Hackaday Prize 2023: Bolt Bot Micro Servo Droids

This Hackaday prize entry from [saul] is the beginning of a reconfigurable kit of 3D printed parts and servo motors for robotics learning. With just access to a printer, a few cheap-as-chips servo motors, an Arduino, and some nuts and bolts, you could be hacking together robot walkers within a few hours of starting!

Bolt Bots is very simple to understand, with all the mechanics and wiring out there in the breeze, but strictly for indoor use we reckon. If you want to add remote control to your application, then drop in one of the ubiquitous nRF24L01 boards and build yourself a copy of the remote control [saul] handily provides in this other project.

There really isn’t a great deal we can say about this, as it’s essentially a build kit with quite a few configuration options, and you just have to build with it and see what’s possible. We expect the number of parts to proliferate over time giving even more options. So far [saul] demonstrates a few flavors of ‘walkers’, a rudimentary ‘robot arm’, and even a hanging drawbot.

The bolt hardware can be found in this GitHub repo, and the remote control code in this second one.

Servo-based designs are sometimes sneered at due to their dubious accuracy and repeatability, but with a little of effort, this can be vastly improved upon. Also, multi-legged walkers need multiple servos and controllers to drive ’em. Or do they?

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3D Printed Light Pipe Turns Overly-Bright LED Into Design Harmony

There are a number of ways to efficiently and elegantly limit an LED’s brightness, but [Tommy] found that using a light pipe or diffuser can integrate better with a device, especially when the device itself is mostly 3D printed in the first place.

Infill has an effect on appearance. 20% infill on the left, 100% infill on the right.

For some problems the Goldilocks approach is the way to go. [Tommy] designed a small array of different LED cover options, and tested each to see what yielded the best results for his printed kit. Some of the biggest takeaways include:

  • 100% infill is best for even results (although interesting shadows happen at less than 100% infill.)
  • Interesting things happen with 7 to 11 mm of top layers of clear PLA, when illuminated from below with a 5 mm high-brightness LED. An even diffusion of light starts to give way to a circular gradient as the upper layer gets thicker.
  • LEDs emit their light mainly upward in a round pattern. Corners will always be darker, even more so if the guide is not round. This effect becomes noticeably more pronounced as the light guide grows in size, putting a practical upper limit on its effective dimensions.

[Tommy] explores these kinds of issues because he designs and builds electronic synth instruments, and they are mostly 3D printed. He explores efficiency and is always happy to share his findings about what works and doesn’t work.

Of course, the usual ways to deal with an overly-bright LED are to limit its current or control its brightness by driving it with a PWM signal. The right approach depends on the application and the scale of the design, and there are actually quite a few ways to crack this nut. Luckily, our own [Inderpreet Singh] is here to tell you all about how best to control LED brightness.

Velomobile Gets Electric Assist

What do you get when you throw all accepted bicycle designs out the window and start fresh? Well, it might look a bit like [Saukki’s] velomobile.

Most bikes come in a fairly standard, instantly-recognizable shape which has been popular for over a century now. While it’s a vast improvement over its predecessor, the penny-farthing bicycle, there’s no reason that a bike needs to have this two-triangle frame shape other than that a pretentious bicycle racing standards group says they have to. If you want to throw their completely arbitrary rulebook out of the window, though, you can build much more efficient, faster bikes like recumbents or even full-fairing velomobiles. And if you want to go even faster than that, you can always add a standard ebike motor kit to one.

This is a lot harder than putting a motor on a normal bicycle. Bicycles tend to have standardized parts and sizes, and [Saukki]’s velomobile is far from the standard bike. First, he needed custom mounts for the display and also for the battery, which he needed to make extra wide so its weight wouldn’t rip through the carbon fiber body. The emergency brake lever motor cutoff needed to be dismantled to work with his control system too, and finally the mid-drive motor needed a custom mount as well. It’s a TSDZ2 motor that comes with torque-sensing pedal assist.

The changes didn’t stop there. The velomobile max speed is much higher than a standard bike. This called for some gear ratio changes, in the form of a monster 60-tooth chain ring.

This leads to the one major problem with this build which is that the velomobile can achieve such high speeds on its own that the electric assist cuts out for most of the ride. There is a legal requirement over much of Europe that e-bikes only have pedal assist (without a throttle) and that they stop assisting above a specific speed. But if you want to build an e-bike that pushes the boundary of the law instead of strictly adhering to it, take a look at this one which uses a motor from a washing machine.

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Build Your Own 3D Printed Bluetooth Headphones

A few years back, [Shannon Ley] wondered how hard it would be to build a pair of Bluetooth headphones from scratch. Today, we have our answer. The Homebrew Headphones website is devoted to just one thing: explaining how you can use common components and some 3D printed parts to build an impressively comprehensive pair of wireless headphones for around $50 USD.

The headphones pair a CSR8645 Bluetooth audio receiver with a TP4056 USB-C charging module, a 500 mAh LiPo pouch battery, a pair of Dayton Audio CE38MB-32 drivers, and replacement ear covers designed for the Bose QuietComfort QC15. Some perfboard, a couple buttons, a resistor, and an LED round out the parts list.

All of the components fit nicely into the meticulously designed 3D printed frame, and assembly is made as simple as possible thanks to an excellent step-by-step guide. It’s all so well documented that anyone with even basic soldering experience should be able to piece it together without too much fuss.

Of course, these aren’t the first 3D printed headphones we’ve ever seen. But the quality of the documentation and attention to detail really make these stand out.

Arduino Drum Platform Is Fast

Drums are an exciting instrument to learn to play, but often prohibitive if there are housemates or close neighbors involved. For that problem there are still electronic drums which can be played much more quietly, but then the problem becomes one of price. To solve at least part of that one, [Jeremy] turned to using an Arduino to build a drum module on his own, but he still had to solve yet a third problem: how to make the Arduino fast enough for the drums to sound natural.

Playing music in real life requires precise timing, so the choice of C++ as a language poses some problems as it’s not typically as fast as lower-level languages. It is much easier to work with though, and [Jeremy] explains this in great detail over a series of blog posts detailing his drum kit’s design. Some of the solutions to the software timing are made up for with the hardware on the specific Arduino he chose to use, including an even system, a speedy EEPROM, hardware timers, and an ADC that can sample at 150k samples per second.

With that being said, the hardware isn’t the only thing standing out on this build. [Jeremy] has released the source code on his GitHub page for those curious about the build, and is planning on releasing several more blog posts about the drum kit build in the near future as well. This isn’t the only path to electronic drums, though, as we’ve seen with this build which converts an analog drumset into a digital one.

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Build Your Own CRT TV

There was a time following the Second World War when TV sets for the nascent broadcast medium were still very expensive, but there was an ample supply of war-surplus electronic parts including ex-radar CRTs. Thus it wasn’t uncommon at all for electronics enthusiasts of the day to build their own TV set, and magazines would publish designs to enable them. With a burgeoning consumer electronics industry the price of a new TV quickly dropped to the point of affordability so nobody would consider building one themselves today. Perhaps that should be amended to almost nobody, because [Retro Tech or Die] has assembled a small black-and-white CRT TV from a kit he found on AliExpress.

We have to admit to having seen the same kit and despite a sincere love for analogue telly, to have balked at the price. It’s an exceptionally cheap set of the type that was available from discount stores for a laughably low price around the final few years of mainstream analogue TV broadcasting, and having a couple in the stable we can confirm that the value here lies in building the thing rather than owning it.

The unboxing and building proceeds as you might expect, with the addition of very poor documentation and extremely low-quality parts. Satisfyingly it works on first power-up, though some adjustment and the reversing of a deflection yoke connection is required for a stable picture. The scanned area doesn’t fill the screen and he doesn’t find the solution in the video, we hope that by his next video someone will have suggested moving the deflection yoke forwards.

Perhaps merely assembling a kit might not seem the most exciting subject for a Hackaday story, but this one is a little different here in 2022. CRT TV sets are now a long-gone anachronism, so for a younger generation there is very little chance to see them up close and thus watching one built has some value. If you want to spend the cash and build your own he’s dropped the link in the YouTube description, otherwise watch the progress in the video below the break.

Fancy learning a bit more about analogue TV? Have a dive into the video waveform. Or for a bit more CRT goodness, learn about converging a delta-gun colour set from the days when a TV weighed almost as much as you did.

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Small synth held in two hands

3D Printed Synth Kit Shares Product Design Insights

We’ve always been delighted with the thoughtful and detailed write-ups that accompany each of [Tommy]’s synth products, and the background of his newest instrument, the Scout, is no exception. The Scout is specifically designed to be beginner-friendly, hackable, and uses 3D printed parts and components as much as possible. But there is much more to effectively using 3D printing as a production method than simply churning out parts. Everything needed to be carefully designed and tested, including the 3D printed battery holder, which we happen to think is a great idea.

3d printed battery holder, showing inserted spring contacts
3D printed battery holder, with spring contacts inserted by hand.

[Tommy] also spends some time explaining how he decided which features and design elements to include and which to leave out, contrasting the Scout with his POLY555 synth. Since the Scout is designed to be affordable and beginner-friendly, too many features can in fact be a drawback. Component costs go up, assembly becomes less straightforward, and more complex parts means additional failure points when 3D printing.

[Tommy] opted to keep the Scout tightly focused, but since it’s entirely open-sourced with a hackable design, adding features is made as easy as can be. [Tommy] designed the PCB in KiCad and used OpenSCAD for everything else. The Scout uses the ATmega328, and can be easily modified using the Arduino IDE.

STL files can be downloaded here and all source files are on the project’s GitHub repository, which also contains detailed assembly and modification guides. Watch it in action in the video, embedded below.

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