This is a wheel base i made for my inmoov robot. The basic idea is from Gael Langevins wheel base who is the owner of the inmoov project. You can find his great job at http://inmoov.fr .
You must have some welding skills to complete this base construction.
The servos i use is turnigy 1270HV 40kg.
The "metal tube" stl i publish it only as a guide for the dimensions of the metal tube you need.
The best value for the two resistors for centering the wheel servo is 2.2kΩ.
Do not forget to remove the metal pin (end stop) from the main gear of the wheel servo for continius rotation.(i will include photo later).
Do not try to print the "all parts stl" , i post it to show the complete construction.
On two axles you must make a center hole in order to screw the bolt. (I will update them later).
Bad english, i know but i'm trying :)
As smaller the layer height and thickest the infill are, especially for the axles they will be strongest. I use 2mm height and 40% infill. Don't try them with ABS, i believe is a waste of time, only PLA.