Misc Hacks

4173 Articles

Ground Effect Aerodynamics On An RC Car

December 21, 2021 by 3 Comments

Ground effect aerodynamics will return to Formula 1 in a big way in the 2022 season, hopefully washing away the bad taste left in fan’s mouths after the recent controversial season decider. [Engineering After Hours] has experimented with F1 aerodynamics on RC cars before, and decided that it was time to try and implement a proper ground-effect design himself.

The aim of ground effect aerodynamics is to create a constriction for airflow between the bottom of the car and the ground underneath. This constriction accelerates the flow beneath the car, and as per Bernoulli’s principle, causes a corresponding pressure drop, sucking the car down onto the track. Viscosity also plays a role; from the car’s perspective, the road beneath the vehicle is moving backwards at some speed, pulling on the fluid thanks to the boundary layer on the ground itself. This further helps increase the strength of the effect.

A vacuum-formed undertray complete with side skirts was installed on the RC car in order to generate ground effect downforce. A quick test with a leaf blower indicates the system works, and that the side skirts are a key component.

Lateral acceleration was significantly improved by around 20% in testing with the ground effects installed, though [Engineering After Hours] admits that without a wind tunnel, the results aren’t the most scientific. However, with the undertray being relatively lightweight, we suspect the aero elements are likely providing plenty of benefit without too much of a negative effect on acceleration or handling.

Check out some of the other aero experiments [Engineering After Hours] has undertaken, too. Video after the break. Continue reading “Ground Effect Aerodynamics On An RC Car” →

The Assassin’s Teapot Is A Mischievous Design

December 20, 2021 by 31 Comments

Many films use a similar trope when it comes to poisoning. The aspiring murderer ingests a drink poured from the same vessel as that given to their intended victim to indicate the liquid is safe to imbibe. The Assassin’s Teapot is a way one could achieve such a ruse, allowing two different liquids to be poured from what is seemingly a regular teapot, as shown by [Steve Mould]. (Video after the break.)

The trick is simple. Two separate cavities exist within the teapot, exiting via their own paths in the same spout. Each cavity also has an air hole in the top. If the hole for a given cavity is blocked by the pourer’s thumb, the liquid will not flow.

Each cavity can be filled with its own liquid. For example, one can be filled with tea, the other with poisoned tea. The murderer blocks the hole for the poison cavity when pouring their own beverage, delivering tea to their own glass. Then, when pouring for the enemy, the hole for the tea cavity is blocked, and poison is allowed to flow into the glass of one’s target.

The workings are simple; if air cannot flow into the cavity of the teapot to replace liquid flowing out, air pressure will stop the liquid flowing at all. The concept is demonstrated ably by [Steve]’s 2D recreation, letting us visualize the workings of the teapot quite easily.

It also shows a minor flaw in the design, which should be accounted for –  if the spout isn’t designed carefully, sometimes flow from one cavity can dribble into the other. Between this and the chance of getting confused about which hole to cover to pour the poison, it would pay to keep some antidote on hand. Or, alternatively, just pour your guests tea instead – they’ll appreciate it!

We’ve seen [Steve] explore similarly interesting liquid vessels before too, such as this simple breakdown of the workings of the Gluggle Jug.

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A wooden device with an LED display and speakers

The Inspirer Keeps Your Mood Up With Inspirational Quotes And Soothing Music

December 19, 2021 by 2 Comments

While some people enjoy the cold weather and long, dark nights in the Northern Hemisphere these days, others may find it hard to keep a positive mindset all through the winter. [Michael Wessel] decided he needed to do something about that and came up with The Inspirer, a desktop display that shows inspirational quotes and plays soothing music.

The design is deliberately bare-bones: a strip of wood, standing upright thanks to two metal brackets, onto which a bunch of components have been screwed, glued and taped. The actual display consists of a row of 14-segment LED modules that can show basic alphanumeric characters; these displays emit white light, but [Michael] added a red color filter in front to give them a more “retro” look.

This device is fully off-grid, so no Internet connection issues will disrupt your flow. A huge database of quotes and a selection of music tracks are stored on a pair of micro SD cards; an MP3 player module handles the music while an Arduino picks a quote, drives the display, and reads the buttons. You can select quotes based on a certain theme: examples include friendship, gardening, money, and love. But if you’re open to anything, you can just set it to “random” and get something from any of the 120 categories.

[Michael]’s simple and straightforward design should hopefully prove inspirational to many hardware enthusiasts. But if you’re looking for something more advanced, we featured a neat pomodoro timer that displays quotes a few weeks ago. Of course, this being Hackaday, we’ve also seen a clock based on literary quotes.

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Building A Custom Branding Iron With Swappable Date Blocks

December 17, 2021 by 6 Comments

Branding can be done on wood with just about any old bit of hot metal, but if you want to do it well, properly-crafted tooling will go a long way. [Wesley Treat] has built just that with this modular branding iron design.

The branding tooling itself is machined out of brass on an X-Carve CNC router, using [Wesley]’s own logo. The part is sanded after machining to remove tooling marks. A smaller brass slug is then machined with the numerals for various years with which [Wesley] may wish to stamp his projects.

Rather than hacking something sloppy together, the iron itself is assembled with a beautifully wood-turned handle of his own creation and a steel backing plate to hold the tooling. The date is separately removable from the main logo itself for easy changes in future. Naturally, the tool graphics are done in reverse so as to register the right way around when burned onto wood.

The tool is used with a torch to heat the brass up such that it can leave its impression on wooden surfaces. The final results are solid, if not quite perfect; getting the temperature across the tool perfectly matched would be key to getting the cleanest results. An electric heating element running in closed loop could be a way to achieve this.

Fundamentally, it’s a tidy way to mark your wooden projects in a hurry. We’ve seen wood burning reach even greater heights, too, such as with this CNC pyrography machine. Video after the break.

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Gluggle Jug Is Neat Application Of Hydrodynamics

December 17, 2021 by 8 Comments

The Gluggle Jug is an aptly-named thing – it’s a jug that makes loud, satisfying glugging noises when poured. But how does it work? [Steve Mould] set out to investigate. 

[Steve]’s first plan was to cut apart an existing Gluggle Jug to see how it worked, but cutting ceramics can be difficult and time-consuming, and the asymmetric design only made things harder. Instead, he simply smashed a jug to see what it looked like inside, and replicated the basic design in a transparent laser-cut version.

The design is simple – the glug sounds are from bubbles passing into a closed cavity within the jug as the water is poured out. Stop pouring, and air from that cavity then escapes back through the open mouth of the jug via more bubbles, making an even louder glugging sound. The frequency of the sound is determined by the height of the jug, which is essentially acting as a closed-pipe resonator.

With an understanding of the mechanisms at play, producing your own Gluggle jug is as simple as whipping up a design in your CAD software of choice and printing it in a food-safe way. Video after the break.

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RC Sub Built With A Water Bottle

December 15, 2021 by 8 Comments

Submarines are one of the harder modes of transport to build in radio-controlled form. Doing so involves tangling with sealing electronics from water ingress and finding a way to control the thing underwater. It’s a challenge, but one relished by [Project Air] in his latest build.

The body of the sub was built from a drink bottle, serving as a stout container upon which could be mounted all the necessary hardware. Filling the bottle with water allowed buoyancy to be adjusted to a neutral level. Twin brushless motors were used for drive, while servos were waterproofed using a combination of rubber gaskets, olive oil, and sealing spray.

Control was via a floating 2.4 GHz receiver, as high-frequency radio signals don’t penetrate water very far. The floating box also carries an FPV transmitter to allow the sub to be piloted via video feed. Rather than using a ballast system, the sub instead dynamically dives by thrusting itself beneath the water’s surface.

Unfortunately, water sloshing around in the partially-filled drink bottle meant controlling the sub in pitch was virtually impossible. To fix this, [Project Air] filled the bottle completely, and then used some plugged syringes on the outside of the body to adjust buoyancy. The long heavy tether was also replaced with a much shorter one, and the sub became much more fun to drive around under water.

The build was actually built for a friendly contest with [DIY Perks], a fellow Youtuber whose efforts we covered recently. It also bears noting that better results can be had by using lower-frequency radio gear. Video after the break.

Continue reading “RC Sub Built With A Water Bottle” →

Heavy-Duty Starter Motor Powers An Awesome Drift Trike

December 15, 2021 by 11 Comments

Starter motors aren’t typically a great choice for motorized projects, as they’re designed to give engines a big strong kick for a few seconds. Driving them continuously can often quickly overheat them and burn them out. However, [Austin Blake] demonstrates that by choosing parts carefully, you can indeed have some fun with a starter motor-powered ride.

[Austin] decided to equip his drift trike with a 42MT-equivalent starter motor typically used in heavy construction machinery. The motor was first stripped of its solenoid mechanism, which is used to disengage the starter from an engine after it has started. The housing was then machined down to make the motor smaller, and a mount designed to hold the starter on the drift trike’s frame.

A 36V battery pack was whipped up using some cells [Austin] had lying around, and fitted with a BMS for safe charging. The 12V starter can draw up to 1650 amps when cranking an engine, though the battery pack can only safely deliver 120 amps continuously. A Kelly controller for brushed DC motors was used, set up with a current limit to protect the battery from excessive current draw.

The hefty motor weighs around 50 pounds, and is by no way the lightest or most efficient drive solution out there. However, [Austin] reports that it has held up just fine in 20 minutes of near-continuous testing, despite being overvolted well beyond its design specification. The fact it’s operating at a tenth of its rated current may also have something to do with its longevity. It also bears noting that many YouTube EVs die shortly after they’re posted. Your mileage may vary.

For a more modern solution, you might consider converting an alternator into a brushless electric motor. Video after the break.

Continue reading “Heavy-Duty Starter Motor Powers An Awesome Drift Trike” →