Cable Driven Robotic Joint

April 26, 2020 by Danie Conradie 14 Comments

Even the oldest of mechanisms remain useful in modern technology. [Skyentific] has been messing with robotic joints for quite a while, and demonstrated an interesting way to use a pulley system in a robotic joint with quite a bit of mechanical advantage and zero backlash.

Inspired by the LIMS2-AMBIDEX robotic arm, the mechanism is effectively two counteracting sets of pulley, running of the same cable reel, with rollers allowing them to act around the bend of the joint. Increasing the mechanical advantage of the joint is simply a matter of adding pulleys and rollers. If this is difficult to envision, don’t work as [Skyentific] does an excellent job of explaining how the mechanism works using CAD models in the video below.

The mechanism is back drivable, which would allow it to be used for dynamic control using a motor with an encoder for position feedback. This could be a useful feature in walking robots that need to respond to dynamically changing terrain to stay upright, or in arms that need to push or pull without damaging anything. With properly tensioned cables, there is no backlash in the mechanism. Unfortunately cables can stretch over time, so it is something that needs to be considered when using this in a project.

Pulley systems have been with us for a very long time, and remain a very handy tool to have in your mechanical toolbox. A similar arrangement is used in the Da Vinci surgical robots to control their tiny manipulators. It would also be interesting to see this used in the already impressive robots of [James Bruton]. Continue reading “Cable Driven Robotic Joint” →

A Double-Hybrid Mini-Lathe, From Scratch

October 23, 2019 by Dan Maloney 4 Comments

It’s a treadle lathe! No, it’s a power lathe! It’s a wood lathe! No, it’s a metal lathe! Actually, [Uri Tuchman]’s homebrew lathe is all of the above, and it looks pretty snazzy too.

To say that [Uri]’s creations are quirky is a bit of an understatement – birds, crustaceans, hands, and feet all appear repeatedly as motifs in his work – but there’s no overstating his commitment to craftsmanship. [Uri] turns wood and metal into wonderful tools, nonsense machines, and finely detailed instruments, like this exquisitely engraved astrolabe we featured a while back.

[Uri] mostly works with hand tools, supplemented by an old Singer treadle-powered sewing machine that he turned into a scroll saw. The video below shows how he added a small scratch-built lathe to the treadle base. His first pass at a headstock, using pillow blocks for bearings, didn’t work as well as he wanted, so he built a new headstock around off-the-shelf lathe parts. The aluminum extrusion bed holds the headstock, tailstock, and a custom-built tool rest of heavy brass, all of which look great alongside the rich wood accent pieces and base. And for those times when his feet are tired, he added a surplus electric motor to turn the spindle. We especially like the two settings on the motor speed control: “0” and “>0”. Classic [Uri].

If you haven’t heard of [Uri] before, do yourself a favor and go check out his YouTube channel right now. Or start with our other coverage of his unique projects, from building an intricately detailed hammer to his lobster claw ink-dipping machine and even this unusual take on preserved lemons.

Continue reading “A Double-Hybrid Mini-Lathe, From Scratch” →

Cat Robot’s Secret To Slim Legs? Banish The Motors!

September 15, 2018 by Donald Papp 6 Comments

The first thing to notice about [Bijuo]’s cat-sized quadruped robot designs (link is in Korean, Google translation here) is how slim and sleek the legs are. That’s because unlike most legged robots, the limbs themselves don’t contain any motors. Instead, the motors are in the main body, with one driving a half-circle pulley while another moves the limb as a whole. Power is transferred by a cable acting as a tendon and is offset by spring tension in the joints. The result is light, slim legs that lift and move in a remarkable gait.

[Bijuo] credits the Cheetah_Cub project as their original inspiration, and names their own variation Mini Serval, on account of the ears and in keeping with the feline nomenclature. Embedded below are two videos, the first showing leg and gait detail, and the second demonstrating the robot in motion.

Continue reading “Cat Robot’s Secret To Slim Legs? Banish The Motors!” →

Pulleys Within Pulleys Form A Unique Transmission For Robots

September 25, 2017 by Dan Maloney 36 Comments

After a couple of millennia of fiddling with gears, you’d think there wouldn’t be much new ground to explore in the field of power transmission. And then you see something like an infinitely variable transmission built from nested pulleys, and you realize there’s always room for improvement.

The electric motors generally used in robotics can be extremely efficient, often topping 90% efficiency at high speed and low torque. Slap on a traditional fixed-ratio gearbox, or change the input speed, and efficiency is lost. An infinitely variable transmission, like [Alexander Kernbaum]’s cleverly named Inception Drive, allows the motor to stay at peak efficiency while smoothly changing the gear ratio through a wide range.

The mechanism takes a bit of thought to fully grok, but it basically uses a pair of split pulleys with variable spacing. The input shaft rotates the inner pulley eccentrically, which effectively “walks” a wide V-belt around a fixed outer pulley. This drives the inner pulley at a ratio depending on the spacing of the pulley halves; the transmission can shift smoothly from forward to reverse and even keep itself in neutral. The video below will help you get your head around it.

We’ve seen a couple of innovative transmissions around here lately; some, like this strain-wave gear and this planetary gearbox, are amenable to 3D printing. Looks like the Inception Drive could be printed too. Hackers, start your printers and see what this drive can do.

Continue reading “Pulleys Within Pulleys Form A Unique Transmission For Robots” →

Robot Graffiti

September 13, 2017 by James Hobson 11 Comments

There’s talk of robots and AIs taking on jobs in many different industries. Depending on how much stock you place in that, it might still be fair to say the more creative fields will remain firmly in the hands of humans, right?

Well, we may have some bad news for you. Robots are now painting our murals.

Estonian inventor [Mihkel Joala] — also working at SprayPainter — successfully tested his prototype by painting a 30m tall mural on a smokestack in Tartu, Estonia. The creative procedure for this mural is a little odd if you are used to the ordinary painting process: [Joala] first takes an image from his computer, and converts it into a coordinate grid — in this case, about 1.5 million ‘pixels’. These pixels are painted on by a little cart loaded with five colours of spray paint that are able to portray the mural’s full palette once combined and viewed at a distance. Positioning is handled by a motor at the base of the mural controlling the vertical motion in conjunction with tracks at the top and bottom which handle the horizontal motion.

For this mural, the robot spent the fourteen hours trundling up and down a set of cables, dutifully spraying the appropriate colour at such-and-such a point resulting in the image of a maiden cradling a tree and using thirty cans of spray paint in the process.

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[Homo Faciens] Builds A Winchbot

March 11, 2017 by Elliot Williams 16 Comments

The trademark hacker style of Hessian YouTuber [Homo Faciens] is doing a lot with a little. Given a package of parts from a sponsor, he could have made something “normal” like a fancy robot arm. Instead, he decided to make a winchbot. (Video embedded below.)

What’s a winchbot? It’s a big frame that supports three relatively heavy motors that pull steerable gripping arms around. It’s a little bit like the hanging Hektor / wallbot / plotterbot and a little bit like a delta-style 3D printer. Although [Homo Faciens]’s build doesn’t showcase it, a winchbot is also a great way to lift heavy things because the parts that need to be beefy — the frame and the lifting motors — don’t have to move. We love the gimballed square rod that works in concert with the winches!

With five extra servos on hand, and the computing power of a Raspberry Pi, [Homo Faciens] couldn’t just stop with lifting a claw. Instead, the gripping-arms part of the bot is mounted with four degrees of freedom and is powered with software that makes it stay parallel with the table and rotate around the gripper to make programming easier. Watch it in action in the video to see what we mean.

The biggest unsolved problem that we can see is the jerkiness that it displays in moving things around. That doesn’t stop it from building up a tower and a domino knock-down. We suspect that there’s some combination of firmware and hardware tweaking that can solve this problem, or it could just be run slowly so that the wobbles damp themselves out. We’re also quite confident that [Homo Faciens] will come up with an elegant and cheap solution. Have you seen his CNC machine?

Continue reading “[Homo Faciens] Builds A Winchbot” →

Pulley Lamp Stands Up With You

October 14, 2016 by Elliot Williams 33 Comments

Standing desks are either the best thing since sliced bread, or the fastest way to make your legs tired and get you ridiculed by your coworkers in the bargain. This leads some folks to compromise and make standing desks that can be re-lowered to sitting height when you need to take a break. But now the distance from your desktop to the light source that illuminates it has changed. We can’t have that!

[John Culbertson] came up with a very elegant solution to the “problem”. He made lights that are suspended on pulleys that raise and lower with the desk itself. We’re not sure that you’re in the same situation he is, but we’re sure that you’ll agree that he did a nice job.

Besides the pulley mechanism, the light shades are a work of art. [John] clearly wanted a retro feel, so he used low-voltage lightbulbs, but augmented them with LED strips to pump out the lumens. All in all, there’s a tremendous attention to detail in the project, and it shows.

Disclaimer: your humble author is writing you this missive from a standing desk. Ours is just a regular desk put up on bricks — a temporary solution that’s become permanent. We’re always keeping our eyes out for mechanisms to make the desk convertible, but everything that we’ve seen is either overkill or ridiculously overpriced or both. It’s hard to beat 24 bricks at $0.35 apiece. Anyone have any suggestions?

Of course, with an adjustable desk come the problems of moving your lighting along with it, but [John] has solved that one for us.