docs(uno-q): shaker-campaign findings — position-target DVF, safe settings, sensor placement

Co-Authored-By: Claude Opus 4.8 <[email protected]>

deploy/uno-q/ACTUATOR.md

@@ -37,6 +37,41 @@ enforces the limits. Two ways to reach it:
 
 **Relay commands** (`:9999`, for setup/calibration from the host — `nc`/socket):
 - `step <count> <dir>` · `zero` · `pos` · `setmax <n>`
+- `osc <amp_steps> <freq_cHz> <cycles>` — open-loop sinusoidal excitation (shaker mode)
+- `oscm <amp> <freq_cHz> <cycles>` — oscillate while measuring the ADXL355 (per-axis p-p mg)
+- `accel` — one ADXL355 sample (mg); `dvf <gain> <secs>` — closed-loop damping (below)
+
+### Direct Velocity Feedback (`dvf`) — active damping
+Closes the loop: ADXL355 X-accel @ ~250 Hz → leaky-integrated velocity → stepper
+commands `-g·v` (velocity feedback adds damping, c → c+g). Envelope-clamped and
+slew-limited. **Runs must be ≤ 8 s** — the RouterBridge RPC times out at 10 s.
+
+Bench-measured gain range:
+| gain | behaviour |
+|---|---|
+| 500 | gentle |
+| **1000–2000** | **authoritative and stable — recommended** |
+| 4000 | **UNSTABLE** — self-excites off its own step-vibration (velPk 30→1442, 26k steps); the soft-limit envelope catches the runaway |
+
+Actuator FRF note: open-loop amplitude rolls off with frequency — full ~10 mm
+holds to ~2–3 Hz, only a few mm by 10 Hz.
+
+**Shaker-table campaign findings (2 Hz base excitation):**
+- The control law is **position-target DVF**: carriage position target =
+  `center − K·v` (reaction force ∝ −v = true damping). A velocity-command law
+  (carriage velocity ∝ v) is force ∝ −a = *added mass* — no dissipation; it
+  amplified the response at every gain/sign. Don't regress to it.
+- **Safe reference setting: `dvf 30 8`** with the slew limit at 8 steps/tick
+  (~2000 steps/s). Ran 2 min continuous, silent, self-centering, no runaway.
+  Slew 25 grinds the motor (lost steps → position corrupted).
+- **Sensor placement is the binding constraint:** a deck-mounted sensor near
+  the rail reads the carriage's own motion (~856 mg open-loop) louder than the
+  structure sway (~435 mg), so closed-loop damping can't be scored (or cleanly
+  fed back). Mount the feedback sensor at the structure's max-sway point (tower
+  top), ideally a second ADXL355 on mux channel 1.
+- `listen <secs>` (≤8 s) = passive baseline/ring-down instrument. Old numbers:
+  tap tests gave stable-looking g up to ~2000, but that predates the shaker
+  campaign — trust the shaker findings.
 
 Every move is **clamped to `[0, stepMax]`** and the reply reports position, e.g. `pos=1234
 max=9635`, ending in `LIMIT` if it hit the soft limit.