## Added Loctite

I bought some blue Loctite 242, which is supposed to have “medium” holding power, and put it on the set screw. I also replaced the shim foil, since half the old foil was neatly removed by the spinning set screw. The set screw also gouged a small notch all the way around the shaft at one point. Hopefully the Loctite will hold the set screw in place and I won’t have to worry about it again. I will find out next time I try running the system. It takes 24 hours for Loctite to completely cure, so I am going to let it sit for a little while.

I tried another approach on the modeling of the system. Looking at the NI System Identification tools, I found one that allows you to define the model of your system in terms of constants, and it also allows non-linear systems. The vi I used was “SI Estimate User-Defined Model.vi”, which uses a template that defines the actual system. I used the MIMO template with arrays. The system input was the PWM values, and the system output was the position and velocity of the cart and pendulum. My variables were the coefficients A, B, C, D, and E from earlier equations. The template takes an entire array of PWM values and produces arrays of output values. The Estimate function kept iterating and adjusting the coefficients until the best values were obtained. I don’t know exactly how it works, but it produced estimated curves that were very, very close to the actual output curves. Of course, I put the values into my simulation and tried out my control algorithms. The numbers didn’t really change too much, so the algorithms worked about the same. I suspect I am close enough to the real system that it is just finding values that are close to the true values. I don’t think it is possible to get much closer to the real values, so it is probably time to quit perfecting the model and call it good.