Is it possible to turn off auto-calibration?

Not in current firmware. 

The system was originally designed for use with higher end PL glass which have hard stops built in. When using the system with Nikon/ Canon/ Third party EF/AF lenses (which often have a focus ring that turns indefinitely) you will need to 'fake stop' the motors. 

1. Unmesh the motor from the lens gear.

2. Power up the motor.

3. Physically grab the motor gear to stop it turning.

4. After a few seconds of it turning the other direction stop the gear a second time. 

When rough fake stops have been established you will be able to mesh the motor onto the lens gearing and access the 'Manual Recalibration' setting in the Controller Menu to set more precisely where you want the actual lens stops to be. 

Please note that we are looking into the option of switching 'auto cal' off for use with DSLR lenses as we know this is not ideal for our users. We will keep you posted on this.