diff --git a/src/voxelburst/core.clj b/src/voxelburst/core.clj
index bbb1a4d..b3db4fb 100644
--- a/src/voxelburst/core.clj
+++ b/src/voxelburst/core.clj
@@ -46,8 +46,9 @@
 ;;; trace
 ;;;
 
-(def start-radius 2)
-(def start-lifespan 20)
+(def start-radius 3.0)
+(def start-lifespan 100)
+(def radius-step (/ start-radius start-lifespan))
 
 (defrecord Trace [position velocity radius lifespan])
 
@@ -57,25 +58,27 @@
 (defn update-trace [trace bounds]
   (let [t (Trace. (next-pos (:position trace) (:velocity trace))
                   (next-vel (:velocity trace))
-                  start-radius
-                  (dec start-lifespan))]
-    (when (and (in-bounds? (:position t) bounds)
+                  (- (:radius trace) radius-step)
+                  (dec (:lifespan trace)))]
+    (if (and (in-bounds? (:position t) bounds)
                (> (:radius t) 0)
                (> (:lifespan t) 0))
-      t)))
+      t
+      (do #_(println "died at " (:lifespan t))
+          nil))))
 
 ;;;
 ;;; physics
 ;;;
 
-(def gravity [0 0 -0.2])
+(def gravity [0 0 -0.1])
 
 (defn random-vel
   []
   #_(mapv #(* 2 (- % 0.5)) (repeatedly 3 rand))
-  (vector (* 2 (- (rand) 0.5))
-          (* 2 (- (rand) 0.5))
-          (* 4 (rand))))
+  (vector (* 8 (- (rand) 0.5))
+          (* 8 (- (rand) 0.5))
+          (* 12 (rand))))
 
 (defn next-pos
   "Position at t+1"
@@ -99,19 +102,19 @@
 
 (defn trace-trajectory
   [trace bounds]
-  (loop [pts []
+  (loop [traces []
          trace trace]
     (let [new-trace (update-trace trace bounds)]
       (if (not new-trace)
-        pts
-        (recur (conj pts (:position trace)) new-trace)))))
+        traces
+        (recur (conj traces trace) new-trace)))))
 
-(defn trajectory-voxels [trajectory]
-  (reduce set/union (map #(sphere (round-point %) 3) trajectory)))
+(defn trajectory-voxels [traces]
+  (reduce set/union (map #(sphere (round-point (:position %)) (:radius %)) traces)))
 
 (defn sample-trace []
-  (let [bounds [[10 490][10 490][10 490]]
-        origin [250 250 250]]
+  (let [bounds [[10 990][10 990][10 990]]
+        origin [500 500 500]]
     (trajectory-voxels (trace-trajectory (new-trace origin) bounds))))
 
 (defn sample-traces [count]
@@ -127,7 +130,7 @@
 ;;;
 
 (defn sample-tree [count]
-  (let [tree (svo/voxeltree 500 1.0)
+  (let [tree (svo/voxeltree 1000 1.0)
         trace (sample-traces count)]
     (svo/apply-voxels svo/set-at tree trace)))