need of very small circuit for a medical device

[Faezeh]

Hi all,
I am a medical engineering student and I have no idea about electronic! But for my project I need to have a very small circuit with a button which rotate a shaft for me! the shaft is very light since it is made of plastic.
Someone suggested servo motors to me but when I was searching about it, they all look so big. it will be used on a patient so the patient wants it to be as less conspicuous as possible!
I would really appreciate any helps. I really have no idea what to do!
Thanks

[pebe]

You need to provide more detail to get an answer.

Does the motor run continuously or just for a few revs?
At what rotational speed?
What exactly does the button do?
What exactly does the device do?
Is it to be battery operated?
At what voltage?

The more detail you can give, the better.

[Faezeh]

basically this is a valve like a circle that will be placed on the patients neck when the valve rotates 90 degrees it will be closed and another 90 degrees makes it open and it needs to be pretty quick. the size of the valve is slightly bigger than your thumb and it is very light just couple of grams. I need a simple circuit that cause the rotation of the valve. I have no idea about the voltage :/

[pebe]

You can get very small servos (about the size of your valve) for model helicopters. These give a 45º swing either side of the norm (90º) total.
So you could go (90º) in one direction and back again. Would one of those do the job?