2.007 Spring 2012

Like last year, this spring I'm an undergraduate assistant (UA) for 2.007, which is basically an intro to design class that features a robot competition.  Over IAP I helped out preparing for the class.  I contributed a little to the contest table, mostly by painting a few things.  In the end it turned out great, and I think the carnival theme will be a lot of fun!

Robot Carnival!

 As seen above, there are four objects you can interact with in the competition.  At the front is a ticket booth where your robot can press the Easy Button and collect tickets.  On each side is a clown that will be holding a balloon that a robot can inflate by pumping air into a nozzle in the middle.  In the corner is a high striker, where your robot can test its strength and try to ring the bell (hammer not included).  Spanning both sides of the table is the Ferris wheel that can be spun by the robots to gain a score multiplier.

The biggest project I had over IAP was redesigning the kit display board for the class.  Each student participating in the robot competition receives a bin of materials and components at the beginning of the class.  They have to construct their entire robot from this kit throughout the course of the class, so we decided it was important to redo the old display board which was outdated and worn out.  I tried to make it look clean, with functional parts (such as the springs, wheels, and balloon pump), and here's the finished product:

For this semester, one difference for me is that I am going to assisting the electric vehicle section instead of focusing on the traditional labs that participate in the robot competition.  I'll be helping 9 or 10 students design their own personal electric vehicle, such as a scooter or a go-kart.  It should be interesting, so I'll probably be updating any significant progress on here.  Until then I have my own project to work on!

Eli-Kart Design

I like starting posts with shiny renderings.

This is Eli-Kart!  It's a miniature, three wheeled, 2-seater go kart.  Its frame is simple yet robust, and is made up of a 1/2" sheet of clear plexi supported by steel box extrusions, allowing you to see through most of the vehicle.  It has 8" pneumatic tires, Ackermann geometry steering, and a high quality brushless motor controller.  The battery pack is pretty high powered at 39.6V and 7.5Ah which should give me around 15 minutes of fun.  Right now I'm planning on using the same motor I have on 2x4 Scooter, but I'm going to be retrofitting my own custom motor eventually.

Getting more into the details, the steering wheel will be waterjet with the words "Eli Kart" on it, then welded together.  There will be brakes on the back wheel, but the throttle is yet to be determined.  However, both throttle and brakes will be hand operated.  Other parts of the steering mechanism are waterjet and assembled with t-nuts, as you might be able to tell from the picture above.  The controller is a Kelly KBS KBS48121 with the high speed option (allowing up to 70,000 ERPM), and I will probably install external hall effect sensors on my motor so I can control it.

This has easily been the biggest design project I've done.  Luckily, doing all of the designing in Solidworks will make it very simple to build.  Apart from the welding and machining a few parts myself, all I need to do is waterjet some aluminum plate, and order some McMaster parts.  I will be using Eli-Kart in my undergraduate thesis so I'll provide updates when I finish!

2x4 Scooter Build

Ta daa!

I just finished building 2x4 Scooter!  Its mostly functional, although the steering is a tad floppy and the throttle is a bit scary.  From the previous CAD design, I put in a few extra pieces including a piece to brace the wheels and a front bumper to help make the steering more rigid.  I also made the motor mount adjustable so I can tension the drive belt over time.

Most of the body was straightforward.  I cut the 2x4 stock down to size with a radial miter saw.  The hardest part to make was the steering column, which I used a bandsaw to cut down and sanded it with a belt sander until circular and smooth. Using 2.5" wood screws, I assembled the frame with a hand drill (although I wished I had a hammer drill).

Once the frame was together, I had to put together the wheels.  Everything I had came in parts, so I had to press some bearings into the hubs, stuff the wheel with an inner tube, screw the hubs together, and then pump up the tire.  I mounted the wheels on 200mm long M10 screws, which made for a simple axle.

Next I had to figure out the electronics.  First I went to work on the battery pack.  With some help from Charles Guan and some spare A123 26650 cells, I was able to solder up a 8S3P pack which would give 26.4V nominal (the maximum for my ESC) and over 6Ah of charge.  It took me in a few hours to make, partially due to having to hand crimp and assemble the appropriate connectors to balance the cells, but after I shrink-wrapped the whole thing it turned out nicely!

The last part to tackle was the throttle.  Using a force sensor I had leftover from a class, I wrote up an Arduino program to give me throttle control that was dependent on how hard the sensor was pressed.  Its very sensitive, but since I have some other things to work on, I'm leaving it for now.  In the future I plan to fix the throttle issue, make a new drive pulley (the current one isn't centered), and possibly stabilize/redesign the steering.  For now, here's a video!

By the way, I did pretty much all of the work at MITERS, so many thanks to them for their hospitality!

Did I Mention I Like Cars

Last week I attended the New England International Auto Show.  I was pretty cool, and I got 50% off the tickets with Groupon so I went with my girlfriend Alina.  I got to explore/sit in a bunch of new cars and ogle more expensive ones, so all in all it was a good trip.  For example, they had a Fiat 500 Abarth!

Yes, I did fit.  Barely.

There were a bunch of things I liked, including engines, rims, and various shiny things.  They even had some fancier cars such as the Lexus LFA, Mercedes SLS, and my all time favorite the Audi R8 :D

I could barely contain my excitement.

Winter Break

MIT's Independent Activities Period is good and bad.  Its good because there are a lot of opportunities and it gives students a break from regular semester classes.  Its bad because it lasts until February so that I won't graduate until June!  Regardless, I have been making the most of my time recently by keeping busy.  I was lucky enough to spend over a week at home which my family, which included Christmas and New Years.  Despite the festivities I somehow got some work done!

First off, I had to help my dad fix the tire on our minivan.  He teaches a high school auto shop class, so its really cool to see where he works and learn from him.  The front-right tire pressure was dropping to around 15 psi just days after filling it up, so we knew something was wrong.  After a quick inspection it turned out the culprit was a huge nail the van must had run over recently.  As I learned, the way to plug the hole is apparently to coat it in industrial rubber cement and jam a sticky, jerky-like stick in the hole.  My dad told me he's been doing it that way for decades, so it must work pretty well.  Once you let it set for a minutes, you just pump up the tire again, trim the ends off, and voila!

The ends wear off as you drive. Who said car maintenance was pretty?

I also finished up the CAD for my first electric vehicle.  Its not terribly exciting, but the project is suitable for a beginner.  I was inspired by the idea of wanting to make a scooter, but not having the materials or money to make an expensive one.  I present to you.... 2x4 Scooter!

Composed almost entirely of wood 2x4s, it has two 8" wheels, rear wheel drive via a brushless outrunner motor coupled with a timing belt, and I plan on making a lithium-ion battery pack to give it plenty of power.  I'll post the build once its finished!

Alpha Prototype: Cobolt

     That's right, the electronic bike lock I've been working on is done (and underwent another name change)!  Here's a picture of the prototype while opened, with the keyfob in the mechanical backup.

We named it Cobolt to signify strength, technology, and reference its locking ability with "bolt."  Mechanically, the team implemented the changes we needed to make it lock more reliably and securely.  Electronically, I figured out the RF transmitter and receiver bugs and helped program the microcontroller.  In the end, we had a working alpha prototype!  Here's our presentation given in MIT's own Kresge Auditorium, followed by the audience Q&A which features yours truly!

Presentation

Q&A

 

I really like the concept, and I don't think it would take that much more work have it be useable on a daily basis.  Who knows, you might see something like it on a bike rack sooner than you think!

SigmaSecure (Happy Thanksgiving!)

That's right, we had a name change.  Our 2.009 electronic bike lock has made a lot of progress since I last posted.  It's sleeker, more secure, and the electronics are a lot more developed.  Plus, it's no longer just a CAD model! After several weeks of hard work, we got an actual working prototype.  Here are they key features:

• One piece
• Spring-loaded hinge design
• Key-less entry
• Wireless communication via XBee
• Solenoid powered dead-bolt
• Button activated
• Backup key for mechanical override

Check out a few pictures taken at our technical review, along with a Solidworks screenshot:

 

 

 I was in charge of electronics, so once we ditched RFID I decided to go with Xbee.  They turned out to be a very convenient solution with longer range capability.  By having an XBee on a low-power mode in a keyfob paired with an XBee in the lock, SigmaSecure can tell when you're nearby and unlock when you press the button. Even better, you can program XBee to signal when it is communicating with another XBee.  With this, we were able to trigger a transistor to allow our 9V battery to power the solenoid.  Since the XBee runs off about 3V, we simply used a voltage regulator to allow it to run off the 9V as well.

Next, we are looking into either using a latching solenoid or motor powered locking system to prevent some failures related to our spring-return solenoid.  Since the final presentation is only 3 weeks away, we are going to quickly make these last-minute changes so that we can end up with a polished product.

Now, back to the festivities at my girlfriends house...