The inverted pendulum setup has been modified to fix the problems that have been brought to my attention.
The problems that have been fixed are:
Below you will see the modified cart with all three of the above problems fixed.
The bump in the track was fixed by the addition of a hard platform that the matt will rest on top of. This platform is slightly raised from the bottom so the wire can go under it with out causing a bump, see Figure 2 and Figure 4. It is important to note that now that the bottom is rigid you can raise one end of the platform to make a nice even hill so you can do your velocity control experiments.
The center pivot was fixed by screwing it in to the hard bottom, see Figure 3. This can be removed after each lab session and added again later.
The center encoder getting twisted was fixed by the addition of an eye-loop to the fixture that the encoder wire passes through. This causes the force that the twisting wire has on the encoder to pass through the middle of the encoder thus causing no torque on the encoder.
Figure 1: Modified matt for inverted pendulum cart setup
Figure 2: Hard backing for the mat of the cart system
Figure 3: Center Pivot point with eye-loop around the cord of the encoder and Screws in the bottom of the center pivot
Figure 4: Screw holes from the center pivot as well as the hole for the power/data cable
If you like this fix I will make a full parts list and procure the parts to start to fix all of the kits in the lab.