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May 23 2018

Mechanisms: Solenoids

Since humans first starting playing with electricity, we’ve proven ourselves pretty clever at finding ways to harness that power and turn it into motion. Electric motors of every type move the world, but they are far from the only way to put electricity into motion. When you want continuous rotation, a motor is the way to go. But for simpler on and off applications, where fine control of position is not critical, a solenoid is more like what you need. These electromagnetic devices are found everywhere and they’re next in our series on useful mechanisms.

A Coil and a Plunger

A physicist will tell you a solenoid simply a coil of wire through which current can be passed. That’s it. Other than in the physics lab, though, such a simple device is not of much mechanical use, so what we tend to think of as a solenoid is slightly more complicated. A practical solenoid has a coil, but it’s also going to have several mechanical parts to make it work as an actuator.

Plunger-type solenoid. Source: UniqueMachines

A plunger solenoid is a good example of the basics. The air core of the solenoid’s coil is partially occupied by an iron or mild steel plunger, held in place by a return spring. When current is applied to the coil, a magnetic field forms, and the plunger is pulled forcefully into the solenoid’s core. When current stops flowing, the magnetic field collapses, and the return spring forces the plunger back to the resting state. This is characteristic of most solenoids — they’re either actuated or they’re not. This makes them great for jobs that require something to be positioned in either one position or another over a short distance, like valves that stop the flow of liquid through a pipe or tubing.

Plunger solenoids range in size from the very tiny to the ludicrously large. On the small side, plunger solenoids see service as actuators for microfluidics valves in scientific and medical applications, and in the drive head for the impact style of dot-matrix printers (yes, each one of those dots is the plunger of a solenoid).

You likely interact with medium-sized solenoids on a daily basis. The click at the beginning and end of your refrigerator’s ice maker is what switches the water on and off to refill the tray. You’ll hear a similar click in fountain soda machines. And those pinball wizards among us will attest that the forces throwing that silver ball around the playfield are generated by solenoids.

Stepping up the scale, there’s a fairly large solenoid inside the starter motor of almost every car and truck on the road, at least those with internal combustion engines. The solenoid sits atop the starter motor and is responsible for connecting and disconnecting the starter from the system. The solenoid’s plunger is attached to the motor drive shaft via a lever. When the ignition key is turned, the solenoid coil is energized, pulling the plunger in and moving the lever out along the now-spinning motor shaft. This drives a pinion gear out to engage with the engine flywheel to crank the engine until it starts.

Solenoid Styles

One type of rotary solenoid. Source: UniqueMachines

Other styles of solenoid are available, including rotary solenoids. These are exactly what they sound like: actuators that can rotate between two positions. Designs vary, but the most common types have a permanent magnet rotor on a shaft inside the solenoid’s core. When the coil is energized, the rotor experiences a torque due to the magnetic field, much like the rotor of a permanent magnet motor. The rotor only moves to a physical stop, though, and is returned to the resting position by a spring when the coil is de-energized. If the polarity of the coil is reversed, then the rotor and shaft can swing the other way, making this style of rotary solenoid bistable. Other rotary solenoids use a metal disc with ramped grooves and ball bearings; when the plunger is sucked into the core, the ball bearings force the disc and shaft to rotate along the grooves.

AC, DC, and Snubbing

As electrically simple devices, solenoids can run on either AC or DC. A DC solenoid tends to be quieter because the magnetic field is constant while the coil is energized. An AC solenoid tends to chatter as the magnetic field varies and the force of the return spring overcomes it at the instant the current changes direction in the coil. This tendency can be mitigated by the use of a shading ring to alter the magnetic circuit of AC solenoids. A shading ring is just a small copper ring that sits inside the core of the solenoid so it contacts the plunger when it’s fully retracted. The magnetic field of the energized coil induces a current inside the ring, which in turn creates its own magnetic field that lags the phase of the solenoid’s field by 90°. When the solenoid’s field falls to zero as the AC waveform passes the zero point, the magnetic flux from the shading ring keeps the solenoid retracted, eliminating the bothersome chatter.

While any solenoid will run on AC or DC, care needs to be taken to observe the coil’s specs. Solenoids represent an inductive load, and so their impedance is much higher in AC applications. So if a solenoid rated for 24 VAC were powered by 24 VDC, it would probably burn out quickly as the current through it would exceed the design specs. This could be avoided with a current limiting resistor or by lowering the DC supply voltage.

Like their cousin the relay, solenoids have the potential to damage whatever circuit is controlling them. When the current flowing through a solenoid or relay coil is removed, the voltage spikes as the magnetic field collapses. If that spike gets into sensitive components, like a transistor driving the coil, the device could be destroyed. The classic remedy for this with DC coils is the snubber diode, connected in parallel across the coil with the anode on the negative side. The snubber gives the induced current somewhere to go when the power is removed from the coil to prevent it from inducing the high voltage spike. Snubber diodes won’t work on AC coils, so an RC snubber, with a small resistance and capacitance in series with each other placed in parallel across the coil, serves the same purpose.

This is only a brief look at what solenoids are and do, and how to incorporate these mechanisms into your designs.

Reposted fromhackaday hackaday

October 29 2017

MapMap - Projection Mapping Central

MapMap - Projection Mapping Central
http://projection-mapping.org/tools/mapmap
http://projection-mapping.org/wp-content/uploads/2017/08/mapmap-workshop-1280x960.jpg

MapMap is a free software of projection mapping which is mainly aimed at artists and small teams. Its intuitive interface facilitates learning and promotes artistic expression. Visit: http://mapmap.info for more.

#projection_mapping

Reposted fromcheg00 cheg00

October 28 2017

6637 62af 500

prostheticknowledge:

Progressive Growing of GANs for Improved Quality, Stability, and Variation

Research from @Nvidia has taken neural network image synthesis to much higher visual definition than has previously been achieved:

The video below has no audio and example results starts approximately 38 seconds into it:

We describe a new training methodology for generative adversarial networks. The key idea is to grow both the generator and discriminator progressively, starting from low-resolution images, and add new layers that deal with higher resolution details as the training progresses. This greatly stabilizes the training and allows us to produce images of unprecedented quality, e.g., CelebA images at 1024² resolution. We also propose a simple way to increase the variation in generated images, and achieve a record inception score of 8.80 in unsupervised CIFAR10. Additionally, we describe several small implementation details that are important for discouraging unhealthy competition between the generator and discriminator. Finally, we suggest a new metric for evaluating GAN results, both in terms of image quality and variation. As an additional contribution we construct a higher quality version of the CelebA dataset that allows meaningful exploration up to the resolution of 1024² pixels. 

More Here

Reposted fromcheg00 cheg00

July 05 2015

Reposted fromherrkammer herrkammer viamakros makros

July 04 2015

Efficiency, please.
Reposted frompischus pischus viar3xio r3xio
6876 1469
Reposted fromlokrund2015 lokrund2015 viasofias sofias

June 24 2015

7430 c23f

Initiative NEW RADIO
Amateurfunkgeräte für die Zukunft!
Reposted frommetafunk metafunk vialeyrer leyrer

June 22 2015

June 20 2015

Google Research Blog: Inceptionism: Going Deeper into Neural Networks

Artificial Neural Networks have spurred remarkable recent progress in image classification and speech recognition. But even though these are very useful tools based on well-known mathematical methods, we actually understand surprisingly little of why certain models work and others don’t. (...)

One way to visualize what goes on is to turn the network upside down and ask it to enhance an input image in such a way as to elicit a particular interpretation. (...)

The techniques presented here help us understand and visualize how neural networks are able to carry out difficult classification tasks, improve network architecture, and check what the network has learned during training. It also makes us wonder whether neural networks could become a tool for artists—a new way to remix visual concepts—or perhaps even shed a little light on the roots of the creative process in general.
This orange battery was built by photographer Caleb Charland (previously) as part of his ongoing alternative energy photographs using fruit, vegetables, and other objects to create light for his long-exposure photographs. The electricity powering the lightbulb inside the orange is generated through a chemical reaction between citric acid and the zinc nails inserted into each wedge. I think this is by far the most lovely piece he’s done in the series, but before you start work on a bunch of orange lights to keep on the nightstand, the light generated was so dim this particular photograph required a 14 hour exposure.
Reposted fromsober sober viaPhlogiston Phlogiston

June 07 2015

7952 1d32
Reposted fromsuperlog superlog

Hubo wird Weltmeister [Mathlog]

Team KAIST hat mit dem DRC-Hubo gestern in Pomona/Kalifornien die DARPA Robotics Challenge gewoonen, einen von DARPA (einer Behörde des US-Verteidigungsministeriums) organisierten Wettbewerb für humanoide Roboter.

KAIST steht übrigens für “Korea Advanced Institute for Science and Technology” und ist die führende Technische Universität in Korea. (Formal ist auch mein Institut, das “Korea Institute for Advanced Study”, dem KAIST angegliedert, räumlich sind wir allerdings fast 150 Kilometer vom Hauptsitz in Daejeon entfernt.) Ich hatte vor 2 Jahren mal einen Artikel über das Discovery Center in Daejeon geschrieben, dessen Attraktion die humanoiden Roboter sind, die in einer 20-minütigen Show zum Beispiel auf Zurufe reagieren und mit den Kindern Schere-Stein-Papier spielen.

Auf YouTube gibt es schon ein neues Video über den diesjährigen Wettbewerb. Das Video ist fast 4 Stunden lang, aber es ist auch schon interessant, einfach mal zwischendurch an ein paar Stellen beliebig hineinzuklicken. Wie man sieht, ging es vor allem um den Einsatz von Robotern als Katastrophenhelfer.

Reposted from02mysoup-aa 02mysoup-aa

Darpa Robotics Challenge: Hubo ist der beste Roboter für den Katastrophenfall

Ein Ventil öffnen, Auto fahren und weitere Aufgaben mussten Roboter bei einem Wettbewerb des US-Verteidigungsministeriums möglichst schnell bewältigen. Der Gewinner Hubo schaffte den Parcours in weniger als 45 Minuten - und hat seinen Erbauern 2 Millionen US-Dollar Preisgeld verschafft. (Roboter, Technologie)
Reposted fromzeitung zeitung

June 06 2015

Reposted fromdoener doener
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Reposted fromkalafiorowa kalafiorowa viasalvinorum salvinorum

3-D printing tough biogel structures for tissue engineering or soft robots

Lasagna? No, an open lattice of 3-D printed material, with materials having different characteristics of strength and flexibility indicated by different colors (credit: the researchers)

Researchers at three universities have developed a new way of making tough — but soft and wet — biocompatible hydrogel materials into complex and intricately patterned shapes. The process might lead to scaffolds for repair or replacement of load-bearing tissues, such as cartilage. It could also allow for tough but flexible actuators for future robots, the researchers say.

The new process is described in a paper in the journal Advanced Materials, co-authored by MIT associate professor of mechanical engineering Xuanhe Zhao and colleagues at MIT, Duke University, and Columbia University.

Zhao says the process can produce complex hydrogel structures that are “extremely tough and robust,” but still allow for encapsulating cells in the structures. That could make it possible to 3D-print complex biostructures.

Biocompatible structures

Hydrogels are defined by water molecules encased in rubbery polymer networks that provide shape and structure. They are similar to natural tissues such as cartilage, which is used by the body as a natural shock absorber.

While synthetic hydrogels are commonly weak or brittle, a number of them that are tough and stretchable have been developed over the last decade. However, making tough hydrogels has usually involved “harsh chemical environments” that would kill living cells encapsulated in them, Zhao says.

The new hydrogel materials are generated by combining polyethylene glycol (PEG) and sodium alginate, which synergize to form a hydrogel tougher than natural cartilage. The materials are benign enough to synthesize together with living cells — such as stem cells — which could then allow high viability of the cells, says Zhao, who holds a joint appointment in MIT’s Department of Civil and Environmental Engineering.

3-D printing strong, flexible biomaterials

3-D printed tough, biocompatible PEG–alginate–nanoclay hydrogels in ear and nose shapes (credit: Sungmin Hong et al./ Advanced Materials)

Previous work was not able to produce complex 3-D structures with tough hydrogels, Zhao says. The new biocompatible tough hydrogel can be printed into diverse 3-D structures such as a hollow cube, hemisphere, pyramid, twisted bundle, multilayer mesh, or physiologically relevant shapes, such as a human nose or ear.

The new method uses a commercially available 3D-printing mechanism, Zhao explains. “The innovation is really about the material — a new ink for 3-D printing of biocompatible tough hydrogel,” he says, specifically, a composite of two different biopolymers.

“Each [material] individually is very weak and brittle, but once you put them together, it becomes very tough and strong. It’s like steel-reinforced concrete.”

The PEG material provides elasticity to the printed material, while sodium alginate allows it to dissipate energy under deformation without breaking. A third ingredient, a biocompatible “nanoclay,” makes it possible to fine-tune the viscosity (how easily it flows) of the material, improving the ability to control its flow through the 3D-printing nozzle.

The material can be made so flexible that a printed shape, such as a pyramid, can be compressed by 99 percent, and then spring back to its original shape, Sungmin Hong, a lead author of the paper and a former postdoc in Zhao’s group, says; it can also be stretched to five times its original size. Such resilience is a key feature of natural bodily tissues that need to withstand a variety of forces and impacts.

Such materials might eventually be used to custom-print shapes for the replacement of cartilaginous tissues in ears, noses, or load-bearing body joints, Zhao says. Lab tests have already shown that the material is even tougher than natural cartilage.

Enhancing resolution

The next step in the research will be to improve the resolution of the printer, which is currently limited to details about 500 micrometers (0.5 millimeters) in size, and to test the printed hydrogel structures in animal models. “We are enhancing the resolution,” Zhao says, “to be able to print more accurate structures for applications.”

The technique could also be applied to printing a variety of soft but tough structural materials, he says, such as actuators for soft robotic systems.

“This is really beautiful work that demonstrates major advances in the utilization of tough hydrogels,” says David Mooney, a professor of bioengineering at Harvard University who was not involved in this work. “This builds off earlier work using other polymer systems, with some of this earlier work done by Dr. Zhao, but the demonstration that one can achieve similar mechanical performance with a common biomedical polymer is a substantial advance.

“It is also quite exciting that these new tough gels can be used for 3-D printing, as this is new for these gels, to my knowledge.”

The work was supported by the National Institutes of Health, the Office of Naval Research, AOSpine Foundation, and the National Science Foundation.

Abstract of 3D Printing of Highly Stretchable and Tough Hydrogels into Complex, Cellularized Structures

A 3D printable and highly stretchable tough hydrogel is developed by combining poly(ethylene glycol) and sodium alginate, which synergize to form a hydrogel tougher than natural cartilage. Encapsulated cells maintain high viability over a 7 d culture period and are highly deformed together with the hydrogel. By adding biocompatible nanoclay, the tough hydrogel is 3D printed in various shapes without requiring support material.

Reposted fromsigaloninspired sigaloninspired

May 16 2015

5134 df5d

permapunk:

blunt-science:

The Strandbeest: Art and Engineering.

Created by Dutch artist Theo Jansen, the Strandbeest is created by rudimentary objects such as PVC piping, wood and sails and contains no electrical or motorised parts; it is instead powered by the wind. 

The Strandbeest has steadily evolved into more complex working structures. Some even having the ability to store wind power in the absence of a breeze, being able to nail pins into the sand when wind power becomes too great, and even sensing when they have entered the water or encountered an object so they can then avoid the obstruction. 

Theo Jansen is ever improving and changing these creatures, and does have a final plan for them saying: “over time, these skeletons have become increasingly better at surviving the elements such as storms and water, and eventually I want to put these animals out in herds on the beaches, so they will live their own lives”.

(Youtube)

Oh wow.

Reposted fromsuperlog superlog

May 14 2015

Electron – Die elektrische Rakete [Was geht?]

Wer noch meinen Artikel “Angriff der Miniraketen” im Hinterkopf hat erinnert sich vielleicht an diese Rakete. Da wir nun die auch etwas mehr über Raketentriebwerke wissen, lohnt sich ein zweiter Blick.

Das besondere an der Electron sind die “Rutherford” Triebwerke. Wie viele Raketentriebwerke, werden auch diese mit Kerosin und flüssigem Sauerstoff angetrieben. Das funktioniert noch ganz klassisch. Aber das Problem ist ja immer, das Zeug in das Triebwerk hinein zu pumpen und das macht man hier zum ersten mal mit elektrischen Pumpen. (Das hier ist die zweite Stufe. Die Batterien sind schätzungsweise die grauen Kästen.) Die Idee ist nicht wirklich neu und wurde auch schon wissenschaftlich untersucht.

second-stage

 

Der erste Gedanke ist eigentlich, dass das nicht gehen sollte. Nach allem was man über die Elektrofahrzeuge gehört hat, kommen Batterien niemals an die Energiedichte von Benzin oder Kerosin heran. Und das stimmt auch. Aber bei einem Raketentriebwerk wird die Sache komplizierter. Anders als ein Auto, muss die Rakete ihren eigenen Sauerstoff mit schleppen. Das ist schon sehr viel Masse. Das Atomgewicht von Sauerstoff beträgt 16, Kohlenstoff wiegt 12 und Wasserstoff 1.

Der Kohlenstoff verbrennt zusammen mit zwei Sauerstoffatomen zu CO₂. Zu einem Kohlenstoffatom mit Gewicht 12, kommen zwei Sauerstoffatome mit Gewicht 16 hinzu. Der Sauerstoff wiegt also fast 3 mal so viel wie der Kohlenstoffanteil des Kerosins. Normalerweise bekommen wir davon nichts mit, denn der Sauerstoff kommt nicht aus dem Tank, sondern aus der Luft. Beim Wasserstoff ist es noch schlimmer. Das Sauerstoffatom in H₂O wiegt 8 mal so viel wie die beiden Wasserstoffatome.

Kerosin besteht nun im wesentlichen aus Kohlenwasserstoffketten, in denen sich Gruppen von einem Kohlenstoffatom und zwei Wasserstoffatomen aneinander reihen. Jede dieser Gruppen hat ein Atomgewicht von 14 und braucht drei Sauerstoffatome mit einem Gewicht von 48 um verbrannt zu werden. Das Gewicht wird mehr als vervierfacht. Das allein reicht aber nicht im Ansatz, um dem mit einer Batterie konkurrenz zu machen. Wenn im Hauptstromverfahren der gesamte Treibstoff benutzt wird und auch die Abwärme noch durch die Brennkammer hindurch kommt, hat die elektrische Pumpe keine Chance.

Aber dieses Verfahren ist aufwändig und führt zu komplexen Triebwerken. Wenn es einfach, klein und billig sein soll, braucht man etwas anderes und meistens ist das ein Gas-Generatorzyklus im Nebenstromverfahren.

Wir erinnern uns: Das Problem ist, dass die Turbine niemals die Temperaturen aushalten würde, wenn man Kerosin und Sauerstoff in der optimalen Mischung verbrennt. Man muss zusätzlich Kerosin einspritzen, damit die Temperaturen niedrig bleiben. Der Unterschied beim Nebenstromverfahren ist, dass das Abgas mit dem zusätzlichen Kerosin durch den Auspuff nach draußen geht, ohne nennenswert Schub zu erzeugen. Das typische Mischverhältnis für so einen Gasgenerator liegt unter 0,5. Das heißt, dass halb so viel Sauerstoff wie Kerosin verwendet wird. Dabei müsste es für die optimale Energieausbeute eigentlich bei 3,4 liegen. Schon sinkt die Energiedichte des Treibstoffs auf etwa ein Achtel des üblichen Wertes.

Dazu kommt noch, dass die Turbine bestenfalls die Hälfte der Energie auch in Arbeit umwandelt, der Elektromotor hingegen fast alles. Und wenn man das alles zusammen nimmt, dann haben die neuesten Batterien gegen die ineffizientesten Turbopumpen geradeso eine Chance. Und die gibt man ihr gerne, denn im Vergleich zu anderen Triebwerken wird mit Elektropumpen (der grüne und der rote Zylinder) alles sehr viel einfacher.

rutherford

Das Ergebnis ist ein elegantes, kleines Triebwerk, mit sehr gutem spezifischem Impuls und miserablem Schub/Gewichtsverhältnis. Normalerweise liegt dieses Verhältnis bei Werten von etwa 1:80 bis 1:150. Das kleine Rutherford Triebwerk mit 1,8 Tonnen Schub dürfte also nur etwa 12-24 kg wiegen. Tatsächlich habe ich noch keine Gewichtsangabe gefunden.

Aber die Leute im Nasaspaceflight-Forum haben einiges zusammengetragen, mit dem man zumindest ein paar Schätzungen anstellen kann. Eine Batterie die 3 Minuten lang 80kW leistet, braucht eine Kapazität von 4kWh. Wenn man der Wikipedia glauben darf, wiegen Lithium-Polymer Batterien (die hier verwendet werden) allein wenigstens 16kg um diese Kapazität zu erreichen. Dazu kommt noch das Gewicht für eine robuste Verpackung und dem ganzen Rest des Triebwerks. Insgesamt dürfte das Triebwerk etwas mehr als 30kg wiegen, bei einem Verhältnis von 1:50 bis 1:60.  Das gilt aber nur für die neun Triebwerke der ersten Stufe.

Das Triebwerk der zweiten Stufe muss etwa doppelt so lang arbeiten und dürfte eine etwa 40kg schwere Batterien mit sich tragen. Dazu kommt noch die viel größere Düse, die im Vakuum für mehr Schub sorgt (2,2 Tonnen), aber eben auch mehr wiegt.

Zusätzliches Gewicht ist in der obersten Stufe besonders ärgerlich. Denn jedes Kilo zusätzliche Masse in der letzten Stufe, ist ein Kilo weniger Nutzlast. Dazu kommt, dass die zweite Stufe noch Masse für ein zusätzliches kleines Steuertriebwerk braucht. Ein Triebwerk allein kann zwar die Lage der Rakete im Raum beliebig ändern, kann aber die Rakete nicht um die eigene Achse drehen. Dafür braucht es zumindest noch ein weiteres bewegliches Triebwerk oder zwei starre Düsen. Dem Bild nach zu urteilen, kommt dafür eine einfache Kaltgasdüse zum Einsatz.

Nun liegt die Nutzlast nur noch bei etwa 100kg in dem angestrebten, Sonnensynchronen Orbit und man schleppt ein über 50kg schweres Triebwerk mit. Ideal ist das alles nicht, aber für eine Rakete in dieser Größe im Prinzip gar nicht schlecht. Mit der weiteren Entwicklung der Batterietechnik könnte die Rakete auch ganz ohne Verbesserungen des Triebwerks an sich eine größere Nutzlast bekommen.

Falls die Electron erfolgreich ist, ist es durchaus möglich, dass noch ganz andere Hersteller auf diese Technik zurückgreifen werden.

Reposted from02mysoup-aa 02mysoup-aa
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