some things I learned in the course of (almost) making 'Spin Mode'

• how to crimp DuPont and JST style connectors
  
• how to use a metal lathe to machine a tube to a given outer diameter
  
• that shoulder bolts, shaft collars, braided fishing line, in-line fuses, and thread-rolling screws for plastic are things
  
• how to trim DuPont style sockets to size
  
• what buck converters and logic level shifters are and how to use them
  
• how to control DC and stepper motors in an Arduino context
  
• the A4988 is an easy way to control a stepper motor
  
• how to model many things in OpenSCAD
  
• spinning arms really do need counterweights
  
• metrics screw sizes
  
• the many fixtures and fasteners available for it make t-slot convenient for various projects
  
• one should avoid using the Adafruit Feather HUZZAH ESP8266's I2C pins for anything other than an I2C device when using the wire library
  
• desoldering a multi-pin through-hole component is nearly impossible
  
• what the common types of crimp terminals are (and that the fork type is great when you have to connect to screw terminals)
  
• spring terminals can connect and disconnect wires simply and quickly without requiring any tools
  
• there aren't really any robust screwdrivers with nonconductive tips
  
• the voltage labels on AC/DC adapters are not to be trusted
  
• how to solder wires to USB connectors
  
• how to use a program to pose customizable human figures
  
• aluminum tubing can be cut and drilled much like wood
  
• Thingiverse's search function is kind of crappy
  
• McMaster-Carr's shipping is next-day, but you pay for it, and you don't know in advance how much you'll pay for it
  
• big-box home improvement stores don't generally stock fasteners smaller than M6 or M5
  
• various methods of effecting linear motion with a motor
  
• there's a Micro Center in my area where I can pick up many electronics tools and parts (including Adafruit ones!) as well as a decent selection of 3D printer filament
  
• many ways not to make a useful Gantt chart
  
• three points of constraint are one too many for a rotating axle
  
• slip rings can transmit power and data signals from a stationary to a rotating structure but should not support the weight of that structure
  
• how to eliminate brush noise from a DC motor
  
• where to find the average historical solar radiation for a fixed-tilt or tracking collector for any given month in any given U.S. state
  
• the segmented guides around cables like the ones on my 3D printer that need to move in the course of operation are called cable carriers or drag chains and you can totally buy the stuff to use in your own projects