The struct needs to be packed, otherwise the little trick with converting to a char pointer can backfire badly.

Author: aentinger

src/lib/motors/SmartServo.h

@@ -106,7 +106,7 @@ class SmartServoClass
   mbed::Callback<void()> _onError;
 
 
-  struct {
+  struct __attribute__((packed)) {
     uint8_t header [2];
     uint8_t id;
     uint8_t length;