Robot Arm - sprockets and challenges

Robot Arm

Progress!

Received and deployed the chain and sprockets:
  • Now using a 3:1 reduction on the bottom of the arm (which bears the most strain), and use my 270 degree servo for that (giving me a 90 degree effective range, and converting my 20kg-cm to ~60kg/cm).
  • using a 2:1 reduction on the middle of the arm.
  • using 1:1 sprockets for the rotation.
Chains and Sprockets!  
Largest (48 tooth) gear at bottom of arm,
 middle size (32 tooth) in the middle joint
smaller (16T) on the servos (and on the underside to rotate the arm)

Challenges

I don't have a chain breaker, and that part was a lot harder than I imagined.  I pounded the pins out on my vise with a hammer and nailset, a nail, and a broken drill bit... just like the pros.

I had trouble with a 3rd servo.  I traced through the various issues and determined it was particular to one of the "channels" I'd built to power the servos.  I tried a billion combinations of wires, and found that it was specifically the hot supply in channel #3.  It wasn't the power supply itself, and it still failed after i resoldered my home-made connections, so that left only the store-bought regulator.  My multimeter said it was giving good voltage and amperage, but it worked when i replaced it with a different one.  No idea what's wrong with it.

I burned out my raspberry pi.  As you can probably see in the pictures, my work area is a disastrous mess with tools and supplies and pieces and waste from of a bunch of projects all over it.  I think i nudged the pi so that the pins on the underside shorted on a metal washer.  It immediately died and won't boot.  It was a foolish waste of $30 and time i could have tinkered - i should keep cleaner, but i also need to juggle multiple projects.

State

Waiting on a new Pi to arrive, but with upcoming family events and the ongoing hearth saga, I may not have much time to work on it in the next week and a half.

Even so, the sprockets are effective, and the arm has enough strength so far.  Long may it last.

smooth as silk.

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