OpenRC truggy central differential: stronger motor gear

original design is standard gear of many comecial differential, when you print it carefully, it's gear only contain one 'shiled', then it will always broken when you really use it daily.

i broken many of them, finanlly, i redesign the 'gear' part of the central differential, with this strong one, it unlikely it will broken before other printed gear does. and it's fully compatible with OpenRC truggy project.

i design 13T/17T, locker or non locker version, enjoy!