BEGIN_PUBLIC

Zero all of act_dot when there are custom actuator dynamics, but no callback.
END_PUBLIC

PiperOrigin-RevId: 564712105
Change-Id: I107481727a42eb2577d62e29ac4e1496c56bb634

src/engine/engine_forward.c

@@ -264,7 +264,7 @@ void mj_fwdActuation(const mjModel* m, mjData* d) {
           mjcb_act_dyn(m, d, i);
         }
       } else {
-        d->act_dot[j] = 0;
+        mju_zero(d->act_dot + j, m->actuator_actnum[i]);
       }
     }
   }