Recreating The Pop Ball

Those who were kids in the 80s may remember a sweet little toy called the Pop Ball. A simple rubber hemisphere, this rubber cup could be turned inside out and thrown on the ground, where it would hit and bounce sky high whilst knocking itself right side out. The black ones worked particularly well, and were the first to be banned from [electrosync]’s school along with yo-yos, slap bracelets, and any number of toys that eventually became weaponized by enterprising children.

An industrial Vegemite injection-molded version that only kind of worked.

You can still find Pop Balls today, but they don’t work nearly as well as they did originally because of a lower Shore hardness in the rubber. Naturally, as an adult with futuristic toys at hand, [electrosync] just had to try re-creating the ’80s version. But it wasn’t easy.

They started by studying the patents and anything else they could find. They even managed to get a hold of Peter Fish, the original creator of the Pop Ball, to get some questions answered about the things. According to Peter, the black Pop Ball was made from recycled rubber and worked almost too well. Peter sent [electrosync] an old-stock Pop Ball, which they used to modify their CAD design.

It’s easy to root for [electrosync] throughout this journey, which consists of many failed prints and injection molding attempts. At last, they are able to at least recreate the snap of the modern Pop Ball once they finally found the right filament — the extremely elastic Recreus Filaflex 60A TPU. Of course, it wasn’t all lollipops and rainbows from there, because the filament is notoriously difficult to print with, but [electrosync] made it work. Check it out after the break.

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A tennis racket and a tennis ball with a spinning motor inside

A Self-Spinning Tennis Ball To Surprise Your Opponent

In many ball sports like golf, football and tennis, controlling the ball’s spin is an important skill. Expert players can make golf balls curve around obstacles, launch footballs towards goal posts from impossible angles, or confuse their opponents by making a tennis ball bounce in a completely unexpected direction.

[Luis Marx], by his own admission, is not an expert tennis player at all, so when he found himself humiliated on the court by his roommate he set about finding a different way to win. In other words, to cheat. The basic idea was to make a tennis ball that would start spinning at the push of a button, rather than by skillful wielding of a racket: a spinning ball that flies through the air will follow a curved trajectory, so if you can make a ball spin at will, you can change its direction in mid-air.

Making a ball spin by itself is not as hard as it may sound. All you need is an electric motor that’s small enough to fit inside, along with a power source and some way to turn it on. When the motor inside the ball starts to spin, Newton’s third law ensures that the outside will spin in the opposite direction. [Luis] found a suitable DC motor and mounted it on a small custom-designed PCB along with an ESP8266 controller and powered it with a tiny lithium battery. A pushbutton mounted on his tennis racket operates the wireless interface to turn the motor on and off.

Although getting this setup to work wasn’t as easy as [Luis] had hoped, turning it into a ball that’s good enough to play tennis with was not straightforward either. [Luis] decided to 3D-print the outer shell using flexible filament in order to create something that would have the same amount of bounce as an ordinary rubber tennis ball. It took several rounds of trial and error with various types of filament to end up with something that worked, but the final result, as you can see in the video (in German, embedded below), was quite impressive.

Tests on the tennis court showed that [Luis] could now easily beat his roommate, although this was mostly due to the erratic bouncing caused by the ball’s spin rather than any aerodynamic effects. Still, the magic tennis ball achieved its objective and even survived several games without breaking. If you’re looking for a more brute-force approach to cheating at tennis, this 180 mph tennis ball trebuchet might come in handy.

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Tame Your Flexible Filaments With This Belt-Drive Extruder

[Proper Printing] clearly enjoys pushing the boundaries of 3D printed materials, and sometimes this requires building custom 3D printers or at least the business end of them. Flexible filaments can be a bit of a pain to deal with, simply because most extruders are designed to push the filament into the hot end with a simple hobbed bolt (or pinch roller setup) and only work reliably due the rigidity of the plastic itself. Once you go flexible, the rigidity is reduced and the filament often deflects sideways and the extruder jams. The longer the filament path leading to the hotend, the harder it gets.  The dual belt drive extruder (they’re calling it ‘proper extruder’) grips the filament on two sides with a pair of supported belts, guiding it into the hotend without allowing it to deflect sideways. The extruder body and gears were resin printed (but, we checked — the design is suitable for FDM printing as well) proving that resin printing on modern printers, does indeed maintain adequate dimensional accuracy allowing the building of mechanisms, despite the naysayers! Continue reading “Tame Your Flexible Filaments With This Belt-Drive Extruder”

3D Printed Shoes Make Bigfoot Tracks

[Stephan Henrich] is probably going to set off a wave of bigfoot sightings if his new shoe, the Cryptide sneaker takes off. The shoe is completely 3D printed in flexible TPE using a laser sintering printer from Sintratec. The shoe takes a name from cryptozoology and, in fact, would leave a puzzling footprint due to its articulated toes and scaly-looking sole.

Judging from the look of the sole, it should be pretty cushy and we presume if you were 3D printing these, you’d scan or precisely measure the intended foot for a perfect fit. You can see a video about the shoe below.

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Modular Rover Platform Rolls On 3D Printed Flexible Tank Tracks

Master of 3D printed robots, [James Bruton], plans to do some autonomous rover projects in the future, but first, he needed a modular rover platform. Everything is cooler with tank tracks, so he built a rover with flexible interlocking track sections.

The track sections are printed with flexible Ninjaflex filament. Each section has a tab designed to slot through two neighboring pieces. The ends of the tabs stick through on the inside of the track fit into slots on the drive wheel like gear teeth. This prevents the track from slipping under load. The Ninjaflex is almost too flexible, allowing the tracks to stretch and almost climb off the wheels, so [James] plans to experiment with some other materials in the future. The chassis consists of two 2020 T-slot extrusions, which allows convenient mounting of the wheel bogies and other components.

The interlocking track pieces

For initial driving tests [James] fitted two completely overpowered 1500 W brushless motors that he had on hand, which he plans to replace with smaller geared DC motors at a later stage.

A standard RC system is used for control, but it does not offer a simple way to control a skid steer vehicle. To solve this, [James] added an Arduino between the RC receiver and the motor ESC. It converts the PWM throttle and turn signal from the transmitter, and combines is into differential PWM outputs for the two ESCs.

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Starshine Is A MIDI Controller For The Musically Shy

What keeps people from playing music? For one thing, it’s hard. But why is it hard? In theory, it’s because theory is confusing. In practice, it’s largely because of accidentals, or notes that sound sour compared to the others because they aren’t from the same key or a complementary key.

What if there were no accidentals? Instruments like this exist, like the harmonica and the autoharp. But none of them look as fun to play as [Bardable]’s Starshine, the instrument intended to be playable by everyone. The note buttons on the outside are laid out and programmed such that [Bardable] will never play off-key.

We love the game controller form factor, which was also a functional choice. On the side that faces the player, there’s a PSP joystick and two potentiometers for adding expression with your thumbs. The twelve buttons on this side serve several functions like choosing the key and the scale type depending on the rocker switch position. A second rocker lets [Bardable] go up or down an octave on the fly. There’s also an OLED to show everything from the note being played to the positions of the potentiometers. If you want to know more, [Bardable] made a subreddit for this and other future instruments, and has a full tour video after the break.

If this beginner-friendly MIDI controller isn’t big enough for you, check out Harmonicade’s field of arcade buttons.

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Printed Separator Separates Printed Pages

We all know people trapped in aging bodies who can’t do all the things they used to do. It’s easy to accept that you may never move small furniture around by yourself again, but losing the ability to do something as simple as separating the pages of your newspaper to keep reading it is an end to enjoyment.

When [Randomcitizen4] visited his grandma over the holidays, she mentioned having trouble with this, among other things. He fired up his printer and got to work designing a device to help her get back to the funny pages. This simple gripper mechanism uses rubber bands for tension and flexible filament to get a firm grip on the paper. The jaws default to the open position so they’re ready to grab some newsprint, and a light squeeze of the handles slides the top page back from the stack, creating a gap for Grandma’s fingers. You can see a demo on page 32 after the break.

Although the device does work on some books and magazines, he’d like to improve the design of the grips to make the device more universally useful. [Randomcitizen4] says he tried a few things already, but we wonder if a more complex surface pattern might do the trick — maybe less like fins and more like a tire tread pattern. All the STLs are available if you want to give it a go.

If Grandma’s newspaper ever goes out of print, she should still be able to read it on a tablet or an e-reader. Then maybe [Randomcitizen4] can build some kind of remote-controlled page turner for her.

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