Trebucheting Tennis Balls at 124 MPH

A trebuchet is one of the older machines of war. It’s basically a sling on a frame, with a weight that you can lift up high and which pulls the sling arm over on release. Making one opens up the doors to backyard mayhem, but optimizing one opens up the wonders of physics.

[Tom Stanton] covers just about everything you need to know about trebuchet building in his four-part video series. Indeed, he sums it up in video two: you’ve got some potential energy in the weight, and you want to transfer as much of that as possible to the ball. This implies that the optimal path for the weight would be straight down, but then there’s the axle in the way.  The rest, as they say, is mechanical engineering.

Video three was the most interesting for us. [Tom] already had some strange arm design that intends to get the weight partially around the axle, but he’s still getting low efficiencies, so he builds a trebuchet on wheels — the classic solution. Along the way, he takes a ton of measurements with Physlets Tracker, which does video analysis to extract physical measurements. That tip alone is worth the price of admission, but when the ball tops out at 124 mph, you gotta cheer.

In video four, [Tom] plays around with the weight of the projectile and discovers that he’s putting spin on his tennis ball, making it curve in flight. Who knew?

Anyway, all four videos are embedded below. You can probably skip video one if you already know what a trebuchet is, or aren’t interested in [Tom] learning that paying extra money for a good CNC mill bit is worth it. Video two and three are must-watch trebucheting.

We’re a sad to report that we couldn’t find any good trebuchet links on Hackaday to dish up. You’re going to have to settle for a decade-old catapult post or this sweet beer-pong-playing robotic arm. You can help. Submit your trebuchet tips.

Thanks [DC] for this one!

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Shoelace-Tying Robot With Only Two Motors

Many things that humans do are very difficult for machines. Case in point: tying shoelaces. Think of the intricate dance of fingers crossing over fingers that it takes to pass off a lace from one hand to the other. So when a team of five students from UC Davis got together and built a machine that got the job done with two hooks, some very clever gears, and two motors, we have to say that we’re impressed. Watch it in action on Youtube (also embedded below).

The two-motor constraint would seem at first to be a show-stopper, but now that we’ve watched the video about a hundred times, we’re pretty convinced that a sufficiently clever mechanical engineer could do virtually anything with two motors and enough gears. You see, the secret is that one motor is dedicated to moving a drive gear back and forth to multiple destinations, and the other motor provides the power.

This being Hackaday, I’m sure that some of you are saying “I could do that with one motor!” Consider that a challenge.

Meanwhile, if you need to see more gear-porn, check out this hummingbird automaton. Or for the miracles of cam-driven machines, check out [Fran Blanche]’s work with the Maillardet Automaton.

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We’re Hiring: Come Join Us!

You wake up in the morning, and check Hackaday over breakfast. Then it’s off to work or school, where you’ve already had to explain the Jolly Wrencher to your shoulder-surfing colleagues. And then to a hackspace or back to your home lab, stopping by the skull-and-cross-wrenches while commuting, naturally. You don’t bleed red, but rather #F3BF10. It’s time we talked.

The Hackaday writing crew goes to great lengths to cover all that is interesting to engineers and enthusiasts. We find ourselves stretched a bit thin and it’s time to ask for help. Want to lend a hand while making some extra dough to plow back into your projects? We’re looking for contributors to write a few blog posts per week and keep the Hackaday flame burning.

Contributors are hired as private contractors and paid for each article. You should have the technical expertise to understand the projects you write about, and a passion for the wide range of topics we feature. You’ll have access to the Hackaday Tips Line, and we count on your judgement to help us find the juicy nuggets that you’d want to share with your hacker friends.

If you’re interested, please email our jobs line and include:

  • One example post written in the voice of Hackaday. Include a banner image, at least 150 words, the link to the project, and any in-links to related and relevant Hackaday features. We need to know that you can write.
  • Details about your background (education, employment, interests) that make you a valuable addition to the team. What do you like, and what do you do?
  • Links to your blog/project posts/etc. that have been published on the Internet, if any.

What are you waiting for? Ladies and Gentlemen, start your applications!

One Square Inch Expanded in the Time Dimension

No, we’re not talking about spooky feats of General Relativity. But you should know that the Return of the Square Inch Project just got its deadline extended.

If you missed the call the first time around, our favorite user-contributed contest on is up and running again. tossed in some good money for prizes, and folks started thinking about what functionality they could cram inside a 25.4 mm x 25.4 mm square. But while one constraint can help bring out creativity, adding a tight deadline to a tight squeeze caused a number of our entrants to ask for an extension.

If you’re working on the Square Inch Project, you’ve got until October 1st to get your boards ready. Breathe a quick sigh of relief and then get back to soldering! We’re looking forward to seeing all the great entries.

Superconference Submission Deadline Extended

Who among us doesn’t procrastinate from time to time? We can’t count the number of times that we’ve taken advantage of the Post Office staying open until midnight on April 15th. And when the 15th falls on a weekend? Two glorious additional days to put off the inevitable!

If you’ve been sitting on submitting your talk or workshop proposal to the 2018 Hackaday Superconference, we’ve got the next best thing for you: we’re extending the deadline until 5 pm PDT on September 10th.

The Hackaday Superconference is a singularity of hardware hackers: more of the best people in the same space at the same time than anywhere else. And that means that your ideas and experiences will be shared with the people most likely to appreciate them. From heroic hacks to creative robotics or untold hardware histories, if there’s a crowd who’ll appreciate how a serial console saved your bacon, it’s this one.

And if you give a talk or workshop, you get in free. But it’s more than that — there’s a different experience of a convention, even a tight-knit and friendly one like Hackaday’s Supercon, when you’re on the other side of the curtain. Come join us! We’d love to hear what you’ve got to say. And now you’ve got a little more time to tell us.

(If you want to get in the old-fashioned way, tickets are still available, but they won’t be once we announce the slate of speakers. You’ve been warned.)

Ask Hackaday Answered: The Tale of the Top-Octave Generator

We got a question from [DC Darsen], who apparently has a broken electronic organ from the mid-70s that needs a new top-octave generator. A top-octave generator is essentially an IC with twelve or thirteen logic counters or dividers on-board that produces an octave’s worth of notes for the cheesy organ in question, and then a string of divide-by-two logic counters divide these down to cover the rest of the keyboard. With the sound board making every pitch all the time, the keyboard is just a simple set of switches that let the sound through or not. Easy-peasy, as long as you have a working TOG.

I bravely, and/or naïvely, said that I could whip one up on an AVR-based Arduino, tried, and failed. The timing requirements were just too tight for the obvious approach, so I turned it over to the Hackaday community because I had this nagging feeling that surely someone could rise to the challenge.

The community delivered! Or, particularly, [Ag Primatic]. With a clever approach to the problem, some assembly language programming, and an optional Arduino crystalectomy, [AP]’s solution is rock-solid and glitch-free, and you could build one right now if you wanted to. We expect a proliferation of cheesy synth sounds will result. This is some tight code. Hat tip!

Squeezing Cycles Out of a Microcontroller

Let’s take a look at [AP]’s code. The approach that [AP] used is tremendously useful whenever you have a microcontroller that has to do many things at once, on a rigid schedule, and there’s not enough CPU time between the smallest time increments to do much. Maybe you’d like to control twelve servo motors with no glitching? Or drive many LEDs with binary code modulation instead of primitive pulse-width modulation? Then you’re going to want to read on.

There are two additional tricks that [AP] uses: one to fake cycles with a non-integer number of counts, and one to make the AVR’s ISR timing absolutely jitter-free. Finally, [Ag] ended up writing everything in AVR assembly language to make the timing work out, but was nice enough to also include a C listing. So if you’d like to get your feet wet with assembly, this is a good start.

In short, if you’re doing anything with hard timing requirements on limited microcontroller resources, especially an AVR, read on!

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The Square-Inch Project Rides Again!

Want to play a game? Your challenge is to do something incredible with a printed circuit board that measures no more than one inch by one inch. It’s The Return of the One Square Inch Project and it’s going to be amazing!

We can’t believe that it’s been three years! The original One Square Inch Project was a contest dreamt up by user [alpha_ninja] back in 2015, and we thought it was such a great idea that we ponied up some prizes. The entries were, frankly, the best we’ve ever seen. So we’re doing it again!

Last time around, the size constraint focused the minds and brought out the creativity in some of the best and brightest of What functionality or simply amusement can you pack into a square PCB that’s just a tad over 25 mm on a side? We’d like to see.

We’ll be featuring entries throughout the contest. We think geek ‘cred is the best reward but if you want something more to sweeten the pot here you go:

  • Grand Prize:

    • $500 Cash!
  • Four Top Entries Win Tindie Gift Certificates:

    • Best Project – $100
    • Best Artistic PCB Design – $100
    • Best Project Documentation – $100
    • Best Social Media Picture or Video – $100
  • Five Runner-Up Entries:

    • $100 OSH Park gift cards
Quadcopter in One Inch

Want some inspiration? Last time the winner was a quadcopter in one square inch, but there were tons of useful and amusing projects crammed into tight quarters, and many of them transcend their constraints. There were not one but two hi-fi sound cards: one for your laptop’s USB port and one for your microcontroller projects that is now officially supported by the Teensy Audio Library. Need a MPPT power converter for a small solar project? How about a plug-load meter that fits on a US mains plug or an I2C to WS2818 converter to make blinking easier?

There were breakout boards for nearly every imaginable chip, a radio downconverter from our own [Jenny List], and a great magnetic rotary encoder design. Key Pass, an Arduino in the size of a DIP-8, and of course a bat detector, a bubble display volt meter, a smart watch, and a capacitive touch wheel.

It’s been three years, and parts have gotten cheaper, smaller, and more capable. What’s newly feasible in a square inch that wasn’t way back in 2015? Show us what you got.