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AntBot: Tweaking the modules

The app should be in a working state, so now we shall do some very simple edits of the code.

To set this up properly, instantiate all 4 example modules as descrbied in the previous tutorial, call the Haferlach PI “HF” when registering it.

Tweaking the Combiner (Adjusting Weightings)

If you open up the WeightedCombiner you will see it works by taking the mean of all 4 modules, we’re going to edit this to give more preference to the Trig Path Integrator.

The combiner consists of a single function ‘nextCommand’ which works by calling the ‘getOpinion’ method on each module and storing their headings, it then performs some collection of operations on these to create it’s own heading to be returned.

In this case, the combiner simply takes the average of all 4 modules’ headings and returns this. Currently, the average gives an equal weighting to each – we want this to be skewed so jump to lines 28 and 29 and change the weighting of the modules from 0.25 on all to 0.7 on PI and 0.1 on the others.

double wAngle = PI[0] * 0.7 + VH[0] * 0.1 + SS[0] * 0.1 + HF[0] * 0.1;
double wDist = PI[1] * 0.7 + VH[1] * 0.1 + SS[1] * 0.1 + HF[1] * 0.1;
double[] weightedHeading = { wAngle, wDist };

Now we have a weighted combiner that favours the trig PI. This is in essence the basics of how a combiner works – but what if we want to condition the weightings on the status of the modules?

More Tweaking the Combiner (Examining state of modules)

Each module has a method called ‘getStatus()’ which returns a string describing what it is doing. Looking at the source code for a module will tell you what the format of this string is.

In this case, we want to condition the weighting on the distance from the nest – as such we need to look at the status of the trig path integrator whose status is a string of the format <antbotOrientation> <angleFromNest> <distanceFromNest>.

We can retrieve and split this into tokens with

String[] PI_status = navigationModules.get("PI").getStatus().split("\\s+");
double nestDistance = Double.valueOf(PI_status[2]);

Now we know the nest distance, we can simply surround the weighting with an if statement:

double wAngle;
double wDist;

if(nestDistance > 0.5)
wAngle = PI[0] * 0.25 + VH[0] * 0.25 + SS[0] * 0.25 + HF[0] * 0.25;
wDist = PI[1] * 0.25 + VH[1] * 0.25 + SS[1] * 0.25 + HF[1] * 0.25;
wAngle = PI[0] * 0.7 + VH[0] * 0.1 + SS[0] * 0.1 + HF[0] * 0.1;
wDist = PI[1] * 0.7 + VH[1] * 0.1 + SS[1] * 0.1 + HF[1] * 0.1;


Tweaking Visual Homing

To give a basic example of how tweaking a module would work, we shall change the type of pixelwise error calculation that the visual homing module uses.

Visual Homing works by taking in frames from the camera sensor  and calculating the average value of the pixels in the frame – this is done with the “calculateError()” function.

Open up VisualHoming and declare a new function “sumSquare()”:


private double sumSquare()
// Get difference
Core.subtract(currentFrame, homeFrame, diffFrame);

// Get square
Core.multiply(diffFrame, diffFrame, sqFrame);

// Get sum of the array
Scalar sum = Core.sumElems(sqFrame);
double errorArr[] = sum.val;
double ss = errorArr[0] / 2;

return ss;

Now go into calculateError() and replace “currentError = rootMeanSquare();” with “currentError = sumSquare();”.

Just like that we have modified the module.

AntBot: Setting up the App

Now that you have the projects set up and ready to start development, it is time to examine the code itself.

This post will cover ‘wiring up’ an App with the pre-packaged combiners and navigation modules.

What is Pre-Packaged?

With the AntBot codebase comes with 2 combiners and 4 navigation modules. The ‘Simple Combiner’ ignores all modules apart from one and issues that as the path to be followed. The ‘Weighted Combiner’ takes the average angle and distance of all 4 modules and submits it.

The Navigation modules represent Path Integrators that work through basic trigonometry and one based on Haferlach’s model. The other two implement visual homing based on pixel-wise error and the ‘Run-Down’ algorithm and a simplistic Systematic Search generator.


First, open MainActivity and declare the modules and combiner that you want to use at the top of the class (we will only use the trig path integrator for now):

WeightedCombiner weightedCombiner;
VisualHoming visualHoming;
TrigPathIntegration trigPathIntegration;
SystematicSearch systematicSearch;

The method ‘onCreate’ holds the actual setup code. First the combiner is instantiated and registered with the framework:

weightedCombiner = new WeightedCombiner();

Now, the modules are set up – for each module it must be instantiated, subscribed to it’s feeds and registered with the combiner (where it is given a name so it can be identified), for example:

visualHoming = new VisualHoming();
simpleCombiner.addModule("VH", visualHoming);

The trig path integrator has to be subscribed to the controller fragment and should be called “PI”. The systematic search generator should be subscribed to the trig path integrator and the controller fragment. It should be called “SS”.

If data is to be sent to the server the Network Fragment must be subscribed to the modules which will supply it with said information:


Finally, a further step is needed for any modules that make use of OpenCV (such as the Visual Homing module), below onCreate is another method named onOpenCVLoaded – it is recommended that all vision based modules be placed into a dormant state until the library is loaded, after which they can be ‘woken up’ (this stops function calls being made to non-existant libraries):


This is all that setup consists of – pressing the Run app button should load the app onto the phone ready for use.

Swapping Modules

To swap modules in and out you simply need to comment out/delete their code. If you wanted to replace the trig path integrator with the haferlach path intergator you would simply have to do the following:

//trigPathIntegration = new TrigPathIntegration();
//simpleCombiner.addModule("PI", trigPathIntegration);

haferlachPathIntegration = new HaferlachPathIntegration();
simpleCombiner.addModule(“PI”, haferlachPathIntegration);

Having said that, the system is of course module agnostic so it is more than possible to have the two modules coexist happily (but with one of them would have to be called something that isn’t PI).

The weighted combiner could be swapped for the simple combiner in the same way, but only one combiner can be used at a time.


Now we have the app working, let’s tweak the modules!

AntBot: Setting up the Development Environment

This guide expects you to have basic familiarity with Eclipse.

Download the project from GitHub

Download Android Studio, Eclipse & Arduino IDE

To begin with, download Android Studio and follow the instructions on the site – on Linux you may need to install extra packages so this is particularly important.

To compile the AntBotServer code you will also need Eclipse – specifically the ‘Eclipse IDE for Java Developers’.

After Downloading both, run them for the first time – Android Studio particularly may need to set up Android SDKs (for reference, AntBot is built for Android 4.4 and higher).

It should be noted that whenever I use the term ‘workspace’ within this guide it can refer to a space both programs use or separate ones.

The Ardunio IDE can be found here. Like the above, it will use a ‘workspace’ folder which it calls ‘sketches’. Arduino IDE requires no further setup outside of installation.


There are two libraries the AntBot app and AntBotServer depend on: USBSerialForAndroid (this is actually included in the source code) and OpenCV – both the desktop and android versions.

The Arduino code requires a library to monitor the wheel encoders called Encoder.

Set up OpenCV

Compiling OpenCV (hopefully optional)

Unless you are using Windows, this is required for the desktop version – I have included a compiled version of the library for linux which can be found under AntBotServer/opencv3.0.0/ubuntu-14.04. Hopefully this will work, if not or if you want to compile it yourself this guide will demonstrate how to compile it. If it does, skip to setting OpenCV up as a user library.

You will need the OpenCV source (from the above link) and cmake. Once you finish the ‘Build’ section of the guide, the desired files will be opencv-3.0.0/bin/opencv-300.jar and opencv-3.0.0/lib/

Now that there is a compiled version of OpenCV you can set it up as a user library in eclipse with this guide.  It should be noted that in the section of the guide that tells you to set the native path to ‘OpenCV-2.4.6/build/java/x64’ should actually say ‘OpenCV-2.4.6/lib’.

Installing OpenCV on the Android Device (hopefully optional)

Assuming you are testing with an Android device, you will need to load the OpenCV library onto it. Within the OpenCV Android zip there will be a folder called ‘apk’ – take the contents and follow this guide.

Importing OpenCV as an Android Module

Before you use the OpenCV Android library you will need to have it set up as a project in your workspace. Doing this is relatively simple – just place the OpenCV Android library in your workspace folder and perform either File -> Import Project or from the splash screen do Import Project and select the OpenCV-android-sdk folder from your workspace.

Import Projects

Now that the requirements are in place, simply import AntBot into Android Studio and AntBotServer into Eclipse using the same method as above. Android Studio may need to download a different version of the Android SDK to run – allow it to do so. Eclipse will require you to add the OpenCV user library to AntBotServer.

Allow USB Debugging

If you are just getting started or are doing this on a new computer, you will need to authorise USB debugging on your computer – when plugging in the Android Device this should automatically come as a pop up. If not, follow this guide.

Now it’s time to set up the app!

AntBot: Make Your Own AntBot



Above we can see AntBot ‘in the flesh. Ignoring the lego framework that supports the camera, to assemble your own AntBot you need the following*:



*You will also need some standard issue male-female copper wires to connect the boards as well as a Serial-USB cable to connect the Arduino to the smartphone.

The prices quoted are taken from Proto-Pic at the time of writing and as such it may be prudent to shop around in case these have changed. While a Nexus 5 is listed, the framework can theoretically be deployed on any Android smartphone with a sufficient level of processing power.


To connect the chassis to the motor driver board, simply connect as directed in the following. Each ‘channel’ corresponds to a wheel, i.e. Channel 1 -> Wheel 1 etc.


To connect the Ardunio to the motor driver board, connect like so:



The colours correspond to the channels in the picture above.


First step done, now it’s time to calibrate the chassis!

RoboAnt: Build your own Android robot

Nowadays smartphones are affordable, compact and capable computers. Mike had the ingenious idea that they can do a perfect robot brain. Packed with computing power and useful sensors,  the one thing they can’t do (I think) is control external analog components – like motors. This is where the Arduino comes in. The hugely popular embedded platform has tons of accessories built by its restless community. One of them – Zumo Shield from Pololu, is the final ingredient we need. Stir… and RoboAnt is born.

Here is how to make your own.

Continue reading RoboAnt: Build your own Android robot