Aasimon.org Wiki

Date: September 26th 2008
Duration of activity: 8-12
Participants: Kasper, Bent and Johnny

The Purpose of this exercise is too make a balancing robot, using the NXT.

Experiments with the LEGO sejway, legway.

First we set out to build a robot with two wheels, following the build instructions on http://www.philohome.com/nxtway/nxtway.htm

We used the code from Brian Bagnall, Maximum Lego NXTBuilding Robots with Java Brains, Chapter 11, 243 - 284. (http://www.variantpress.com/books/maximum-lego-nxt) as a basis for our own program.
The default values of the PID control parameters seemed to act too violently, so initially we tried changing the them and the scale factor:

// PID constants
final int KP = 28;
final int KI = 4;
final int KD = 33;
final int SCALE = 18;

We increased the D parameter to minimize the overshoot.

The easiest way to tune the parameters would be if it was possible to do a simulation and see the phasemargin, but this is not available. Therefore we have observed the behaivor of Marvin and used the manual tuning methods listed on Wikipedia at http://en.wikipedia.org/wiki/PID_controller#Manual_tuning