Add <dcmotor> actuator and related docs and tests.

PiperOrigin-RevId: 892927987
Change-Id: I38ed6412801341ba03ddf5fe7b93a6081df24d37

doc/includes/references.h

@@ -635,19 +635,22 @@ 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;
 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;
 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;
 typedef enum mjtObj_ {            // type of MujoCo object
@@ -3659,6 +3662,10 @@ const char* mjs_setToMuscle(mjsActuator* actuator, double timeconst[2], double t
                             double range[2], double force, double scale, double lmin,
                             double lmax, double vmax, double fpmax, double fvmax);
 const char* mjs_setToAdhesion(mjsActuator* actuator, double gain);
+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);
 mjsMesh* mjs_addMesh(mjSpec* s, const mjsDefault* def);
 mjsHField* mjs_addHField(mjSpec* s);
 mjsSkin* mjs_addSkin(mjSpec* s);