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.

We’re just a group of Racer tech wizards who drive a Barbie, but rely on a cowboy.

Members of OMG recently attended Maker Faire Kansas City. While hopeful that we’d be able to race our latest project “Barbie”–a souped-up power wheel–in the Power Racing Series, several set-backs caused us to withdraw from the event. Team OMGFTW (Omaha Maker Group for the win) may have been knocked out this time around, but we’ve already begun working out Barbie’s kinks, which means one thing–we’re already ahead of the game! Though we didn’t get to race, the Omaha World Herald wrote an article about the trials and tribulations of taking Barbie from a mere girly power wheel toy to a lean mean winning machine. We’re just a group of Racer tech wizards who drive a Barbie, but rely on a cowboy.

Special Event at OMG – May 28th, 7pm – Paint and Pizza!

I am honored to announce that the website, Instructables.com, has contact Omaha Maker Group and asked us to participate in their inaugural “Instructables Build Nights”!
The idea for Build Nights is that Instructables picks a topic and sends supplies/materials to select Makerspaces for their use in creating an event around that topic.  And just to make it more enjoyable, they kick in some cash for pizza, too!  All we have to do in return (in addition to hosting the event) is produce 3-4 new Instructables to their website.  Our Instructables don’t even have to be about the topic, though that certainly helps.  And as long as we tag/link Omaha Maker Group in our Instructables (more details on how to do that later), we get credit.  If we hit the 3-4 mark, we qualify to participate in future Build Nights.  If we manage 10 Instructables, we could be looking at a new laser cutter, new 3D printer, electronics kit, or more!
The topic for May is conductive paint.  You may have seen the new paint pens at Radio Shack from Bare Conductive.  These pens allow you to “draw” an electronic circuit.  The paint cleans with soapy water, so if you don’t like your circuit, just wash it away and start a new one.
Here’s a link to their website, so you can start getting some ideas: http://www.bareconductive.com/
And here is a link to some Instructables that have already been submitted for Bare Conductive paint, again to give you some ideas:  http://www.instructables.com/group/bareconductive/
Since this is our first Build Night, and the first time we have really talked about Instructables, I will be sure to send out information over the next couple of weeks to give you an introduction to making an Instructable, what constitutes a “quality” Instructable, and how to link your Instructable to OMG. At any time, please email me if you have questions.
The Bare Conductive Build Night will take place at The Makery on May 28th.  Doors will open by 6:00pm, and the event will kick off at 7:00.  We will have pizza from Varisty/Roman Coin, but please BYOB (and any snacks you might want).  Hope to see you there!