Question 1:
How close do the rpm’s have to match between one motor to the other in the drive system( atwood motor to the drill motor).
Question 2:
Since we cant fix this mechanicaly, how can we fix this in the code?
From what Dr Joe has written, I gather that you’ll be ok if you arrange gearing so that at the no load speed of each of the motors, each would turn the output shaft at the same speed if given 12 V. This will be enough to let the motors work without programming anything extra.
This is the mechanical fix.