How much torque?

 As far as I know, Babbage never discussed how much torque he expected would be needed to rotate the various shafts with gears. My prototype mill section wasn't functioning well because the answer for me was "too much".

Consider giving off a number from the A register digit stack to the anticipating carriage. The gear train goes from the digit wheel, to the long pinion connector, to the fixed long pinion, perhaps to the reversing gear (depending on whether it is for addition or subtraction), to the carriage connector, and finally to the anticipating carriage digit wheel. So there are either 5 or 6 gears in series. 

The torque required to turn the A register stack finger shaft is a combination of:

• rotational friction of all the vertical shafts
• friction from meshing of the gear teeth at all the interfaces
• spring tension holding the the weak locks on the anticipating carriage
• friction at the interface between the carriage wheel point and the carry warning arms
• rotational friction of the carry warning arms
• spring tension holding the detents against the carry warning arms

In general giving off worked fine. The problem occurred only when more than 2 of the carry warning arms had to flip, at which  point the torque required to rotate the fingers on the A register digit stack exceeded what the motor could provide. 

To quantify how much additional torque each carry operation added, I got a digital torque screwdriver and rotated the digit stack by hand.  Measurements varied a lot with repeated tests, so all numbers are gross approximations.

• no locks, no carries: 1.5 in-lb
• locks, no carries: 3.7 in-lb
• locks, 1 carry: 6.6 in-lb
• locks, 2 carries: 7.4 in-lb
• locks, 3 carries: 8.9 in-lb
• locks, 4 carries: 10.9 in-lb

Clearly the carry arm was the problem. The arm seemed to rotate freely, so I suspected the detents. I temporarily disabled them and then the 1-carry case went from 6 to 7 in-lb to about 3.8. 

Problem solved! I backed off the detents to the minimum that would hold the carry warning arms, and now the 4-carry case works fine.

I need to work on a better, softer detent mechanism -- especially since it needs to work reasonably for 20-30 simultaneous carries, not just 4.

That said, there are probably other things I can do to reduce the required torque. Smoothing and polishing the sliding surfaces, like those on the carry warning arm and the trigger point on the carriage wheel, would probably help.  Right now I'm doing almost no post-processing of the 3D printed parts. I've also had good results in other places using coatings or oil with PFTE (Teflon) to reduce friction.