Opening and closing an air vent

What would be a good way to open and close an air vent? I have a servo from an old RC airplane that would do the job, but I am hoping to use a less expensive device if possible.

The air vent opening would be a tube of about 10cm in diameter. Somehow I need to open and close a vent with the Arduino controlling it. When closed it should be insulated (hot/cold insulation not electrically isolated). It could be mounted on a flat wall or surface. I was thinking of a piece of styrofoam with a hinge along the top, which would swing up to open the vent and fall down to close it. There would not be a lot of pressure on the vent. I would expect the vent to open and close about 100 times a day.

I can picture how to do it with the servo I have, but is there any other way that could be done with less expensive equipment? Maybe a small motor or solenoid? Maybe in combination with a latch so the solenoid did not have to be powered the entire time? Step motor? Eventually I would hope to run it off of a solar powered battery, so low amp draw devices would be good. Durability is important, it should be able to run at least a year or more, hopefully.

The project is to build a refrigerator that is cooled by outside air during the winter. There will also be a fan and thermistors to measure when outside air is cool enough to chill the fridge, and to turn the fan on and off to adjust the fridge temperature. The air vent "valve" is not strictly necessary, but when the furnace and hot water heater are running in the house, they produce a vacuum that will pull cold air in, which potentially could freeze the stuff in the fridge (not good).

You may want to note [u]this[/u] as fallback solution if you can't repurpose something you have lying around. Its a full size servo for less than $8 shipped. You can get a smaller servo that has less torque from the same place for a few bucks less

Wow, I didn't know servos were that cheap. I guess it is not worth fooling around with scrounged parts when these are available.

wow, thats a good deal for a servo!

is it any good, with it's strength? i got some servos that were moving around 3 pounds of weights easily, could these do that? the site isint to specific about details...

it might be worth investigating the standard HVAC 24v vent baffles. This way all you have to do is send 3v to a relay w/ a 24v power supply and you can get a vent that opens and closes. Just a thought, rather than rigging a couple of servos together.

You could also consider going to the junk yard and picking off an intake manifold from a car. Use it's idle air control valve (IAC) and the piping that it already sits in. The IAC would be either stepper motor based or solenoid based. The Arduino should be up to the challenge.