I'm sure someone else can provide a detailed answer, but I'll give a quick one.
When you set a PWM output from 0 to 255 you are not setting voltage or current What you're actually setting is the duty cycle output of the Victor to the motor. Duty cycle is a percentage and the rough equation is (On Time)/(Off Time).
Examples:
- PWM Value: 127
Duty Cycle: 0 % - PWM Value: 255
Duty Cycle: 100% (Normal polarity) - PWM Value: 0
Duty Cyle: 100% (Reverse polarity)
The current a motor draws is related to the amount of power required to turn the output shaft. The more friction in the mechanism the higher the current draw will be. This is a mechanical issue not a programming issue.