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Self-Balancing Robot Uses Android and Lego NXT

LEGO NXT + Android = Self Balancing Robot

Self-balancing robots are pretty cool, but sometimes a bit too complex to make. [HippoDevices] shows us that it’s really not that hard, and you can even do it with Lego NXT and an Android device!

First step is to build your two-wheeled robot – go nuts! As long as the Lego NXT motors are strong enough you’ll be able to make most different shaped robots easy to balance. You’re going to need an Android ADK board to provide communication between the Lego motors and your Android device. [HippoDevices] is using their own design, called the Hippo-ADK which is on Kickstarter currently.

This allows your Android device to read the status and control the Lego Motors — from there it’s just a matter of programming it to balance according to the device’s gyroscope.

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Self-Balancing Robots Wobble, But They Don’t Fall Down

[Trandi] can check ‘build a self-balancing robot’ off of his to-do list. Over a couple of weekends, he built said robot, and, in his own words, managed not to over-design it. It even kept the attention of his 2-year-old son for several minutes, and that’s always a plus.

He was originally going to re-purpose one of his son’s RC cars, but didn’t want to risk breaking it. Instead, he designed a triangular 3-D printed chassis to hold a motor and some cogs to fit both the motor shaft and some re-used Meccano wheels. [Trandi]‘s design employs an MPU 6050 6-DOF IMU for the balancing act and is built on an Arduino Nano clone.

[Trandi] is controlling the motor with an L293D, which has built-in flyback diodes to minimize spikes. He found that the Nano clone was not powerful enough to handle everything, so he added an L7805CV voltage regulator. After the break, watch [Trandi]‘s cute bot tool around on various types of terrain, with and without a payload.

Don’t have an IMU lying around? You don’t really need one to build a self-balancing bot, as this IR-based lilliputian bot will demonstrate.

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Self-Balancing Robot Keeps Getting More Features

self-balancing-robot-gets-more-features

It’s a lot of fun to see a self-balancing robot project. Rarely do they go much further than being able to keep themselves upright while being piloted remotely and annoyingly shoved by their creator as proof of their ability to remain standing on two wheels. This little anthropomorphic guy is the exception to the rule. It’s the product of [Samuel Matos] who says he didn’t have a specific purpose in mind, but just kept adding features as they came to him.

Starting with a couple of carbon fiber plates [Samuel] cut the design by hand, using stand-offs to mount the NEMA 17 stepper motors and to connect the two halves of the chassis. It looks like he used some leftover material to make a nice little stand which is nice when coding at his desk as seen above. There’s also a carbon-fiber mask which makes up the face atop an articulated neck. It has two ultrasonic range-finding sensors as eyes, and the Raspberry Pi camera module as the nose. The RPi board powerful enough to run OpenCV which has kept [Samuel] busy. He set up a course in his living room containing tags directing where the little guy should go. It can also follow a tennis ball as it rolls around the room. What we found most impressive in the clip after the break is its ability to locate the next tag after making a turn.

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Building a Ball-Balancing Robot

robotBallBalance

If you want a different kind of feedback systems challenge, ditch the Segway-style robots and build one that can balance on a ball. UFactory is a startup in Shenzhen, and this impressive little guy is a way of showing their skills applied to the classic inverted pendulum. At nearly 18 inches tall and weighing just over six pounds, the robot boasts a number of features beyond an accelerometer and gyroscope: it has both a WiFi module and a camera, and can be controlled via a homemade remote control or a Kinect.

The build uses plastic omni-directional wheels attached to 3 brushed dc motors, which attach to the base of the robot with custom-made aluminum brackets. The UFactory gang constructed the robot’s body out of three acrylic discs, which hold the electronics directly above the wheels. The brain seems to be an STM32 microcontroller that connects up to the motors and to the sensors.

You won’t find the code on their Instructable yet, but according to the comments they have plans to make the entire project open source. If you’re desperate for more details, the UFactory team seems willing to provide source code and other information via email. Make sure you see the video after the break, particularly the end where they demonstrate interference and carrying loads. This isn’t the first ball pendulum we’ve seen; take a trip down memory lane with the BallP ball balancing robot from 2010.

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Self-balancing Arduino does it without an IMU

BalancerMini-1

The miniscule size of this self-balancing robot makes it a cool project. It actually uses the motor and wheels from a small toy car. But when you look into how the balancing act is performed it gets way more interesting. The larger versions of this trick pretty much all use Inertial Measurement Units (IMUs) which are usually made up of an accelerometer and a gyroscopic sensor. This has neither.

The black PCB seen to the right of the robot is an IR reflectance sensor. It shines an IR led at the floor and picks up what reflects back. [Sean] added this hack because the gyro sensor he ordered hasn’t arrived yet. The board has a trimpot which is used to adjust the sensitivity. You have to tweak it until it stands on its own. See for yourself after the break.

Self balancing robot builds are a great way to teach yourself about Proportional-Integral-Derivate (PID) algorithms used in a lot of these projects.

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Salvaging parts from broken Roomba robots

salvaging-parts-from-broken-roombas

The great thing about hacking on Roombas is that iRobot used quality parts to build them. [Jason] got his hands on a broken 5XX series Roomba and posted an article about how he reused the salvaged parts.

What you see above is one of the results of his work. This little bot takes commands from an IR television remote control. But he also used the setup to make a self-balancing bot. The two motors from the Roomba have magnetic rotary encoders with 8-bit resolution. Pair this with a well-tuned PID algorithm and you’re in business. The video below shows him testing a motor with his PID code.

You don’t get very much info on the guts of the donor robot. If that’s what you’re looking for you need to look at [Dino's] Roomba 4000 teardown.

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Kalman filter keeps your bot balanced

If you’re looking to improve the stability of your self balancing robot you might use a simple horrifying equation like this one. It’s part of the journey [Lauszus] took when developing a sensor filtering algorithm for his balancing robot. He’s not breaking ground on new mathematical ideas, but trying to make it a bit easier for the next guy to use a Kalman filter. It’s one method of suppressing noise and averaging data from the sensors commonly used in robotic applications.

His robot uses a gyroscope and accelerometer to keep itself upright on just two wheels. The combination of these sensors presents an interesting problem in that accelerometer input is most accurate when sampled over longer periods, and a gyroscope is the opposite. This filter takes those quirks into account, while also factoring out sensor noise. Despite the daunting diagram above, [Lauszus] did a pretty go job of breaking down the larger function and showing us where to get the data and how to use it in microcontroller code.

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