First working iteration of actuated crawler scene, prefabs and code complete. Can train, not sure whether learn though. Camera follow is broken.

UnitySDK/Assets/ML-Agents/Examples/Crawler/Brains/CrawlerStaticLearning.asset

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UnitySDK/Assets/ML-Agents/Examples/Crawler/Scripts/ArticulatedCrawlerAgent.cs

 using UnityEngine;
 using MLAgents;
 
-[RequireComponent(typeof(JointDriveController))] // Required to set joint forces
+[RequireComponent(typeof(ArticulatedJointDriveController))] // Required to set joint forces
 public class ArticulatedCrawlerAgent : Agent
 {
     [Header("Target To Walk Towards")][Space(10)]
 
         if (bp.arb.transform != body)
         {
-            // Will need to rewrite this because body parts are in hiearchy, not flat like in RigidBody case
-            //var localPosRelToBody = body.InverseTransformPoint(arb.position);
-            //AddVectorObs(localPosRelToBody);
+            var localPosRelToBody = body.InverseTransformPoint(arb.transform.TransformPoint(arb.transform.position)); // Translate from world space to body local space, since all articulations are children of body in hiearchy
+            AddVectorObs(localPosRelToBody);
             AddVectorObs(bp.currentXNormalizedRot); // Current x rot
             AddVectorObs(bp.currentYNormalizedRot); // Current y rot
             AddVectorObs(bp.currentZNormalizedRot); // Current z rot

UnitySDK/Assets/ML-Agents/Examples/Crawler/Scripts/ArticulatedCrawlerManualControl.cs

 {
     public class ArticulatedCrawlerManualControl : MonoBehaviour
     {
-        public GameObject upperLeg;
-        public GameObject foreLeg;
-        private ArticulationBody m_AbUpper;
-        private ArticulationBody m_AbFore;
+        public GameObject upperLeg0, upperLeg1;
+        public GameObject foreLeg0, foreLeg1;
+        private ArticulationBody m_AbUpper0, m_AbUpper1;
+        private ArticulationBody m_AbFore0, m_AbFore1;
-        private Vector3 m_rotationUpper;
-        private Vector3 m_rotationFore;
+        private Vector3 m_rotationUpper0, m_rotationUpper1;
+        private Vector3 m_rotationFore0, m_rotationFore1;
 
         public bool useAlternativeKeySetForInput = false;
         public float maxJointForceLimit = 1000;
         /// </summary>
         public void Start()
         {
-            m_AbUpper = upperLeg.GetComponent<ArticulationBody>();
-            m_AbFore = foreLeg.GetComponent<ArticulationBody>();
+            m_AbUpper0 = upperLeg0.GetComponent<ArticulationBody>();
+            m_AbFore0 = foreLeg0.GetComponent<ArticulationBody>();
+
+            m_AbUpper1 = upperLeg1.GetComponent<ArticulationBody>();
+            m_AbFore1 = foreLeg1.GetComponent<ArticulationBody>();
-            m_rotationUpper = m_rotationFore = Vector3.zero;
+            m_rotationUpper0 = m_rotationFore0 = m_rotationUpper1 = m_rotationFore1 = Vector3.zero;
         }
 
         /// <summary>
         {
-            m_rotationUpper = Vector3.zero;
-            m_rotationFore = Vector3.zero;
+            m_rotationUpper0 = m_rotationFore0 = m_rotationUpper1 = m_rotationFore1 = Vector3.zero;
 
             /*
             m_AbUpper.transform.position = new Vector3(0f, -4f, 0f) + transform.position;
         public void FixedUpdate()
         {
             //float maxTorque = 1000f;
-            float deltaRotation = 0.01f;
+            float speed = 100f;
+            float deltaRotation = speed * Time.fixedDeltaTime;
+
+            m_rotationUpper0.x = m_AbUpper0.xDrive.target;
+            m_rotationUpper0.y = m_AbUpper0.yDrive.target;
+            m_rotationUpper0.z = m_AbUpper0.zDrive.target;
+            
+            m_rotationUpper1.x = m_AbUpper1.xDrive.target;
+            m_rotationUpper1.y = m_AbUpper1.yDrive.target;
+            m_rotationUpper1.z = m_AbUpper1.zDrive.target;
+            
-                m_rotationUpper.x += deltaRotation;
+            {
+                m_rotationUpper0.x += deltaRotation;
+                m_rotationUpper1.x += deltaRotation;
+            }
+
-                m_rotationUpper.x -= deltaRotation;
+            {
+                m_rotationUpper0.x -= deltaRotation;
+                m_rotationUpper1.x -= deltaRotation;
+            }
+
-                m_rotationUpper.y += deltaRotation;
+            {
+                m_rotationUpper0.y += deltaRotation;
+                m_rotationUpper1.y += deltaRotation;
+            }
+
-                m_rotationUpper.y -= deltaRotation;
+            {
+                m_rotationUpper0.y -= deltaRotation;
+                m_rotationUpper1.y -= deltaRotation;
+            }
+
-                m_rotationUpper.z += deltaRotation;
+            {
+                m_rotationUpper0.z += deltaRotation;
+                m_rotationUpper1.z += deltaRotation;
+            }
+
-                m_rotationUpper.z -= deltaRotation;
+            {
+                m_rotationUpper0.z -= deltaRotation;
+                m_rotationUpper1.z -= deltaRotation;
+            }
-            
-            m_rotationUpper.x = Mathf.Clamp(m_rotationUpper.x, -Mathf.PI * 0.5f, Mathf.PI * 0.5f);
-            m_rotationUpper.y = Mathf.Clamp(m_rotationUpper.y, -Mathf.PI * 0.5f, Mathf.PI * 0.5f);
-            m_rotationUpper.z = Mathf.Clamp(m_rotationUpper.z, -Mathf.PI * 0.5f, Mathf.PI * 0.5f);
+
+            m_rotationUpper0.x = Mathf.Clamp(m_rotationUpper0.x, -180.0f, 180.0f);
+            m_rotationUpper0.y = Mathf.Clamp(m_rotationUpper0.y, -180.0f, 180.0f);
+            m_rotationUpper0.z = Mathf.Clamp(m_rotationUpper0.z, -180.0f, 180.0f);
+
+            m_rotationUpper1.x = Mathf.Clamp(m_rotationUpper1.x, -180.0f, 180.0f);
+            m_rotationUpper1.y = Mathf.Clamp(m_rotationUpper1.y, -180.0f, 180.0f);
+            m_rotationUpper1.z = Mathf.Clamp(m_rotationUpper1.z, -180.0f, 180.0f);
+            
+            m_rotationFore0.x = m_AbFore0.xDrive.target;
+            m_rotationFore0.y = m_AbFore0.yDrive.target;
+            m_rotationFore0.z = m_AbFore0.zDrive.target;
+
+
-                m_rotationFore.x += deltaRotation;
+            {
+                m_rotationFore0.x += deltaRotation;
+                m_rotationFore1.x += deltaRotation;
+            }
+
-                m_rotationFore.x -= deltaRotation;
+            {
+                m_rotationFore0.x -= deltaRotation;
+                m_rotationFore1.x -= deltaRotation;
+            }
+
-                m_rotationFore.y += deltaRotation;
+            {
+                m_rotationFore0.y += deltaRotation;
+                m_rotationFore1.y += deltaRotation;
+            }
+
-                m_rotationFore.y -= deltaRotation;
+            {
+                m_rotationFore0.y -= deltaRotation;
+                m_rotationFore1.y -= deltaRotation;
+            }
+
-                m_rotationFore.z += deltaRotation;
+            {
+                m_rotationFore0.z += deltaRotation;
+                m_rotationFore1.z += deltaRotation;
+            }
+
-                m_rotationFore.z -= deltaRotation;
+            {
+                m_rotationFore0.z -= deltaRotation;
+                m_rotationFore1.z -= deltaRotation;
+            }
+
+            m_rotationFore0.x = Mathf.Clamp(m_rotationFore0.x, -180.0f, 180.0f);
+            m_rotationFore0.y = Mathf.Clamp(m_rotationFore0.y, -180.0f, 180.0f);
+            m_rotationFore0.z = Mathf.Clamp(m_rotationFore0.z, -180.0f, 180.0f);
-            m_rotationFore.x = Mathf.Clamp(m_rotationFore.x, -Mathf.PI * 0.5f, Mathf.PI * 0.5f);
-            m_rotationFore.y = Mathf.Clamp(m_rotationFore.y, -Mathf.PI * 0.5f, Mathf.PI * 0.5f);
-            m_rotationFore.z = Mathf.Clamp(m_rotationFore.z, -Mathf.PI * 0.5f, Mathf.PI * 0.5f);
+            m_rotationFore1.x = Mathf.Clamp(m_rotationFore1.x, -180.0f, 180.0f);
+            m_rotationFore1.y = Mathf.Clamp(m_rotationFore1.y, -180.0f, 180.0f);
+            m_rotationFore1.z = Mathf.Clamp(m_rotationFore1.z, -180.0f, 180.0f);
-            SetJointTargetRotation(m_AbUpper, m_rotationUpper.x, m_rotationUpper.y, m_rotationUpper.z);
-            SetJointStrength(m_AbUpper, 0.0001f);
+            SetJointTargetRotation(m_AbUpper0, m_rotationUpper0.x, m_rotationUpper0.y, m_rotationUpper0.z);
+            SetJointStrength(m_AbUpper0, 0.0001f);
-            SetJointTargetRotation(m_AbFore, m_rotationFore.x, m_rotationFore.y, m_rotationFore.z);
-            SetJointStrength(m_AbFore, 0.0001f);
+            SetJointTargetRotation(m_AbUpper1, m_rotationUpper1.x, m_rotationUpper1.y, m_rotationUpper1.z);
+            SetJointStrength(m_AbUpper1, 0.0001f);
+
+            SetJointTargetRotation(m_AbFore0, m_rotationFore0.x, m_rotationFore0.y, m_rotationFore0.z);
+            SetJointStrength(m_AbFore0, 0.0001f);
+
+            SetJointTargetRotation(m_AbFore1, m_rotationFore1.x, m_rotationFore1.y, m_rotationFore1.z);
+            SetJointStrength(m_AbFore1, 0.0001f);
 
 
             if (Input.GetKey(KeyCode.Escape))

UnitySDK/Assets/ML-Agents/Examples/Crawler/Scripts/ArticulatedJointDriveController.cs

             currentXNormalizedRot =
                 Mathf.InverseLerp(xDrive.lowerLimit, xDrive.upperLimit, xRot);
             
-            // What is this ? Vilmantas Why lowerLimit is not used ?
-            currentYNormalizedRot = Mathf.InverseLerp(-yDrive.upperLimit, yDrive.upperLimit, yRot);
-            currentZNormalizedRot = Mathf.InverseLerp(-zDrive.upperLimit, zDrive.upperLimit, zRot);
+            currentYNormalizedRot = Mathf.InverseLerp(yDrive.lowerLimit, yDrive.upperLimit, yRot);
+            currentZNormalizedRot = Mathf.InverseLerp(zDrive.lowerLimit, zDrive.upperLimit, zRot);
 
             //joint.targetRotation = Quaternion.Euler(xRot, yRot, zRot); // Original code
             xDrive.target = xRot; yDrive.target = yRot; zDrive.target = zRot;
         /// </summary>
         public void SetupBodyPart(Transform t)
         {
+            // Either parent(in case of legs) or game object itself(in case of body) must have ArticulationBody
+            var arb = t.GetComponent<ArticulationBody>();
+            if (arb == null)
+                arb = t.parent.GetComponent<ArticulationBody>();
+            
-                arb = t.GetComponent<ArticulationBody>(),
+                arb =  arb,
                 startingPos = t.position,
                 startingRot = t.rotation
             };

UnitySDK/Assets/ML-Agents/Examples/Crawler/Scripts/CrawlerAcademy.cs

     public override void InitializeAcademy()
     {
         Monitor.verticalOffset = 1f;
-        Physics.defaultSolverIterations = 12;
-        Physics.defaultSolverVelocityIterations = 12;
+        // Not needed for articulations
+        //Physics.defaultSolverIterations = 12;
+        //Physics.defaultSolverVelocityIterations = 12;
         Time.fixedDeltaTime = 0.01333f; // (75fps). default is .2 (60fps)
         Time.maximumDeltaTime = .15f; // Default is .33
     }