One response was helpful, one response was rude. No matter.
I can most likely operate each servo with a single cable attached. The vents are fairly short travel, so probably 1/2" of travel is all I expect, but for the doors, I may need a couple inches of travel, so a fairly large pulley attached. The idea with all of these is that the servo pulls the cable to open panels. Upon the servo release, a fairly weak spring pulls the cable back through it’s sheath and aids in keeping the openings closed. I have never used servos for anything before and have no idea what rating should be used in these applications. I can’t imagine I would need more than a few pounds of pressure.
I don’t understand the comment about previous responses and don’t recognize the quote, but I’ll try and give you some helpful information. generally speaking though, starting (or maybe re-starting in this case?) a please help me thread on a negative vibe isn’t the best way to go… but I’ll dive in anyway and see if the situation works itself out.
servos are generally rated for some maximum torque output. for instance a 76oz-in rating implies it can apply as much as 76oz at a radial distance of 1 inch from the output shaft, or 1 oz of force 76 inches (if you can imagine a 6 foot long arm that weighs nothing) radially outward. servo displacement is usually specified in terms of plus and minus degrees from a 0 degree center reference. A output hub or arm is frequently attached to the servo shaft to translate angular displacement into roughly linear displacement. That 0 degrees corresponds to a specific input condition, a pulse duration of 1500us delivered at a 50hz rate. A standard servo rotates +/- 45 degrees of it’s reference 0, and that corresponds to a pulse length of 1000us to 2000us. In practive many servos can be made to rotate further, some as much as +/- 90 degrees, by using even shorter and longer pulse lengths.
your question really seems to focus on the mechanical aspects of design. what you need to figure out, or maybe just build and measure, is how much force is required to open/close the vents, and how much linear displacement of the cable is required to acomplish it. Ideally you want to keep the displacement on the shorter side, something in the half inch to one inch range is good. once you know this though you can use a little trig to calculate the length of arm needed between the cable and the servo output shaft. that length multiplied by the force required gives you a rough torque number. then you pick a servo that has more torque than your requirement.
there are some pecularities to controlling servos that need to be considered. in particular when you first turn them on they are not necessarily at the position they were when you turned them off. In your case consider shutting off a PC with the vents open. the weight (or springs) of the vents will move the servos slightly or a maybe lot. when you turn the power back on they might jump to either the open or closed position. a problem with using springs is when the vents are extended the force required to hold them open is both the weight they represent plus that of the springs.
another consideration is that there are two different types of servo, analog and digital. probably the biggest single difference between them for your purposes is that an analog servo ALWAYS needs signal or it can do anything from nothing all the way to running into and endpost. a digital signal will generally hold the last position commanded even if signal goes away. this may be useful when you are figuring out how to control the vents during power up and down situations.
hopefully this is enough information to at least get you started. good luck as you move forward with your project.
