For those of you who were wondering about what happened with our extremely problematic wheel base, I have the rest of the details here:
We found that wiring the motors across all 3 circuit breakers would stop both of the motors that were in the cortex. Upon closer investigation, the 3-wire cables used to plug the motors into the cortex were flipped around, and that they were also flipped around one the power expander. Thus, they only worked on the power expander. We flipped them around the right way and tested the wheel base. We attempted and succeeded in pushing a cart loaded with 100 lbs of cargo for long periods of time. It only stalled out once.
We would like to thank all of the people who gave us suggestions on fixing this problem!
Glad you found the problem. In a previous life when I was doing systems engineering for post production facilities, we found that 9 out of 10 problems could be traced back to cable issues (damaged connectors, crushed cables etc.) I guess the lesson to be learned is to always check for the simplest of mistakes first before looking for complex answers.
I think we all ran out of ideas. Our teams have moved to a more or less standardized way of distributing the motors across the available circuits that has proved to be consistent and reliable. This, combined with good building practice for the drive, has virtually eliminated the problems you were describing. If you start with the premise that the control system is inherently capable of working then you are left with the type of things we were suggesting. No one had suggested incorrect wiring, that’s mostly taken for granted but perhaps it should be number one on the list of things to suggest first the next time a similar problem arrises.
The next time a team posts about problems like these, I’ll be sure to suggest it.
However, you were right about the circuit breakers and your suggestions worked in the end. The inverted wires only hindered the implementation of the solotions.
There are 3 circuit breakers on our robot. 2 are on the cortex and one is in the power expander. We spread the drive motors between these three breakers, instead of just one, with one motor in port 2, another in port 9, and the other two in the power expander. The two motors that were in the cortex stopped working altogether, while the power expander motors continued to work. This appeared to make our stalling problem worse, because the two functional motors had to overcome the resistance given by the other two motors. We knew it was not a problem with the cortex, because our lift and intake motors still worked. It also was not the motors themselves, because we tried plugging all of the drive motors into the cortex and all 4 of them stopped. We found that all four wheel motors were plugged into the cortex the wrong way, and that they were also the wrong way in the power expander. This was the reason why the motors would function when plugged into the power expander but not when directly plugged into the cortex.
I hope this clears things up.