diff --git a/rcbasic_runtime/rc_gfx.h b/rcbasic_runtime/rc_gfx.h
index 3128fda..e186cc4 100644
--- a/rcbasic_runtime/rc_gfx.h
+++ b/rcbasic_runtime/rc_gfx.h
@@ -328,7 +328,8 @@ bool rc_windowOpenEx(std::string title, int x, int y, int w, int h, uint32_t win
 	rc_physics3D.TimeStamp = SDL_GetTicks(); //device->getTimer()->getTime();
 
 	rc_physics3D.maxSubSteps = 1;
-	rc_physics3D.fixedTimeStep = irr::f32(1.) / irr::f64(60.);
+	//rc_physics3D.fixedTimeStep = irr::f32(1.) / irr::f64(60.);
+	rc_physics3D.fixedTimeStep = -1;
 
 	rc_physics3D.world->setInternalTickCallback((btInternalTickCallback)myTickCallback2);
 
@@ -3047,7 +3048,8 @@ void rc_preUpdate()
 	//rc_physics3D.TimeStamp = device->getTimer()->getTime();
 	rc_physics3D.DeltaTime = SDL_GetTicks() - rc_physics3D.TimeStamp;
 	rc_physics3D.TimeStamp = SDL_GetTicks();
-	rc_physics3D.world->stepSimulation(rc_physics3D.DeltaTime*0.001f, rc_physics3D.maxSubSteps, rc_physics3D.fixedTimeStep);
+	float fixed_timestep = rc_physics3D.fixedTimeStep < 0 ? rc_physics3D.DeltaTime*0.001f : rc_physics3D.fixedTimeStep;
+	rc_physics3D.world->stepSimulation(rc_physics3D.DeltaTime*0.001f, rc_physics3D.maxSubSteps, fixed_timestep);
 
 	for(int i = 0; i < rc_canvas.size(); i++)
 	{
@@ -3459,7 +3461,8 @@ bool rc_update()
 			//rc_physics3D.TimeStamp = device->getTimer()->getTime();
 			rc_physics3D.DeltaTime = SDL_GetTicks() - rc_physics3D.TimeStamp;
 			rc_physics3D.TimeStamp = SDL_GetTicks();
-			rc_physics3D.world->stepSimulation(rc_physics3D.DeltaTime*0.001f, rc_physics3D.maxSubSteps, rc_physics3D.fixedTimeStep);
+			float fixed_timestep = rc_physics3D.fixedTimeStep < 0 ? rc_physics3D.DeltaTime*0.001f : rc_physics3D.fixedTimeStep;
+			rc_physics3D.world->stepSimulation(rc_physics3D.DeltaTime*0.001f, rc_physics3D.maxSubSteps, fixed_timestep);
         }
 
         for(int i = 0; i < rc_canvas.size(); i++)
diff --git a/rcbasic_runtime/rc_gfx_core.h b/rcbasic_runtime/rc_gfx_core.h
index 1e2ff96..3a7596d 100644
--- a/rcbasic_runtime/rc_gfx_core.h
+++ b/rcbasic_runtime/rc_gfx_core.h
@@ -307,6 +307,7 @@ struct rc_physicsWorld2D_obj
 	b2World* world;
 
 	rc_contactListener_obj* contact_listener;
+	float time_stamp;
 	float timeStep = 1/60.0;      //the length of time passed to simulate (seconds)
 	int velocityIterations = 8;   //how strongly to correct velocity
 	int positionIterations = 3;   //how strongly to correct position
diff --git a/rcbasic_runtime/rcbasic_runtime.depend b/rcbasic_runtime/rcbasic_runtime.depend
index fbb8ccd..28d399f 100755
--- a/rcbasic_runtime/rcbasic_runtime.depend
+++ b/rcbasic_runtime/rcbasic_runtime.depend
@@ -1247,7 +1247,7 @@
 1727545973 /home/n00b/Projects/RCBASIC4/rcbasic_runtime/RealisticWater.h
 	<irrlicht.h>
 
-1733023077 /home/n00b/Projects/RCBASIC4/rcbasic_runtime/rc_gfx.h
+1733027113 /home/n00b/Projects/RCBASIC4/rcbasic_runtime/rc_gfx.h
 	"SDL.h"
 	<SDL2/SDL.h>
 	<irrlicht.h>
@@ -1271,7 +1271,7 @@
 	"rc_joints.h"
 	<irrtheora.h>
 
-1732372339 /home/n00b/Projects/RCBASIC4/rcbasic_runtime/rc_gfx_core.h
+1733027113 /home/n00b/Projects/RCBASIC4/rcbasic_runtime/rc_gfx_core.h
 	"SDL.h"
 	"btBulletDynamicsCommon.h"
 	"BulletSoftBody/btSoftRigidDynamicsWorld.h"