[2.70] Desk Project White Paper

Proposed desk: Cantilevered "Floating Desk"
A wall-mounted, motorized, no-legs cantilevered desk that accommodates standing and sitting heights.

Functional Requirements (in order of importance)
  • Goes up and down, to accommodate sitting and standing-desk heights
  • No legs! Full cantilever / wall mounted
  • "Real Desk": holds ~300lbs when locked (I could stand on it), ~50lbs when moving.
  • "Precision", repeatable position control and unnoticable (visual or tactile) deflection under load
  • Quiet under operation (nom. load 50 lbs) and reasonable power requirements (wall plug w/ min. risk of fire)
  • Avoid buying stuff: use ballscrews, motors, and linear rails I already have in my room
  • Flat-pack Disassembly
Design Parameters
  • Hollow desk top with internal structural truss (help with cantilever/ "floating desk" look)
  • French cleat attachment mechanism (help with cantilever)
  • Robust linear rails that can take large moments
  • Re-use Ballscrew & stepper with optical encoder position feedback
Different methods of making a cantilevered, legless desk: 1, 2
Different examples of internal trusses to enable cantilever loads: 1, 2

Risks & Countermeasures
  • No legs! Gotta address moments and stresses all applied at the cantilever contact point and in the linear carriage.
    • Biggest issue I'm expecting will be moments/rattle on the bearings in the rails that would cause them to bind
  • No legs! How deep of a desk can I get away with before cantilever attachment becomes a problem?
  • "Precision" over time. I probably need to add an encoder & closed-loop position control to avoid motor-skipping errors
  • The ballscrew I have + available stepper combos might end up being loud...
  • Can the stepper handle load without a lock? Or do I need to make a mechanical lock that doesn't mar bearing surfaces?
Analysis Needed
  • First-order analysis of linear rails - week 2 project fun
    • would be good to make a scale model using steel-honeycomb for the desk top and 2 rails
  • truss/cantilever math for desktop moment/stresses imposed on the rails
  • energy accounting for motor & transmission, and finding out resonance of the motor

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