Nothing brings out the worst in humanity like war. Perversely, war also seems to exert an opposite if not equal force that leads to massive outbursts of creativity, the likes of which are not generally seen during times of peace. With inhibitions relaxed and national goals to meet, or in some cases where the very survival of a people is at stake, we always seem to find new and clever ways to blow each other to smithereens.
The run-up to World War II was a time where almost every nation was caught on its heels, and the rapidity of events unfolding across Europe and in Asia demanded immediate and decisive response. As young men and women mobilized and made ready for war, teams of engineers, scientists, and inventors were pressed into service to develop the weapons that would support them. For the British, these “boffins” would team up under a directorate called Ministry of Defence 1, or MD1. Informally, they’d be known as “Churchill’s Toy Shop,” and the devices they came up with were deviously clever hacks.
Current. Too little of it, and you can’t get where you’re going, too much and your hardware’s on fire. In many projects, it’s desirable to know just how much current is being drawn, and even more desirable to limit it to avoid catastrophic destruction. The humble current shunt is an excellent way to do just that.
Ohm’s Law.
To understand current, it’s important to understand Ohm’s Law, which defines the relationship between current, voltage, and resistance. If we know two out of the three, we can calculate the unknown. This is the underlying principle behind the current shunt. A current flows through a resistor, and the voltage drop across the resistor is measured. If the resistance also is known, the current can be calculated with the equation I=V/R.
This simple fact can be used to great effect. As an example, consider a microcontroller used to control a DC motor with a transistor controlled by a PWM output. A known resistance is placed inline with the motor and, the voltage drop across it measured with the onboard analog-to-digital converter. With a few lines of code, it’s simple for the microcontroller to calculate the current flowing to the motor. Armed with this knowledge, code can be crafted to limit the motor current draw for such purposes as avoiding overheating the motor, or to protect the drive transistors from failure.
In fact, such strategies can be used in a wide variety of applications. In microcontroller projects you can measure as many currents as you have spare ADC channels and time. Whether you’re driving high power LEDs or trying to build protection into a power supply, current shunts are key to doing this.
In one hand you hold the soldering iron, in the other the solder, and in two more hands the parts you’re trying to solder together. Clearly this is a case where helping hands could be useful.
One reason is to take advantage of standardized, open source creativity. Anyone can share a model of their design for all to use as is, or to modify for their needs. A case in point is the ball and socket model which I downloaded for a helping hand. I then drew up and printed a magnifying glass holder with a matching socket, made a variation of the ball and socket joint, and came up with a magnetic holder with matching ball. Let’s takea look at what worked well and what didn’t.
If you’ve made it through the last two posts on quantum computing (QC), then you’ve seen the Quirk simulator, a little of IBM’s web-based offering, and how entanglement and superposition can do strange and possibly wonderful things. However, the superdense encoding I showed you didn’t really feel like a real computer algorithm. This time we will look at Grover’s algorithm which is often incorrectly billed as an “unstructured database search.” In reality, it is an algorithm for making a state — that is a set of qubits — match some desired state without simply setting the state.
By analogy, consider a web service where you guess a number. Most discussions of Grover’s algorithm will tell you that the service will only tell you if the number is correct or not. If the number was from 1 to 16, using traditional computing, you’d have to query the values one at a time to see which is correct. You might get lucky and hit the first time. Or it might take 16 times. With qubits you can get the same result in only four attempts. In fact, if you try more times, you might get the wrong answer. Of course, what you really get is an answer that is probably correct, because that how QC works.
When I first started getting into 3D printed projects that would require final assembly from multiple parts, I wanted to make sure I had an adhesive that would really hold up. I couldn’t imagine anything worse than spending 10’s of hours printing and assembling something, only to have it fall apart because my adhesive wasn’t up to the task. So I spent a lot of time trolling 3D printing message boards and communities trying to find the best way of gluing PLA. It should come as no surprise that, like everything else in the world, there are a ridiculous number of opinions on the subject.
If you’re printing with ABS, the general wisdom is that solvent welding with acetone is the best bet. You put some acetone on the printed parts, rub them together, and the plastic fuses together. This happens because the ABS melts slightly when exposed to the acetone, so they end up essentially melding into one piece. This sounded like exactly what I wanted, but unfortunately, acetone doesn’t have this same effect on PLA.
After some more research I found people suggesting Weld-On #16, an acrylic adhesive that will actually melt PLA. A little of this applied to the parts, they said, and you can solvent weld PLA just like acetone on ABS. Sure enough, the stuff works great and I’ve used it to put together nearly everything I’ve printed in PLA over the last few years. Only problem is, this stuff is a bit nasty, takes 24 hours to fully cure, and nobody has it locally.
So as an experiment I thought I’d take a look at a few adhesives sold at the local big box retailer and see if I couldn’t find something comparable. Do I need to keep ordering this nasty goop online every time, or can I pick something up off the shelf? More to the point, is solvent welding PLA really any better than just gluing it?
From the time Mae Jemison was a little girl, she was convinced that she would go to space. No one could tell her otherwise. She was sure that space travel would be as common as air travel by the time she was an adult. That prediction didn’t pan out, but that confidence combined with her intellect, curiosity, and the above-average encouragement of her parents drove Mae to do everything she wanted, including space travel.
Some people might become a doctor or a researcher, a dancer or an astronaut. But Mae became all of these things. Not everyone supported her non-traditional path—many people just pick a career and stick with it. Her path is impressive and through it all she gained a really interesting perspective on how education is approached, and what effects that approach has on society. After practicing medicine, joining a shuttle mission, appearing in Star Trek, and retiring from NASA, she became a voice for minority students and an advocate for integrating the arts and sciences in the standard curriculum.
We’ve been having a lively discussion behind the scenes here at Hackaday, about SpaceX’s forthcoming launch of their first Falcon Heavy rocket. It will be carrying [Elon Musk]’s red Tesla Roadster, and should it be a successful launch, it will place the car in an elliptical orbit round the Sun that will take it to the Martian orbit at its furthest point.
On one hand, it seems possible that [Musk]’s sports car will one day be cited by historians as the exemplar of the excesses of the tech industry in the early 21st century. After all, to spend the millions of dollars required to launch the largest reusable space launch platform ever created, and then use it to hurl an electric vehicle into orbit round the Sun seems to be such a gratuitous waste of resources, an act of such complete folly as to be criminal.
Surely even given that there is a reasonable chance of a first launch ending in fiery destruction it must be worth their while canvassing the universities and research institutions of the world with the offer of a free launch, after all there must be a significant amount of science that would benefit from some cost-free launch capacity! It seems a betrayal of the famous “Why explore space” letter from the associate science director of NASA to a nun who questioned the expenditure while so many in the developing world were starving.
Testing
But on the other hand, first launches of rockets are a hazardous endeavour, as the metaphorical blue touchpaper is lit on the world’s largest firework for the first time. Satellites are expensive devices, and it would be a foolhardy owner who entrusted their craft to a launch vehicle with a good chance of a premature splashdown.
Launch of first Arianne 5. Not where you want your pricey satellite.
First launches traditionally carry a ballast rather than a payload, for example NASA have used tanks of water for this purpose in the past. SpaceX has a history of novelty payloads for their test launches; their first Dragon capsule took a wheel of cheese into space and returned it to Earth. We picture Musk looking around a big warehouse and saying, “well, we got a lot of cars!”
There is a fascinating question to be posed by the launch of the car, just what did they have to do to it to ensure that it could be qualified for launch? Satellite manufacture is an extremely exacting branch of engineering, aside from the aspect of ensuring that a payload will work it must both survive the launch intact and not jeopardise it in any way. It’s safe to say that the Roadster will not have to function while in orbit as the roads of California will be far away, but cars are not designed with either the stresses of launch or the transition to zero gravity and the vacuum of space in mind. Will a glass windscreen originally specified for a Lotus Elise on the roads of Norfolk shatter during the process and shower the inside of the craft with glass particles, for example? There must have been an extensive space qualification programme for it to pass, from vibration testing through removal of any hazards such as pressurised gases or corrosive chemicals, if only the folks at SpaceX would share some its details that would make for a fascinating story in itself.
Space Junk
So the Tesla Roadster is a huge publicity stunt on behalf of SpaceX, but it serves a purpose that would otherwise have to have been taken by an unexciting piece of ballast. It will end up as space junk, but in an orbit unlikely to bring it into contact with any other craft. If its space-suited dummy passenger won’t be providing valuable data on the suit’s performance we’d be extremely surprised, and when it is finally retrieved in a few centuries time it will make a fascinating exhibit for the Smithsonian.
Given a huge launch platform and the chance to fill it with a novelty item destined for orbit,the Hackaday team stepped into overdrive with suggestions as to what might be launched were they in charge. They varied from Douglas Adams references such as a heart of gold or a whale and a bowl of petunias should the rocket abort and the payload crash to earth, to a black monolith and a few ossified ape remains to confuse space historians. We briefly evaluated the theory that the Boring Company is in fact a hiding-in-plain-sight construction organisation for a forthcoming Evil Lair beneath the surface of Mars, before concluding that maybe after all the car is a pretty cool thing to use as ballast for a first launch.
It may be reaching towards seven decades since the first space programmes successfully sent rockets beyond the atmosphere with the aim of exploration, but while the general public has become accustomed to them as routine events they remain anything but to the engineers involved. The Falcon Heavy may not have been developed by a government, but it represents every bit as astounding an achievement as any of its predecessors. Flinging an electric vehicle into orbit round the Sun is a colossal act of showmanship and probably a waste of a good car, but it’s also more than that. In hundreds of years time the IoT devices, apps, 3D printers, quadcopters or whatever else we toil over will be long forgotten. But there will be a car orbiting the Sun that remains a memorial to the SpaceX engineers who made its launch possible, assuming it doesn’t blow up before it gets there. What at first seemed frivolous becomes very cool indeed.
