diff --git a/src/jaxsim/high_level/model.py b/src/jaxsim/high_level/model.py
index d1314bf9a..1ef0886c1 100644
--- a/src/jaxsim/high_level/model.py
+++ b/src/jaxsim/high_level/model.py
@@ -491,7 +491,7 @@ def joint_positions(self, joint_names: tuple[str, ...] = None) -> jtp.Vector:
 
     @functools.partial(oop.jax_tf.method_ro, static_argnames=["joint_names"])
     def joint_random_positions(
-        self, joint_names: tuple[str, ...] = None, key: jax.random.PRNGKeyArray = None
+        self, joint_names: tuple[str, ...] = None, key: jax.Array = None
     ) -> jtp.Vector:
         """"""
 
@@ -1505,64 +1505,48 @@ def integrate(
     # Motor dynamics
     # ==============
 
-    # @functools.partial(oop.jax_tf.method_rw, static_argnames=["joint_names"])
+    @functools.partial(oop.jax_tf.method_rw, static_argnames=["joint_names"])
     def set_motor_inertias(
-        self, inertias: jtp.Vector, joint_names: List[str] = None
+        self, inertias: jtp.Vector, joint_names: tuple[str, ...] = None
     ) -> None:
-        if joint_names is None:
-            joint_names = self.joint_names()
+        joint_names = joint_names or self.joint_names()
 
         if inertias.size != len(joint_names):
             raise ValueError("Wrong arguments size", inertias.size, len(joint_names))
 
         self.physics_model._joint_motor_inertia.update(
-            {
-                j: im
-                for j, im in zip(
-                    self.physics_model._joint_motor_inertia.keys(), inertias
-                )
-            }
+            dict(zip(self.physics_model._joint_motor_inertia, inertias))
         )
 
         logging.info("Setting attribute 'motor_inertias'")
 
-    # @functools.partial(oop.jax_tf.method_rw, static_argnames=["joint_names"])
+    @functools.partial(oop.jax_tf.method_rw, static_argnames=["joint_names"])
     def set_motor_gear_ratios(
-        self, gear_ratios: jtp.Vector, joint_names: List[str] = None
+        self, gear_ratios: jtp.Vector, joint_names: tuple[str, ...] = None
     ) -> None:
-        if joint_names is None:
-            joint_names = self.joint_names()
+        joint_names = joint_names or self.joint_names()
 
         if gear_ratios.size != len(joint_names):
             raise ValueError("Wrong arguments size", gear_ratios.size, len(joint_names))
 
         # Check on gear ratios if motor_inertias are not zero
-        jax.lax.cond(
-            pred=(jnp.diag(self.physics_model._joint_motor_inertia) != 0).any(),
-            operand=gear_ratios,
-            true_fun=lambda gr: gr,
-            false_fun=lambda: (_ for _ in _).throw(
-                ValueError("Motor inertias are zero")
-            ),
-        )
+        for idx, gr in gear_ratios:
+            if gr != 0 and self.motor_inertias()[idx] == 0:
+                raise ValueError(
+                    f"Zero motor inertia with non-zero gear ratio found in position {idx}"
+                )
 
         self.physics_model._joint_motor_gear_ratio.update(
-            {
-                j: gr
-                for j, gr in zip(
-                    self.physics_model._joint_motor_gear_ratio.keys(), gear_ratios
-                )
-            }
+            dict(zip(self.physics_model._joint_motor_gear_ratio, gear_ratios))
         )
 
         logging.info("Setting attribute 'motor_gear_ratios'")
 
-    # @functools.partial(oop.jax_tf.method_rw, static_argnames=["joint_names"])
+    @functools.partial(oop.jax_tf.method_rw, static_argnames=["joint_names"])
     def set_motor_viscous_frictions(
-        self, viscous_frictions: Tuple, joint_names: List[str] = None
+        self, viscous_frictions: jtp.Vector, joint_names: tuple[str, ...] = None
     ) -> None:
-        if joint_names is None:
-            joint_names = self.joint_names()
+        joint_names = joint_names or self.joint_names()
 
         if viscous_frictions.size != len(joint_names):
             raise ValueError(
@@ -1570,17 +1554,35 @@ def set_motor_viscous_frictions(
             )
 
         self.physics_model._joint_motor_viscous_friction.update(
-            {
-                j: kv
-                for j, kv in zip(
-                    self.physics_model._joint_motor_viscous_friction.keys(),
+            dict(
+                zip(
+                    self.physics_model._joint_motor_viscous_friction,
                     viscous_frictions,
                 )
-            }
+            )
         )
 
+        # self.physics_model._joint_motor_viscous_friction |= dict(
+        #     zip(
+        #         self.physics_model._joint_motor_viscous_friction.keys(),
+        #         viscous_frictions,
+        #     )
+        # )
+
         logging.info("Setting attribute 'motor_viscous_frictions'")
 
+    @functools.partial(oop.jax_tf.method_ro, jit=False)
+    def motor_inertias(self) -> jtp.Vector:
+        return jnp.array([*self.physics_model._joint_motor_inertia.values()])
+
+    @functools.partial(oop.jax_tf.method_ro, jit=False)
+    def motor_gear_ratios(self) -> jtp.Vector:
+        return jnp.array([*self.physics_model._joint_motor_gear_ratio.values()])
+
+    @functools.partial(oop.jax_tf.method_ro, jit=False)
+    def motor_viscous_frictions(self) -> jtp.Vector:
+        return jnp.array([*self.physics_model._joint_motor_viscous_friction.values()])
+
     # ===============
     # Private methods
     # ===============