The Complementary Filter for Dummies

For 6.UAT (Undergrad Presentation Class), I had to give a talk to high schoolers about some technical subject. Since BabyCopter and Segboard both need to measure angle, I talked about the complementary filter. Here is my lolzy presentation. I tried to put it on youtube to preserve my multiple animations (a picture's worth a thousand words, an animation's worth ten thousand). If it's too fast, spacebar is your best friend.

Things That Are Entertaining :P

Term started (booooo) but I'm pretty excited about classes :D I get to take another lab class from my favorite professor so far, Steve Leeb, but this time on microcontrollers (6.115). I've had some experience with Atmel products, but only at a high level. Most of it was attempting to write C/developing Arduino boards at the Media Lab. Arduino actually uses Atmegas, both 168 and 328 chips. However, most of the programming is an Arduino developed IDE which basically uses pseudo-Java (Processing). Now I'm writing in Assembly, a low-level machine language. The last time I touched Assembly was during 6.004 where everyone makes a beta processor. However, that's written in wannabe Verilog, and you don't write in Assembly until like half-way through the semester.

Anyway, what I've learned so far is that stacks are hard and you can't mess with them too badly or else all the sadness happens. :(

I miss compliers SOOOOOO MUCH.

Also, I twerked segboard again for MIT Techfair. Check out some video of its new lolzy wireless remote.

Did you know that the interfacing with wireless wii nunchuks depends a lot on the nunchuk? Different brands will have different communication setups, so that really, really, really sucks. However, there exists a good amount of documentation in case you run into trouble. I used a Nyko Kama Wireless Wii Nunchuk for segboard.

*Sigh* Now back to my daily amount of Institute hosage.

Seeya.

First of the Year!

Well, Segboard is finally happy enough I feel relatively safe riding it. Working on turning and more safety controls. Check out me riding it. :P

I Hate Motor Controllers (The Journey of Segboard)

Well, I suppose I kinda failed on the updating more regularly part, but oh well. My apologies. Finals and final projects tend to suck the life out of you. Anyhow, I wanted to give you all an update on Segboard (for which I'll be redesigning the power electronics this winter break).

Here is my first and happiest video of Segboard functioning. 

My friend Charles taped this better version while I was frantically taping a crappy version with my Ipod. Props to Shane for test riding it. Also I super love my tights here. You can get them at Urban Outfitters for $10.

However, there is one catch. This test was done with a commercial motor controller from Pololu. Yup, this is not with my janky home-made motor controller. You see, what I hadn't predicted was the pain and suffering of transforming theory into reality. 

And boy does that pain suck.

Problem 1:

I AM NEVER ETCHING A MOTOR CONTROLLER EVER AGAIN THERE IS NOT ENOUGH  COUTURE IN THE WORLD TO MAKE ME UGH!!!!!!!!!!!!!!!!!!!!!

Some of you might know the process of etching printed circuit boards (PCBs) with ferric chloride and toner paper. Some of you might've seen my post about it. Some of you might even think it's a good idea. Well, it is - but mainly for some things. Like small microprocessor breakout shields or something tiny and not high current. DO NOT ETCH SOMETHING HIGH CURRENT OR YOU WILL HATE YOUR LIFE UNLESS YOU ARE A GOD[ESS] OF ETCHING.

You see, etching can be fun in some sense. 

Here are the steps for normal boards:

Step One:

You sandpaper some copper board.

Just as you'd put on primer before applying eyeshadow, sanding your copper is like the same thing. You want a clean copper plate for the toner to stick onto, so sand and acetone that sucker. Also sanding will make your toner stay on more robustly, like preventing eyeshadow creasing. Do this about 5 times. 

Step Two:

You iron your circuit board toner print.

I'm really digging coral right now. I tried this coral nail polish from OPI,  but my skin tone looks weird in this picture. 

This part takes a while. You kind of stand there like a wife from the fifties, except instead of ironing your husband's shirt, you iron your circuit board. Note: Both shirts and PCBs burn, so watch out. 

Step 3:

You somehow remove the paper backing. 

This part is a real pain. The paper doesn't always come off nicely and you have to wait until you can rub it off with your fingers. Also you might rub off the toner, so then you cover up the broken traces with Sharpie (which really works). 

Step 4:

You let it soak in ferric chloride until all the excess copper is eaten away. 

FYI this is one of my worst etchings. The more you make, the better they get.

Step 5:

Drill the component holes and populate the board. Tin the ground plane if so desired.

It looks so innocent, doesn't it?

Theoretically, then you're done!

... (Yeah right)

As I've said before, ETCH HIGH CURRENT BOARDS AT YOUR OWN RISK. DEBUGGING THIS WAS THE WORST EXPERIENCE OF MY LIFE. Want to know why? At high currents these traces have a tendency to pop. THEY WILL LITERALLY EXPLODE. And then you have to look real hard at the back and do all the continuity checks. In addition, solder connections can be weak if you mill out the holes just a little too largely, there can be microscopic breaks in the copper, Gremlins might like your board for some reason, etc, etc. ALL SORTS OF PROBLEMS EXIST IN REAL LIFE. 

Unless you're making a relatively small control board or else have RIDICULOUSLY THICK copper traces, DON'T DON'T DON'T DON'T DON'T etch motor controllers. Just send them out to 4PCB or Gold Phoenix. It's worth the money, I SWEAR.  

Problem 2: 

MAKING A GROUND PLANE IS NOT ALWAYS A GOOD IDEA. 

That ground plane (the big piece of copper that surrounds my traces) was the cause of so many inadvertent shorts and mishaps and UGHHHHHHHH.

If you're doing some sensitive analog controls stuff, having a ground plane reduces the amount of noise on your chips. This is good because you get more reliable logic. However, with something big and clunky like a motor controller, a ground plane is not so great (especially on a homemade board) because when you short your entire board, you blow out a number of things you don't expect. 

I'll alter this statement a bit. If you had your PCB professionally printed, then maybe a ground plane is good, but if you etch your own YOU'RE PRACTICALLY DOOMED. 

Also watch out for ground loops. They will make your controls quite sad. 

Problem 3:

Regenerative breaking is hard. 

Courtesy of "How Stuff Works"

I'm pretty sure a lot of you have heard about regenerative (regen) braking. It's used in a lot of new electric and hybrid vehicles. Essentially, what happens is that when you brake, your wheels are an input of energy (basically a generator) back into your batteries.

I designed my motor controller to use synchronous rectification (basically an H-Bridge) to run my motors. (Note, please looks these up if you don't understand the terms, that's half the fun of learning!) While I thought this was hella-baller, I didn't design anything for the regen that I hadn't really planned, leading to DEATH, DEATH, BLOODY MURDER, DEATH. 

Essentially, this happened each time. 

I would test my motor controllers on the power source with a PWM signal from a micro, it would look fine and work wonderfully. Note, there was no hard braking performed.

I would attach motor controllers to Segboard and then, as I was braking, DEATH OF EVERYTHING AHHHHH WHY ARE MY MOSFETS DYING?????????

Anyway, I figured out why my FETs kept dying. When I was braking, I was regen-ing back into my batteries. However, because my motor controller hadn't been designed to either short out that regen or else somehow bridge it back to battery, my FETs kept avalanching and my voltage regulator died. The voltage regulator (24V to 15V) gave it away. My awesome boyfriend Joe had worked with high-power LED controllers before and had witnessed voltage regulators failing. Apparently they really only die by one thing - the output voltage being greater than the input. This lead to the regen Ah-Ha! moment. This also lead to the fastest and jankiest demo-fix ever as I soldered a diode across my regulator to take the regen braking and them demo'ed a somewhat working Segboard for my power electronics class. Surprisingly, it worked well enough to show it functioning, and that's what really mattered (for that class).

I only kind of hate you. JK! <3

In the end, I've learned a lot. One: theory != reality. Two: Friends are the best thing ever. If they hadn't kept my sanity, I would've just been a lot sadder through this whole ordeal. Anyway, this is just an update of Segboard for now. Like I said, I'm planning a total redesign during winter break (just for fun, not for any class). I can't wait until I ride across campus as MIT's most chic engineer! That should be entertaining. :P

Happy Holidays and Happy New Year!

XOXO

Jordan

lolboad frame

Not quite done (needs 2 chains and some trimming on the rod and some shaft collars), but it definitely fleshes the project out :)

It's also entertaining to see a skateboard on the mill (I drilled holes for the motors and wheels). I also got to lathe for once! The spacers from the wheel assemblies were a little too long, so I trimmed them. Lathes are definitely the most scary of all the machine tools. Not sure why though. Probably because it looks like an angry spinning monster of death (and it spews the most coolant on me).

Now for all the code, code, code, cooooooooooooooooooooode............

Motor Controller Etching

I'm an h-bridge! :D

Etching is gross and fun :P I've etched a prototype of one h-bridge of Segboard's motor controller to test. I like etching because it's much faster than ordering PCBs (which takes like 2-3 days for shipping and stuff). Also etching is much cheaper. The only problem is that it's pretty messy if you're not graceful (ferric chloride stains your hands and clothes) and your board isn't the nicest looking thing. Oh well, I'm cheap and in college.

I look nice in theory!

I look gross in reality!

Gonna test over Thanksgiving. Yaaaaaaaaaaaaaay!

Power Electronics + Segway Skateboard Motor Controller!

Here at MIT, one of our lab classes is Power Electronics (6.131). It's taught by Prof Leeb who's just a bit crazy in the best way. We learn a bunch of basic power management design, (your typical Buck, Boost, and variations) along with some motors. It's my first lab class, and I must say THIS IS MY MOST FAVORITE CLASS SO FAR. Please, please, please if you come to MIT, take 6.131! The thing that bothers me the most about the majority of my classes is that they're all pretty theoretical. I like to make things first-hand, and looking at a bunch of math which doesn't relate to any physical system bores me. 6.131 is the complete opposite. You make the systems you've learned from lecture, which involve lots of building! It's unbelievably satisfying seeing your lecture material turn into a real object you've hand-crafted. But anyhow, I'm getting off topic from what I really want to rant about.

For 6.131 we all have a final project. In fact, it's one of the reasons why I wanted to take this class. I've done more microprocessor projects before, but I've never touched high-power much. For my final project, I'm making *drum roll* SEGBOARD!

You're probably going to see several posts about Segboard soon. Segboard is basically a segway skateboard, based off of the one created by XenonJohn. However, I'm making my own motor controller which changes things up. Not only is my software going to be a bit different, I'm going to have to debug a motor controller. Regardless, physically Segboard should look similar to XenonJohn's.

As some of you might know, my main research deals with wearables (what I like to call fashion engineering), and one might wonder how a segway skateboard has anything to do with that. Well, an addendum to this project is a wearable UI. In order to turn on Segboard, the duty cycle for each motor has to change accordingly, and while this turning mechanism has been implemented with controllers, I want to make a wearable one. My two main ideas for how to do this is through a glove or some kind of jacket, but that's later on (I'll probably first implement Segboard with a hand controller that isn't a true "wearable").  Anyway, I haven't seen many "high-power wearables" (even if through a UI), so I think this could be an excellent example of fashion engineering without LEDs :P This project is legitimately what some might call "hardcore".

I've only the motor controller schematic (below) made now, but I thought I should put it up for fun. Plan for lots of drama, joy, and electronics in the future as I desperately try to finish Segboard before the semester finishes. We'll see if I make it!