Taming Robot Arm Jump With Accelerometers

June 24, 2016 by Rud Merriam 46 Comments

Last fall, I grabbed a robot arm from Robot Geeks when they were on sale at Thanksgiving. The arm uses servos to rotate the base and move the joints and gripper. These work well enough but I found one aspect of the arm frustrating. When you apply power, the software commands the servos to move to home position. The movement is sufficiently violent it can cause the entire arm to jump.

This jump occurs because there is no position feedback to the Arduino controller leaving it unable to know the positions of the arm’s servos and move them slowly to home. I pondered how to add this feedback using sensors, imposing the limitation that they couldn’t be large or require replacing existing parts. I decided to try adding accelerometers on each arm section.

Accelerometers, being affected by gravity when on a planet, provide an absolute reference because they always report the direction of down. With an accelerometer I can calculate the angle of an arm section with respect to the direction of gravitational acceleration.

Before discussing the accelerometers, take a look at the picture of the arm. An accelerometer would be added to each section of the arm between the controlling servos.

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Driving BB-8: More Than One Way To Move This Bot

June 24, 2016 by Steven Dufresne 30 Comments

BB-8 is the much loved new droid introduced in the 2016 movie Star Wars: The Force Awakens, though in my case from the very first trailer released in 2014 I liked it for the interesting engineering problems it posed. How would you make a robot that’s a ball that rolls along, but with a head that stays on top while the ball rolls under it?

BB-8 in 1st Star Wars: The Force Awakens trailer

Hamster in hamster wheel

To make the ball roll, the answer most people found obvious at first was to use the analogy of a hamster wheel. The hamster running inside makes the wheel turn. In the BB-8 building world, which is quite large, the drive mechanism has come to be called a hamster drive, or just a hamster.

For the head, it seemed obvious that there would be magnets inside the ball, perhaps held in place near the top of the ball by a post extending up from the hamster. Corresponding magnets in attraction would then be attached to the underside of the head, and balls (also mounted under the head) would keep the head moving smoothly over the ball.

The magnet approach for the head has turned out to be the method used by all BB-8 builders that I’ve seen. However, the hamster has turned out to be only one of multiple solutions. Since the original debut many different methods have been used in builds and we’re going to have a lot of fun looking at each separate approach. It’s almost like revealing a magic trick; but really it’s all just clever engineering.

Note that for the actual movie, a combination of 7 or 8 props and CGI were used. The official working BB-8s that are shown at various promotional events were built after the movie was made and as of this writing, few details of their construction have been released. One notable detail, however, is that they aren’t using hamster drives.

Below are details of all the different BB-8 drive systems I’ve seen so far that have been built along with how they work.

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HobbyKing Cheetah: Building Running Robots From Hobby Motors

June 24, 2016 by Gerrit Coetzee 15 Comments

[Ben Katz] is building a running robot from hobby level brushless motors, all on his blog under the tag, “HobbyKing Cheetah.”

One of the features of fancy modern industrial motor and controller sets is the ability for the motor to act as a mass-spring-damper. For example, let’s say you want a robot to hold an egg. You could have it move to the closed position, but tell the controller you only want to use so much force to do it. It will hold the egg as if there was a spring at its joint.

Another way you could use this is in the application of a robot leg. You tell the controller what kind of spring and shock absorber (damper) combination it is and it will behave as if those parts have been added to the mechanism. This is important if you want a mechanical leg to behave like a biological leg.

[Ben] had worked on a more formal project which used some very expensive geared motors to build a little running robot. It looks absolutely ridiculous, as you can see in the following video, but it gives an idea of where he’s going with this line of research. He wanted to see if he could replace all those giant geared motors with the cheap and ubiquitous high performance brushless DC motors for sale now. Especially given his experience with them.

So far he’s done a very impressive amount of work. He’s built a control board. He’s characterized different motors for the application. He’s written a lot of cool software; he can even change the stiffness and damping settings on the fly. He has a single leg that can jump. It’s cool. He’s taking a hiatus from the project, but he’ll be right back at it soon. We’re excited for the updates!

A Robot In A Day

June 23, 2016 by James Hobson 5 Comments

While building a robot (nearly) from scratch isn’t easy, it needn’t be a lengthy process. Is it possible to build a bot in a single day? With some musical motivation (a 10 hour loop of the A-Team theme song), [Tyler Bletsch] answers with a resounding ‘yes’ in the shape of his little yellow robot that he built for a local robotics competition.

Designing and fabricating on the fly, [Bletsch] used Sketchup to design the chassis, and OpenSCAD to model the wheels while the former was being 3D printed. Anticipating some structural weakness, he designed another version that could bolt to wood if the original failed, but the addition of some metal support rods provided enough stability. Mouse pad material gave the wheels ample traction. An Arduino with the L298 control module receives input via an HC-06 Bluetooth board. Eight AA batteries provide 12V of power to two Nextrox mini 12V motors with an integrated voltmeter to measure battery life.

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Building A Swarm Of Autonomous Ocean Boats

June 17, 2016 by Mike Szczys 9 Comments

There’s a gritty feel to the Hackerboat project. It doesn’t have slick and polished marketing, people lined up with bags of money to get in on the ground floor, or a flashy name (which I’ll get to in a bit). What it does have is a dedicated team of hackers who are building prototypes to solve some really big challenges. Operating on the ocean is tough on equipment, especially so with electronics. Time and tenacity has carried this team and their project far.

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Beautiful Cardboard Robot Build

June 16, 2016 by Elliot Williams 16 Comments

[Miloslav Stibor] may have built Mimobot 2.1 out of cardboard so that it’s not very heavy, but the robot is absolutely no lightweight. Read through his logs (in Czech, or in translation) and you’ll see what we mean.

Our favorite feature is the recharging dock and docking connectors, made respectively out of spring-loaded rivet ferrules and copper-tape-covered cardboard. The video found on that page is also absolutely brilliant: watch in awe as it climbs over children’s books, pulls a wooden train, or scales a mountain of pillows.

We wrote [Miloslav] and asked about the continuous-rotation servos, because they ran so smoothly at low speeds. He replaced the potentiometer with a pair of “carefully matched” 2.2 k resistors, and drives them with a PWM signal. Sounds easy, and obviously works very well. We were always under the impression that it was a little bit more complicated to get proportional control of hobby servos. We’ll have to experiment.

The wheels and lightweight frame (made of “military grade” cardboard — saturated with a wood/paper glue) make it entirely capable in living-room environments covered in cables or rugs, which is something we can’t say about our purchased vacuum-cleaner-bot. And the cell-phone remote interface that lets him control the onboard camera and its elevation and lighting. Driving the thing around with the phone control looks fun.

In short, if you build small robots, give this one a look. Something very much like this is now on our short must-build list. And we can’t wait to see Mimobot v3!

Robot Bites Man!

June 15, 2016 by Elliot Williams 49 Comments

The old newspaper saying holds that a dog biting a man isn’t news, but “Man Bites Dog” is a stellar headline. So instead of focusing on the usual human-on-small-robot ~~torture~~ experiments as we usually do, we bring you “The First Law“, an art piece by [Alex Reben].

[Alex] built a robot that “intentionally” defies Asimov’s First Law: doing no harm to humans. A human puts its little pink finger in the slot, is sensed, and a robot arm with a needle comes down and smashes through the meatbag’s puny fleshy appendage. Or maybe it doesn’t — it’s got a randomization routine that can be said to be “choosing” to prick you or not.

Yeah, the pin-prick is trivial, and yeah, the robot is not really deciding, but the point of the ‘bot is to get people talking. In a world where killer robots are not (yet, explicitly) against the Geneva Convention, soon we’re going to be facing this problem for real. If we need robot-art that makes literary references to get us thinking about these issues, so be it.

Of course, you don’t need to wait until there’s moral consensus to build your own terribly dangerous “robots” at home. How about an automated flamethrower or a knife-wielding tentacle? Or maybe this once, we’ll say that it makes more sense to just sit back and read about other folks doing it.

Via [Fast Company]. Thanks [fishocks367] for the tip!