Modifying Robostar SRS-3216HTG for compliance

Hello, I am considering to modify the above servo for compliance by removing its microcontroller and connecting its potentiometer directly to a Raspberry Pi for my project. Before doing so however, I have noticed that the robostar servos are stiff even when unpowered unlike most hobby servos, which would prevent me from using it as a compliant actuator. Hence, may I ask if anyone here knows the reason for this stiffness, and/or has a way to modify the servo to make it rotatable by external forces when unpowered? Thanks a lot in advance!

submitted by /u/techman007
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