Archive for the ‘Show-n-Tell’ Category

Alex sanding the boat, early in the process.

Alex sanding the boat, early in the process.

Last weekend, Jeremy, Wim, Alex, and I got together to paint the Hackerboat. The original plan was to get it all done during daylight hours last Saturday... but the filling and sanding steps took much longer than anticipated, so we only got to primer. Just that made a major improvement in the boat's appearance ahead of MakerFaire next month.

The paint I bought for the job was Blue Water Mega Gloss topside paint. It's a single-part polyurethane marine paint. Since this iteration of the Hackerboat won't spend long periods in the water, we're going to do the whole thing with topside paint. It's not too horribly expensive -- about $18/qt. I want to paint the boat safety orange (so it can be seen easily), while Wim would like to paint it with dazzle camo. So we compromised on safety orange and black dazzle camo. I picked up one quart each of black, bright orange, and white primer.

The polyurethane paint is supposed to be very thoroughly mixed before use. Wim and I, in a bout of optimism, stirred both the primer and the orange paint. When the orange paint dried on the stir stick afterwards, we discovered that Blue Water's color department believes that ketchup is bright orange. I hope it will look more like orange over primer, but I am not all that hopeful.

The fiberglass work we did on the hatch coamings a couple of years back was pretty rough, so the first order of business was to get it filled and sanded. We went through about 3/4 of a gallon of Bondo getting the topsides in somewhat paintable shape. We probably could have used the rest of the gallon, but it was getting late and we wanted to get the primer on before the end of the day. There's not much description here because the tubes are full of tutorials on how to do this and it's not the world's most interesting work.

Bottom primed

Bottom primed

Once we'd gotten the last coat of Bondo on the boat, we immediately flipped it over to sand and prime the underside. This was nice and uneventful, and it made the bottom of the boat look less busted immediately.

The can of primer had led us to believe we'd be waiting a couple of hours before we could flip it over and finish sanding the Bondo. This turned out to be very pessimistic -- the first primer we laid down was dry to the touch by the time we were done priming the boat. We still waited half an hour (and time for a picture) before flipping the boat.

Wim and Alex priming the boat.

Wim and Alex priming the boat.

We masked off the hardware we couldn't remove and primed the topsides. It went on as quickly and painlessly as the primer on the bottom, and was mostly dry by the time we finished the coat. It took about 3/4 of a quart can to do the whole topsides. I think this is because we did not thin it; however, it is clear from that experience that we will have to thin the orange paint if we want to get two coats out of the can. We'll do the stripes in black over that as a third coat.

The boat looks better even with just the fill and primer; I am looking forward to finishing up the paint job today.

Filled and primed

Our launch last fall proved that the Hackerboat hardware was working fine (other than the GPS) but that the software needed a complete rewrite. We've been working on that for the last few minutes. Debugging is a bit on the slow side, but we anticipate being ready to get back in the water in the next couple of weeks. We will be at both MakerFaire Bay Area and Toorcamp with the Hackerboat in tow. This weekend, we're going to put some paint on the boat to it looks a bit better in preparation for the next launch and for public show. There will be pictures! But let's talk about the systems in preparation to talk about the software.

The current electronics configuration of the Hackerboat has a bit of a Rube Goldberg quality. The underlying intent is to build a system out of relatively small modules that can be added to without major hardware surgery. Here's a schematic diagram of the various bits and pieces. Dark red is power and power control, green is computers, yellow is propulsion, orange is communication, blue is sensors, and purple is non-propulsion actuators.


The first thing to notice is that we have two on-board computers -- a Beaglebone and an Arduino. The intent is that the the Arduino will handle all of the low-level real time functions while the Beaglebone handles all of the higher-level navigation, obstacle avoidance, and mission functions. Among other things, the relatively more power hungry Beaglebone can be put into a low-power sleep mode for extended periods, especially while in the open ocean. On the flip side, we can use the Linux environment and fast processor on the Beaglebone to support all manner of cool navigational modes and mission applications.

The communications is likewise a layer cake. Our ship to shore radio is a Ubiquiti 900 MHz Ethernet bridge. The shore side radio has a directional antenna built in to the radio and the ship side uses an external antenna on the mast. For internal data on the boat, we use a standard WiFi router. This means we don't have to futz with waterproof Ethernet cabling (expensive and troublesome)... and we can add new equipment to the boat for the cost of a WiFi interface.

Right now, the sensor fitout is very basic. We have an IMU/magnetometer combo for heading, a GPS for position, and start/stop buttons on the outside of the boat. We're planning to add cameras next, and of course we have the option to mount any sort of instruments we like for mission requirements later.

Next update will be painting, and after that I will get into our software architecture.

The Arachnio is something I've been working on for a few months, and it's now up on Kickstarter! The subject line is the elevator pitch -- it's the first Arduino Micro variant with onboard WiFi, via the increasingly popular ESP8266. It's pin and software compatible with the existing Arduino Micro, and only slightly larger to accommodate the antenna. Naturally, it's entirely open source (unlike other Arduino variants with on-board WiFi, such as the Yun).



The Arachnio

The Arachnio

Putting WiFi together with the Arduino, especially in a small, low power package, is a really natural fit. For example, every Arduino-powered robotics or LED project is made immensely cooler by having the capability to control it from your smartphone baked right in.

Since the Arachnio is small and low power, it also makes a great brain for a remote sensor. The fact that it's an Arduino variant makes the programming simple and the wealth of on-board peripherals make it straightforward to connect most common sensors. WiFi lets your remote sensor connect to your phone or tap into the Internet to get the data back to you.

Including both the ESP8266 and the 32u4 on a single board provides a much more useful package than either one alone. The capabilities of the ESP8266 and the 32u4 complement each other nicely. Here are some of the advantages of the Arachnio over an ESP8266 module alone:

  • More GPIO -- The Arachnio has more than twice as many GPIO pins available as any ESP8266 module.
  • More ADC -- The Arachnio has twelve usable analog to digital channels versus a single channel for an ESP8266.
  • Hardware PWM
  • Dedicated hardware I2C and SPI interfaces
  • Full Arduino library compatibility 
  • Native USB -- The Arachnio's ATmega32u4 provides a full speed hardware USB interface. The Arduino environment provides libraries that make the USB function as a serial port, a mouse, or a USB keyboard.
  • Breadboard compatible -- The Arachnio's headers are on 0.1" centers and narrow enough to fit into standard breadboards with room to plug jumpers in on both sides.

And of course the ESP8266 provides WiFi and, for more advanced users, a more powerful processor to use for more computationally intensive tasks.

All of the vital statistics can be found on the Arachnio product page.

I decided I also needed a couple of expansion boards available immediately in order to really make it sing. The first is of course a prototyping board, the ArachnoProto.

ArachnoProto with Arachnio and supports

ArachnoProto with Arachnio and supports

The ArachnoProto is designed to fill the same role as an Arduino protoshield. It has two large prototyping areas, a programming header,  mounting holes for 3mm screws, two LEDs and a pair of push buttons.

You can tell this is a prototype because the board house managed to mess up my logo on the board.

There's also another less obvious feature here, which is that this board has been assembled with bottom-entry headers on the underside. The upshot of this is that the assembled Arachnio + ArachnoProto is much thinner than with conventional headers. These headers are included with every ArachoProto.

The Arachnode is designed to give users a way to quickly build flexible and independent sensor and network nodes. It has a solar battery charger, a real time clock, a microSD card slot, and an optional crypto module.

I just got a new release candidate board which has some tweaks arising from the testing we've been doing, mostly to improve fit and clearances. This is the first one that's really feature complete, since I've been focusing on the Arachnio rather than the Arachnode for most of my development. I haven't had time to assemble the new ones, but here's the bare PCB:

Arachnode bare board

Arachnode bare board

One of the things I've enjoyed doing that I wish more Kickstarter creators would do is post Instructables for the Arachnio. I've only got two of them up so far, but they address questions that people have asked me about using the Arachnio.

Please don't forget to back the Arachnio on Kickstarter so we can make it a reality!


Thanks to gorgeous weather here in Seattle yesterday, I was able to get some great pictures of the ArachnoProto and Arachnode prototypes.








In our last post we discussed the goal and methods around capturing the birefringence found in frozen soap bubbles.   The good news is that we established a solid method for capturing birefringence, but so far have yet to see any real noticeable birefringence on soap bubbles.

Along the way we did capture some amazing photos of soap bubbles in several different states of frozen, and finally just shot some images of just ice crystals forming.  We have some videos of the growth of crystals which we might post later.

In order to capture images such as these, you need to polarizing sheets.   One covers your light source (flash, led, etc), the other over your camera. It is important that the polarizing sheet is the last optical element before the subject you wish to photograph.

First, more photos of "ice crystals we really wished showed birefringence ".  We have a few theories about why this doesn't work (including: thin film from glycerine causing scatter, too many layers of ice, etc).  At this point it's still unknown, any comments welcomed!  The good news is that the soap is showing it's lovely colors!

Well, that sure was neat, but we didn't really get the birefringence in water crystals we wanted. So it was time to just try old fashioned ice crystals and liquid nitrogen. The results where spectacular:

Here's where it got interesting. By rotating the polarizing film different parts of the crystals would show birefringence based on the changing angles interacting with each other.

Frozen bubbles!

Posted by 3ricj on 3 February 2013

Transparent solids can show birefringence when they are under mechanical stress. This stress can be present in a part after it's manufactured (in the case of plastic) or present due to thermal expansion. You can view these birefringence patterns if you view it between two crossed polarizers.

These patterns can also be found in ice. I decided, on a whim, that would attempt to photograph birefringent (cross polarized) crystals in frozen soap bubbles. This is what is hopefully going to be short set of posts with attempts to do so.

For starters, making frozen bubbles has it's own challenges. When air cools, it compresses. This would likely lead to a fracture of the bubble. The first attempt to make frozen bubbles confirmed this - if you inflate a bubble using (warm) air from your lungs, it pops the moment it gets close to something cold. In this case, we tried this with a pool of liquid nitrogen - -  it fractured well before hitting the liquid. We did manage to make some 'broken half bubbles', which floated around on the gaseous nitrogen. I don't have any photos of this, but let's just say it didn't work so well. After some trials and tribulations we developed the following method to make frozen bubbles:

  • Take a short (12") copper pipe
  • dip one end into a "bubble solution", adding additional glycerin may help.
  • Make sure that there is bubble solution coating the outside of the pipe; a thin film will work fine.
  • Submerge the other end into a cup of liquid nitrogen.
  • The warm copper will cause a phase change in the nitrogen, which will inflate the bubble with chilled nitrogen.
  • Before it pops, gently shake the pipe such that bubble 'slides' down to the pipe.
  • Take the pipe and hold it carefully over a pool of liquid nitrogen. There will be a thermal gradient there which enables the bottom of the bubble to freeze.
  • With some luck and skill, you can "thaw" and "refreeze" your bubble many times before it bursts.

Here are some photos of our first round of testing.  At the time we didn't have a good setup for capturing the birefringence in the crystals then we ran out of liquid nitrogen!. We will have to try again. On the next post I'll provide more information about how to capture birefringence using a camera.

A nitrogen filled bubble:

Frozen bubbles!

A shot of an old fashioned ice-cube under cross polarization (you can see birefringence!!):


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