Add <dcmotor> actuator and related docs and tests.

PiperOrigin-RevId: 892927987
Change-Id: I38ed6412801341ba03ddf5fe7b93a6081df24d37

include/mujoco/mjmodel.h

@@ -244,7 +244,8 @@ typedef enum mjtDyn_ {            // type of actuator dynamics
   mjDYN_INTEGRATOR,               // integrator: da/dt = u
   mjDYN_FILTER,                   // linear filter: da/dt = (u-a) / tau
   mjDYN_FILTEREXACT,              // linear filter: da/dt = (u-a) / tau, with exact integration
-  mjDYN_MUSCLE,                   // piece-wise linear filter with two time constants
+  mjDYN_MUSCLE,                   // piecewise linear filter with two time constants
+  mjDYN_DCMOTOR,                  // DC motor electrical dynamics
   mjDYN_USER                      // user-defined dynamics type
 } mjtDyn;
 
@@ -253,6 +254,7 @@ typedef enum mjtGain_ {           // type of actuator gain
   mjGAIN_FIXED        = 0,        // fixed gain
   mjGAIN_AFFINE,                  // const + kp*length + kv*velocity
   mjGAIN_MUSCLE,                  // muscle FLV curve computed by mju_muscleGain()
+  mjGAIN_DCMOTOR,                 // DC motor gain: K or K/R
   mjGAIN_USER                     // user-defined gain type
 } mjtGain;
 
@@ -261,6 +263,7 @@ typedef enum mjtBias_ {           // type of actuator bias
   mjBIAS_NONE         = 0,        // no bias
   mjBIAS_AFFINE,                  // const + kp*length + kv*velocity
   mjBIAS_MUSCLE,                  // muscle passive force computed by mju_muscleBias()
+  mjBIAS_DCMOTOR,                 // DC motor bias: back-EMF, cogging, LuGre friction
   mjBIAS_USER                     // user-defined bias type
 } mjtBias;
 

include/mujoco/mujoco.h

@@ -1726,6 +1726,12 @@ MJAPI const char* mjs_setToMuscle(mjsActuator* actuator, double timeconst[2], do
 // Set actuator to active adhesion; return error if any.
 MJAPI const char* mjs_setToAdhesion(mjsActuator* actuator, double gain);
 
+// Set actuator to DC motor; return error if any.
+MJAPI const char* mjs_setToDCMotor(mjsActuator* actuator, double motorconst[2], double resistance,
+                                   double nominal[3], double saturation[4], double inductance[2],
+                                   double cogging[3], double controller[5], double thermal[6],
+                                   double lugre[6], int input_mode);
+
 
 //---------------------------------- Assets --------------------------------------------------------