Slow Down That Hot Rod Camera Dolly

[Eric Strebel]  uses a small homemade vehicle with his camera mounted on it to get great tracking shots for the intros to his videos. If the movement is slow enough then the effect is quite professional looking. But he wanted it eight times slower. We not only like the simple way he did it, along with how he machined parts for it, but the result makes it look like a hot rod, hence his name for it, the dolly hot rod. He also has an elegant mechanism for disengaging the motor while he repositions the dolly.

Machining Bondo body filler cylinder
Machining Bondo body filler cylinder

The are many ways to slow down a rotation. We’re assuming he was already at the minimum speed for the vehicle’s 8 RPM motor transmission and electronic speed controller. Gears or pulleys would probably be the next options. But [Eric] went even simpler, switching from roller blade wheels to larger diameter scooter wheels.

As simple as that sounds though, it led to that age-old conundrum, how to attach the wheels to the vehicle. The axle is made up of PVC tubes. So he machined square the ends of some PVC plugs and bolted the plugs to the wheel bearings. That left only to push the PVC plugs into the axle’s tubes. There are a number of ways he could have machined the PVC plugs, and the full explanation of the one he chose is best left to his video below. But basically, it involved first machining a Bondo body filler cylinder with a bolt embedded in it and then using the cylinder to hold onto the PVC plug while he machined that.

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High Speed Imaging Of Magnetic Fields

Some time before experimenting with MRI machines and building his own CT scanner, [Peter Jansen] wanted to visualize magnetic fields. One of his small side projects is building tricoders — pocket sensor suites that image everything — and after playing around with the magnetometer function on his Roddenberry-endorsed tool, he decided he had to have a way to visualize magnetic fields. After some work, he has the tools to do it at thousands of frames per second. It’s a video camera for magnetic fields, pushing the boundaries of both magnetic imaging technology and the definition of the word ‘camera’.

When we last looked at [Peter]’s Hall effect camera, the device worked, but it wasn’t necessarily complete. The original design used I2C I/O multiplexers for addressing each individual ‘pixel’ of the Hall effect array, limiting the ‘framerate’ of the ‘camera’ to somewhere around 30 Hz. While this would work for visualizing static magnetic fields, the more interesting magnetic fields around us are oscillating — think motors and transformers and such. A much faster magnetic camera was needed, and that’s what [Peter] set out to build.

Instead of an I/O expander, [Peter] re-engineered his design to use analog multiplexers and a binary counter to cycle through each pixel, one at a time. Basically, the new circuit uses two analog muxes for the columns and rows of the Hall effect array, a binary counter to cycle through each pixel at Megahertz speed, and a fast ADC to read each value. It is, bizarrely, the 1970s way of doing things; these are simple chips, and the controller (a Chipkit Max32) only needs to read a single analog value and clock the binary counter really fast.

With the new design, [Peter] is able to get extremely fast frame rates of about 2,000 Hz. That’s fast enough for some beautiful visualizations of spinning motors and transformers, seen in the video below. Further improvements may include three-axis magnetometers, which should allow for some spectacular visualizations similar to [Ted Yapo]’s 3D magnetic field scanner.

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Pipes, Tees, and Gears Result in Smooth Video Shots

It’s depressingly easy to make bad videos, but it only takes a little care to turn that around. After ample lighting and decent audio — and not shooting in portrait — perhaps the biggest improvements come from stabilizing the camera while it’s moving. Giving your viewers motion sickness is bad form, after all, and to smooth out those beauty shots, a camera slider can be a big help.

Not all camera sliders are built alike, though, and we must admit to being baffled while first watching [Rulof Maker]’s build of a smooth, synchronized pan and slide camera rig. We just couldn’t figure out how those gears were going to be put to use, but as the video below progresses, it becomes clear that this is an adjustable pantograph rig, and that [Rulof]’s eBay gears are intended to link the two sets of pantograph arms together. The arms are formed from threaded pipe and tee fittings with bearings pressed into them, which is a pretty clever construction technique that seems highly dependent on having the good fortune to find bearings with an interference fit into the threads. But still, [Rulof] makes it work, and with a little epoxy and a fair amount of finagling, he ends up with a complex linkage that yields the desired effects. And bonus points for being able to configure the motion with small adjustments to the camera bracket pivot points.

We saw a similar pantograph slider a few months back. That one was 3D-printed and linked with timing belts, but the principles are the same and the shots from both look great.

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Zen and the Art of Foam Core

Some of our pastimes are so deeply meditative that we lose ourselves for hours. Our hands seem to perform every step, and sequence like a pianist might recite her favorite song. If [Eric Strebel]’s voice and videos are any indications, working with foam core can have that effect.

Foam core is a staple of art stores, hobby stores, and office supply stores. It comes in different colors, but the universal trait is a sheet of foam sandwiched between a couple of layers of paper. This composition makes a versatile material which [Eric] demonstrates well in his advanced tutorial making a compound surface and later on a speaker mockup.

After the break, you can catch a couple of beginner tutorials which explain the differences between a slapdash foam core model, and one which will draw appreciation. Proper tools and thoughtful planning might be the biggest takeaways from the first two videos unless you count the Zen narration. The advanced videos, linked above, show some ingenious ways to use foam core like offset scoring, adjustable super-structures, and paper transfers.

Each video is less than ten minutes long, so if you just started your coffee break, you can complete a video right now. Or look at another 2D material turned into amazingness with a papercraft strandbeest, then step up your game with another look at vinyl cutters.
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All The Stuff You Wished You Knew About Fourier Transforms But Were Afraid To Ask

The Fourier transform underpins so much of our technological lives, in most cases probably without our realising it. The ability to mathematically split a waveform into its frequency components and vice versa underpins much of the field of digital signal processing, and DSP has become an essential part of many electronic devices we take for granted.

But while most of us will know what a Fourier transform is, fewer of us will know anything of how one works. They are a function called from a library rather than performed in themselves. Even when they are taught in schools or university courses they remain something that not all students “get”, and woe betide you if (as your scribe did) you have a sub-par maths lecturer.

The video below the break then is very much worth a look if Fourier transforms are a bit of a mystery to you. In it [Grant Sanderson] explains them through a series of simple graphical examples in a style that perhaps may chalk-and-talk mathematics teachers should emulate. You may still only use Foruier transforms through a library, but after watching this video perhaps some of their mysteries will be revealed.

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Celebrating the Olympics With Flaming Windmills

Like many of us, [Gustav Evertsson] was looking for an excuse to set stuff on fire and spin it around really fast to see what would happen. Luckily for him (and us) the Winter Olympics have started, which ended up being the perfect guise for this particular experiment. With some motors from eBay and some flaming steel wool, he created a particularly terrifying version of the Olympic’s iconic linked rings logo. Even if you won’t be tuning in for the commercials Winter Games, you should at least set aside 6 minutes to watch this build video.

The beginning of the build starts with some mounting brackets getting designed in Fusion 360, and you would be forgiven if you thought some 3D printed parts were coming up next. But [Gustav] actually loads the design up on a Carbide 3D CNC and cuts them out of wood.

A metal hub is attached to each bracket, and then the two pieces are screwed onto a length of thin wood. This assembly is then mounted up to the spindle of a geared motor rated for 300 RPM. The end result looks like a large flat airplane propeller. Five of these “propellers” are created, one for each ring of the Olympic’s logo.

Once the sun sets, [Gustav] takes his collection of spinners outside and lines them up like windmills. At the end of each arm is a small ball of fine-grade steel wool, which will emit sparks for a few seconds when lighted. All you’ve got to do is get the 10 pieces of steel wool alight at the same time, spin up the motors, and let persistence of vision do the rest. If you can manage the timing, you’ll be treated with a spinning and sparking version of the Olympic rings that wouldn’t look out of place in a new Mad Max movie.

Generally speaking, we don’t see much overlap between the hacker community and the Olympics. You’d have to go all the way back to 2012 to find another project celebrating this particular display of athleticism. We would strongly caution you not to combine both of these Olympic hacks at the same time, incidentally.

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Always Misplacing Your Keys? You Can Fix That With Some Logic Chips

Every time he came home, it was the same thing. As soon as he crossed the threshold, his keys just disappeared. There was no other logical explanation for it. And whenever it was time to leave again, he had to turn the house upside down to find them.

One day, [out-of-the-box] decided he’d had enough and built a door-activated alarm system out of stuff he had on hand—a decade counter, a cheapo reed switch-based door alarm, and some transistors. When the door is closed, the decade counter’s output is set to light up a green LED. When he comes home and opens the door, the reed switch closes, triggering the decade counter to shift its output to the next pin. The red LED comes on, and NPN transistor grounds the piezo, sounding the alarm. The only way to stop it is by inserting a shorted 1/4″ phone plug conveniently attached to his key ring into a jack on the circuit board until he hears that satisfying click of safe key-ping.

For those times when immediately plugging the keys into the wall isn’t feasible, or if his keys should disappear before he has the chance, there’s a momentary on the board that will stop the symphony of robotic cicadas blasting out from the piezo. It’s also good for family members who don’t want to play along or haven’t yet earned their 1/4″ plug.

Be sure to check out the build video after the break, which is just through that door there. And keep an eye on your keys, eh? Hackaday is not responsible for lost or stolen personal articles. Should you lose them, we can only suggest making a new car key from the spare and printing replacements for any standard keys.

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