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(#66) NASA's Ingenious Mechanisms · Mechanical Engineering Made Simple

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  Welcome back design junkies, to Mechanical Engineering Made
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  Simple. Today we are strapping in for a
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  a true deep dive into mechanical engineer.
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  Our mission really, is to zoom in on those brilliant, often
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  hidden mechanisms, the ones that manage extreme force, ensure
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  absolute precision, or, you know, enable technologies that
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  quite literally reach for the stars.
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  We've pulled from a huge stack of sources covering everything
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  from basic drives to NASA robotics.
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  And if you think about it, what we're really exploring is this
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  fundamental tension that every single engineer faces.
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  How do you get maximum rigidity or this really complex smooth
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  movement while at the same time fighting friction, minimizing
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  wear, and of course, keeping everything as small and wide as
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  possible? We're looking at some really
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  clever solutions for motion for control and assembly across just
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  vastly different scales, OK? Let's unpack that.
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  Let's start with with mechanisms designed to solve scale and
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  structural integrity. Think about something that seems
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  deceptively simple. Springs and booms.
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  Like a tape measure. Exactly like a tape measure or
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  an old antenna. You know the problem.
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  They extend super easily, but when they're fully out, they
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  have almost no torsional or flexural rigidity.
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  They just. Flop everywhere.
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  They just flop, and if you're engineering, say, a long boom
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  for a spacecraft floppy is just well.
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  It's not an option, not at all. That floppy mode means
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  instability vibration. It could mean catastrophic
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  failure in an environment where precision is everything.
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  So the early solutions had to get clever with geometry.
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  To solve this, we see approaches like De Havilland Stem and
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  Hunter Springs Helix. Right, which both used
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  overlapping material. Yeah, that overlap creates a
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  stronger sort of double walled structure.
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  But the real ingenuity kicks in when you move beyond just simple
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  overlapping. Take a design like Melpar's
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  Tubomatic. They're the strip of metal that
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  unrolls isn't just overlapping, it actually has interlocking
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  tabs and slots. So they physically lock
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  together. Precisely when it's fully
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  extended, those tabs lock and it forms a truly robust self
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  supporting tube. And here's where it gets really
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  interesting for anyone who cares about application.
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  Melpar also added a row of perforations right down the
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  middle of that strip. And those weren't just for
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  looks. Not at all.
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  They were a control mechanism. Exactly.
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  Those perforations help to accurately control the length
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  during extension or contraction. It acts almost like a ratchet or
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  a counter. Which made it much more
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  attractive as a precision positioning device, not just a
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  structural element. Right, for things like scanning
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  systems or deploying A delicate sensor.
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  And all of that structural integrity depends on the
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  material holding its shape. Which brings us to the genesis
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  of pre stressing metal. This is all about material
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  memory. It is.
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  I mean, John Jay Park and NASA Goddard was facing a situation
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  where the technical papers just didn't exist.
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  He needed a metal strip to hold a tight curl after being
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  flattened and extended over and over again.
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  And nobody had written the manual for that yet, no.
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  He had to start completely from scratch.
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  So he basically pioneered the method.
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  He figured out how to give these metal strips a new memory.
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  He did. He used strips of beryllium
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  copper alloy, which is already a fascinating choice, 2 inches
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  wide and only two thousandths of an inch thick.
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  And the method itself was, well, it was elegant in its
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  simplicity, yeah. It really was.
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  He rolled the strips lengthwise into a glass tube about 0.65
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  inches in diameter, and then he just heated it in a furnace
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  under very controlled conditions.
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  And he found that the heat treatment was everything.
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  Everything. The longer or hotter the
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  treatment, the tighter and more permanent the curl.
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  So he could basically dial in the geometry at the atomic
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  level. I think one example was 920°F
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  for 5 minutes. And that resulted in a tube that
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  perfectly maintained that 0.65 inch diameter.
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  Yeah, that's the kind of precision that makes long life
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  space systems possible. And that idea of mastering
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  controlled deformation is a perfect pivot to talk about
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  motion, where friction is the number one enemy.
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  Let's talk about flexures. Flexures or flexible
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  suspensions. They're really counterintuitive
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  solution. Because they don't roll or slide
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  at all, do they? Not at all.
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  They completely avoid the mechanics of rolling or sliding
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  bearings because they just flex. They act like a spring that
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  allows for rotation. And that simplicity translates
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  into massive reliability. But absolutely no rubbing parts
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  means nowhere. They don't need complicated
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  lubrication and critically, they aren't really subject to
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  backlash. That little bit of slop or lost
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  motion you get when a gear reverse direction.
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  Exactly. And for high precision systems,
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  that's a huge deal. And they do some unbelievably
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  heavy duty work. I'm thinking of the Apollo
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  Applications program. A single Fletcher pivot, barely
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  2 inches high, was holding a £5000 telescope.
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  And keeping it pointed at the sun with and this is a quote,
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  unprecedented accuracy. That's frictionless precision
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  supporting extreme weight. And it works on Earth too.
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  They're used in submarine gimbal mounts, satellite safety
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  shutters, even high precision balance scales.
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  They replace the old knife edges that get gumped up with dirt and
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  dust. That need for robustness doesn't
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  stop at pivots, it's critical in safety and control mechanisms.
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  Which brings us to Rotary override spring mechanisms.
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  These are just brilliant for motion control.
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  They introduce a kind of controlled segmentation.
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  What do you? Mean by that?
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  Well, they're designed to transmit only a small specific
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  part of a total rotation to an output lever, or they can be
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  used to strictly limit the travel of that lever, even if
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  the input is still spinning. So if the input shaft spins a
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  full 360°, the output might only move for say, 40° of that, and
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  the spring handles the rest. Precisely, we've seen designs
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  capable of segmenting 270° of movement and others limited to
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  just about 40. The beauty of it is the
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  principal scales up. You can use it in heavy duty
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  machinery just by strengthening the components.
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  It's all about controlled, repeatable, yielding under a
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  load. And if we're talking about
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  controlled yielding, monitoring sheer force is critical,
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  especially with high tension cables.
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  Thomas Grubbs at NASA came up with this marvelously simple
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  lever system for that. It really is mechanical elegance
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  at its best. You have two pulleys on a single
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  pivoted lever. The cable you're monitoring runs
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  between them. As the cable tension changes,
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  the lever pivots up or down just a tiny bit.
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  And that tiny movement is what you measure.
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  That's it. The pivoting motion pulls on a
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  little flat metal tongue. And that tongue is what
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  translates the mechanical action into a signal.
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  Exactly. A strain gauge is cemented right
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  onto that metal tongue. The force from the lever
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  directly strains the gauge, which gives you a continuous,
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  immediate electrical reading of the tension.
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  No complex gears, no linkages, just it's a simple lever.
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  It's incredibly reliable. That is elegant, but the
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  complexity really jumps when we talk about integrated safety
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  systems like a crane overload warning device that has to
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  process two different inputs at the same time.
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  It's basically an early analog safety computer.
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  It's dealing with two critical linked factors. 1st is the boom
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  angle. Right.
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  A low angle creates a much greater overturning torque, but
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  then there's the compression load, or the cable tension,
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  which is often greatest at high boom angles when you pull
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  straight up. And the system has to know which
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  combination is the dangerous one.
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  It always has to warn of the danger, no matter the cause.
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  So how does a purely mechanical and hydraulic system do that?
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  How does it integrate load and angle at the same time?
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  OK, so first attention to pressure transducer converts the
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  load into proportional hydraulic pressure.
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  That pressure feeds a Borden 2 pointer.
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  Which is basically a coiled tube that tries to straighten out
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  under pressure. Exactly, and the pointer on the
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  end of it carries a small magnet, so the position of that
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  magnet tells you the load. OK, that's the load.
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  What about the angle? The boom angle is monitored by a
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  Cam which is linked directly to the boom itself, and this Cam
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  positions a series of magnetic Reed switches along the path of
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  that pointer. I see where this is going, the
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  alert. Only triggers if the mag the
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  load component gets close enough to one of the switches.
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  The angle component, the Cam is shaped so that at a dangerous
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  angle it moves the switches closer to the magnets starting
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  position. So it takes less load to trigger
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  the alarm. That's it.
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  It's fail safe. It flags an unsafe lift whether
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  the danger comes from a heavy load alone or a lighter load at
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  a dangerously extended angle. Truly ingenious non digital
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  integration. OK, moving from force management
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  to merchant transformation, let's talk about gearing.
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  Specifically, gearing designed for high power redundancy and
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  high ratio efficiency. A great place to start is the
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  Twin Motor Planetary Gear drive, a brilliant solution for safety
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  and things like hoists and cranes.
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  The genius here is providing redundancy without really
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  sacrificing performance, right? It's mechanical synergy at its
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  best. You have two motors of equal
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  rating. One drives the ring gear, the
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  other drives the sun gear. If both run at the same speed,
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  the output, which is the cage holding the planet gears,
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  revolves at that speed. But the safety factor kicks in
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  IF1 motor fails. Exactly.
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  If one motor fails completely, the cage still revolves, but now
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  in exactly half its original speed.
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  And critically, critically, the unit maintains its full lifting
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  capacity. The working motor is still
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  providing full torque. It's a beautifully reliable
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  system that also gives you 2 working speeds without complex
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  shifting. OK, so contrast that robust
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  safety first design with something like the Harmonic Dr.
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  reducer, which is all about getting massive speed ratios in
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  a tiny space. The harmonic Dr. is mechanically
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  complex. It actually uses elastic
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  mechanics. You have 3 components, a wave
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  generator, a flexible spline, the flex spline and a circular
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  spline. And the ratio comes from the
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  wave generator intentionally distorting that flex spline,
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  right? It forces the teeth the flex
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  spline to mesh with the fixed circular spline, but only at 2
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  points 180° apart. And because the flex spline has
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  a slightly different number of teeth, one full revolution of
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  that wave generator causes only a tiny, tiny rotation in the
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  output. You get huge speed reductions,
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  hundreds to 1. And a very small volume, but
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  there is a key mechanical drawback you have to manage
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  which is wind up. You mean a torsional spring
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  rate? Yes, as the torsional load
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  increases like in a robotic joint, the flex plant itself has
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  to flex slightly. This can cause adjacent teeth to
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  engage a little bit before they're supposed to.
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  If you need absolute 0 backlash precision that wind up is a
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  critical factor you have to design around.
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  While those drives manage big rotational loads, the IBM Linear
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  Micron Positioner takes us to the total opposite.
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  Extreme micro precision linear control with simple mechanics.
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  This thing is incredible. A low cost mechanism that
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  achieved fine focus control for a camera lens down to 10
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  millionths of an inch, and it uses a very simple differential
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  circumference principle. Imagine 2 concentric cylinders
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  with slightly different diameters connected by flexible
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  Shim stock bands. So when you rotate the inner
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  cylinder, the difference in circumference between the two
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  dictates the tiny linear travel of the output.
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  That's all it is, and if the diameters are very close, the
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  reduction ratio is massive, theoretically capable of 10,000
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  to 1. You see that same need for hyper
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  precision in something like the NASA triple gang lead screw
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  mechanism. Right, which was designed for
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  tuning microwave resonant cavities.
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  Where the challenge wasn't just tiny movement, it was
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  maintaining absolute parallelism.
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  If that moving plate tilts even slightly, the whole cavity is
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  ruined. The solution was pure mechanical
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  synchronization. A large central gear
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  simultaneously drives three separate, perfectly synced lead
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  screws, one at each corner. This guarantees the movable
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  plate never tilts. That's a great transition into
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  our final section, where mechanisms get really tiny,
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  autonomous, and use some pretty advanced material science.
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  We have to 1st acknowledge the role of computer aided design or
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  CAD. The shift from 2D CAD, which was
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  really just automated drafting to.
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  Full 3D solid modeling. That's where the design
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  intelligence really lives. It is. 3D modeling gives you
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  incredible visual fidelity, sure, but more importantly it
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  consolidated all the information for faster flaw detection,
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  stress analysis. You build complex assemblies
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  using boolean operations, union, subtraction, intersection on
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  simple shapes like prisms and spheres.
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  It's digital construction. But the real revolution in tiny
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  machines is microelectromechanical systems.
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  MEMS machines fabricated directly onto a silicon chip.
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  To Silicon isn't just for electronics anymore, it's a
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  structural material. And it's an almost perfect
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  mechanical material. It lacks mechanical hysteresis,
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  which means doesn't lose energy or change shape permanently when
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  you bend it. Its yield strengths is greater
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  than stainless steel and its strength to weight ratio is
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  better than aluminum. And the manufacturing is
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  basically just advanced micro circuitry fabrication.
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  You're using lithography to build gears and springs.
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  Exactly. Processes like Summit VA 5 level
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  Micro Machining Process let you build incredibly intricate
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  things like microtransmissions right on the chip.
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  And how do you power something that's small?
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  One common way is a comb Dr. which uses electrostatic force.
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  So it relies on the attractive force generated between those
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  little interdigitated fingers in the comb structure.
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  Right, and the force is governed by the energy stored.
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  Equation calculated is E equals CV squared divided by two, where
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  C is capacitance and V is voltage.
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  You need a huge number of those little fingers to generate a
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  useful amount of force. And finally, let's go back to
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  NASA for robotic mechanisms designed for hostile
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  environments where a human hand just can't go the probe and
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  socket fastener. This was designed to be robot
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  operated, so it had to be foolproof self aligning.
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  To prevent it from binding during insertion.
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  Right, the socket has these tapered grooves and ridges that
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  match perfectly with the probe, forcing it into alignment.
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  The whole thing uses spring loaded lock pins that are
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  retracted by an actuator so the robot can just push click and
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  it's made it securely. And for ultra fine adjustments
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  in huge structures, there's the inchworm actuator.
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  Proposed as an active trust member to counteract subtle
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  vibrations or even change the configuration of a whole Truss.
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  And it uses piezoelectric actuator.
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  Three of them, along with Belleville washers,
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  piezoelectric devices expand or contract with extreme accuracy
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  when you apply electricity. The clever bit is the Belleville
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  washers, which are cone shaped springs.
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  They apply constant preload. Which is key because it means
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  the overall length is maintained without constant power.
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  It locks its position mechanically.
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  It does, and the precision is staggering a stroke accuracy of
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  0.0001 centimeters. You get micro level control over
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  macro level structure. We've really traveled today from
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  thermal set copper booms to purely mechanical analog safety
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  computers, and then all the way down to machines built on
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  silicon. It really emphasizes how
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  engineers solve problems. Sometimes it's by leveraging
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  simple, elegant forces like springs and lovers, and other
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  times by exploiting cutting edge material science to get
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  precision at any scale you can imagine.
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  The core principles really do stay the same even as the scale
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  shrinks. They do.
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  You know, we saw how James Daniels mechanical linkage could
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  produce near perfect straight line motion without any
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  guideways, just through link proportions and pivot placement.
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  So here's a thought for you to Mull over.
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  In a world moving so fast toward MEMS and fully digital control,
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  what classic, purely mechanical mechanism do you think will
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  remain irreplaceable just because of its inherent elegance
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  and robustness? That's it for today, design
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  junkies. If you're getting something out
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