MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
I used MK8 gears with a outer diameter of 7mm. I got really good results using 172.50 steps with PLA, ABS, and PETG once spring tension set correctly.
I also had the issue of the one filament being pulled out when the other was being pushed in. If you look at the pendulum I posted it has dimples near the drive gears, however this is for a DyzEnd that I never really got working. What works really well for me was those dimples using super glue + baking soda on the original design, which corrected this in/out issue for me.
I had a lot of issue with the servo and finally resolved by using external +8V power supply. I posted this with some firmware info on the comments below.
The extruder offset that I used the provide the best alignment was:
Hope that helps.