Fail of the Week: Good Prosthetic Hand Design Goes Bad

Is this a case of a good design gone wrong in the build phase? Or is this DIY prosthetic arm a poor design from the get-go? Either way, [Will Donaldson] needs some feedback, and Hackaday is just the right place for that.

Up front, we’ll say kudos to [Will] for having the guts to post a build that’s less than successful. And we’ll stipulate that when it comes to fully articulated prosthetic hands, it’s easy to fail. His design is ambitious, with an opposable thumb, fingers with three phalanges each, a ball and socket wrist, and internal servos driving everything. It’s also aesthetically pleasing, with a little bit of an I, Robot meets Stormtrooper look.

But [Will]’s build was plagued with print problems from the start, possibly due to the complex nature of the bosses and guides within the palm for all the finger servos. Bad prints led to creaky joints and broken servos. The servos themselves were a source of consternation, modified as they were for continuous rotation and broken apart for remotely mounting their pots in the hand’s knuckles. The video below relates the tale of woe.

There’s a lot to admire with [Will]’s build, but it certainly still has its issues. He’s almost to the point of other more successful DIY hand builds but just needs a little help. What say you in the comments line? Continue reading “Fail of the Week: Good Prosthetic Hand Design Goes Bad”

Dog-Operated Treat Dispenser

Every good dog is deserving of a treat. [Eliasbakken]’s dog [Moby] is a certified good boy,  so he designed a dispenser with a touchscreen that his dog can boop to treat himself when he isn’t barking up a ruckus.

Adding a touchscreen to a treat dispenser when a button would suffice is a little overkill, but we’re not here to judge. [Eliasbakken] is using a BeagleBone Black — a Linux-based development platform — as this dispenser’s brains, and a Manga touchscreen that is likely to see a lot of use.  A wood-like material called Vachromat was laser cut for the frame and glued together, while an RC servo with a 3D-printed jointed pushing arm to dispenses the treats. The dispenser’s hopper only holds fifteen, so we expect it will need to be refilled every fifteen seconds or so.

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Three Thumbs, Way, Way Up!

At least one in their lives — or several times a day — everyone has wished they had a third hand to help them with a given task. Adding a mechanical extra arm to one’s outfit is a big step, so it might make sense to smart small, and first add an extra thumb to your hand.

This is not a prosthetic in the traditional sense, but a wearable human augmentation envisioned by [Dani Clode], a master’s student at London’s Royal College of Art. The thumb is 3D-printed out of Ninjaflex and mounted to a printed brace which slides over the hand. One servo rotates the thumb, and a second pulls it closed using a bowden cable system — not unlike that of a bicycle brake. Control of the thumb is achieved by pressure sensors in the wearer’s shoes, linked via Bluetooth to a wristband hosting the servos and the electronics. We already use our hands and feet in conjunction, so why not capitalize on this intuitive link?

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Hackaday Prize Entry: Very, Very Powerful Servos

A few years ago, [patchartrand] decided to build a robot arm. The specs were simple: he needed a drive system that would be at least as strong as a human arm. After looking at motors, [patch] couldn’t find a solution for under $3,000. This led to the creation of the Ultra Servo, an embiggened version of the standard hobby servo that provides more than ten thousand oz-in of torque.

Your typical hobby servo has three main components. The electronics board reads some sort of signal to control a motor. This motor is strapped into a gear train of some sort, and a potentiometer reads the absolute position of a shaft. This is basically what the Ultra Servo is doing, although everything is much, much bigger.

The motor used in the Ultra Servo is a very large brushed DC motor. This is attached to a 160:1 planetary gearbox and the electronics are built around four reasonably large MOSFETs. The electronics are built around the ATmega168 microcontroller, and the specs for the completed servo include 12 V or 24 V operation, TTL, SPI, and standard RC communication, 60 RPM no load speed, and 60 ft-lbs of torque.

This is not your standard servo. This is a massive chunk of metal to move stuff. If you’ve ever wanted a remote-controlled Cessna, here you go. That said, servos of this size and power will always be pricey, and [patch] is looking at a cost of $750 per unit. Still, that’s much less than the thousands of a comparable unit, and a great entry to the Hackaday Prize.

Use the Force to Turn On This Lamp

Holocrons are holographic data storage devices used in the Star Wars universe by both Jedi and Sith as teaching devices or for storing valuable information. After the fall of the Jedi, they became rare and closely guarded artifacts. [DaveClarke] built one to light the room.

[DaveClarke] built the lamp around a Particle Photon – a STM32 ARM-M0 based microcontroller with a Cypress wifi chip. All [Dave] needed for the workings were an IR proximity sensor, a servo and a bunch of super-bright white LEDs. When the sensor detects something, it starts up the system. The servo rotates a gear which raises the lamp and fades in the LEDs. The next time the sensor detects something, the servo lowers the lamp and the lights begin to fade out. And since the Photon is connected to the cloud, the system can be accessed with a web interface as well.

Okay, so it’s just an IR sensor detecting reflected infrared light and not the Force that’s used to turn it on, but it’s still pretty cool. There are plenty of pictures and videos at [DaveClarke]’s site, along with a schematic, 3D printer designs, and the source code. The whole thing was designed using Autodesk Fusion 360 and 3D printed in about 30 hours and press-fits together. A very simple yet clever design. There have been some other great lamps on the site, like this blossoming flower lamp or this laser cut lamp with which also has a unique switch.

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Folding Mass Effect Pistol!

Video game props require a dedicated maker with a repertoire of skills to create. When those props are pulled from the Mass-Effect universe, a little more technological mastery is needed. Bringing those talents to bear,  [Optimistic Geometry] has built a motorized, folding M-3 Predator Pistol!

The gun was modeled in Fusion 360 and 3D printed on an Ultimaker 2 at the  MAKLab Glasgow. [Optimistic Geometry] felt constrained by the laws of our reality, so opted for the smaller firearm thinking it would be an appropriate entry-level challenge. I’m sure you can guess how that went.

There wound up being three main build phases as well as a spring-loaded version to testing purposes. Throughout, [Optimistic Geometry] struggled with getting the parts to latch fully open or closed, as well as working with the small form factor. However, overhauling the motor design — and including some limiters lest it deconstruct itself — a custom latching circuit, and — obviously — a few LEDs for effect, produced a magnificent prop.

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Upgraded Roboceratops Still Not Extinct

We first heard about [Robert Stephenson]’s robotic baby dinosaur a few years ago, and recently he made some upgrades.

Roboceratops V2 uses 10 servos in the jaw, neck, tail, and front and back legs with 16 degrees of freedom—the two front legs each got an additional degree of freedom in the upgrade. [Robert] is currently in the process of swapping out the Hitec HS645 MGs for higher-torque New Power XLDs.

The older version had aluminum legs covered with upholstery foam, but [Robert] has refined the design. The head, body, and legs are made from laser-cut MDF sanded to give a more natural, bone-like rounding. Finally, to better make use of the new servos [Robert] rewrote the gait engine, giving Robosaurus a more natural motion as it adjusts its center of gravity with each step.

So, for the next version are we all on board for simulated skin?

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