A 3D-Printed Robot Actuator

Somehow, walking robots at our level never really seem to deliver on the promise that should be delivered by all those legs. Articulation using hobby servos is simple enough to achieve, but cumbersome, slow, and not very powerful. [Paul Gould] has a plan to make a better, 3D-printed articulated robot actuator.

His solution is both novel and elegant, a fairly conventional arm geometry that has at its joints a set of brushless motors similar to but a little larger than the kind you might be more familiar with on multirotors, paired with 3D-printed cycloidal gearboxes. Magnetic encoders provide the necessary positional feedback, and the result is a unit that is both compact and powerful.

With such a range of small brushless motor controllers on the market, it’s at first sight unexpected that he’s designed his own controller board. But this gives him complete control over his software, plus the CAN bus that ties everything together. He’s given us a video which we’ve placed below the break, showing the build process, the impressive capabilities of his system, and a selection of builds including a robot dog complete with tail. This is definitely a project to watch.

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Making Robot Snakes That Slither, Sidewind, And Strike

[Will Donaldson] has been making robot snakes of all sorts. One of his snakes hugs the ground, slithering across it with a sine wave motion. Flipping it on its side and calling different code, that same snake also moves like an inchworm. Another of his snakes lifts parts of itself upward to move sideways across the ground, again using sine waves.

3D printed scales
3D printed scales

At first, his slithering snake would only oscillate in place on the floor. Looking more closely at biological snakes, he found that part of the reason they moved forward was due to their scales. The scales move smoothly over the ground in one direction but grip when pushed backward or sideways. He also found work done at Harvard University where they combined pumped air and papercraft to make scales which change shape. And so [Will] designed and 3D printed some scales for his snake. However, as you can see in the video below, they didn’t work on carpet.

His success came when he added wheels to each segment. They didn’t work like a car, there was no engine turning the wheels. Instead, they acted more like scales, rotating freely in one direction and gripping when pushed sideways. This success also allowed him to add a parameter to his code for turning left or right.

As we said above, he can flip the ground hugger sideways and run it as an inchworm and he also has a working sidewinder snake variation. The sidewinder can even lift up its head and strike like a cobra. Check out his hackaday.io page if you want to make your own. He’s provided STL files, code, and construction details.

[Will] has a lot of future plans for his snakes. Currently, they’re tethered to a modified ATX power supply but he’d like to incorporate LiPo batteries into the snakes instead. His original goal was to make a tree climbing snake like the one by the Biorobotics lab at Carnegie Mellon University (updated link for the article) but his first snake wasn’t long enough. He still plans on pursuing that as well as an underwater electronic eel. There seems to be no limit to the things he can try. For now, check out the video below to see his successes and his failures so far. Maybe you even have some suggestions for those tricky scales. The undersides of his snake’s segments do seem modular, lending themselves to experimentation.

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Rescuing K-9

Fans of the long-running and ever-fantastic British TV show Dr. Who will no doubt hold a soft spot in their hearts for the Doctor’s little robot companion. No, not one of his many human sidekicks, we’re talking about K-9, the angular dog-like android that burst onto British screens back in 1977.

There were a number of original [K-9] props made by the BBC, and these were eventually sold by the corporation. One found its way to Abertay University, and it was there that [Gary Taylor], a computer science student found it. Sadly the years had not been kind to the robotic mutt, in particular water from a roof leak had damaged its internals beyond repair. With little more than the fibreglass shell to work with, he set out to rebuild K-9 and make the task the subject of his dissertation.

The original robo-dog was little more than a 1970s remote-controlled car, but its upgrades bring it firmly into the 21st century. At its heart is the inevitable Raspberry Pi 3, coupled with an Arduino mega 2560 that handles motor control and interfacing to an array of ultrasonic sensors. The Pi’s Bluetooth radio talks to an app on an Android phone, that serves as the K-9’s controller. All of which makes for an impressive upgrade, but we hope has disturbed as little of the original prop work as possible

Not everyone is lucky enough to find an original K-9, but for those destined for classic BBC prop disappointment there is always the possibility that you could build your own.

[James Bruton] Is Making A Dog: OpenDog Project

There was a time when a two-legged walking robot was the thing to make. But after seeing years of Boston Dynamic’s amazing four-legged one’s, more DIYers are switching to quadrupeds. Now we can add master DIY robot builder [James Bruton] to the list with his openDog project. What’s exciting here is that with [James’] extensive robot-building background, this is more like starting the challenge from the middle rather than the beginning and we should see exciting results sooner rather than later.

James' motor and ball screws
James’ motor and ball screws

Thus far [James] has gone through the planning stage, having iterated through a few versions using Fusion 360, and he’s now purchased the parts. It’s going to be about the same size as Boston Robotic’s SpotMini and uses three motors for each leg. He considered going with planetary gearboxes on the motors but experienced a certain amount of play, or backlash, with them in his BB-9E project so this time he’s going with ball screws as he did with his exoskeleton. (Did we mention his extensive background?)

Each leg is actually made up of an upper and lower leg, which means his processing is going to have to include some inverse kinematics. That’s where the code decides where it wants the foot to go and then has to compute backwards from there how to angle the legs to achieve that. Again drawing from experience when he’s done it the hard way in the past, this time he’s designed the leg geometry to make those calculations easy. Having written up some code to do the calculations, he’s compared the computed angles with the measurements he gets from positioning the legs in Fusion 360 and found that his code is right on. We’re excited by what we’ve seen so far and bet it’ll be standing and walking in no time. Check out his progress in the video below.

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High Voltage Switching with MOSFETs

Using a MOSFET as a switch is generally pretty simple. Make the gate voltage sufficient with respect to the source and current flows through the channel. However, if you are switching higher voltages, you may need some additional circuitry to protect the device’s gate and possibly the microcontroller driving the whole thing, too. [Lewis] discusses high voltage switching in the latest in his series of videos dealing with MOSFETs. You can see the video below.

You’ll see in the video a breadboard setup driving a 50 V load and also a higher-voltage H-bridge. There are three major topics covered: Using an optoisolator, using a gate bleeder resistor, and using a zener diode to limit gate voltage.

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Japanese Fire-Fighting Dragon Rides Water Jets

If you are building a robot to fight fires, why not use the water that you are fighting fires with to propel your robot? That seems to be the idea behind the Dragon Fire Fighting robot built by [Professor Satoshi Tadokoro], and his team at Tadohoku University. Their dragon robot is raised by the same directed jets of water that are used to stop the fire.

The three-meter robot also uses these jets of water to steer, moving the dragon’s head by firing water jets at angles. I’m not sure how practical it really is, though: the jets that the robot uses to steer could do as much damage as the fire itself if it wasn’t used carefully. The idea is to attach it to the end of a ladder or crane used by firefighters, so it can explore a building on fire without anyone having to step inside.

The robot was built as part of the Tough Robotics Challenge, a program that is looking to build robots that can help in disasters. Japan is one of the most disaster-prone places on the planet, thanks to earthquakes, nuclear meltdowns, and Godzilla attacks, so the program is looking to build robots that can help out. Some of the concepts they are looking at include cyborg animals, a listening drone that can help find survivors after a disaster using a sensitive microphone array and a serpentine robot that can map pipes and underground structures.

[Via TechXplore and Qes]


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Turning That Old Hoverboard Into A Learning Platform

[Isabelle Simova] is building Hoverbot, a flexible robotics platform using Ikea plastic trays, JavaScript running on a Raspberry Pi and parts scavenged from commonly available hoverboards.

Self-balancing scooters a.k.a. Hoverboards are a great source of parts for such a project. Their high torque, direct drive brushless motors can drive loads of 100 kg or more. In addition, you also get a matching motor controller board, a rechargeable battery and its charging circuit. Most hoverboard controllers use the STM32F103, so flashing them with your own firmware becomes easy using a ST-link V2 programmer.

The next set of parts you need to build your robot is sensors. Some are cheap and easily available, such as microphones, contact switches or LDRs, while others such as ultrasonic distance sensors or LiDAR’s may cost a lot more. One source of cheap sensors are car parking assist transducers. An aftermarket parking sensor kit usually consists of four transducers, a control box, cables and display. Using a logic analyzer, [Isabelle] shows how you can poke around the output port of the control box to reverse engineer the data stream and decipher the sensor data. Once the data structure is decoded, you can then use some SPI bit-banging and voltage translation to interface it with the Raspberry Pi. Using the Pi makes it easy to add a cheap web camera, microphone and speakers to the Hoverbot.

Ikea is a hackers favourite, and offers a wide variety of hacker friendly devices and supplies. Their catalog offers a wide selection of fine, Swedish engineered products which can be used as enclosures for building robots. [Isabelle] zeroed in on a deep, circular plastic tray from a storage table set, stiffened with some plywood reinforcement. The tray offers ample space to mount the two motors, two castor wheels, battery and the rest of the electronics. Most of the original hardware from the hoverboard comes handy while putting it all together.

The software glue that holds all this together is JavaScript. The event-driven architecture of Node.js makes it a very suitable framework to use for Hoverbot. [Isabelle] has built a basic application allowing remote control of the robot. It includes a dashboard which shows live video and audio streams from the robot, buttons for movement control, an input box for converting text to speech, ultrasonic sensor visualization, LED lighting control, message log and status display for the motors. This makes the dashboard a useful debugging tool and a starting point for building more interesting applications. Check the build log for all the juicy details. Which other products from the Ikea catalog can be used to build the Hoverbot? How about a robotic Chair?

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