Noted the blue is Vcc & the black is GND for the motor encoder.  Reverse the polarity & you get to order new hall effect sensors on the slow boat from China with $10 shipping.  The encoder board is soldered onto the motor terminals.

The brain board was just a bundle of wires with a small chip inside.  The leading theory was to use lots of excess wire & shorten it over time.  A certain amount of excess wire is required to access the boards.

Still insisting on using up all the atmegas, an attempt to recycle some more Atmega8's from dead ESC's resulted in a dead uart transmit pin.  It showed a very weak ability to go low.  It couldn't go low at all with the receive pin pulled up & was very slow with receive low.  Maybe it was damaged over years of driving.

The recycling process also required soldering on a crystal to all of the scavenged atmega's to change the fuse bits.  Some of the new atmega328's from 10 years ago also required a crystal to accept a 1st program.  Noted they didn't require loading capacitors.  Must remember to try that for the bricked ones & put in pads for soldering a crystal.  

With a week burned on trying to reuse atmegas, the decision was made to put the last of the new atmega328's in all of them.  The next step is connecting the final wiring outside the nozzle, using lengths from the 1st nozzle, then testing all the protocols, motors & signals outside the nozzle.  Another idea is making a 4th board for a debugging output, IR receiver, & LED.  That would reduce the number of power rail connections on the brain board.

Staring at it for a while, it became clear that the most efficient board placement was not under the motors.  The boards could be on the longest part of the tube segments with wires going sideways to the motors.  The motor mounts could be narrower.  The boards could be hot glued on.  2 more standoffs could be modeled into the tubes for a board platform.

The pinion gears slide too easily off the motor shafts.  There could be side ridges to keep the pinions in place.

The 22 year old stereo remote control is showing signs of old age.  The buttons are fading & have to be pressed a lot harder.  The stereo lasted 10 years before its relays went out.  Its remote lasted 22 years.