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Dynasplint

April 5, 2010

Almost a year ago, I broke the humerus in my right arm:

True Life: I did this arm wrestling with an old housemate… “Arm wrestling? Sure, I haven’t done that in forever, what’s the worse that could happen?”

While the bone was healing, my arm was in a sling for five weeks.  I learned to be pretty good at one-handed typing with my left hand, since I was submitting my master’s thesis in four weeks.  After getting my arm out of the sling, I had lost quite a bit of my range of motion.  I could not extend my arm because the bicep and connective tissue had become so taught from being held up in the sling for so long:

Shortly after getting out of the sling. (Coke museum in Atlanta with my sister).

I was distraught to see how messed up (and weak) my arm had become.  Fortunately for me, help was on the way IN THE FORM OF TECHNOLOGY.  My physical therapist hooked me up with a Dynasplint rental.  A Dynasplint is basically a medieval torture device in which you crank down on some springs with a key which then forces your arm (or leg or jaw(?) etc) to stop misbehaving, and extend like normal.

The Dynasplint representative said I should have worked up until I was able to wear it all night while sleeping but this thing HURTS LIKE HELL.  The rental was pricey but definitely worth it–I’m pretty sure that the Dynasplint did more to help me regain something close to my original range of motion than sessions with the physical therapist did.  I’ll mention again that it HURTS LIKE HELL.  I don’t think I ever made it much beyond an hour and fifteen minutes wearing the device.  The pain would just increase as time wore on while wearing it too–it was nuts.  I definitely never fell asleep wearing the Dynasplint, but the pain was worth getting my range of motion back.  And, after about five months in the gym, I was back to my pre-break weight lifting strength too.

Getting medieval on my misbehaving arm

Due to the construction of the thing, I couldn’t really tell how the springs in the design worked on your arm.  There might be powerful clock springs in the elbow joints on either side of your arm, and cranking on the key was what tightened them.

The key for tightening the springs is inserted at the “hand end” of the forearm rod

Alternatively, linear springs in the forearm rods may have connected to a feature in the elbow joint which was offset from the center of the elbow pivot point to provide the necessary torque.  I’m just not sure–too much of the hardware was hidden under the rods and joints.  The designers were smart to provide a graduated tension scale in the forearm rods on both sides of the forearm rods in order to allow the user to make sure that the torque was equal on both sides of the arm:

I highly recommend the Dynasplint for anyone fresh off of breaking a bone and is in physical therapy, trying to regain range of motion.  With pain comes gain, and I attribute getting most of my elbow extension back to the Dynasplint.

Autorotation

April 4, 2010

I was watching the movie “Road Warrior” yesterday on Netflix (which probably qualifies as required viewing for anyone who digs the science fiction genre).  I was intrigued by a helicopter-looking machine in the movie which looked a lot like that shown in the video above.

What really puzzled me about this helicopter-like machine was the spindly, relatively unsupported structure supporting the main rotor.  Helicopters with powered main rotors usually have beefy structures supporting the main rotor for transmitting engine torque and adjusting the pitch of the blades to maneuver the aircraft.  But this machine didn’t even look like power was being transmitted from the engine to the main rotor; this made me wonder, “How the heck is this thing being held aloft without a powered main rotor; and how is the main rotor even spinning then?”

As it turns out, there is actually a class of machines that do have unpowered main rotors which are still providing lift for the vehicle and they are called Autogyros.  They rely on a principle called autorotation, which is a term for the aerodynamic effect of air rising up through the main rotor, as opposed to being drawn down through the rotor, as helicopters do when moving forward in flight.

Air rising up through a rotor can force a properly designed airfoil to spin and provide lift.  While the principle of autorotation is the method by which helicopters can land safely if engine power is lost, it also can be exploited to provide lift for a machine whose main rotor is not powered by an engine at all, and this is what autogyros do.

By angling the main rotor backwards, so that air is forced up through the rotor while in forward flight, the main rotor is both forced to rotate by the motion of forward flight through the air, while simultaneously providing lift.

Image above: main rotor angled backwards clearly displayed here. Rear rotor provides forward thrust required to force air up through main rotor.

As the wikipedia article on the principle of autorotation explains, different regions along the span of the main rotor blades serve different purposes:

  • Driven Region: aerodynamic drag on this portion of the blade provides lift, but counteracts torque on the rotor, slowing it down.
  • Driving Region: net aerodynamic thrust on this portion of the blade provides the force which forces the rotor to rotate.
  • Stall Region: blade in this region is stalling–i.e., operating above max. angle of attack, causing drag, and slowing the rotor down.

To simplify a very complex aerodynamics problem: by adjusting the pitch on the rotor blades, the ratios of the three regimes are adjusted and this alters the net forces acting on the vehicle which enables maneuvering.  I thought this was a pretty unique application of aerodynamic principles in an uncommon method of flight, similar to the Fanwing I discussed earlier.

Welding

April 3, 2010

Several of the companies I’m currently pursuing for interviews rely on welding for some portion of their operations, so I wanted to refresh that technology in my mind.  Welding is defined as “a materials joining process in which two or more parts are coalesced at their contacting surfaces by a suitable application of heat and/or pressure [1].”  Fusion welding–in which heat is used to melt and join the base materials with a filler metal sometimes added–is described here.  Solid-state welding is less common, but includes diffusion welding (two surfaces held together under pressure at high temperature, allowing atomic diffusion/fusion to occur), friction welding (friction between the two surfaces generates the heat for coalescence), and ultrasonic welding (moderate pressure is applied between the parts while an ultrasonic oscillation parallel to the contacting surfaces achieves atomic bonding) [1].  The following post will be divided into the following sections:

  • Surface Preparation
  • Weld Joint Geometry
  • Safety
  • The Various Welding Technologies
    • Oxyfuel
      • Oxyacetylene
    • Arc Welding
      • Consumable Electrode
      • Shielded Metal Arc (stick welding)
      • Gas Metal Arc
      • Submerged Arc
      • Nonconsumable Electrode
      • Gas Tungsten Arc (TIG)
    • Resistance Welding
      • Resistance Spot Welding
      • Resistance Seam Welding
      • Resistance Projection Welding
    • Heat Sealing
  • Design Factors; Strength & Fatigue

Read more…

Personal Blimp

March 13, 2010

Neat project here… I doubt it will revolutionize transportation, but building a Personal Blimp in your backyard is a pretty awesome project.  I think the physical scale and the relatively slow speed of airships probably won’t allow them to displace the automobile for personal transit any time soon.  But they do have a certain aesthetic appeal about them, and I could even see how the nature of the airship could allow it to be quite useful under certain conditions.

In particular, the thing I like about their design is the structure used to give the balloon its shape. The following image is taken from the “Technology” page of their website.  I think it’s a very clever application of tensioned structures.  By tightening the “Tensioning Line,” the flexible ribs expand outwards, while also being restrained in their final shape by the fabric exterior.  Very clever!

When there is a necessity for heavy transport to places inaccessible by roads, or for surveillance, I would think buoyant aircraft would be an ideal technology.  An example might be the war in Afghanistan; I’ve heard from veterans that well-maintained roads don’t really exist there, and particularly when it rains, the dirt roads which do exist just turn to muck.  And not surprisingly, there is some buzz on the internet which suggests researchers in war technology haven’t lost interest in airships.  It seems the tech would work great in those applications, but I just can’t couple the image of a flying walrus with the epic music accompanying this video:

(RSS) Feed Me

March 9, 2010

I wanted to spruce up the homepage of this website with one more thing.  I decided to modify the (previously) ho-hum RSS Icon in the sidebar.  Recalling an earlier post on the cognitive process of creativity, and another post (very similar to this one) which illustrated this creative process in action within the context of facebook…  Here are the design constraints and design variables for this project:

Design Constraints:

  • RSS Icon Shape: the RSS icon shape must be retained in whatever design I implement.  The RSS icon shape is a universally acknowledged symbol, understood by web users to mean “Click this shape for the RSS feed for this website.”  Altering the RSS icon shape would detract from the user’s ability to understand the website.
  • “RSS Feed”–the name & its purpose: similar to bullet point one, the term “RSS feed” means one thing to almost all web users…  It is an internet tool to get updates on new content for a website.  I don’t want to muddy that at all, since that’s the purpose I’m trying to achieve: ‘by clicking this image, you will get the RSS feed for this website.’

Potential Design Variables:

  • Color: the RSS icon is not like a ‘STOP’ sign–it does not have to be red, or any other color for that matter.  The shape’s form is really the “constant” which must be retained to maintain the user’s ability to understand what the image is trying to convey–the color and texture of the image are potential variables.
  • Orientation: the RSS icon shape, as long as it is visually evident, does not necessarily have to be oriented within the plane of the webpage.

One of the constants noted above is the term “RSS feed.”  With a pun on the word ‘feed,’ I created the following RSS icon out of some wood, paint, and fake plastic greenery from a craft store:

(also: go green!)

This project made me recognize something which I had not before, about the cognitive process of creativity and the process of design.  Namely: the interplay between design constraints and design variables.  In coming up with this “apple” idea for this project, I had leveraged one of the design constraints (the word ‘RSS feed‘) directly into the iterative mental process of adjusting the color and orientation of the RSS object I was creating.  I varied the color and orientation of the RSS object so that it would suit the constraint of ‘RSS feed’ even better than if there had been no relation between this constraint and the variables at all.

An analogy for this process in the world of mechanical design might be designing with fibrous composite materials.  When designing a structure with fiber-based composites, certain structural shapes are more suitable than others…  This is because the fibers comprising these suitable shapes can be oriented to optimally bear whatever load the structure is subjected to.  So, given the ‘orientational strength constraint’ of fibrous composite materials, you will want to ‘vary the shape’ of the structure to favorably agree with the constraining nature of the material you are designing with…  Just as I had ‘varied the RSS Icon’s color and shape’ to favorably align with the constraint of the icon’s purpose: to serve as an RSS feed.  This could even be one good working definition of optimal design–adjusting the design features which can be varied in order to agree, as best as possible, with the design requirements or constraints.

Finally, the ‘spark of insight’ which enabled the pun on ‘RSS feed’ is just another example of the cognitive process involving ‘constraints/variables’ in creativity, too.  This time, the ‘constraints/variables’ are phrases and word definition.  Observing the phrase “RSS Feed” one can then ask the question–what are the conceptual features of this term which can be varied?  One feature of a phrase which can be varied is ‘definition of its individual terms’ (i.e., the definition of a pun).  This is what I chose to vary here–the alternative definition of ‘feed,’ as in: to eat.

FanWing

March 3, 2010

Check out the video below of the FanWing.  It’s a pretty genius application of Beroulli’s principle to the technology of flight.  If you are going to rely on Bernoulli and airfoils to get into the air, you can either force the wing through the air to generate lift (with jet engines, rotors, or the like)…  Or you can force the air across the wing to generate lift.  The latter is exactly what Patrick Peebles has done with his FanWing!  If he wasn’t the first to think of this alternative method of implementing airfoil-based flight, then I’ll bet that he was the first to successfully pull it off.  Here’s the video (fun part begins around 0:40):

It will be interesting to see if this tech can be scaled up for human transport.

Brad Litwin is a Genius

August 30, 2009

On youtube, I stumbled across the channel of Brad Litwin.  The man is a mechanical genius, an extremely talented machinist, and an artist (and a jazz and blues musician).  He makes kinetic art that is right up there with the mechanical fountains of Jean Tingueley.  Nice work, Brad!  I’d love to become half the mechanic/machinist/artisan that you are!  A few of my favorite machines by him are below, and check his channel for a lot more!

“The Rotapult”:

“Mechanical Atom-Smacker” (air piston-powered suction for ball-bearing; cool!):

“The Sway of Public Opinion”:

“Tetra-Cycling”: