Elevator
I teach a class where the final project is often an elevator using a Programmable Logic Controller. (Laddrer logic to run the elevator.)
In several years, I've only seen one that worked fully, and one that worked marginally. The problem is almost always the same. Not the electronics, not the programming, but the mechanics. So be warned this is the hardest part, if you do not have high mechanical aptitude.
My observations...
The second most often cause for failure is the use of stepper motors. Students don't realize that typical small stepper motors are very low torque devices. They will usually not lift the weight of the container. I did see one clever arrangement where the container had a counter-weight behind the elevator to offset the weight and make the job easier for the stepper motor.
The most successfull mechanical solution I saw was achieved by attaching the container to several really long, thin threaded shafts. A motor turned the shafts. Bolts on the shafts moved up or down depending on the direction. The container was connected to these bolts.
As to floor sensors, both optical and mechanical limit switches all seem to work fine, so I'd say go with switches if you are a novice and want the easiest solution, or try optical/IR sensors to play with that technology if you wish.
I'll probably put some photos of a good elevator on
www.picrobots.com soon, and you can email me at
rvannoy@itt-tech.edu if you have more questions.