To do that, I use pySerial. I started with this tutorial here: http://pushbuttons.io/blog/cinema4d-ardunio-pan-tilt-servo You should also pay attention to the comment section.
But do consider, that serial communication slows down you micro controller a lot. If you send a lot of data over serial, especially when using Stepper Motors, it will slow down the speed drastically.
But anyway, I'll try using FK for now ... but I fell like it will be a pain in the ass :/