Tuesday, September 14, 2010

Edit on camper fridge project

Just a note that I finished the camper fridge project with pictures and explanation of the results.

Hoberman Switch Pitch toy ball

This is a really cool toy from Hoberman, who also made the spheres made out of linkages that would expand the sphere to many times its size when pulled on.

The Switch Pitch is a ball that will switch colors when thrown. Linkages that make up the ball have surfaces that act as the surface of the ball when it is collapsed. When thrown with a little spin (sudden acceleration works too), the momentum pulls the linkages out and flips them around. One thing I noticed is that faces of the ball (circular nodes flat on the surface) turn into vertices and vice versa (nodes that are pushed into the sphere, but still visible).

Hoberman has multiple similar toys and an interactive animation showing the switch on their website.


How a mechanical watch works video

Found on makezine.com: http://blog.makezine.com/archive/2010/09/how_a_mechanical_watch_works.html

Older video explaining the gearing and seconds regulation with escapements.

Ball in cage alarm switch

Found on makezine.com: http://makeprojects.com/Project/Ball-in-Cage-Alarm-Switch/240/1

Cool, simple idea for a mechanical motion detector. Hook electrical leads up to two wires crisscrossing over a metal ball. If the ball moves/rolls and touches the wires, it connects the circuit and you can have it buzz an alarm or something.

The link is a how-to on making your own.

Posting frequency 2

For any of you who follow, sorry that I haven't posted in a while. I've become very busy in the past couple of days so I think I'll only be able to post when I find time in the future. This should be about once a week, though, so it won't be too bad.

Monday, September 6, 2010

Camper refridgerator project

We own a pop-up camper that has an inside refrigerator. It can run on propane, 12v batteries, or 120v AC hook-up from the site. We've seen on multiple camper forums that one project/"mod" some people do is improve their fridge's efficiency. The main things people did were to add a fan and a better baffle (explained later). It wasn't too hard and the results were reportedly very good, so we tried it ourselves.

First, an explanation of refrigeration, the issues with the camper fridge, and the fixes.

Refrigeration is sort of a complex process that I don't fully understand. It involves the sequence of heating and cooling and pressurizing and depressurizing a coolant liquid so that it can be cooled (and re-cooled). One thing to remember if you're trying to learn the process is that, in physics, you don't "get cold," you lose heat/transfer heat/energy to something else. This is the idea of an important part of the refrigerator sequence, the cooling fins, which is what we dealt with and improved.

Cooling fins and fridge compartment with the working pieces (explained below).



The cooling fins are thin plates of metal attached to a tube. Heated liquid runs through this tube and gives it's heat to the air through the fins, effectively cooling down. Thin metal plates are used because they radiate heat easily because of their thickness. The heat would not as easily radiate out of the thick tube itself. Normally, new, colder air flows through the fins by convection, which is the principle that hot air rises and cold air sinks (the cooling fins are at the top of the fridge unit to catch all the moving air). But if you add a fan, you can blow or suck the air through the fins faster and more effectively. This is what we did with our camper.
As an analogy, this is similar to a car's radiator. To keep it from overheating, a car pumps coolant through its parts, mainly the engine. This fluid takes away the heat from the engine (remember, you don't "get cold," you lose heat). The coolant is now hot and must be cooled to be used again. It is piped to the radiator, which is at the front of the car. If you look through a car's front grill, you'll likely see all the thin plates of the radiator. This radiator has many more fins and is much bigger than a camper's cooling fins. There are also multiple tubes that share the fins (many smaller tubes radiate more heat than one big one). When you drive, flowing air blows through the radiator fins and take the heat from the fins and coolant. Some (most?) cars have fans that start to blow the air if the car has been sitting still for a while.

Another part of the fridge you can improve is the baffle. This is just a separator, a wall so to speak, that separates the incoming air from the used, "hot" air that has gone through the fins. If there was no baffle, especially when just using convection, the air could flow around and go through fins again, or not really go anywhere. Furthermore, a baffle helps to direct air only through the fins, instead going around them and out the camper (like the hot, used air). The previous baffle on our camper was a pitiful board that was too small to do anything whatsoever to section "in" from "out." There are multiple ways to make a new baffle (types of materials, shape, etc), but the idea is to make a successful seal.





















Pictures of Modifications:
General picture of above area modification. We found some metal L-brackets to mount the fan (Radio Shack 12v) and stapled and taped some Refletix inside as a baffle. Refletix is a bubble-wrap-shiny-plastic material you can buy in rolls, mostly for insulation. For here, it's easy to shape to the area. The silver ducting tape is stiff and provides support for the bends.


Close-up on cooling fins and inside:


Lower area with added switch for fan. This taps into the 12v battery wires on the bottom left that powers the fridge. The other fridge controls are also here. Note the red and blue wires on the left going up to the fan.


Close-up on switch. Bought one from Radio Shack and made a box to hold it out of sheet metal/flashing. Crude but it works. Screwed it down and folded it up.


Results:
The baffle seems to have done the most work and the fan only really works on very hot days. Before the modifications the fridge kept itself at about the low 60s F. After, we can keep it at the 50 degree mark. Other people have reported different levels of efficiency on camping websites and forums. It depends on the model of fridge and how good of a job you do. We could have gone all out and made a perfect seal with the baffle by covering up the sides of the cooling fins too.

Hope that was interesting and possibly helpful for any other projects!

Replication: carpenter's bench clamp

A replication of mechanism #180 from 507 Mechanical Movements, Mechanisms, and Devices by Henry T. Brown.

This is a clamp with a jaw/lever that pushes down on an object that's pushed into it. Pushing the object in pushes the jaw up and the back of the jaw down into the object. Pulling the object out releases the pressure.

I have thought that this might be useful for robots gripping an object. It's one of those "smart mechanism" that works in a clever way and doesn't need extra operation.



video

507 Mechanical Movements, Mechanisms, and Devices by Henry T. Brown



This is an excellent book for inspiration on mechanisms. It was first published around the turn of the century and has had many editions. There are pictures on one page and explanations on the opposite. They have retained the original drawings and text, so everything on the inside looks old fashioned. Some of the illustrations and explanations are quite short and simple, but you can often still figure things out. Many terms are not explained, as much of the book is meant for an audience who knows these things already. However, you soon learn by context what it's talking about.

There are many ingenious mechanisms in this book; I will try to replicate some with my Lego Mindstorms kit and post about them. They'll be labeled with the tag "replications."

Saturday, September 4, 2010

Designing without a computer in the '60s

Found on Makezine.com: http://blog.makezine.com/archive/2010/08/how-to_design_something_without_a_c.html

An interesting video on how things were designed without computers, 3D modeling, or rapid prototyping. This is example is from the '60s on a decanter design project.


Design story: The Decanter from Landor Associates on Vimeo.

OK Go's Rube Goldberg machine

Found on wired.com: http://www.wired.com/gadgetlab/2010/03/ok-go-rube-goldberg/

A while ago the band OK Go made a music video for their song This Too Shall Pass which featured a giant Rube Goldberg machine in tune with the music. It took an hour to reset and a month and a half to build.



A Rube Goldberg machine gets something done in a complex way with many steps, often only accomplishing something simple. It's named after the cartoonist who drew such silly mechanisms and described how they (should) work.

Fastest helicopter in the world

Found on IEEE Spectrum: http://spectrum.ieee.org/aerospace/aviation/the-fastest-helicopter-on-earth/

If you try to get a helicopter to go fast, the blades start to mess with the lift of the helicopter. On a moving helicopter, when the blades swing around forwards, they experience faster air than when they swing backwards. It's like throwing a baseball on a moving car. If you throw forwards, the baseball will go faster and experience all that wind hitting it; if you throw backwards, it's moving more with the wind and experiences less. This becomes dramatic as the helicopter moves faster and the blades move even faster to get it to do so. Quote from article: "[when the helicopter is moving] 300 km/h, the wind on the advancing side would reach 1100 km/h, while the wind on the opposite side would be 500 km/h." There comes a point where the helicopter can't balance this difference in lift and can't go faster.

Sikorsky's X2 has been designed with two sets of rotors that spin in opposite directions, countering this problems. It has broken the record of 400 km/h at a speed of 435 km/h (248.5 mph and 270.3 mph respectively). (They still need to do a couple things with the record keeper organization to make it official).

If you want to read more, the article is quite long, has lots of details, and a bunch of history.

Speed sensor with camera and computing based on flies

Found on IEEE Spectrum: http://spectrum.ieee.org/computing/hardware/a-flyeye-inspired-speed-sensor

An interesting idea of measuring speed using camera images. The computation is based on how flies measure their speed with vision. It's an alternative to encoders (car speedometer, measuring how fast colored lines change on a spinning wheel), accelerometers (small chips which sense acceleration), or GPS.

The sensor has a camera on it with a lens that gives it 180 degree vision. The images it gets are sent to the processor. Here's the details:

The chip is looking for two variables: temporal frequency (variation of a signal over time in one point) and spatial frequency (variation of a signal such as light intensity in space in one moment). Approximating a division of the temporal frequency by the spatial frequency can yield a remarkably spot-on measure of absolute speed.
Temporal frequency is easy, but spatial frequency is trickier and more computationally expensive. That means it burns a lot of power—anathema to a small, portable sensor.
Vissee’s algorithm lightens the computational load by using methods derived from the fruit-fly brain to filter out any data that does not help the processors calculate speed.

Friday, September 3, 2010

Posting frequency

EDIT: see Posting frequency 2.

Some blogs/websites/whatever say what their posting frequency is, like 1-2 times a week, for example.

I think I'll try posting every other day. So expect something tomorrow. Like I said in my first post, I've got a whole bunch of links bookmarked backed up that I can post. Plus, two of my resources I follow produce good stuff quite often: Wired.com and Makezine.com. Also, I think I'm going to follow IEEE Spectrum's website now. So that might bring in more. Also note that sometimes I'm able to quickly slam in more than one post at a time.

However, I don't know if I'll be able to keep that up. We'll have to see. Maybe I'll switch to 2 times a week.

Thursday, September 2, 2010

Magnetically controlled bacteria move small structures

Found on Makezine.com: http://blog.makezine.com/archive/2010/09/cnc_bacteria_swarm_builds_tiny_pyra.html

From a nanorobotics laboratory (I believe in France); about 5,000 bacteria are directed to move/push around blocks to make a (2D) pyramid. The bacteria respond to magnetic fields, so that is how the scientists move them around. An explanation from IEEE Spectrum:

The bacteria, of a type known as magnetotactic, contain structures called magnetosomes, which function as a compass. In the presence of a magnetic field, the magnetosomes induce a torque on the bacteria, making them swim according to the direction of the field. Place a magnetic field pointing right and the bacteria will move right. Switch the field to point left and the bacteria will follow suit.
View the video here, which I can't get to embed right.

Making "organic" oddly-shaped gears

Found on Makezine.com: http://blog.makezine.com/archive/2010/09/how-to_make_organically-shaped_gear.html

Really cool idea of making gears of odd shapes. Looks like you can make your own or base it off something real, like an animal shape or real world object. Surprizingly, if you make it right, they still work and turn great. The author of this How To is a recognized DIY clock maker, Clayton Boyer. View his YouTube channel here and website here.

Wednesday, September 1, 2010

Sariel gearboxes

Sariel is a Lego enthusiast that makes crazy amazing Lego models. Most are working models of real vehicles, for which he has designed multiple gearboxes to drive them with. They are all interesting and cool to watch. Here's the page for his gearbox tag. And here's a couple of them:

4 speed gearbox
A video of it:


And a 2 speed automatic gearbox. It automatically changes to a lower gear when receiving resistance.

Nature by Numbers video

Nature by Numbers video, pretty good.

High speed robotic hands

This video has gotten a lot of attention. It's from Ishikawa Kumoro Labratory, which has a whole bunch of other high speed hand/arm robotics work here.

Mechanical Animations

Found through Makezine.com and other linked sites.

Only some of the couple cool animations on mechanisms from this blog, World of Technology.

This is known as the Maltese Cross.

How a sewing machine works.
How a manual transmission works.

Rotary or Wankel engine, with an interesting concept. The center blue triangle piece is made of the intersection of 3 circles.


Here's another cool site that I found when looking around that has animations on lots of basic mechanical devices. They're flash, so I can't embed them in this blog like a gif.

World Builder short film

Cool and interesting short film. Guy makes a virtual world for his sweetheart.