This past fall I took a robotics class as part of my masters in Mechanical Engineering, and for the final project I developed a control algorithm for this robotic arm. This was a very interesting project, and it was the first time I’ve used Matlab to control the NXT. I used some software that had been developed by Linus Atorf, Alexander Behrens, Achim Knepper, Til Aach at RWTH Aachen University to interface between Matlab and the NXT. This toolkit was very impressive and made the whole project alot easier. The robot itself was not the focus of the class.
The build was just a simple linear joint, topped with two rotational joints. However by using the control logic I was able to impliment code that would draw on the paper. This might sound like a simple feat, however keeping all three motors in sync so that the pen would always be on the paper as it moved in a linear fashion was acutlay quite involved. I was able to use the feedback sensors in the NXT motors to impliment a PID control law, that was undoubtly way overkill for this small project.
Dear Jim, it’s great to see you’ve been succesfully using our toolbox. I’d be interested in some feedback if that’s no trouble for you. Which version did you use? How did you manage to accomplish the motor precision you needed?
Is your sourcecode available, or parts of the PID implementation? Where the Bluetooth latencies a problem, or did you use the USB connections?
Regards, Linus
Sure, i’ll do a more extensive write-up one of these days with my source code and such. I used USB so BT latencies weren’t an issue, and really I needed very little precession from the motors, there was far more slop in the model than anythign related to the motors themselves.
Dear Jim,
I’m very pleased to hear that the RWTH – Mindstorms NXT Toolbox was a helpful tool for developing your student project.
Your robot application sounds very interesting and known from own projects an appropriate plotter-control is indeed challenging.
Thus, I would be very happy if a short description of your project and your study course can also be posted on our frequent visited webpage
http://www.mindstorms.rwth-aachen.de/trac/wiki/Projects
Please let me know.