I've updated the components used to parts that are more commonly available. The output transistors Q1-4 in the H bridge are still Darlington pair, look closely and you'll see a double line on the Collector. This is new to me, but apparently this is a new symbol for a Darlington pair.

I was also not happy with how the symbol looked for the 555 timer.

I'll be making more drastic changes so the forward and reverse currents can be set independently, and without altering the base drive currents.