product-search for a fan speed controller (or speed controllers for other AC motors)

My goal is to make my desk fans slow down, even below their lowest setting, for use during winter.

• en.wikipedia.org/wiki/Variable-frequency_drive
  • These are sometimes combined with a single-phase to three-phase inverter for use in a wood shop or metal shop, for people who don't have access to three-phase in their house.
• https://www.amazon.com/s?k=motor+speed+controller+120

modifying electronic components

If you're willing to tinker with the innards of a fan, most commercial off-the-shelf (COTS) fans use a speed controller that's either capacitor-based or triac-based. (TODO — is this actually right? I need to find more sources to confirm this)

For capacitor-based speed controllers [2], you could adjust the capicatance values for the high/med/low settings, or install a variable capacitor to achieve "stepless" speed control.

For triac-based speed controllers [2] [3], (TODO)

random information

• I believe most fans incorporate a universal motor?
• "speed control of universal motors is achieved using phase angle control or PWM chopper control" [2]
• Most motors have a certain rated speed range, and going above or below that can reduce the motor's lifespan.