Finished Soldering all Smaller PCBs & Got RS-485 communication

working from main board to servo PCBs

First, I finished soldering the PCBs. I added the connectors for power
and the small data connectors. I also finished the servo expansion
boards that hold the magnetic encoder and sensor. I also finished
soldering the joint encoder PCBs that will track shoulder and elbow lift
servo positions.

I also got the bus communication to work. It was really really painful
and I was really scared it wouldn’t work.

First, the PCBs wouldn’t communicate at all. But eventually, I realized
that it was because I wasn’t supplying 3.3V to the main board. This is
when I realized that I haven’t adjusted the buck converters on the main
board to supply the correct voltage, so I was about to unsolder the buck
converter when I realized that I could just set the power supply to 5V
(which the ICs on the mainboard can handle luckily), and then adjust the
voltage down to 3.3V.
But after a really long time of debugging, it still wasn’t working. The
connection would sometimes work but was really flaky.

Eventually, I soldered on the RPi Pico 2 onto the board completely and
then found out the reason, it was because the ATtiny3216 was set to
clock at a slow speed that would mess with the communication. I made
them use the SerialTransfer library to send data more reliably and it now can communicate properly :)