YouTube video walkthrough of making the robot arm:
Part 2 of making the arm
Successfully printed the planetary gears without needing to sand the parts afterward. Found that 0.1mm layer height at 235 degrees C and 65 degrees heated bed on my Ender 3 using Amazon Basics PLA gave me perfect results. I had to use a raft to get the gears to have a perfect base. Without the raft, you get a mushy effect on the bottom of the gear which is painful to clean up with filing. I also randomized the "Z seam alignment" rather than using Cura's default "Sharpest Corner" to get the print as smooth as possible.
The fit is tight when assembling, but breaking in each planet gear one by one by running the stepper motor for about 10 minutes per gear seemed to do the trick.
I got the airsoft 6mm bb's and those work great.
Since I only had NEMA 17 stepper motors with full shafts, rather than flat shafts, I did drill out the sun gear with a 5mm drill bit to get it to fit while I wait for the new NEMA 17's. I'd love to still get the original CAD files so I could create a modified sun gear.
To drive the stepper motors I used a couple ESP32's running the NodeMCU Lua environment to create step signals from the I2S bus. I added a couple of buttons to stop/start the motors and reverse directions to make testing/breaking in the gears easy. I'm using a DRV8825 chip to drive the steppers.
I'm using the ChiliPeppr ESP32 for Lua workspace to write the code for driving the steppers. http://chilipeppr.com/esp32
Update: printed another large actuator with 0.06mm layer height and the fit was amazing at 100% size on the planetary gears.
Also, finally printed the small actuator at the 0.06mm layer height and that worked pretty well. I got the Moon's small stepper motors delivered, crazy glued the shaft to the main sun gear. I'm finding that the DRV8825 stepper motor drivers I'm using are pumping too much current into the small stepper. It only takes 150ma and getting those drivers to accurately only pump that low of current is tough. May have to move to a DRV8824 driver.
Inner guts of gear with some speed tests:
With hall effect sensor as endstop:
0.1mm on actuators. 0.2mm on body parts. 0.006mm layer on small actuators with 0.3 nozzle.
Amazon Basics PLA