I had my eye on the new Lego Mindstorms set for a while. Finally I decided to order it from Amazon. It’s still a bit pricey but I think it’s worth it. I read nice review of EV3 here which also includes comparisons to the previous generation of the Mindstorms kit.

Programming EV3: The Official Way

Programming the kit is very easy using Lego’s official graphical programming tool. You just have to drag and drop the components and fiddle with the parameters. Check out the following very basic application:

It powers the motors connected to ports B and C. It keeps doing that in a loop as long as the value read from Infrared Sensor is larger than 20. If there is an object closer to 20 centimetres it breaks and ends the program.

Programming EV3: The .NET Way

The .NET API is an open-source project. I recommend watching the introductory video which shows the basics. It shows how to move the robot by sending direct commands to turn the motors and how to read values from the sensors. The following part the test application shows the event handlers for the direction buttons and setup code to connect to the brick.

I also added a similar implementation of the NXT-G program above. It’s a while loop which breaks when the value from the IR sensor is lower than 10.

And voila! Now my clever robot senses the object in front of it and avoids the collision by stopping!

You can find the source code for the test application on GitHub

Tips & Tricks

• When I first implemented the NXT-G equivalent version the sensor value wasn’t updating properly. I checked the discussion forums in the CodePlex project page and found out that other people were having a similar issue. A workaround was adding the Thread.Sleep(10) line. After that I could read the updated sensor values without any problems. Although it doesn’t feel like the right solution it works fine as a temporary workaround.

• During the testing and debugging I managed to crash the Lego brick a few times. First I feared I actually “bricked” the brick but luckily a reset resolved it. Resetting the brick is not obvious though, I had to check the manual for that. So in case you need to reset it you have to hold down Back, Center and Left buttons. Then release the Back button when the screen goes blank and release the other two when the screen says “Starting”.

Resources

• Lego EV3 review and comparison to NXT 2.0
• Channel9 video on programming EV3 with .NET API
• Source code for the test application

CLIQUE (CLustering In QUEst) algorithm is a grid-based clustering algorithm that partitions each dimension of the dataset as a grid.

CLIQUE Implementation

The algorithm starts by assigning each data point to the closest grid in the matrix.

After loading the data it looks something like this:

In order for a grid cell to be considered as “dense” it has to have data points more than or equal to the threshold. In this sample the threshold was provided as 2. So after the adjacent dense cells are joined together we get 3 clusters:

Resources

• Source code

My previous post was about grid-based clustering. DBSCAN (Density-Based Spatial Clustering of Applications with Noise) takes another approach called density-based clustering. It grows regions with high density (above threshold provided) into clusters and discovers clusters of arbitrary shape.

DBSCAN Implementation

First off the data is loaded and a distance matrix is calculated based on the data points.

The algorithm visits every data point and finds its neighbours. If the neighbours are dense enough than the cluster is expanded to include those points as well.

So data points that are close enough to each other are included in the same cluster.

Joining dense clusters is a similar approach taken in grid clustering. The difference is this way the clusters can have arbitrary shapes.

Resources

• Wikipedia article
• Source code