I am trying to create a motorized door unlock. I have a uno r3, and a step motor (28byj-48, 5v dc). And this is what my lock looks like. Will this motor be able to turn the lock? Any ideas on how to connect the lock to the step motor axle?
Estimate or measure the torque needed by the mechanism. Then read the data for the motor and check wheater the torque of the motor is enough or not.
A servo would be a better bet anyway, torque for those usually in the spec and more powerful size for size than a stepper .
droidus:
Will this motor be able to turn the lock?
Having no specifications on the lock itself, all I can say is: try it out!
Any ideas on how to connect the lock to the step motor axle?
Having no specifications on the lock itself, all I can say is: duct tape.
Your picture gives absolutely no indication of how you plan to connect the motor to the lock.
Will the motor be on the other side of the door ?
Please draw a diagram of what you have in mind and post a photo of the drawing.
I agree that a servo would probably make more sense.
...R
All that needs to happen is that it needs to be rotated clockwise about 90 degrees. I tried it with duct tape, but the pin coming out of the motor just slipped on the duct tape. Any other tacky solutions? 
Stupid question, but how does this work/help me?
Slide it over your motor's axle with the protruding pin in the slot of the left-hand part of the pump coupling.
The points sticking out on other other end of the coupling could then grab the door knob as seen in a previous image.