Hinge joints are usually the simplest to use for robotic applications, but if you want motion that looks more organic, rolling joint (or rolling contact) mechanisms are worth a look. [Skyentific] is experimenting with this mechanism and built a 6-degree-of-freedom robotic arm with it.
The mechanism doesn’t necessarily need the physical surfaces to roll across each other to work, and you can get to two degrees of freedom with the virtual rolling sphere mechanism. [Skyentific] demonstrates how these work with both cardboard cutouts and 3D printed models. Stacking three of these mechanisms on top of each other, with each stage driven by three Dynamixel servos, the motion seems almost serpentine.
Since the servos are driving the small bottom linkages of each stage, they are operating at a significant mechanical disadvantage. The arm can just barely keep itself upright on top of the table, so [Skyentific] mounted it upside down to the bottom of the table to reduce the load of its weight. With the front stage removed, the load is significantly reduced, and it doesn’t struggle as much.
An interesting advantage of this mechanism is that there is always a straight path down the center for cabling. The length of this line between the two plates remains the same throughout the entire range of motion, so it can also be used to route a rigid drive shaft. This is actually what was done on the LIMS2-AMBIDEX robot to rotate its hand, and is also where saw this mechanism for the first time. Interestingly, that implementation didn’t drive the linkages themselves, but used tension cables around the mechanism. We also see this in a very similar tentacle robot, so it might be a better option.
We all bring our own areas of expertise to our work when we build the projects that find their way in front of Hackaday writers, for instance a software developer brings clever brains to their microcontroller, or an electronic engineer might bring a well-designed piece of circuitry. [Yvo de Haas] is a mechanical engineer, and it’s pretty clear from his animatronic tentacle that he has used his expertise in that field to great effect.
If you think it looks familiar then some readers may recall that we saw a prototype model back in February at Hacker Hotel 2020. In those last weeks before the pandemic hit us with lockdowns and cancellations he’d assembled a very worthy proof of concept, and from what we can see from his write-up and the video below he’s used all the COVID time to great effect in the finished product. Back in February the control came via a pair of joysticks, we’re particularly interested to see his current use of a mini tentacle as a controller.
At its heart is a linkage of 3D-printed anti-parallelograms linked by gears, with cables holding the tension and controlling the movement of the tentacle from a set of winches. The design process is detailed from the start and makes a fascinating read, and with its gripper on the end we can’t wait for an event that goes ahead without cancellation at which we can see the tentacle for real.
Welcome back to the final chapter in our journey exploring two-stage tentacle mechanisms. This is where we arm you with the tools and techniques to get one of these cretins alive-and-kicking in your livingroom. In this last installment, I’ll guide us through the steps of building our very own tentacle and controller identical to one we’ve been discussing in the last few weeks. As promised, this post comes with a few bonuses:
Depending on your situation, some design files may be more important than others. If you just want to get parts made, odds are good that you can simply cut the pre-offset DXFs from the right plate thicknesses and get rolling. Of course, if you need to tune the files for a laser with a slightly different beam diameter, I’ve included the original DXFs for good measure. For the heavy-hitters, I’ve also included the original files if there’s something about this design that just deserves a tweak or two. Have at it! (And, of course, let us know how you improve it!)
Ok, now that we’ve got the parts on-hand in a pile of pieces,let’s walk through the last-mile tweaks to making this puppet work: assembly and tuning. At this point, we’ve got a collection of parts, some laser-cut, some off the shelf. Now it’s time to string them together.
A few weeks back, we got a taste for two-stage tentacle mechanisms. It’s a look at how to make a seemily complicated mechanism a lot less mysterious. This week, we’ll take a close look at one (of many) methods for puppeteering these beasts by hand. Best of all, it’s a method you can assemble at home!
Without a control scheme, our homebrew tentacle can only “squirm around” about as much as an overcooked noodle. It’s pretty useless without some sort of control mechanism to keep all the cables in check at proper tension. Since the tentacle’s motion is driven by nothing more than four cable pairs, it’s not too difficult to start imagining a few hobby servos and pulleys doing the job. To get us started, though, I’ve opted for hand controllers just like the puppeteers of the film industry.
Enter Manual Control
Hand controllers? Of all the possibilities offered by electronics, why select such an electronics-devoid caveman approach? Fear not. Hand controllers offer us a unique set of opportunities that aren’t easy to achieve with most alternatives.
What’s not to love about animatronics? Just peel back any puppet’s silicone skin to uncover a cluster of mechatronic wizardry that gives it a life on the big screen. I’ve been hunting online for a good intro to these beasts, but I’ve only turned up one detailed resource–albeit a pretty good one–from the Stan Winston Tutorials series. Only 30 seconds into the intro video, I could feel those tentacles waking up my lowest and most gutteral urge to create physical things. Like it or not, I was hooked; I just had to build one… or a few. This is how you built a very real animatronic tentacle.
If you’re getting started in this realm, I’ll be honest: the Stan Winston Tutorial is actually a great place to start. In about two hours, instructor Richard Landon covers the mindset, the set of go-to components, and the techniques for fabricating a tentacle mechanism with a set of garage tools–not to mention giving us tons of real-film examples along the way .
We also get a sneak peek into how we might build more complicated devices from the same basic techniques. I’d like to pick up exactly where he left off: 4-way two-stage tentacles. And, of course, if you’ve picked up on just how much I like a certain laser-cuttable plastic at this point, I’m going to put a modern twist on Landon’s design. These design tweaks should enable you to build your own tentacle and controller with nothing more but a few off-the-shelf parts, some Delrin, and a laser cutter… Ok, fine, a couple 3D printed parts managed to creep their way in too.
In a good-ol’ engineers-for-engineers fashion, I’m doing something a little different for this post: I’m finishing off this series with a set of assembly videos, a BOM, and the original CAD files to make that beast on the front page come to life. As for why, I figured: why not? Even though these mechanisms have lived in the robotics community and film industry for years, they’re still lacking the treatment of a solid, open design. This is my first shot at closing that gap. Get yourself a cup of coffee. I’m about to give you every bleeding detail on the-how-and-why behind these beasts.
[ivorjawa] is putting on a haunted house this Halloween that we really don’t want to go to. His robot tentacle is already supremely creepy, and we’re assuming it will only be more frightening once it’s covered in fabric and foam rubber.
Each tentacle can move on two axes thanks to four steel cables running through this strange Geiger-esque contraption. In the base of the tentacle are two stepper-motor driven cylinders that take up slack on one cable and draw out another cable. Two of these control boxes, driven by a stepper motor and an Arduino motor shield, allow the tentacle to reach out and grab in any direction. You can check out the mechanics of the build on [ivorjava]’s flickr
On a semi-related note, even though we’re more than a month out from Halloween, we should have more Halloween builds in our tip line by now. If you’re working on one, don’t be afraid to send it in, even if you’re just showing off a work in progress.
Soft robots are a peculiar wing of technology. They don’t use frames and motors for locomotion, but as the name implies they are made of soft materials. They move by pumping fluid — it could be air or liquid — in and out of bladders that push or pull against the body itself. [Matthew] points out that fabricating soft robots has traditionally been a time-consuming and difficult task. He’s trying to make it easier by 3D printing molds into which soft robots can be cast. This way the parts can be designed in CAD, converted to a mold design, and pushed to a 3D printer.
The object with which he’s been testing the technique functions like an octopus tentacle. The image at the bottom left illustrates the internal structure, with rings separated to allow the appendage to flex, and tubes running parallel to the appendage to provide the force needed to bend it. Above that image you can see one of the molds that was used, and the final product is on the right. The video after the break shows a demonstration of this bending left and right as air is pumped in using the bulb of a blood pressure cuff (or Sphygmomanometer for those paying attention).