diff --git a/software/lib/MMM/Motion.cpp b/software/lib/MMM/Motion.cpp
index f10dd6f..85dd0f6 100644
--- a/software/lib/MMM/Motion.cpp
+++ b/software/lib/MMM/Motion.cpp
@@ -50,6 +50,10 @@ void Motion::init(SENSOR_INPUT sensor)
     tick = millis();
 }
 
+void Motion::update_position() {
+    Xin = analogRead(_s); // may take some time
+}
+
 void Motion::update_mass_spring_damper() {        
     
     // todo: filtering
diff --git a/software/lib/MMM/Motion.h b/software/lib/MMM/Motion.h
index 70b84fe..5318b98 100644
--- a/software/lib/MMM/Motion.h
+++ b/software/lib/MMM/Motion.h
@@ -51,6 +51,7 @@ public:
     
     void init(SENSOR_INPUT sensor);
     
+    void update_position();
     void update_mass_spring_damper();
         
     // raw position vector