I'm trying to implement the automatic door opener. Like this one Overview | Arduino Lesson 14. Servo Motors | Adafruit Learning System.
The problem I have is that O don't know which servo to get. The website and other stores have servos which provide different torque values. How much torque would I need to turn the deadbolt on a door. I know different locks will require different amounts of torque, but how do I know how much I need?
I was also looking into stepper motors but based on what I read, a servo is a better option for this. Could anybody provide me any feedback on this?
No one better than you to figure that out. Get a torque wrench and verify the amount of torque required to open the door and add a bit more to accommodate if someone is pushing/pulling the door and the lock has some friction to overcome.
Not knowing this just get one and try it. If it doesn't work you have to look for one with a higher torque rating.
Steppers, perhaps, if they have a very fine angle. There are also geared DC motors you could use that have much more torque than a servo. look for those with metallic gears.
There are also locks activated by an electric solenoid, such as those found on communal doors in flats, that you can open from an intercom, by pressing a button.