I have used Brushed DC motor with encoder as servo motor for a while. (VNH5019, and will try G2 soon as it arrive).
I would like to suggest BLDC motor driver for using as servo (not run continuously). As I can find more power-density than BDC.
Specification as below.
1. Receive 3-phase hall sensor from motor as input, used for bridge selecting only. Better in TTL. Also, include BDC driver mode (hard-wire hall sensor channels to VCC or ground).
2. locked anti-phase interface with microcontroller. Microcontroller only tell which way, but the driver automatically select bridge from hall sensor.
3. No auto-shutdown safety like other BLDC driver often do (shutdown driver when hall is stalled) <-- this is the main problem that I can't use any available BLDC driver.
3. Bidirectional current sensing with adjustable current chopping (cut power and enter slow decay mode for very short time, about few 10us). If possible, seperate between current sensing ground and digital interface (which may get noise from motor driver) so that user can install isolator for driver interface if needed.
4. Power-specification upto 10A. If possible, make it support 36 VDC supply instead of 34 VDC (It is difficult to find power-supply between 25-35 VDC)
Price: If it is very hard to failed (with high safety) 70.00$+ per channel is gladly accepted. As it can use with both BDC and BLDC.