# Universal Robots Vision-Based LEGO Stacker

[Thomas Kølbæk Jespersen] and his classmates at Aalborg University’s Robot Vision course used MATLAB code and URscript to program a Universal Robots UR5 to stack up Duplo bricks. The Duplo bricks are stacked into low-fi Simpsons characters — yellow for Homer’s head, white for his shirt, and blue for his pants, for example.

The bricks are scattered randomly on a nearby table, while a camera mounted above the table scans the bricks and assists in determining the location, color, and orientation of the elements. This involves blob analysis which helps the computer decide what pixel is part of a brick and what isn’t. After running a recursive grassfire algorithm with 4-connectivity, the computer gives each pixel a number and assigns it to a blob.

To determine the orientation (the bricks are all assumed to be stud-side up and not overlapping) the blob is divided into quadrants and within each quadrant, the distance between the center of the blob and its farthest pixel is measured. This technique is not likely to work as well with a brick that isn’t square. Each brick’s location in pixels is translated into Cartesian coordinates, making it a cinch for the robot to pick it up. See [Thomas]’s GitHub for MATLAB and URscript code.

Looking for more UR5 projects? Check out the Sewbo garment-making robot we published last year.

# LEGO® My Single-Phase Induction Motor

[Diato556] made a really cool single-phase induction motor with parts mounted on Duplo blocks. He has posted an Instructable where he uses these modular parts to  demonstrate the motor and the principles of induction as described after the jump.

# Building a digital scale from scratch

[Raivis] was given a particular task at his university – find a way to measure how many Duplo bricks are stacked together. There are a number of ways to do this, everything from computer vision to using a ruler, but [Raivis] chose a much more educational method. He built a digital scale from scratch out of a strain gauge and a Wheatstone bridge. The build log is immensely educational and provides some insight into the challenges of weighing things digitally.

A strain gauge is a simple piece of equipment, just a small force sensitive resistor. When attached to a metal bar and a force is applied, the resistance inside the strain gauge changes, but not by much. There’s only a few micro Ohms difference between the minimum and maximum of [Raivis]’ load cell, so he needed a way to measure very slight changes in resistance.

The solution was a Wheatstone bridge, or four resistors arranged in a square. When one of the resistors in the bridge is replaced with a strain gauge, very small changes in resistance  can be measured.

With a custom ‘duino amplifier shield, [Raivis] can measure the resistance of his load cell with 10-bit resolution, or a maximum weight of 1.32 kg with a resolution of two and a half grams. A single duplo block weighs about 12 grams, so we’ll call this one a success.

# Connecting toy blocks with a universal construction set

We were all children at one time, and surely some of us remember the pain of trying to make one type of building block work with another type of block. The folks at the Free Art and Technology Lab have an answer for your inner child: adapters that connect any type of building block to any other type of building block.

The project is called the Free Universal Construction Kit. This  “gee, I wish I thought of that ideas” is a set of 79 play set adapter that allow any child to mix up their Duplo, Fischertechnik, Gears! Gears! Gears, K’Nex, Krinkles, Lego, Lincoln Logs, Tinkertoy, ZomeTool, and Zoob building sets in any way imaginable. Most of these adapters are up on Thingiverse, ready to be printed out with a 3D printer or sent to Shapeways.

An interesting aspect of the work of the F.A.T. Lab is the legal and intellectual property aspect; since this is the product of reverse-engineering several building sets,  it’s entirely possible the manufactures of these toys wouldn’t want adapters out in the wild. The team really covered their bases, though. Of the ten toy systems included, eight are no longer patent protected, much to the chagrin of the company behind MEGA Bloks. Adapters for the  two remaining systems – Zoob and ZomeTool – won’t be released until the patents run out in 2016 and 2022, respectively.

Check out the video after the break for the wonderful ‘a-ha moment’ one of the inventors had when watching his 4-year-old son playing with Tinker Toys and K’Nex.