The RWTH – Mindstorms NXT Toolbox for MATLAB® was developed as a student project in the Institute of Imaging and Computer Vision at RWTH Aachen University in Aachen Germany.  It provides a Matlab interface with the NXT brick that includes Bluetooth communication, sensor interface and motor interface.  It requires a working Matlab license, of course. 

The package is very easy to set up.  It took me less than ten minutes to successfully test the example programs over Bluetooth.

There are some very nice motor features, such as motor synchronization and speed ramp-up and ramp-down.

I have yet to explore how easy it is to modify or extend the code, but it ought to be a straightforward matter.

The package can be downloaded from
http://www.mindstorms.rwth-aachen.de

Kevin Knuth
Albany NY

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The basic idea is that the instrument has a set of models capable of describing the environment it is exploring.  The instrument uses Bayesian inference to learn from the collected data.  Once the inference process is completed for the most recent data set, the instrument considers all the possible meaurements that it could take and computes the expected gain of information based on what it already knows.  Once the experiment or measurement has been chosen, the instrument collects the new data.  The process then repeats until the instrument learned what it was programmed to learn with an acceptable level of precision.

I have been working to develop these ideas with the help of the LEGO Mindstorms NXT system.  My first prototype is almost complete, and is a robotic arm equipped with a light sensor.  The objective is for the robot to characterize a white circle on a black field by estimating its position and radius with a high degree of accuracy.  The robot is not allowed to scan the scene, but is instead only allowed to take point measurements.  Our preliminary tests show that this is performed with extreme efficiency, and promises to dramatically save on energy, time, data storage, and data transmission.

I recently gave a talk on this project at the MaxEnt 2007 workshop in Saratoga Springs NY.  Below are links to a video of the talk, the slides, and the accompanying research paper.  Enjoy!

Video: Designing Intelligent Instruments, K.H. Knuth

Slides: Designing Intelligent Instruments, K.H. Knuth

Research Paper:
Knuth K.H., Erner P.M., Frasso S. 2007. Designing intelligent instruments. K.H. Knuth, A. Caticha, J.L. Center, A. Giffin, C.C. Rodriguez (eds.), Bayesian Inference and Maximum Entropy Methods in Science and Engineering, Saratoga Springs, NY, USA, 2007, AIP Conference Proceedings 954, American Institute of Physics, Melville NY, In press.

Kevin Knuth
Albany NY

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The instructions for building this mechanism can be downloaded in this zip file.

Kevin Knuth
Albany NY

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I described the rocker-bogie suspension system in a previous post.  The idea originated with the bogie, which is a set of six wheels on a train designed in such a way to keep all the wheels on a curved track.  The innovation here is to add rockers allowing the wheels to move up and down independently.  This enables the rover to handle extremely rough terrain, and as I demonstrate, climb barriers higher than the wheels themselves.  A more detailed description can be found on BrickVista Tech-Notes.

The first demo was filmed in my brother’s backyard in Wisconsin where he had just put in a fence.  The terrain is relatively rough with bumps and dips with sizes on the order of the diameter of the rover’s wheels.

The second demo was filmed in my office in the Physics Department at the University at Albany.  Here the rover climbs a pile of some of my favorite books.  Several of the book heights are on the order of the diameter of the wheels themselves.  Watch how the rockers allow the wheels to climb independently.

The third demo was filmed in the access road just outside the Physics Department.  A small parking barrier, approximately the height of a curb, is the obstacle to be overcome.  The rover is able to climb the barrier, and the rocker-bogie suspension allows its wheels to hug the barrier as it rolls over.  The rover then heads off towards a small tree… perhaps in search of life. 

We improved on the design by increasing the torque on the tires (decreasing the speed) and by replacing the front drive shafts with a gear system.  Long LEGO axles tend to take a good deal of torsion and store this energy like a spring.  This leads to oscillatory motions in the wheels.  In addition, the coupling was too weak to enable our rover to climb the desired obstacles, and our gear system overcomes this.  Another way we found to overcome the torsion of long drive shafts is to construct a shaft out of small axles joined by axle connectors.

There are more improvements to be made.  One design flaw is that the front wheels are too powerful and sometimes lift the entire front end of the rover without allowing the rockers to rotate.  This is because the back wheels are also progressing a given rate of speed and for the rockers to rotate, these wheels would have to slow down.  A properly-placed differential should solve this problem.

In the meantime, this basic rover design is sufficiently robust for outdoor exploration.

Below are several books of potential interest.

Kevin Knuth
Albany NY

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My favorite was the Lego implementation of the Rocker-Bogie suspension, which was used in the Mars Sojourner rover, as well as Spirit and Opportunity.  Note that the figure above is a prototype of Sojourner, which exhibits the Rocker-Bogie suspension.  I am looking forward to building it and learning how it works.

You can buy the book at Amazon.com here…

Kevin Knuth
Albany NY

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