Archive for October, 2007

 

Fridgehack, part I

Oct 28, 2007 in Project Build Reports, Stuff

I had planned to go to Micro Center on Friday afternoon seeking some hardware upgrades for the Chuxx0rb0x. The weekend was here, and I had to get something done besides sit around on Facebook while sipping fine Mountain Dew and doing problem sets. Since the magnets and bearings for Snuffles Reloaded hadn’t arrived yet, there wasn’t anything to do on that. Then I realized that the mutant minifridge plan won’t take that long and would actually be mildly useful, given that said minifridge in its stock condition wasn’t exactly very cold. I grabbed my calipers, some paper, and a pen, and zipped off to Micro Center, 20 minutes away by foot (there’s one hell of an incentive to get SR done).

One look at the colorful selection of CPU temperature maintenance products told me that no, I was not going to afford at least two of the biggest, flashiest, most obnoxious cooling rigs, which I had planned for the hack. Therefore, I had to spend an hour balancing practicality with obnoxious flair. In the end, practicality and utility won, like it does most of the time with me.

But, it only wins until I can get some of these suckers (blowers?) and upgrade everything else to go with it. It’s alot more expensive in-store. In addition, one of the qualifications is that the bottom contact plate must be at least 40x40mm in order to fit over the entire Peltier device on the refrigerator – or be easily wrangled to do so in the form of adaptor plates or machining. Many of the large heatsink/fan assemblies had very small contact plates, meant for the CPU only, which would require intensive modification to work with the Peltier device.

The looks I got from staff while huddled over big CPU coolers with a caliper measuring things and jotting notes were… well, I suppose priceless doesn’t work here, since most of them cost $50 or so.

“Sir, may I help you?”
“Thanks, but I’m collecting engineering data. I’ll put everything away when I’m through.”
“…….”

After browsing, I settled on a new plan. I wanted to see what could be done with minimal additional hardware.

This could have been as simple as getting higher-speed fans and modding the power supply, but I did want to replace one thing.

That’s the tiny aluminum structure on the inside which is the “coldsink” of the heat pump assembly. It attaches to the Peltier device, sandwiching it between the outside heatsink and itself through an aluminum block spacer of sorts. The two beige things are plastic-mounted nuts. This was just so disproportionately small compared to the outside heatsink that I though an upgrade was necessary.

I ended up leaving Micro Center with a 120mm fan, 80mm fan, and a conservatively-sized Pentium 4 cooler which happened to be all-copper with a flat copper slab as a base, perfect for this application.

Taking everything apart for chopping and screwing. The Peltier device is a common enough one such that I could get more on the surplus channels and “stack” them for more temperature differential later on.

I also had a look at the temperature adjust switch. The pot and thermistor board were firmly glued to the plastic covering, so I couldn’t look directly at the circuit. Staring at the PSU board long enough with a voltmeter let me guess that the power output was controlled by voltage through an op-amp on the board itself. The NTC thermistor and “temperature adjust” pot worked together on opposites of a voltage divider circuit. Lower output voltage (higher ambient temperature on the thermistor, or higher resistance on the pot) drove the PSU harder, increasing heat throughput. The voltage seemed to vary from 1.2 to 1.9 volts (outside, room temperature), and in normal operation with the pot set to “max cooling”, was about 1.4.

For the sake of overdriving, I switched out a 20K resistor attached to the pot to 12K. This wasn’t very scientific, and the value was selected based on guess-and-hope. However, experiments found that the output voltage at max setting was now around 1.0 volts (room temperature). This would be higher if the ambient temperature was colder.

While I was playing with the power supply, I took the opportunity to remove several power resistors that were planted right by the outputs, presumably as a form of current limiting. This means the PSU was even closer to meltdown than before, since it now had the opportunity to deliver to the components without the crippling effects of P=I²R on the power resistors. It didn’t concern me that much, since the only major power-sucking things on these are the fans – the Peltier device is directly attached to a 12 volt output.

The fans I got were some Antec things which, curiously enough, were not LED fans even though they were clear. They were, however, 3-speed, selectable by slide switch. These 3-speed non-LED fans were less expensive than the 3-speed LED fans by a fair margin, and had significantly higher throughput than the plain LED single-speed fans. I wasn’t about to pay Antec an extra $10 to wrap some LEDs around it, so I decided to do it myself. Economists would cry at such a waste of labor optimization, and while I could be doing something better besides soldering LEDs, that $10 would go so much better towards lunch for the next few days. I also have something like 500 LEDs.

The 3-speed feature was superfluous and a flagrant violation of my life philosophy – that if something is clear, it must be glowy. I locked the fans to the highest speed setting internally and used the spare clear-insulated wire for glowy hookup.

A little bit of heat helps the adhesives set, so I stuck the fans on top of the radiator for a little while.

Modding up the Pentium 4 cooler. Even though it had a broad copper base, it was just narrow enough to not fit a set of tapped holes for the through-bolts which hold the heat pump assembly together. I had to slam this on the mill at the Media Lab and carefully carve out these indentations to seat the little flanged nuts.

Clamping onto thin sheets of metal and milling using a 1/2″ endmill was an adventure I hope to never repeat, but it was disaster-free.

After wiping the surface down with thermal compound, I stuck it back on the inside and spun up the fan for a test. This one looks fine.

The outside fan is attached with clampy-screw things and now almost covers the entire external heat sink area. I wanted to mill cross-channels into the aluminum heat sink to increase the surface area more, but couldn’t find a narrow endmill. It probably doesn’t matter much in the long run anyway.

Ahh, color over-saturation. At this point in most projects is where I ditch elegant and planned engineering for something spontaneous that works. Here, some duct tape acts as a windguide and directs air from the heat sink over the electronics, which, running everything at over 100% capacity, kept me from getting close out of fear of explosion.

Blocking the side vents means air can only escape from the top vents, right over the electronics. It’s a form of active-passive cooling. The 120mm fan fills the entire indentation in the original sheet metal back like it was supposed to be there or something.

The result looks very much stock, which is what I was going for. Only when the lights turn off does a radioactive blue glow project onto the back wall.

Final cost: $38 for the fans and cooler assembly, throw on a little bit for my time, and add $65 for the original appliance, and I could have just bought a much better performing product, but that’s not fun at all!

Performance is better – it gets down to temperature much quicker for certain, but I haven’t taken a thermometer to it yet. I didn’t take a thermometer to the original either, and so any judgement in temperature difference is purely subjective.

It isnt’ quite at the liquid nitrogen level (that comes later), but it’s enough for now and satisfies my desire to not leave any appliance stock and untouched and any warranty unvoided.

Semi-mutated Minifridge gets its own project page soon!

Map shenanigans!

Oct 27, 2007 in MIT, Bostoncaster, Cambridgeshire, Stuff

On a whim, I decided to check out the MIT campus on Windows Live Maps, something which I haven’t ever used before. What amused me the most was the “bird’s eye view” pictures, taken with the camera not pointed straight down, so the buildings had an illusion of depth.

Now, I understand that imaging companies don’t update their archives daily – and this is to be expected, unless someone has corporate-level OCD. Some times, though, the images are from years ago. Google Maps seems to still think the Walmart near where I lived in Atlanta (built in 2002) is still a dirt lot.

When you add in multiple-angle views to the situation, some times things get a little weird.

Let me direct your attention to the Stata Center, one of the examples of innovative architecture (or unarchitecture, depending on who you ask) on campus.

Repeat after me: THIS IS STAAAAAAAAAATAAAAAAAAAAAAAAAAA

This picture was probably taken in late 2003 to early 2004, when the building was in the last phases of construction. This was okay – Google Maps just shows a big construction-equipment-littered mess, even now.

However, as soon as I scooted north a bit, half of it disappeared.

Rotating the map to face west, it seems to be in a different phase of construction.

 And moving a bit eastward (farther away), it seems to be slightly different again.

The observant will also notice something missing in the previous 3 pictures that was present in the first: the large white-draped building across the street. That would be one of the newest buildings, the Brain & Cognitive Sciences center.

The direct overhead view is the most recent, as it shows both buildings completed. The brain-surgery-like covering over the B&CS is, of course, gone.

Something that matters… kinda.

Oct 26, 2007 in MIT, Bostoncaster, Cambridgeshire, Stuff

Over the past few weeks, I’ve been working with the MIT Smart Cities group as an undergraduate lemming. However, in stark contrast with the horror stories of some of my fellow lemmings with positions in other departments and labs, my job freakin’ rawks. So does the whole Media Lab, in fact. It’s right up there on my favorite places on campus list, right next to the Mexican fast food place. I get to do what I do best – think of things and then build them.

Anyway, I’ve been specifically working on the light electric scooter/motorcycle doohickey, something all -3 of you who read my site should recall me talking about some time in early August. The responsibility of the group here is to create a display stand for the most innovative component – the self-contained in-wheel motor-suspension-et-cetera “wheel robot”.

AHH! It’s a wheel floating in midair!

Actually, the mount for the thing is just clear Lexan. Here’s the upper half of the display stand.

The “wheel robot” close up. The motor is a 600W brushed unit that cogs like a beast – indicative of beastly torque. The actual production model, according to the bigwigs, will be brushless. This I like.

The display stand case, painted “flat institute wall white”. LCD flat panels will fit in the rectangular gaps and interface with a PC on the inside to play boring presentations.

Here’s my main contribution. This unit mates some motor controllers, buttons, blinkenlichten, and an Arduino embedded controller to run both the drive motor and the suspension actuator (the coil-over shocks are replaced with small linear actuators to show the multi-link suspension movement). The Arduino takes button inputs and controls a Victor 48HV and Scorpion XL. It’s all smacked onto a piece of scrap Lexan, which somehow fit perfectly in a convenient location and was selected for the job based on this.

It can be seen running the show in one of the above pics.

Anyway, since this will be going to the Milan Motor Show in a few weeks, the next few days will concentrate on testing and generally beating the shit out of it. Because I’m not going to be in Milan, and therefore it cannot break. Ever. Ever, in this case, is defined as “Not until we get it back here”.

The display stand ships… in a few hours, which is why I went in to help out and to finish this off. After this is all done, there will be more exciting things to come.

It’s not just Battlebots any more.

Oh, and if you’re in Kendall Square any time soon, do not stand here.

A challenger appears!

Oct 25, 2007 in Project Build Reports, Project RazEr, Stuff

Actually, it’s been around for a few years. Here’s a neat video showing the Motorboard 2000XR, which is a compact electric scooter with 1KW drive power and A123 batteries. And it actually looks controllable!

I think I could do one better technology-wise with non-friction drive in the form of Snuffles Reloaded. I’m also going to log all final costs including machining estimates to see if it ends up under $800. Even though most of this is for my own shits and giggles, the cheap plastic gears in my brain are starting to turn a bit…

Snuffles Reloaded: Update 3

Oct 22, 2007 in Project Build Reports, Project RazEr

After browsing and consulting with the folks on RCGroups more, I decided to (once again) modify the (supposedly) final design for the wheelmotor. The tweaks increase the virtual gearing inside the motor by about 20% and also makes winding much easier.

I have to lock myself into a design eventually, otherwise nothing will ever get built as I continually update little things here and there. Therefore, I took the opportunity of a gap in the work scheduling to hop on the Media Lab waterjet with some thin steel sheets and erode myself some new 30T stator plates.

These thin steel formations are probably the most elegant things I have ever cut out of anything. The waterjet is officially my new favorite manufacturing implement.

With the change in number of stator poles comes a change in the required magnet dimensions. I emailed the people at Supermagnetman, my usual source for neo magnets, to see if they could assist me with manufacturing a set of custom magnet segments that will fill up the available magnet ring space 100% with no finicky spacing, trimming, or selective application of epoxy. We’ll see how that goes, but 40 5mm wide, 3mm thick magnets also fit well.

I split the 3D model for the “motor can” into three parts, from two. The left and right hub plates/bearing holders are now identical and symmetrical, so two could be popped off quickly on a CNC lathe. The magnet ring mount, which used to be integrated with one of side plates, is now its own structure. It is quite literally a ring.

Meanwhile, I have also been fiddling around with “internal logistics”. That is, how to squeeze all the necessary parts into a space about 40% of what I had to work with while building the first scooter. Here’s a picture of the new “conversion base”, a Razor A3 I ganked off EBay, as compared to Snuffles 1.

6061 > Shitluminum

The wheelbases are the same, but the aluminum extrusion that forms the chassis of the A3 is half the height of the same on Snuffles 1. This means no more shoving a stack of big NiCd cells – they’re simply too big.

The hope for this build lies in lithium polymer cells, of which 6 4AH cells fit just right in the back two-thirds of the channel such that enough space is left for the controller and wiring.

I’ll get to the juicy parts later.