Tarmo3 Mostly metal drivetrain

#Mostly metal drivetrain upgrade for Tarmo3
I did it just in order to be able to use larger wheels to ride in mud or show without repairing after each 30 seconds of ride.
Also bigger motor has too high torque to use it with plastic diff.

I also added cover for servo that helps to hold servo on place without staggering

Required parts:
- 2x Diff HSP 02024 (!!! they are bit different between different sellers on Aliexpress, and if yours not fit well - just cut out small wall between bearings in diff case and make hole a bit wider with file) - http://ali.onl/1xk2 - fits realy well
- 2x long diff drive wheel HSP 03015 - http://ali.onl/1xk7
- 4x wheel axile HSP 02168 - http://ali.onl/1xk5
- 4x 87mm dog bone HSP 06022 - http://ali.onl/1xka
- 4x wheel hex - http://ali.onl/1xkc
- 8x 10x15x4 bearing
- 8x 5x10x4 bearing