Disable R/C autocalibration without turning off the signal timeout on a Sabertooth?

Sabertooth motor drivers (excepting RC-only versions) require a software setting to use a fixed RC servo range along with the timeout/failsafe feature.

Go to the RC page in DEScribe and check "Use custom range even when Switch 6 is UP (standard RC mode)". Upload Settings and then set Switch 6 to up(ON). This will disable microcontroller mode (turning signal timeout on) while using the fixed calibration you've specified.