Software
In the begining
Friday, November 11, 2022
I'll be the first to admit that I don't know how to code that well.  Back in my "assembly code" days, I was quite good at it, but with advances in hardare came advances in computer programming languages.
I knew 3-4 versions of BASIC, Forth, and Pascal, programs that are not used very much, if at all, today.
I moved from PIC processors using PICBasic Pro to Arduino that uses C++ and it was tough making the transition.  (I think the version of PicBasicPro was superior to the C++.)

Complex programming
Friday, November 11, 2022
What made the programming for this robot complex was the requirement of PID control.  Every balance-bot made has to use PID in order to control the robot's movement in a nice linear fashion.  I couldn't begin to code this, and since others had done it before...why not take what they did?   No sense re-inventing the wheel.

So my quest began to look for computer code that satisfied some requirements: PID control, stepper motor control, and WELL-DOCUMENTED program lines.   The latter cannot be overstate because if one doesn't understand the reasoning for a particular line of code, it really slows down progress and doesn't allow for much "tweaking".

I found it
Friday, November 11, 2022
"Red", the robot shown on the Blueboy first page had very good code and seeing his robot run smoothly as if it was a 3-wheeler was testimony to well written code.  Unfortunately Red used an Arduino Due (for speed) and used DC motors, not steppers.  I MIGHT have been able to convert the DC algorithms to Stepper algorithms, but again, lots of time.

I found what I founded here: http://www.brokking.net/yabr_main.html
Jopp Brokking made exactly what I was looking for though the amount of documentation wasn't quite as much as needed.  I then found this site:
https://techknowtone.co.uk/Projects/P/BalanceBot/balancebot.html who used much of Broking's code, enhancing it along the way.   Documentation was very good.

Big help
Friday, November 11, 2022
Now this is where the "wheat gets separated from the chaff".

It isn't very often one can contact the author of ANYTHING, (let alone a computer program that could elicit many questions), but the developer behind the site allowed me to do just that.

I started with a simple question which Techknowtone answered with an extensive reply full of useful information.