Before the Athens week I started studying the Kalman filter. At the begining of this week I decided to work along with Scott who has been studying the mechanics of Rezero and BallIP as they were presented in the reports we found online. As two heads are better than one, since Monday we have been focusing on the mechanics, control and filters as a whole. The control system as well as the model are different for Rezero from the ones used by BallIP. Certainly Rezero performs better but BallIP seemed more comprehensible at this step. In most of the papers that we read the authors first implemented what was previously achieved with ballbot technology and then built upon those concepts. Therefore today we focused on understanding the planar model (forces, energies, inertia calculations, torque conversion).
Certainly, in practice this model has limitations: the effect of the wheels is not decoupled – this highly influences the angle of tilt (before Rezero the tilt angle achieved was maximum 5 degrees whilst Rezero can recover from a 20 degree tilt). However, we considered we had more chances to understand the planar model before starting directly with the 3D model of Rezero. One of our goals today was to actually implement a Simulink simulation based on the description given in the Rezero report for the planar model.
We discovered that that there is a significant learning curve to designing a Simulink simulation model. We had a nice surprise stumbling upon a 2D model of an inverted pendulum through the Simulink Demos. Though it is not exactly what we need, we intend to use it as a basis for learning and simultaneoulsy adapting it to the planar model.
More on this tomorrow:)
For BallE – Otilia & Scott
P.S. on Monday I have studied the robots’ parameters (mass of the ball, mass of the body, radius of the ball, moment of inertia…). Rezero and BallIP are have significant mechanical differencies: the center of mass of Rezero is significantly higher than the center of mass of BallIP; the ball used for Rezero is a hollow aluminium one of 2.29kg coated with soft rubber whilst the ball of BallIP is a bowling 3.8kg ball coated with Plasti Dip. We could try Plasti Dip as well: http://www.plastidip.com/home_solutions/Plasti_Dip