Scratch-Built Robot Arm Looks Like Something Off The Factory Floor

April 10, 2021 by Dan Maloney 13 Comments

[Jeremy Fielding] is rightly impressed with the power and precision of industrial robot arms. The big arms that you see welding cars on assembly lines and the like are engineering feats in their own right, which is why his leap into scratch-building one in the home shop promises to be quite an adventure, and one we’re eager to follow.

From the look of the video below, [Jeremy]’s arm is already substantially complete, so it seems like he’ll be releasing videos that detail how he got to the point where this impressively large and powerful arm took over so much of his shop. He’s not fooling around here — this is a seven-axis articulated arm built from aluminum and powered by AC servos. [Jeremy] allows that some of the structural parts are still 3D-printed prototypes that he’s using to finalize the design before committing to cutting metal, a wise move as he notes that most of the metalworking skills he needs to complete the build are still fairly new to him. It still looks amazing, and we’re looking forward to the rest of the series to see how he got to this point.

We always appreciate [Jeremy]’s enthusiasm and presentation style, and we generally learn a lot from his videos. Whether it’s a CNC table saw, a homebrew dynamometer, or supersonically melting baseballs, his videos are always great to watch.

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Harmonic Drive Uses Compliant Mechanism To Slim Down

April 7, 2021 by Dan Maloney 15 Comments

[Levi Janssen] has a secret: he doesn’t like harmonic drives. But rather than abandon the torque-amplifying transmission completely, he decided to see about improving them using 3D-printed compliant mechanisms.

For the uninitiated, harmonic drives, also known as strain-wave gears, are a compact, high-torque gearbox that has become popular with “robotic dog” makers and other roboticists. The idea is to have a rigid, internally-toothed outer ring nested around an externally-toothed, flexible cup. A wave generator rotates within the inside cup, stretching it so that it meshes with the outer ring. The two gears differ by only a couple of teeth, meaning that very high gear ratios can be achieved, which makes them great for the joints of robot legs.

[Levi]’s problem with the harmonic drive is that due to the depth of the flexible spline cup, compactness is not among its virtues. His idea is to couple the flex spline to the output of the drive through a flat spring, one that allows flexion as the wave generator rotates but transmits torque efficiently. The entire prototype is 3D-printed, except for the wave generator bearings and stepper motor, and put to the test.

As the video below shows after the excellent introduction to harmonic drives, the concept works, but it’s not without its limitations. Even lightly loaded, the drive made some unpleasant crunching sounds as the PLA springs gave out. We could easily see that being replaced with, say, a steel spring, either machined or cut on a water-jet machine. That might solve the most obvious problem and make [Levi]’s dream of a compact harmonic drive a reality. Of course, we have seen pretty compact strain-wave gears before.

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Cheat At Cornhole With A Bazillion-Dollar Robot

April 4, 2021 by Bryan Cockfield 19 Comments

While the days of outdoor cookouts may be a few months away for most of us, that certainly leaves plenty of time to prepare for that moment. While some may spend that time perfecting recipies or doing various home improvement projects during their remaining isolation time, others are practicing their skills at the various games played at these events. Specifically, this group from [Dave’s Armory] which have trained a robot that helps play the perfect game of cornhole. (Video, embedded below.)

While the robot in question is an industrial-grade KUKA KR-20 robot with a hefty price tag of $32,000 USD, the software and control system that the group built are fairly accessible for most people. The computer vision is handled by an Nvidia Jetson board, a single-board computer with extra parallel computing abilities, which runs OpenCV. With this setup and a custom hand for holding the corn bags, as well as a decent amount of training, the software is easily able to identify the cornhole board and instruct the robot to play a perfect game.

While we don’t all have expensive industrial robots sitting around in our junk drawer, the use of OpenCV and an accessible computer might make this project a useful introduction to anyone interested in computer vision, and the group made the code public on their GitHub page. OpenCV can be used for a lot of other things besides robotics as well, such as identifying weeds in a field or using a Raspberry Pi for facial recognition.

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Putting Your Time In

March 27, 2021 by Elliot Williams 28 Comments

I was absolutely struck by a hack this week — [Adam Bäckström]’s amazing robot arm built with modified hobby servos. Basically, he’s taken apart and re-built some affordable off-the-shelf servo motors, and like the 6-Million-Dollar Man, he’s rebuilt them better, stronger, faster. OK, and smoother. We have the technology.

The results are undeniably fantastic, and enable the experienced hacker to get champagne robot motion control on a grape-juice budget by employing some heavy control theory, and redundant sensors to overcome geartrain backlash, which is the devil of cheap servos. But this didn’t come out of nowhere. In his writeup, [Adam] starts off with “You could say this project started when I ordered six endless servos in middle school, more than 15 years ago.” And it shows.

Go check out this video of his first version of the modified servos, from a six-axis arm he built in 2009(!). He’s built in analog position sensors in the motors, which lets him control the speed and makes it work better than any other hobby servo arm you’ve ever seen, but there’s still visible backlash in the gears. A mere twelve years later, he’s got magnetic encoders on the output and a fast inner loop compensates for the backlash. The result is that the current arm moves faster and smoother, while retaining accuracy.

Twelve years. I assume that [Adam] has had some other projects on his plate as well, but that’s a long term project by any account. I’m stoked to see his work, not the least because it should help a lot of others who are ready to step up their desktop servo-arm projects. But the real take-home lesson here is that if you’ve got a tough problem that you’re hacking on, you don’t have to get it done this weekend. You don’t have to get it done next weekend either. Keep hammering on it as long as you need, but keep on hammering. When you get it done, the results will be all the better for the long, slow, brewing time. What’s the longest project that you’ve ever worked on?

Skid Steer Robot Chassis Takes A Beating

March 26, 2021 by Lewin Day 5 Comments

[Engineering After Hours] wanted a highly maneuverable robot chassis with a tight turning radius. Skid steering seemed to be the perfect solution, but the available commercial options didn’t take his fancy. Thus, a custom build was the answer – with impressive results.

The build packs two large RC motors, one for each side, with each driving two wheels through a belt drive. This reduces the electronics required to the bare minimum for skid steering. It’s all assembled within a plasma-cut metal chassis which is more than tough enough to take some hard knocks.

One of the primary goals on the build was to eliminate the risk of vibrations and shock damaging the motors and gearboxes. Many off-the-shelf designs couple the wheels directly to gearbox output shafts, potentially damaging the expensive components over time. In this design, a separate bearing assembly is used to take the load from the wheels instead.

It’s a great example of how an engineering-first approach can build a sturdy ‘bot with a minimum of fuss. Outfitted with some fat off-road tyres the performance is impressive, with the ‘bot having no trouble tearing it up in mud, snow, and water.

We’ve seen other great builds from [Engineering After Hours] before, like the active aero RC build. Video after the break.

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DIY B-Movie Robot Is A-OK

March 17, 2021 by Kristina Panos 12 Comments

While we certainly agree that “Devil Girl From Mars” is an attractive movie title, we have yet to see this apparent British B-movie delight for ourselves. If [Cory Collins]’ fantastic build of Chani, the lumbering, terrifying robot that accompanies the vinyl-clad and caped Devil Girl in question is any indication, we bet it’s delightfully bad.

[Cory] was able to faithfully reproduce Chani — lights, lumbering and all — for less than $50. This price tag does not include the vacuum former required to make the domed head, but hey, it’s an investment into future projects.

[Cory] started by dissecting an R/C stunt car from Harbor Freight and stringing the innards up to a 3D-printed walking mechanism that’s been modified to use gear-reduced motors so it walks more slowly. While Chani is stomping around on TPU treads, the LEDs from the R/C car’s headlights shine inside of its dome. Chani’s boxy body is a big paper sculpture that looks spot-on to us when compared to the movie’s trailer.

We love the way that Chani walks — it sort of dips and glides along in a forward-facing Moonwalk fashion. As you can see in the video below, [Cory] totally nailed the robot’s gait, and it’s hilarious to watch Chani’s little coolant hose-looking arms dangle and shake as he makes his slow and menacing way across the table. Stick around for some scary nighttime footage of Chani against a thunderstorm.

Want your robots to move more like movie robots? All you gotta do is use the right tools.

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Your Plants Can Take Care Of Themselves Now

March 14, 2021 by Bryan Cockfield 41 Comments

One of [Sasa]’s life goals is to be able to sit back in his home and watch as robots perform all of his work for him. In order to work towards this goal, he has decided to start with some home automation which will take care of all of his house plants for him. This project is built from the ground up, too, and is the first part of a series of videos which will outline the construction of a complete, open-source plant care machine.

The first video starts with the sensors for the plants. [Sasa] decided to go with a completely custom module based on the STM32 microcontroller since commercial offerings had poor communications designs and other flaws. The small board is designed to be placed in the soil, and has sensors for soil moisture as well as other sensors for amount of light available and the ambient temperature. The improvements over the commercial modules include communication over I2C, allowing a large number of modules to communicate over a minimum of wires and be arranged in any way needed.

For this build everything is open-source and available on [Sasa]’s GitHub page, including PCB layouts and code for the microcontrollers. We’re looking forward to the rest of the videos where he plans to lay out the central unit for handling all of these sensors, and a custom dashboard for controlling them as well. Perhaps there will also be an option for adding a way to physically listen to the plants communicate their needs as well.

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