Rocker Bogie Suspension: The Beloved Solution To Extra-Planetary Rovers

September 14, 2023 by Lewin Day 18 Comments

When navigating the vast and unpredictable expanses of outer space, particularly on the alien terrains of distant planets, smart engineering often underlies every major achievement. A paramount example of this is the rocker bogie suspension system. It’s an integral component of NASA’s Mars rovers and has become an iconic feature in its own right. Its success has seen the design adopted by the Indian space program and thousands of hobbyists in turn.

So, what exactly is it that makes rocker bogie suspension such a compelling design solution? Let’s dive into the engineering that makes these six-wheeled wonders so special.

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Mining And Refining: Quartz, Both Natural And Synthetic

September 6, 2023 by Dan Maloney 17 Comments

So far in this series, pretty much every material we’ve covered has had to undergo a significant industrial process to transform it from its natural state to a more useful product. Whether it’s the transformation of bauxite from reddish-brown clay to lustrous aluminum ingots, or squeezing solid sulfur out of oil and natural gas, there haven’t been many examples of commercially useful materials that are taken from the Earth and used in their natural state.

Quartz, though, is at least a partial exception to this rule. Once its unusual electrical properties were understood, crystalline quartz was sent directly from quarries and mines to factories, where they were turned into piezoelectric devices with no chemical transformation whatsoever. The magic of crystal formation had already been done by natural processes; all that was needed was a little slicing and dicing.

As it turns out, though, quartz is so immensely useful for a technological society that there’s no way for the supply of naturally formed crystals to match demand. Like copper before it, which was first discovered in natural metallic deposits that could be fashioned into tools and decorations more or less directly, we would need to discover different sources for quartz and invent chemical transformations to create our own crystals, taking cues from Mother Nature’s recipe book on the way.

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Make Better 3D Printed Molds, For Thermoforming Plastics

September 2, 2023 by Donald Papp 6 Comments

Thermoforming — which includes vacuum-forming — has its place in a well-rounded workshop, and Mayku (makers of desktop thermoforming machines) have a short list of tips for getting the best results when 3D printing molds on filament-based printers.

A mold is put into direct, prolonged contact with a hot sheet of semi-molten plastic. If one needs a mold to work more than once, there are a few considerations to take into account. The good news is that a few simple guidelines will help get excellent results. Here are the biggest ones:

The smoother the vertical surfaces, the better. Since thermoforming sucks (or pushes) plastic onto and into a mold like a second skin, keeping layer heights between 0.1 mm and 0.2 mm will make de-molding considerably easier.
Generous draft angles. Aim for a 5 degree draft angle. Draft angles of 1-2 degrees are common in injection molding, but a more aggressive one is appropriate due to layer lines giving FDM prints an inherently non-smooth surface.
Thick perimeters and top layers for added strength. The outside of a mold is in contact with the most heat for the longest time. Mayku suggests walls and top layer between 3 mm to 5 mm thick. Don’t forget vent holes!
Use a high infill to better resist stress. Molds need to stand up to mechanical stress as well as heat. Aim for a 50% or higher infill to make a robust part that helps resist deformation.
Ensure your printer can do the job. 3D printing big pieces with high infill can sometimes lift or warp during printing. Use enclosures or draft shields as needed, depending on your printer and material.
Make the mold out of the right material. Mayku recommends that production molds be printed in nylon, which stands up best to the heat and stress a thermoforming mold will be put under. That being said, other materials will work for prototyping. In my experience, even a PLA mold (which deforms readily under thermoforming heat) is good for at least one molding.

Thermoforming open doors for an enterprising hacker, and 3D printing molds is a great complement. If you’re happy being limited to small parts, small “dental” formers like the one pictured here are available from every discount overseas retailer. And of course, thermoforming is great for costumes and props. If you want to get more unusual with your application, how about forming your very own custom-shaped mirrors by thermoforming laminated polystyrene?

Converting Wind To Electricity Or: The Doubly-Fed Induction Generator

August 30, 2023 by Bryan Cockfield 97 Comments

Humanity has been harvesting energy from the wind for centuries. The practice goes back at least to 8th century Persia where the first known historical records of windmills came, but likely extends even further back than that. Compared to the vast history of using wind energy directly to do things like mill grain, pump water, saw wood, or produce fabrics, the production of electricity is still relatively new. Despite that, there are some intriguing ways of using wind to produce electricity. Due to the unpredictable nature of wind from moment to moment, using it to turn a large grid-tied generator is not as straightforward as it might seem. Let’s take a look at four types of wind turbine configurations and how each deal with sudden changes in wind speeds. Continue reading “Converting Wind To Electricity Or: The Doubly-Fed Induction Generator” →

The 2003 Northeast Blackout And The Harsh Lessons Of Grid Failures

August 29, 2023 by Maya Posch 87 Comments

The grid failure in 2003 which reverted much of the eastern US and Canada back to a pre-electrification era may be rather memorable, yet it was not the first time that a national, or even international power grid failed. Nor is it likely that it will be the last. In August of 2023 we mark the 20th anniversary of this blackout which left many people without electricity for up to three days, while costing dozens of people their lives. This raises the question of what lessons we learned from this event since then.

Although damage to transmission lines and related infrastructure is a big cause of power outages – especially in countries where overhead wiring is the norm – the most serious blackouts involve the large-scale desynchronization of the grid, to the point where generators shutdown to protect themselves. Bringing the grid back from such a complete blackout can take hours to days, as sections of the grid are reconnected after a cascade scenario as seen with the 2003 blackout, or the rather similar 1965 blackout which affected nearly the same region.

With how much more modern society relies today on constant access to electrical power than it did twenty, let alone fifty-eight years ago, exactly how afraid should we be of another, possibly worse blackout?

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Blame It On The Sockets: Forensic Analysis Of The Arecibo Collapse

August 29, 2023 by Dan Maloney 58 Comments

Nearly three years after the rapid unplanned disassembly of the Arecibo radio telescope, we finally have a culprit in the collapse: bad sockets.

In case you somehow missed it, back in 2020 we started getting ominous reports that the cables supporting the 900-ton instrument platform above the 300-meter primary reflector of what was at the time the world’s largest radio telescope were slowly coming undone. From the first sign of problems in August, when the first broken cable smashed a hole in the reflector, to the failure of a second cable in November, it surely seemed like Arecibo’s days were numbered, and that it would fall victim to all the other bad luck we seemed to be rapidly accruing in that fateful year. The inevitable finally happened on December 1, when over-stressed cables on support tower four finally gave way, sending the platform on a graceful swing into the side of the natural depression that cradled the reflector, damaging the telescope beyond all hope of repair.

The long run-up to the telescope’s final act had a silver lining in that it provided engineers and scientists with a chance to carefully observe the failure in real-time. So there was no real mystery as to what happened, at least from a big-picture perspective. But one always wants to know the fine-scale details of such failures, a task which fell to forensic investigation firm Thornton Tomasetti. They enlisted the help of the Columbia University Strength of Materials lab, which sent pieces of the failed cable to the Oak Ridge National Laboratory’s High Flux Isotope reactor for neutron imaging, which is like an X-ray study but uses streams of neutrons that interact with the material’s nuclei rather than their electrons.

The full report (PDF) reveals five proximate causes for the collapse, chief of which is “[T]he manual and inconsistent splay of the wires during cable socketing,” which we take to mean that the individual strands of the cables were not spread out correctly before the molten zinc “spelter socket” was molded around them. The resulting shear stress caused the zinc to slowly flow around the cable strands, letting them slip out of the surrounding steel socket and — well, you can watch the rest below for yourself.

As is usually the case with such failures, there are multiple causes, all of which are covered in the 300+ page report. But being able to pin the bulk of the failure on a single, easily understood — and easily addressed — defect is comforting, in a way. It’s cold comfort to astronomers and Arecibo staff, perhaps, but at least it’s a lesson that might prevent future failures of cable-supported structures.

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Making Electricity At The South Pole

August 24, 2023 by Chris Lott 78 Comments

In case you’ve ever wondered how the South Pole research stations are powered, then a recent blog post, South Pole Electrical Infrastructure by anonymous IT engineer [brr] is for you. Among the many issues covered, let’s look at how the electricity is made and, spoiler alert, how the specially formulated AN8 fuel blend is transported to the generators.

The main source of power is a trio of Caterpillar 3512B diesel generator sets, de-rated to 750 kW each due to the high altitude and the special fuel mixture. Unsurprisingly, all the fuel must be imported to Antarctica, a horribly inefficient endeavor. Fuel arrives initially at McMurdo Station harbor by tanker ship. From there, it can be sent to the Amundsen-Scott South Pole Station in one of two ways. The Lockheed LC-130 is a modified C-130 Hercules cargo plane developed in the 1950s specifically to support polar operations. It is the least efficient method, consuming 1.33 kg to transport 1 kg of fuel. Alternatively, fuel can be dragged by tractors via the South Pole Overland Traverse (SPoT), a 1600 km highway over compacted snow and ice. The trek takes about 40 days and only consumes 0.56 kg of fuel for every 1 kg, which is much better than air.

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