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/Hexapod_Simulation_Unity/Assets/Serial/Serial.cs

@@ -0,0 +1,119 @@
+using System;
+using UnityEngine;
+using System.Collections;
+using System.IO.Ports;
+using Random = System.Random;
+
+public class Serial
+{
+    private static Serial instance;
+    private int rnd = 0;
+
+    private Serial()
+    {
+    }
+
+    ~Serial()
+    {
+        serialPort.Close();
+        serialPort.Dispose();
+    }
+
+    public static Serial Instance
+    {
+        get
+        {
+            if (instance == null)
+            {
+                instance = new Serial();
+            }
+
+            return instance;
+        }
+    }
+
+    public bool enabled = false;
+
+    public SerialPort serialPort;
+
+    public int[] values = new int[18];
+
+    public static string ByteArrayToString(byte[] ba)
+    {
+        return BitConverter.ToString(ba).Replace("-", " ");
+    }
+
+    public void send(int start, int a, int b, int c)
+    {
+        if (serialPort == null)
+        {
+            serialPort = new SerialPort(@"\\.\" + "COM4", 250000);
+
+            try
+            {
+                serialPort.Parity = Parity.Even;
+                serialPort.StopBits = StopBits.One;
+                serialPort.DataBits = 8;
+                serialPort.Open();
+                serialPort.DiscardOutBuffer();
+                serialPort.DiscardInBuffer();
+                System.Threading.Thread.Sleep(1000);
+
+                enabled = true;
+            }
+            catch
+            {
+                enabled = false;
+            }
+        }
+
+        if (enabled)
+        {
+            values[start] = a;
+            values[++start] = b;
+            values[++start] = c;
+
+            if (serialPort is SerialPort && start == 17)
+            {
+                // string send = "s";
+                byte[] send = new byte[18+1+2];
+                send[18] = 0x00;
+                send[19] = 0xfe;
+                send[20] = 0xff;
+               // send[21] = 0xff;
+
+                //                if (rnd == 0)
+                //                {
+                //rnd = 1;
+                for (int i = 0; i < 18; i++)
+                    {
+                    //string crc = ((i) * (values[i])) + "";
+                    //send = send + (i).ToString() + "_" + (values[i]).ToString() + "," + crc + "=";
+                    byte[] intBytes = BitConverter.GetBytes(values[i]);
+                    if (BitConverter.IsLittleEndian)
+                        Array.Reverse(intBytes);
+                    send[i] = intBytes[3];
+                    send[18] += send[i];
+                }
+
+                   // Debug.Log(ByteArrayToString(send));
+                    serialPort.Write(send, 0, 18+1+2);
+                    serialPort.BaseStream.Flush();
+//                }
+//                else
+//                {
+//                    rnd = 0;
+//                    for (int i = 10; i < 18; i++)
+//                    {
+//                        string crc = ((i + 3) * (values[i])) + "";
+//
+//                        send = send + (i + 2).ToString() + "_" + (values[i]).ToString() + "," + crc + "=";
+//                    }
+//
+//                    Debug.Log(send);
+//                    serialPort.Write(send);
+//                }
+            }
+        }
+    }
+}