         else
             log(F("Invalid motor designator"));
     }
+    else if (c1 == 'd')
+    {
+        if (c2 == 's')
+          set_diff_speed(value);
+        else if (c2 == 't')
+          set_diff_turn(value);
+        else
+          log(F("Invalid drive parameter"));
+    }
     else if (c1 == 's') {
         // "sp" - pan servo, "st" - tilt servo
         

    }
}

///////////////////////////////////////////////
// MOTORS


    read_serial();
    process_bluetooth();
    read_bluetooth();
    update_joystick_drive();
    
    // Check if we need to enter fail-safe mode.
    check_failsafe();
