diff --git a/script/RobotSC.py b/script/RobotSC.py
index af6adc1..af6bf1f 100644
--- a/script/RobotSC.py
+++ b/script/RobotSC.py
@@ -46,6 +46,8 @@ class jfc(ReadonlyRegisterBase):
     def doRead(self):
         if robot.joint_forces == None:
             return  None 
+        if not robot.powered:
+            return None
         return (robot.joint_forces[1]+74)/4  + (robot.joint_forces[2]+30)/4 + (robot.joint_forces[4]-0.8)/0.2
 
 add_device(jf1(), force = True)