I am trying to build a lab vial roller like the following: http://www.phenixresearch.com/products/s-5500-mini-labroller.asp
I want it to be fluid at very low RPMs (0-20). I was thinking of using a stepper motor that way I can control the speed and the rotation. However, I am not sure which configuration to use; spark fun offers two stepper motors (a 200 step and 400 step motor) and two drivers (one with microstepping down to 1/8th and one that goes down to 1/16th). I was planning on using the 400 step motor with the 1/16th microstep however its the most expensive option and I am not sure if its necessary.
stepper 400:http://www.sparkfun.com/products/10846 stepper 200:http://www.sparkfun.com/products/9238 driver 1/8:http://www.sparkfun.com/products/10267 driver 1/16:http://www.sparkfun.com/products/10735