new gear parameter trials

 I've been experimenting with new gear parameters using two teeth per digit -- see the previous post -- that should be more tolerant of backlash. The results so far are encouraging.

For the prototype driven by stepper motors I'm looking for access to a CNC mill capable of making precisely-located holes in 12" x 18" acrylic plates that are 3/8" thick, and I have two good leads. In the meantime I have made a couple of small manual test jigs using my 8" x 10" Genmitsu CNC router to make the holes in the smaller framing plates for those.

long pinion manual testbed

anticipating carriage manual testbed

Both seem to operate pretty smoothly even though the axle-to-axle spacing is at the spec for the gears, unlike the extra-wide spacing I had to use before that made the backlash worse.

In the process of playing with the anticipating carriage mechanism I found and fixed several bugs in my original design:

• The reset pin on the carry sector lifter could interfere with the carry warning point on the digit wheel carry disc. I moved the reset pin to the carry warning lever, and activate it from a protrusion on the carry sector lifter that isn't at the level of the digit wheel carry disc.
• Raising the carry sectors by pushing up near the edge doesn't work; the sleeve cocks and prevents it from sliding on the shaft. Tim Robinson and I had discussed this as a possible problem, and indeed it is.  The fix is to add a second pusher to the lifter so that in both cases -- looking for 9s during addition, or looking for 0s during subtraction -- one of the pushers is near the center, right in front of the axle. 
• I had neglected, when I made the earlier change to remove springs, to provide a mechanism to actively drive the carry sector lifters down before the carry happens. I added a new axle with a rotating scythe-like arm that can be positioned on top of the lifter and moved down. Unfortunately that means two more stepper motors, but I can't see a simpler solution. A salubrious side effect, however, is that the movable "wires" (3/4" clevis pins in my implementation) are now positively driven down too. Tim had warned me that depending on gravity to return them, which he did in his Meccano version, would be a source of unreliability.

I'm working now on the new plans for the framing plates of the stepper-motor version that combines both of these testbeds.