- Debate over actuator choice for humanoid robots: geneh2 argues linear actuators enlarge the force loop and reduce stiffness, while fenn claims compliance (via springs or soft actuators) is preferable for unpredictable environments; L29Ah counters that stiffness simplifies control by letting simple feedback loops abstract away mechanical complexity.  
- Muscle-like actuators discussed: HASEL (hydraulically amplified self-healing electrostatic) devices are copper-free and potentially cheap, but commercial units from Artimus last only ~1 million cycles—hours of operation at actuation speed—limiting practical use.  
- Piezoelectric and ultrasonic motors: geneh2 notes piezos give inherently low-speed, high-torque output, but ultrasonic versions suffer from rapid wear (~3 000 h continuous), far below the 100 000 h expected of industrial robot arms.  
- McKibben “air/fluidic muscle” actuators dismissed by geneh2 after a professor abandoned them for custom electric motors; fenn still favors water-hydraulic McKibben tubes plus an undisclosed primary valve concept.  
- Nature news article (https://www.nature.com/articles/d41586-024-02704-y) and accompanying Cell Reports Physical Science paper (https://www.cell.com/cell-reports-physical-science/fulltext/S2666-3864(24)00436-3) describe electro-active polymer hydrogels that exhibit emergent memory when embodied in a simulated game environment.  
- docl speculates the hydrogel memory effect arises from 2-D confinement altering entropic gradients: ionic currents drag water, leaving conductive “paths of least resistance” that encode prior successful strategies—analogous to grooves on a wax record.  
- Scaling concept: docl envisions warehouse-scale hydrogel “brains” fabricated as thin sheets on spools, addressed laterally without unrolling, paralleling earlier thoughts on spooled microbiological evolution platforms.  
- Extension to legacy media: participants muse whether magnetic tape reels or photographic film could be repurposed for similar analog learning by applying high-voltage side-addressing to modify conductivity patterns.