diff --git a/motor_test.py b/motor_test.py
index 0c43fcd..3a97700 100644
--- a/motor_test.py
+++ b/motor_test.py
@@ -4,6 +4,7 @@ motor_test.py - Yahboom 4-ch driver over UART, motors on M3 + M4.
 
   python3 motor_test.py hand   # motors stay OFF. Turn wheels by hand, watch the counts.
   python3 motor_test.py spin   # WHEELS OFF THE GROUND. Low PWM steps, one motor at a time.
+  python3 motor_test.py reverse  # WHEELS OFF THE GROUND. Why does the board go silent on reversing?
 
 Ctrl-C always stops the motors.
 """
@@ -89,6 +90,77 @@ def hold(d, ch, value, seconds):
         time.sleep(0.1)
 
 
+def measure(d, ch, p, seconds=1.0):
+    """Hold PWM p and return (counts/s, encoder messages received)."""
+    t0, n0, _ = d.get(); s0 = time.perf_counter()
+    hold(d, ch, p, seconds)
+    t1, n1, _ = d.get(); s1 = time.perf_counter()
+    return (t1[ch] - t0[ch]) / (s1 - s0), n1 - n0
+
+
+def ramp(d, ch, start, end, steps=10, dt=0.1):
+    for k in range(1, steps + 1):
+        hold(d, ch, start + (end - start) * k / steps, dt)
+
+
+def report(label, cps, msgs):
+    print(f"{label:<36} {cps:+8.0f} counts/s   {msgs:4d} msgs")
+    return msgs > 0
+
+
+def diagnose(d, gentle):
+    print("\nEncoder stream STOPPED. Re-sending motor type + upload command...")
+    d.send("$mtype:1#")
+    _, n0, _ = d.get()
+    d.send("$upload:1,0,0#")
+    time.sleep(0.5)
+    _, n1, other = d.get()
+    if n1 > n0:
+        print("-> Stream came back after re-sending the settings: the board rebooted and lost them.")
+        if gentle:
+            print("   It died even on a GENTLE reverse, so negative PWM itself is the trigger, not a current spike.")
+        else:
+            print("   Gentle reverse was fine, only the hard one killed it: power dip (brownout) on the board.")
+    else:
+        print("-> Still silent. The board is hung or stopped transmitting. Power-cycle it.")
+    print("   non-encoder lines from the board:", other if other else "none")
+
+
+def reverse(d):
+    ch = CHANNELS["M3"]
+    input("Are the wheels OFF the ground? Press Enter to start, Ctrl-C to abort... ")
+
+    print("\nTest A: gentle reverse on M3 (ramp up, ramp to 0, pause, ramp to -800)")
+    ramp(d, ch, 0, 800)
+    ok = report("  +800 (ramped up)", *measure(d, ch, 800))
+    ramp(d, ch, 800, 0); d.stop(); time.sleep(1.0)
+    ramp(d, ch, 0, -800)
+    ok = report("  -800 (ramped, after a full stop)", *measure(d, ch, -800)) and ok
+    ramp(d, ch, -800, 0); d.stop(); time.sleep(1.0)
+    if not ok:
+        diagnose(d, gentle=True)
+        return
+
+    print("\nTest B: hard reverse on M3 (+1200 -> -1200 instantly)")
+    hold(d, ch, 1200, 0.5)
+    report("  +1200", *measure(d, ch, 1200))
+    ok = report("  -1200 (instant reverse)", *measure(d, ch, -1200))
+    d.stop(); time.sleep(1.0)
+    if not ok:
+        diagnose(d, gentle=False)
+        return
+
+    print("\nTest C: hard reverse on M3 (+2500 -> -1600 instantly, same as the spin test)")
+    hold(d, ch, 2500, 0.5)
+    report("  +2500", *measure(d, ch, 2500))
+    ok = report("  -1600 (instant reverse)", *measure(d, ch, -1600))
+    d.stop(); time.sleep(1.0)
+    if not ok:
+        diagnose(d, gentle=False)
+        return
+    print("\nAll three survived - the spin-test failure didn't reproduce.")
+
+
 def hand(d):
     base, _, _ = d.get()
     print("Motors are OFF.")
@@ -125,7 +197,7 @@ def spin(d):
 
 
 def main():
-    if len(sys.argv) != 2 or sys.argv[1] not in ("hand", "spin"):
+    if len(sys.argv) != 2 or sys.argv[1] not in ("hand", "spin", "reverse"):
         sys.exit(__doc__)
     d = Driver()
     try:
@@ -139,8 +211,10 @@ def main():
         print(f"Driver board is talking ({n} encoder messages so far).\n")
         if sys.argv[1] == "hand":
             hand(d)
-        else:
+        elif sys.argv[1] == "spin":
             spin(d)
+        else:
+            reverse(d)
     except KeyboardInterrupt:
         pass
     finally: