When double consonants

I double the final consonant when two conditions:
i) the last syllable has 2 vowels consonants clamp 1
ii) the accent on the last syllable that

 Example: 

  format -> formatting

  transfer -> transferrin 

  forbid - > forbidding 

  If only satisfy condition i) which does not satisfy condition ii) the final consonant is not doubled. , 

For example:

  open -> opening 

  lower -> lowering  

 sharpen -> sharpening 

 mentor -> Mentoring 

  

Particular case word travel is no exception. satisfying travel i) but does not satisfy ii) by pressing the first syllable (/ 'Trae vl /) should add-ing right when traveling is the American English this time spent traveling, traveled (right law), while British English spent traveling, traveled (unlawful)

 The Same-ed 

  format -> formatted 

  transfer -> Transferred 

  open -> opened

  lower -> lowered

  mentor -> mentored

  

However, when it comes the exception of irregular verbs, the past participle new worth mentioning,