Robot: Teensy 3.6 with the old robot's servo wiring and calibration

- LEGACY/Hexapod_Teensy/: old robot sketch (reference only).
- platformio.ini: robot env targets teensy36 (owner-confirmed board).
- Config.h: per-servo SERVOS table (pin, pulse at 0 deg, signed
  us/deg, pulse limits) built from the old sketch's pins, ranges, trims
  and the old Unity servo directions. Rear-left/front-left coxa offsets
  set to 0: the owner re-horns those two servos (the old +-90 left them
  at the end of travel; the sim showed them clamping).
- ServoDriver: 18 servos on hardware PWM (50 Hz, 16-bit); the Teensy 3.6
  Servo library stops at 12.
- Radio on CE 39 / CSN 15 with SPI SCK on pin 14.
- sim: analogWrite/PWM shims, pulses decoded through SERVOS (API v6).
- Docs: CLAUDE.md, READMEs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-current/robot/README.md

@@ -1,4 +1,4 @@
-# Hexapod robot firmware (Teensy 4.0)
+# Hexapod robot firmware (Teensy 3.6)
 
 This is the **robot-side** firmware. It is fully functional on its own
 (driven by the serial test harness below) and receives commands from the
@@ -10,8 +10,8 @@ sketches compile against.
 
 From the repo root (PlatformIO): `pio run -e robot`, flash with
 `pio run -e robot -t upload`, monitor with `pio device monitor -e robot`.
-RF24 is pulled in automatically via `lib_deps`; Servo ships with the Teensy
-framework.
+RF24 is pulled in automatically via `lib_deps`. Servos are driven by the
+Teensy's hardware PWM directly, so no servo library is needed.
 
 Arduino IDE also works if you copy `shared/HexapodProtocol/` into your
 sketchbook `libraries/` folder and install **RF24** by TMRh20.
@@ -31,15 +31,18 @@ still a placeholder. Check all of it against the real robot:
 - `LEG_CLEARANCE_MM`: how close neighbouring legs may get. Walking speed
   and body pose are scaled down to keep it, so set it to about one leg's
   width.
-- `SERVO_PINS` — must be PWM-capable pins on your Teensy 4.0 wiring
-- `SERVO_US_AT_0DEG` / `SERVO_US_PER_DEG` — calibrate per servo, they vary
-  batch to batch
-- `RADIO_CE_PIN` / `RADIO_CSN_PIN` — your nRF24 wiring. Address, channel,
-  data rate, PA level and payload size are in `shared/HexapodProtocol` so
-  they can't drift from the remote.
-- **Pin conflict:** `SERVO_PINS` leg 3 uses pins 11 and 12, which are the
-  Teensy 4.0's SPI MOSI/MISO that the nRF24 needs. Move those two servos
-  before wiring the radio.
+- `SERVOS`: one entry per servo with pin, pulse at 0°, signed µs per
+  degree (sign = direction) and pulse limits. It's prefilled from the old
+  robot sketch (`LEGACY/Hexapod_Teensy/config.h`): pins, ranges, trims, and
+  directions from the old Unity servo mapping. Check every joint's
+  direction on the bench.
+- **Before powering up:** re-mount the rear-left and front-left coxa servo
+  horns 90° so those legs point straight out at servo center. The old code
+  needed ±90° offsets there, which left the servos at the end of their
+  travel.
+- `RADIO_CE_PIN` / `RADIO_CSN_PIN` / `RADIO_SCK_PIN`: 39 / 15 / 14, as in
+  the old sketch. Address, channel, data rate, PA level and payload size
+  are in `shared/HexapodProtocol` so they can't drift from the remote.
 
 ## Bench-check checklist (do this before the first stand-up)
 
@@ -69,12 +72,12 @@ for your build:
    each foot opposite to the commanded motion. The smoke test checks that
    `+vx` moves the body forward and `+yaw_rate` turns it left (CCW). On
    the bench, confirm `w` walks forward and `z` turns left.
-6. **Per-servo calibration**. `ServoDriver` uses one
-   `SERVO_US_AT_0DEG` / `SERVO_US_PER_DEG` for all 18 servos, so servo
-   center = joint angle 0 (tibia *straight*). On this build the knee servo
-   center is the tibia at 90° to the femur, and the left side is mirrored
-   (per the old Unity/servo code). That needs a per-joint offset and
-   direction before the real robot will stand.
+6. **Per-servo calibration** (`Config.h` `SERVOS`). Arm the robot,
+   stand it on a box, and move one joint at a time (or watch the sim next
+   to it): each servo must turn the way the sim shows. To flip a direction,
+   flip that entry's `dir`. Also check that a femur moves the commanded
+   angle: its old range gives only ≈6.7 µs/° against ≈10.4 for coxa and
+   tibia.
 
 ## Testing in the simulation