So the project is fairly simple. I want to attach a motor to the knob controlling my cat's door. (Idea is to have a button on the wall to open and close it).
I've fiddled around with only servos but realised stepper motors exists too. Is one better suited than the other?
Best regards
Yes. A servo has limited movement and limited torque. But is knows where it is from switch on.
A stepping motor has more torque and unlimited movement. Although it has to be in a known position on power up. This can be done with a limit switch and a self calibration routine on power up.
Pay your money and take your choice.
If I wanted to open and close a pet door I would think about using a linear actuator and look for one with limit switches. There are plenty of good examples of using a linear actuator along with an Arduino online, a simple Google of Linear Actuator Arduino should get you started with ideas. Plenty of inexpensive linear actuator motors out there on outlets like Amazon. Limit switches provide inputs to digital in and a few digital out used to change polarity for Open / Close functions. Open / Close buttons would go to a few additional digital inputs. Nice to have a linear actuator with adjustable limit switches for easier hardware mounting.
Additionally as mentioned make sure your motor can handle the load of moving the door. 
Reminds me we have an old recliner the dogs use to get up into a bay window. Been thinking about cannibalizing any linear actuators in it. The dogs don't need the recliner functions.
Ron
Thanks guys, I managed to pick up a 28BYJ-48 stepper motor today I i got it working fine. Currently setting up a basic rig to test it on the door. I'm using 4 AA batteries in series for power supply but I've noticed the stepper motor is quite warm from just sitting stationary plugged in. Wounder if I should put in a relay into the circuit to avoid the heat?
Please follow the rules and post a schematic.
Sorry, didn't have the time. I based it on someone elses schematic, I'll see if I can find it
Can you find some time now? Just use pen and paper and post a photo. Troubleshooting the thing it's "based on" isn't useful.
Steppers pull current all the time to hold position. And they run hot - that's expected. But obviously bad news if you want to power the system off batteries.
Can you arrange the mechanicals so that it doesn't require the stepper to be powered (and holding) all the time?
Like this, only difference is that I have the 4 AA batteries as the power source instead of his DC contact.
My theory is that the Stepper motor is warm due to it being constantly plugged in with the power supply.
Aaah yeah makes sense, maybe I can use a relay to kill the power after each movement?
So far we know nothing at all about your stepper controller board. Other than, it might be something like the one you modelled your build on.
Or, how the power from the battery is distributed.
Last time I will ask, please draw a complete wiring diagram. Failing that, at least images of your actual hardware.
Probably, yes. That particular stepper has gearing built in, so unless the cat door is heavy, it'll probably stay still - try it just with a switch perhaps.
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