So at this point you're probably thinking something along the lines of, 'That came out pretty well for his first shot at making a prop from a video game, but how the heck is he supposed to see out of the darn thing?'

I was thinking that too; I'm glad we're on the same page.

At The Saturday Thing sometime in the fall of 2012, I got around to trying to make a visor for the helmet. This was supposed to just be practice, but I sorta decided it wasn't worth the effort to do it again. I started out by cutting out the silver chunk and making a frame/jig that I would use to press the acrylic piece into place. I used a heat gun and a large PVC pipe to make a rough bend in the acrylic, pressed it into place with the jig, and glued it into place. Not perfect, but it'll do.

The visor-hole and rough cut/bend of the acrylic piece.

This took a long time.

"So thats our new number Six?"
So there you have it. I have another blank helmet in my garage that I built on a whim, thinking I would have the time to make another helmet. I may try to do something with it, or it may just sit indefinitely.

 I have a few more posts coming soon, mainly something about a phone case and some really tiny things. Happy reading!