Crystals

Recently I've been playing around with growing crystals. It was always a fun and easy thing to do when I was a kid, so I thought I'd try some that are more interesting than the usual salt, sugar, alum, epsom, etc. This is recrystalized acetylsalicylic acid, asprin, from OTC tablets. 10g pulverized, washed with cold water, vacuum filtered, then dissolved in 250mL of 75C water and allowed to cool slowly. Crystals approximately 3-5 mm in length. I will chill this and allow crystal formation to finish, then wash the crystals and recrystallize at a slower rate.
This is benzocaine, extracted from Oragel tooth gel. 0.5g of gel stirred in 15mL cold water until dissolved. Benzoncaine will form white flakes. Centrifuge and draw off supernatant. Add 20mL water and heat in hot water bath. A bead of molten benzocaine will form. Add sufficient water to dissolve the bead. Allow to cool and crystallize. Vacuum filter and collect for recrystallization.
This is what I think is probably salicyclic acid. 1g of OTC tablets, pulverized, heated in 20mL water until dissolved. When cooled the entire 20mL formed one huge crystal block, which was amusing. Melted again, added 10mL water and heated until acetic acid formed. Cooling produced fine, hair-like crystals, which I suspect are salicyclic acid (more research to do). Washed and vacuum filtered, will recrystallize to see if more pure crystals look different.

Macro Images of a Chip

A friend from the Omaha Maker Group gave me an interesting chip a while back. Apparently it is some kind of optically sensitive chip, it has a clear case.
I thought it would be interesting to take some macro photos of it and see if I could capture some of the details of the die. I started out with just some simple shots with the kit lens and extension tubes.
Easy enough to see, but lighting was difficult with the chip as close to the lens as it was. You can see the wires and a little detail of the chip, and the lighting in this one gives a nice shadow on the wires.
I then switched to my long telephoto lens, extension tubes. This let me move the chip back from the lens a few inches, which made getting light in much easier. It didn't produce an image that was any more magnified though.
The chip is about 2.5mm on the short dimension.
From here I added a 10X macro expander lens and also a 10 triplet hand-lens to see if I could get any closer. This was difficult because it's a separate lens and can't easily be mounted on-axis with the camera lens. With a little fiddling around it came out ok. I can see a lot of details, though it's starting to get fuzzy around the outside, only the middle is relatively free of aberration.
Here's a crop from that image.
In the original photo the 2.5mm chip is a bit over 1100 pixels across, giving about 2170 nanometers per pixel. The narrowest traces are about 4 pixels wide, about 0.0003 inches. I'm not sure what the aperture was set to, but this is probably not bad performance for a first attempt. I'll have to do some reading and set up my equipment a little more carefully and see if I can sharpen this up a little more.
Edit: with a little more fiddling I got it down to 580 nanometers per pixel. Pretty sure I can take it farther, but I need to set up something to handle adjusting the sample position for fine focus. It's pretty fiddly. Also need to get some bright light onto it so I can see it in the live view. My dim desk lamp doesn't really cast enough light for this.

2014 Robotics Expo Wrapup

Thanks again to everyone who helped make today’s booth at the Robotics Expo a huge success again this year.  Booth volunteers included Ben, Don, Mike, Michael, Brandon, Nick and Jared, with material support from Patrick, Sarah, Eric, Dave and Katlynn.  [Apologies in advance if I missed anyone].

If you weren’t able to make it out today, but would like to volunteer at some point in the future, just keep your eyes on the mailing list, as we’ll have several more opportunities throughout the year.

Photographic Depth of Field

I was curious why a large aperture on a lens reduces depth of field. To investigate this I set my camera up with a macro extension tube and a subject with lots of depth.


The subject is a potassium sodium tartrate (Rochelle salt) crystal mounted in a brass holder, with a copper contact wire for detecting the crystal's piezoelectric properties. From the perspective of the camera, this setup looks like this:


This image shows a very short field, as is typical with macro photos that are taken from very close to the lens. The focal plane is about 10 degrees off of perpendicular from the surface of the coins, and intersects the subject about where the copper wire wraps around the crystal.

To understand why some parts of the image created when the aperture is large are blurry, it's helpful to visualize the paths the light takes through the lens. I used this simulator to make a simple diagram:


From any given point on the subject on the left, light passes through every point on the lens and is focused onto the camera's sensor. If you imagine a tiny bug with an equally tiny camera walking around on the big lens and taking his own pictures of the subject, you would noticed that depending on where he was standing, his photos would each be slightly different, sometimes from a little higher or lower, or one side or the other. We can simulate the bug camera photos by taking a picture through a pinhole placed in front of the lens.



Because the tiny bug camera has a really tiny aperture, all his photos will have very large depth of field, they'll be sharp all over. My bug-simulator has a fairly large pinhole, you can see it near the top of the image, it's about 2mm wide, so I won't get as much depth of field, but you can definitely see that much more of the depth of the image is in focus, compare to the image above and note how in these both the rubber band near the back of the image and the reeds on the edge of the coin are sharp. Here the bug is walking from one side of the lens to the other:




It's hard to tell in the still images, but the perspective is different in each shot, the angles all change a bit as the bug walks across the lens. It's easier to see this if you user a bigger hole so that you get a full-frame image instead of the circular shot, but it's harder to see the increase in the depth of field. Here is another example with a slot to let in more light. Left side from the top of the lens, right side from the bottom. 



Since the tiny bug camera can only collect a tiny bit of light with each photo, all those slightly-different photos will be quite dark. If we stack them all up to increase the brightness, we get the image we would get from the regular-sized camera. It's a bright, but only the parts that were all the same in the individual images will still look sharp in the combined image. The parts that were all slightly different will be all mixed together, making them appear blurry. 

That's exactly what the big lens is doing, stacking together thousands of different perspectives of the view all taken at the same time. We could get deeper depth of field in the image by using a smaller aperture, but that makes the image darker. To compensate we can increase the light on the subject, leave the shutter open longer, or use a more sensitive sensor.

To really see this effect, it's best to see it in a video, so check this out:


2014 FirLumber Rally Photos

OMG’s innaugeral FirLumber Rally was a great success, with 17 cars competing.  Official results will be posted shortly, but in summary, Dave’s electric cheater was the fastest, Eric’s elephant was the most creative, and Nate’s car was the least effort to build.  Additionally, Dan’s kids’ cars were the fastest among the Squares.

Trebuchet Contest Results

Thanks to all who took part in our Trebuchet Contest! We had perfect weather and all involved had a great time. With nine people competing on six teams, we saw a wide variety of designs and lots of experimentation.

Each team fired three shots, which were analyzed for efficiency and for accuracy. The efficiency score is calculated as the length of the best shot divided by the mass of the counterweight – to discourage anyone from using small cars as counterweight and hurling the projectiles all the way to Dodge Street. The accuracy score is the standard deviation of the three shots. To combine these into a final score, each category was normalized to 5 points for the best team in that area, with proportionally fewer points going to every other team. As a result, the best possible score is ten points, which would only be awarded to a team winning both categories.

Rank Team Efficiency (ft/lb) Accuracy (St Dev) Score
1st Ben 8.5 0.05 9.3
2nd Dave 9.8 2.4 5.1
3rd Eric 8.9 85.2 4.5
4th Kyle and his Dad 7.9 18.3 4.0
5th Kevin 7.6 6.4 3.9
6th Don, Stephanie, and Sarah 6.2 31.2 3.2

Ben, competing with a trebuchet constructed years before and “conveniently” fitting the contest requirements, had the longest throw of the day at 214 feet, but the use of a rather large counterweight dropped his efficiency to mid-pack, though not nearly low enough to offset his astonishing repeatability and accuracy.

Dave, winner of the “Least Effort Possible” award which nobody has bothered to create, gave a spectacular performance, particularly considering that his machine was constructed and tested in under fifteen minutes.

Eric nearly forfeited the contest after some mysterious last-minute bugs, but came back with a very solid 94-foot throw. Unfortunately, with two of his three shots launching backwards, his accuracy score reminded everyone to stand well to one side of a firing trebuchet.

Kyle and his Dad arrived with the only machine too large to be assembled indoors. Installing a competitive amount of counterweight earned them a respectable score, but before and after the contest, their 50-lb maximum capacity gave the neighbors something to think about.

Kevin competed with the only machine requiring three hands to safely load, and was also the only entrant to attempt self-amputation during testing. Despite this, the device proved acceptably reliable and fired many shots without incident.

Don, Stephanie, and Sarah may have earned the lowest score, but they were also the only team to compete with no prior testing. Their trebuchet was not completed until several minutes after the start of check-in and was immediately put to the test with none of the tinkering and tweaking afforded by the other teams.

Once again, a huge thanks to everyone who took part in this contest! We know it was the most difficult challenge we’ve yet conceived, and everyone who took part worked extremely hard to make the firing line yesterday. We promise the next event will carry wider appeal – more on that in the coming weeks.

Congrats to the 2013 Founders’ Prize winners!

 

Founders' Prize 2013Congratulations to the winners of the inaugural 2013 Founders’ Prize:

  • For Opening New Frontiers – Jay Hannah and Dave Knaack
  • For Operational Excellence – Eric Kaplan

As stated at the meeting, the categories for these awards are entirely arbitrary and subject to change in future years;  Also, we estimate that this prize is roughly 1 million times easier to win than a Nobel Prize, and the cash award has been scaled accordingly.

Here’s a bit from Travis about the Opening New Frontiers winners

As for the award for Operational Excellence, this prize is awarded to Eric Kaplan for consistent attention to “things that need done”; He’s involved in everything from staffing booths to designing marketing material and furniture for the space. Furthermore, he successfully facilitated the Makery’s relocation to our new home.

Again, congratulations to all our 2013 winners.

OMG is holding a trebuchet contest!

This is your chance to build the best miniature siege engine in Omaha.  Work by yourself or in a small group to make the best golf-ball*-throwing device you can imagine.  We will then compete for range and accuracy to crown a champion. The contest will take place at the Makery on September 21st.

Although the competition is called “Trebuchet Contest,” your device does not need to look like something out of the middle ages.  You can use any design, any materials, any construction techniques, and in fact any launch techniques you’d like.  We want to keep things interesting, so the rules for this contest are very lenient:

  1. The energy used to launch the projectile may come only from the gravitational potential energy of a mass falling no greater than 16 vertical inches.  No explosives, precompressed springs, compressed gasses, batteries, or any other sources of energy.  Gravity only.  However, you can use all those things as intermediate steps if you’d like – if you use gravity to compress a spring, or use electronic timing to coordinate the firing, that’s just good Maker spirit.  Just be prepared to prove that you’re not contributing any extra energy to the projectile.

  2. Your siege engine requires a remote triggering mechanism.  Mechanical, electronic, whatever.  You need to be ten feet from the firing position during your shots, and away from the most likely misfire direction (for example, on a standard trebuchet you need to be off to the side, out of the plane of the arm).  We want to keep things safe.

  3. You cannot aerodynamically assist the projectile in any way.  If you need wadding to seal the projectile in the barrel of your gravity-charged pneumatic cannon, that’s fine.  If you want to use a sling which stays attached to the projectile instead of the trebuchet, well, you’re the one who thinks it’ll be competitive to throw more weight than anyone else.  But whatever you do, the projectile has to take a ballistic trajectory once it leaves your machine.

We’re trying to keep things interesting and attract the widest range of designs by keeping the rules loose.  Please don’t abuse this privilege – nobody wants to read a ten-page rule book covering every possible situation.  Tech inspection is going to have a “spirit of the rules” philosophy, and you should keep that in mind while working on your design.  If you have a creative idea or think you’ve found a loophole in the rules, please bring it up with Ben as soon as possible.  Most likely it will be allowed, but if you show up on competition day with something ridiculous, having never discussed it with the organizers, you might find yourself disqualified.  We promise flexibility and absolute discretion – if we allow your cunning plan, its secret will be safe, and we promise not to steal it for our own designs.

*Golf balls make ideal trebuchet projectiles.  Unfortunately, they’re a bit dangerous and bouncy.  To dramatically increase the chances of scoring each shot by ensuring we can actually find each projectile, we won’t be using golf balls.  Competition projectiles will be approximately equal in size and exactly equal in mass to a golf ball.  Projectiles will be supplied for scored shots, although you may test with anything you like.

Competitions and Scoring:

The exact equations used for scoring will be revealed the day of competition, to prevent any rules-lawyering and to allow us more time to perfect them.

  • Longest Range

    • You will be scored on your ability to efficiently throw the projectile as far as you can.  The mass of your power weight will be taken into account, so if you decide to increase performance with extra weight, make sure you’re getting a proportional gain in range.

  • Best Accuracy

    • You will be scored on your ability to hit a predetermined target at a distance of your choosing.  The main goal is accuracy, but your chosen range will also affect your score – a 10-foot miss from 100 feet isn’t as impressive as a 10-foot miss at 200 feet.