Bartech is a good option, especially if you're using the fstop/PLC digital receiver/driver, it has a much smaller form factor than the analog one.
If you were looking for something really small and light check out the RT Motion Mk3 if you can find one. I recently used one on a Ronin, it had to be one of the smallest and lightest remote follow focus I've ever seen. The receiver if I remember correctly is about the width/depth of a 9 volt battery and maybe 1-1/2 times as long and the motors were roughly the same size as a Heden motor. Over all it was decent, I felt there was a noticeable bit of lag if you were making big moves even when it was set to it's fastest response but for the most part it did the job and was very small/light.
Edited by evanwalsh, 07 August 2015 - 03:16 PM.