diff --git a/ROMFS/px4fmu_common/init.d/2101_fw_AERT b/ROMFS/px4fmu_common/init.d/2101_fw_AERT
index 19a47cda8c..3631a1e36c 100644
--- a/ROMFS/px4fmu_common/init.d/2101_fw_AERT
+++ b/ROMFS/px4fmu_common/init.d/2101_fw_AERT
@@ -20,3 +20,7 @@
 sh /etc/init.d/rc.fw_defaults
 
 set MIXER AERT
+
+# The ESC requires a specific pulse to arm.
+set PWM_OUT 4
+set PWM_DISARMED p:PWM_DISARMED
diff --git a/ROMFS/px4fmu_common/init.d/2104_fw_AETR b/ROMFS/px4fmu_common/init.d/2104_fw_AETR
index 083eb42330..3113ede87a 100644
--- a/ROMFS/px4fmu_common/init.d/2104_fw_AETR
+++ b/ROMFS/px4fmu_common/init.d/2104_fw_AETR
@@ -20,3 +20,7 @@
 sh /etc/init.d/rc.fw_defaults
 
 set MIXER AETR
+
+# The ESC requires a specific pulse to arm.
+set PWM_OUT 3
+set PWM_DISARMED p:PWM_DISARMED
diff --git a/Tools/px_romfs_pruner.py b/Tools/px_romfs_pruner.py
index aef1cc7a3b..78e4e69f72 100644
--- a/Tools/px_romfs_pruner.py
+++ b/Tools/px_romfs_pruner.py
@@ -76,7 +76,7 @@ def main():
                                                         pruned_content += line
 
                         # overwrite old scratch file
-                        with open(file_path, "w") as f:
+                        with open(file_path, "wb") as f:
                                 f.write(pruned_content)