Firmware simulation, Unity project, and sim-verified robot fixes

Simulation
- sim/: the unchanged robot firmware compiled into hexapod_sim.dll
  against PC stand-ins (Arduino, Servo, Wire + register-level MPU6050,
  RF24 with matching-config radio), a kinematic body model (support
  plane + planted-foot odometry) that also drives the simulated IMU,
  and a headless smoke test (sim_smoke). build.ps1 builds and tests.
- Hexapod_Simulation_Unity/ folded in (history kept in a bundle
  outside the repo). Assets/HexapodSim loads the DLL, drives the
  existing leg rig, and offers joystick / keyboard / robot-serial
  input plus a test panel.

Robot (all found or confirmed in the simulation)
- Config.h geometry taken from the Unity model.
- IK femur elevation sign, gait stance direction, body pose
  rotation direction, yaw lever arm.
- Stance feet integrated from the current command; gait restarts at
  mid-stance; heading integrates the applied turn rate, only while
  walking.
- Leg clearance and reach checks (Limits::feetFeasible); walk command
  and body pose scaled as a whole, pose scale rate-limited, planted
  feet guarded so the body never snaps or legs collide.
- Robot-gyro self-leveling as an integrator.
- Heading mode: steering relative to the body; S walks backward.
- Standing height from the remote (STANCE_HEIGHT_RANGE_MM).

Protocol v3 (reflash both boards)
- CmdPacket gains body_height (22 bytes).

Remote
- Height slider (Nextion hHeight/nHeight, serial [ ]).
- Fixed unspecified I2C read order in RemoteIMU.

LEGACY/: owner's old Nextion HMI and remote hardware assets.

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

2026-current/remote/Config.h

@@ -93,6 +93,9 @@ constexpr float REMOTE_TILT_FADE_PER_SEC   = 2.0f;
 constexpr uint8_t SPEED_SCALE_DEFAULT      = 128;
 constexpr float   SPEED_SCALE_RATE_PER_SEC = 255.0f;  // slider jumps ramp over <= 1 s (robot doesn't smooth twist)
 constexpr uint8_t SPEED_SCALE_STEP         = 25;      // serial console +/- step
+// Standing height slider -> CmdPacket.body_height (-1000..1000, 0 = the
+// robot's default). No smoothing here: the robot rate-limits height itself.
+constexpr int16_t HEIGHT_STEP              = 100;     // serial console [ / ] step
 // FLAG_WALK stays set this long after the left stick returns to center, so
 // hovering at the deadzone edge doesn't chatter STAND <-> WALKING.
 constexpr uint32_t WALK_LINGER_MS = 250;

2026-current/remote/NEXTION.md

@@ -1,5 +1,10 @@
 # Nextion HMI build guide
 
+> The owner's earlier 6-page HMI is in `LEGACY/remote/remote.HMI`. This
+> guide describes the minimal single page the current firmware expects.
+> To reuse the old HMI instead, `NextionUI` has to be changed to match
+> its component names.
+
 The firmware drives the display by **component name**, and the display
 talks back with small custom frames sent from each button's touch event.
 Build one page in Nextion Editor to match the tables below. Layout, fonts
@@ -40,6 +45,8 @@ the firmware writes. Button bounds here allow some slack.
 | `bBGyro` | Button  | –        | bco green / gray (label it "ROBOT GYRO")     |
 | `hSpeed` | Slider  | –        | `val` 0..255 (set **maxval = 255**)          |
 | `nSpeed` | Number  | –        | `val` 0..100 (speed %)                       |
+| `hHeight`| Slider  | –        | `val` 0..200, 100 = default (set **maxval = 200**) |
+| `nHeight`| Number  | –        | `val` -100..100 (height offset %)            |
 | `bCal`   | Button  | 9        | `CAL` / `SAVE CAL`, bco orange while active  |
 | `bCalX`  | Button  | –        | nothing (static "CANCEL CAL")                |
 | `bZero`  | Button  | –        | nothing (static "LEVEL")                     |
@@ -63,6 +70,7 @@ uses **Touch Move** as well so the value tracks your finger). Frame format:
 | `bRGyro`  | `printh 23 01 52`                        | `R` remote-gyro tilt on/off    |
 | `bBGyro`  | `printh 23 01 42`                        | `B` robot self-stabilize on/off |
 | `hSpeed`  | `printh 23 02 56`<br>`prints hSpeed.val,1` | `V` + speed byte             |
+| `hHeight` | `printh 23 02 48`<br>`prints hHeight.val,1` | `H` + height byte (Touch Move + Release) |
 | `bZero`   | `printh 23 01 5A`                        | `Z` zero handset level         |
 | `bCal`    | `printh 23 01 43`                        | `C` start / save stick calibration |
 | `bCalX`   | `printh 23 01 51`                        | `Q` cancel calibration         |

2026-current/remote/NextionUI.cpp

@@ -46,6 +46,7 @@ bool NextionUI::decodeCustom(UiEvent& out) {
     case 'R': out.cmd = UiCmd::ToggleRemoteGyro;  break;
     case 'B': out.cmd = UiCmd::ToggleRobotGyro;   break;
     case 'V': out.cmd = UiCmd::SetSpeed;          break;
+    case 'H': out.cmd = UiCmd::SetHeight;         break;
     case 'Z': out.cmd = UiCmd::ZeroGyro;          break;
     case 'C': out.cmd = UiCmd::CalStartSave;      break;
     case 'Q': out.cmd = UiCmd::CalCancel;         break;
@@ -124,6 +125,10 @@ void NextionUI::pushState(const UiView& v, bool full) {
     cmd("hSpeed.val=%u", v.speed_target);
     cmd("nSpeed.val=%u", (v.speed_target * 100 + 127) / 255);
   }
+  if (full || v.height != s.height) {
+    cmd("hHeight.val=%d", v.height / 10 + 100);   // slider 0..200, 100 = default
+    cmd("nHeight.val=%d", v.height / 10);         // -100..100 %
+  }
   if (full || v.calibrating != s.calibrating) {
     cmd("bCal.txt=\"%s\"", v.calibrating ? "SAVE CAL" : "CAL");
     cmd("bCal.bco=%u", v.calibrating ? COL_WARN : COL_OFF);

2026-current/remote/PacketBuilder.cpp

@@ -13,6 +13,7 @@ CmdPacket PacketBuilder::build(const StickFrame& s, const RemoteIMU& imu, const
   CmdPacket p;
   p.seq = seq_++;
   p.speed_scale = st.speedCurrent();
+  p.body_height = st.height();   // a setting, not motion: sent even while disarmed
 
   uint8_t f = 0;
   if (st.armed())          f |= FLAG_ARMED;

2026-current/remote/README.md

@@ -36,6 +36,13 @@ Stick pots are wired 3.3 V – wiper – GND. **Never feed 5 V into a Teensy
 | Right stick, **ROTATE** (default) | `rx/ry/rz` | body roll / pitch / yaw |
 | Right stick, **MOVE** (`FLAG_RSTICK_XLATE`) | `rx/ry/rz` | body X / Y / Z (height, via twist) offset |
 | Handset tilt | `remote_roll/pitch` | extra body roll/pitch while REMOTE GYRO is on |
+| Height slider | `body_height` | standing height, default ± `STANCE_HEIGHT_RANGE_MM` (robot rate-limits the change) |
+
+In **HEADING** mode the left stick steers, relative to where the robot
+faces at that moment. Forward/back walks forward/back, and sideways
+steers: forward+left or back+left walk while turning left, and left alone
+turns on the spot for as long as you hold it. Let go and the robot holds
+its heading.
 
 Touchscreen: ARM / DISARM, SIT/STAND, TRIPOD/WAVE, DIRECT/HEADING,
 R: ROTATE/MOVE, REMOTE GYRO, ROBOT GYRO, speed slider, LEVEL (re-zero the
@@ -91,6 +98,7 @@ display attached.
 | `m` | direct ↔ heading-hold | `t` | right stick rotate ↔ translate |
 | `r` | remote gyro on/off | `b` | robot gyro on/off |
 | `+` / `-` | speed ±25 | `z` | zero handset level |
+| `]` / `[` | height up / down 10% | | |
 | `c` | start / save calibration | `x` | cancel calibration |
 | `p` | print status (raw + mapped sticks, IMU, link, state, cal) | `d` | toggle 10 Hz packet dump |
 | `R` | reset stick cal to Config defaults | | |

2026-current/remote/RemoteIMU.cpp

@@ -55,8 +55,12 @@ bool RemoteIMU::readRaw(float a[3], float g[3]) {
   Wire.requestFrom((int)IMU_ADDR, 14);
   if (Wire.available() < 14) return false;
 
-  int16_t raw[7];
-  for (int k = 0; k < 7; k++) raw[k] = (Wire.read() << 8) | Wire.read();   // ax ay az temp gx gy gz
+  int16_t raw[7];   // ax ay az temp gx gy gz, big-endian
+  for (int k = 0; k < 7; k++) {
+    uint8_t hi = Wire.read();   // two statements: the order of calls inside one expression is unspecified
+    uint8_t lo = Wire.read();
+    raw[k] = (int16_t)((hi << 8) | lo);
+  }
 
   float chip_a[3] = { raw[0] / 16384.0f, raw[1] / 16384.0f, raw[2] / 16384.0f };
   float chip_g[3] = { raw[4] / 131.0f,   raw[5] / 131.0f,   raw[6] / 131.0f };

2026-current/remote/RemoteState.cpp

@@ -56,6 +56,10 @@ bool RemoteState::handle(const UiEvent& e, Sticks& stick_hw, RemoteIMU& imu, uin
     case UiCmd::SpeedUp:   speed_target_ = (uint8_t)min(255, speed_target_ + SPEED_SCALE_STEP); return true;
     case UiCmd::SpeedDown: speed_target_ = (uint8_t)max(0, speed_target_ - SPEED_SCALE_STEP);   return true;
 
+    case UiCmd::SetHeight:  height_ = (int16_t)constrain(((int)e.value - 100) * 10, -1000, 1000); return true;
+    case UiCmd::HeightUp:   height_ = (int16_t)min(1000, height_ + HEIGHT_STEP);  return true;
+    case UiCmd::HeightDown: height_ = (int16_t)max(-1000, height_ - HEIGHT_STEP); return true;
+
     case UiCmd::ZeroGyro:
       imu.zeroLevel();
       setMessage("Remote level zeroed", now);
@@ -110,5 +114,6 @@ void RemoteState::fillView(UiView& v, uint32_t now_ms) const {
   v.robot_gyro = robot_gyro_;
   v.calibrating = calibrating_;
   v.speed_target = speed_target_;
+  v.height = height_;
   v.message = message(now_ms);
 }

2026-current/remote/RemoteState.h

@@ -29,6 +29,7 @@ public:
   bool robotGyro() const    { return robot_gyro_; }
 
   uint8_t speedTarget() const  { return speed_target_; }
+  int16_t height() const       { return height_; }        // -1000..1000, 0 = default
   uint8_t speedCurrent() const { return (uint8_t)lroundf(speed_.current); }
   float remoteTiltBlend() const { return tilt_blend_.current; }   // 0..1, fades on the gyro toggle
 
@@ -48,6 +49,7 @@ private:
   bool calibrating_ = false;
 
   uint8_t speed_target_ = SPEED_SCALE_DEFAULT;
+  int16_t height_ = 0;
   SmoothedValue speed_{SPEED_SCALE_RATE_PER_SEC};
   SmoothedValue tilt_blend_{REMOTE_TILT_FADE_PER_SEC};
 

2026-current/remote/SerialConsole.cpp

@@ -17,6 +17,8 @@ bool SerialConsole::poll(UiEvent& ui, Local& local) {
       case 'b': ui.cmd = UiCmd::ToggleRobotGyro;   return true;
       case '+': case '=': ui.cmd = UiCmd::SpeedUp;   return true;
       case '-': case '_': ui.cmd = UiCmd::SpeedDown; return true;
+      case ']': ui.cmd = UiCmd::HeightUp;          return true;
+      case '[': ui.cmd = UiCmd::HeightDown;        return true;
       case 'z': ui.cmd = UiCmd::ZeroGyro;          return true;
       case 'c': ui.cmd = UiCmd::CalStartSave;      return true;
       case 'x': ui.cmd = UiCmd::CalCancel;         return true;

2026-current/remote/UiTypes.h

@@ -17,6 +17,9 @@ enum class UiCmd : uint8_t {
   SetSpeed,            // value = 0..255
   SpeedUp,             // serial console only
   SpeedDown,           // serial console only
+  SetHeight,           // value = 0..200, 100 = default standing height
+  HeightUp,            // serial console only
+  HeightDown,          // serial console only
   ZeroGyro,            // capture the handset's current attitude as "level"
   CalStartSave,        // start sweep calibration, or save it if running
   CalCancel,
@@ -39,6 +42,7 @@ struct UiView {
   bool robot_gyro = false;
   bool calibrating = false;
   uint8_t speed_target = 0;
+  int16_t height = 0;          // -1000..1000, 0 = default
   bool link_ok = false;
   uint8_t link_pct = 0;
   const char* message = "";   // always a string literal - NextionUI diffs it by pointer

2026-current/remote/remote.ino

@@ -34,17 +34,17 @@ static void printStatus() {
                 imu.ok() ? "ok" : "MISSING", imu.rollDeg(), imu.pitchDeg());
   Serial.printf("radio %s  link %s  %u%%\n", radio_link.present() ? "ok" : "MISSING",
                 radio_link.linkOk() ? "OK" : "DOWN", radio_link.qualityPct());
-  Serial.printf("armed %d stand %d gait %s mode %s rstick %s remote_gyro %d robot_gyro %d speed %u->%u\n",
+  Serial.printf("armed %d stand %d gait %s mode %s rstick %s remote_gyro %d robot_gyro %d speed %u->%u height %d\n",
                 state.armed(), state.standRequested(), state.gaitWave() ? "wave" : "tripod",
                 state.modeB() ? "B" : "A", state.rstickXlate() ? "xlate" : "rot",
-                state.remoteGyro(), state.robotGyro(), state.speedTarget(), state.speedCurrent());
+                state.remoteGyro(), state.robotGyro(), state.speedTarget(), state.speedCurrent(), state.height());
   sticks.printCalibration(Serial);
 }
 
 static void dumpPacket(const CmdPacket& p) {
-  Serial.printf("#%3u vx %5d vy %5d yaw %5d | r %5d %5d %5d | tilt %5d %5d | spd %3u flags %02X\n",
+  Serial.printf("#%3u vx %5d vy %5d yaw %5d | r %5d %5d %5d | tilt %5d %5d | h %5d spd %3u flags %02X\n",
                 p.seq, p.vx, p.vy, p.yaw_rate, p.rx, p.ry, p.rz,
-                p.remote_roll, p.remote_pitch, p.speed_scale, p.flags);
+                p.remote_roll, p.remote_pitch, p.body_height, p.speed_scale, p.flags);
 }
 
 static void pollInputs(uint32_t now_ms) {